Imagine, if you will, the engineers of the king’s court after Humpty Dumpty’s disastrous fall. As panicked men apparently competed with horses for access to the site of the accident, perhaps the engineers were scoping out scenarios, looking for a better method of reassembling the poor fellow. But presumably none of those plans worked out, given the dark ending to that fairy tale.
A recent study published in Science Advances might be relatable for those fairy tale engineers. Published by Johannes Feldmann, Anders Levermann, and Matthias Mengel at the Potsdam Institute for Climate Impact Research, the study tackles a remarkable question: could we save vulnerable Antarctic glaciers with artificial snow?
Keeping our cool
Antarctica’s ice is divided into two separate ice sheets by a mountain range, with the smaller but much more vulnerable West Antarctic Ice Sheet representing one of the biggest wildcards for future sea level rise. In 2014, a study showed that two of the largest glaciers within that ice sheet—known as the Pine Island Glacier and Thwaites Glacier—had likely crossed a tipping point, guaranteeing a large amount of future ice loss that would continue even if global warming were halted today.
Much of the bedrock beneath the West Antarctic Ice Sheet is actually below sea level, though it’s buried below kilometers of solid ice. This makes for situations where the bed beneath the ice slopes down as you go inland from the coast. That’s inherently unstable, and once a glacier starts retreating downslope, the invading water provides an increasing floating force that reduces the sliding friction that slows the seaward flow of ice.
In the case of the Pine Island and Thwaites Glaciers, it seems that this is exactly what’s happening. Although this process can take centuries to fully play out, this portion of the ice sheet contains enough ice to raise global sea level by more than a meter.
Is there some extraordinary measure that could prevent that loss and preserve these glaciers? It’s the kind of question people will often ask, and scientists (who know the scale of these things) generally ignore as implausible.
But in this case, the researchers decided to go wild. Using a computer model of the ice sheet, they simulated the effects of adding huge amounts of ice near the front of these two glaciers. The idea works like this: Where a glacier meets the sea, it transitions from grounded to floating. Behind this “grounding line,” the glacier sits on the bedrock and sediment beneath; in front it gets thinner and floats as an ice shelf. To preserve the glacier, you need to keep that grounding line from retreating downhill. Thicken the ice on the inland side of the grounding line, and the thickness of ice flowing over the line and into the ice shelf increases—its weight keeps the grounding line pinned in place.
The researchers played around with different amounts of ice added to the glaciers for different periods of time, ranging from 10 year treatments to 50 years. Spreading it out over a longer period could mean a less preposterous addition of ice each year, but they found that the total amount has to increase if you do it that way. So in the end, the scenario they selected was 7,400 billion tons of ice added over 10 years. That was enough to restabilize these glaciers, preventing their inexorable decline.
Two for one special
To put that into context, removing that much seawater from the ocean would lower global sea level by about 2 millimeters per year. Current total sea level rise is a little over 3 millimeters per year, so it would be like nearly halting sea level rise… by bailing water out of the ocean. We can call that a bonus positive.
This analysis is more about what it would take than what such a scheme would look like, but the basic options are to pump water up and hose it around—hoping it freezes quickly—or to freeze it into snow like the world’s most awkwardly located ski resort.
Here, the researchers transition to listing all the reasons this is impractical and all the negative impacts it could have. For starters, the seawater would have to be desalinated since salt would probably affect the physics and behavior of the ice. Simply pumping that much water up the 640 meters and spreading it over an area nearly the size of West Virginia would require the power of something like 12,000 wind turbines—and that’s without the very substantial energy requirements for desalination and snow-making.
“The practical realization of elevating and distributing the ocean water would mean an unprecedented effort for humankind in one of the harshest environments of the planet,” the researchers write.
The impacts on Antarctic ecosystems could also be huge. Pumping that water out of the sea near the coast would significantly alter the circulation of water, which might even become somewhat self-defeating, as it could bring more warm water up against the ice shelf, increasing melt.
In the Potsdam Institute’s press release, Levermann puts it this way: “The apparent absurdity of the endeavour to let it snow in Antarctica to stop an ice instability reflects the breath-taking dimension of the sea-level problem. Yet as scientists we feel it is our duty to inform society about each and every potential option to counter the problems ahead.”
And to be clear, this is in addition to halting climate change—the scenario the numbers are based on assumes the temperatures don’t keep rising. But as the alternative is eventual inundation of parts of the world’s coastal cities, an argument can be made that the cost could be worth paying. It least it gives us an idea just how hard it would be to put Humpty Dumpty back together again.
The potential for collapse of the Antarctic ice sheet remains the largest single source of uncertainty in projections of future sea-level rise. This uncertainty comes from an imperfect understanding of ice sheet processes and the internal variability of climate forcing of ice sheets. Using a mathematical technique from statistical physics and large ensembles of state-of-the-art ice sheet simulations, we show that collapse of ice sheets widens the range of possible scenarios for future sea-level rise. We also find that the collapse of marine ice sheets makes worst-case scenarios of rapid sea-level rise more likely in future projections.
Sea-level rise may accelerate significantly if marine ice sheets become unstable. If such instability occurs, there would be considerable uncertainty in future sea-level rise projections due to imperfectly modeled ice sheet processes and unpredictable climate variability. In this study, we use mathematical and computational approaches to identify the ice sheet processes that drive uncertainty in sea-level projections. Using stochastic perturbation theory from statistical physics as a tool, we show mathematically that the marine ice sheet instability greatly amplifies and skews uncertainty in sea-level projections with worst-case scenarios of rapid sea-level rise being more likely than best-case scenarios of slower sea-level rise. We also perform large ensemble simulations with a state-of-the-art ice sheet model of Thwaites Glacier, a marine-terminating glacier in West Antarctica that is thought to be unstable. These ensemble simulations indicate that the uncertainty solely related to internal climate variability can be a large fraction of the total ice loss expected from Thwaites Glacier. We conclude that internal climate variability alone can be responsible for significant uncertainty in projections of sea-level rise and that large ensembles are a necessary tool for quantifying the upper bounds of this uncertainty.
In marine ice sheets, the grounding line is a critical boundary where ice flowing from the ice sheet interior becomes thin enough to float in ocean water. The grounding line location and ice flux are sensitive functions of the depth of the surrounding ocean (1⇓–3). When the bedrock beneath the grounding line is reverse sloping (i.e., deepens toward the ice sheet interior), a small retreat of the grounding line onto deeper bed leads to greater ice flux and therefore more retreat. This positive flux feedback leads to the potential for rapid and irreversible retreat wherever the bed is reverse sloping, which has been termed the “marine ice sheet instability” (4). Rapid ice loss from the Antarctic ice sheet through this instability will likely drive sea-level rise beyond the next century (5, 6). However, projections of future sea-level rise are uncertain due to imperfect representation of ice sheet processes in models, unknown future anthropogenic emissions, and the internal variability of future climate forcing of ice sheets. Even with improvements in ice sheet models and climate projections, there will always remain a component of sea-level projection uncertainty that cannot be reduced due to the fundamentally unpredictable internal variability of the climate system which causes ice sheet change. This fundamental lower bound in the uncertainty of projections due to internal climate variability (for ice sheets and other elements of the climate system) has been termed “irreducible uncertainty” (7). The inevitability of uncertainty remaining in sea-level projections necessitates robust modeling of the ice sheet dynamical factors which produce uncertainty in future ice sheet projections, for which there is no existing theoretical framework. In particular, it is critically important to constrain the upper bounds of uncertainty in sea-level rise projections, which have a disproportionate influence on planning for coastal adaptation measures (8).
Ice sheets evolve in response to changes in climate variables (i.e., climate “forcing”), such as snowfall and ocean temperature. The amount and structure of uncertainty in projections of the future ice sheet contribution to sea-level rise can thus be determined through large ensembles of ice sheet model simulations, which are plausible realizations of the future evolution of an ice sheet in response to climate forcing (see Fig. 1, Upper for a conceptual illustration of an ensemble). Each ensemble member is distinguished by selecting either a unique set of model parameters or one realization of future variable climate forcing from a distribution of possibilities. At a particular point in time, the statistical properties of the full ensemble represent the probability distribution of ice sheet state, represented by a variable such as extent or volume (conditioned on the probability of the model parameters or climate variability having particular values). The spread (or standard deviation [SD]) of the probability distribution quantifies the amount of uncertainty in the projection. In a probability distribution that is symmetric, the skewness is 0, and the projected change in ice sheet volume is equally likely to fall above or below the mostly likely projection (Fig. 1, Lower Left). A negative skewness of the probability distribution indicates that the probability of ice sheet volume turning out to be below the most likely projection is greater than that of ice sheet volume turning out to be above the most likely projection (and vice versa for positive skewness). Put another way, a negative skewness indicates that the probability of worst-case scenarios (i.e., more ice sheet mass loss and corresponding sea-level rise than is expected from the highest-likelihood projection) is greater than the probability of best-case scenarios (of less sea-level rise than the highest-likelihood projection).
(Upper) Conceptual illustration of an evolving ensemble of ice sheet model simulations, where each solid line is a single plausible realization of the future ice sheet evolution. Dashed colored lines indicate two time slices, for which probability distributions are provided (Lower Left and Lower Right). The statistical properties of the probability distribution of ensemble simulations change with time from a narrow, symmetric distribution at early times (blue dashed line, Lower Left) to a wide, asymmetric distribution with negative skewness (red dashed line, Lower Right), making the probability of ice sheet volumes below the most likely projection many times greater than that of ice sheet volumes above the most likely projection (arrows show example of ice sheet volumes above and below the most likely ice sheet volume projection).
In this study, we develop a framework for determining how marine ice sheet processes produce uncertainty in projections of future sea level. We do so using 2 complementary approaches: 1) Stochastic perturbation analysis of a simple model of marine ice sheet evolution with one evolving quantity and 2) statistical analysis of a large number of simulations of the future evolution of a West Antarctic glacier using a state-of-the-art numerical ice sheet model with many thousands of evolving quantities. These 2 approaches represent end members of the hierarchy of modern ice sheet models. They provide both a theoretical framework for understanding the sources of uncertainty in projections of the future ice sheet contribution to sea level and an application of this framework to an actual glacier that is thought to be undergoing the marine ice sheet instability.
Stochastic Perturbation Theory
Over the past several decades, much of the observed increase in Antarctic ice loss has been caused by ocean-driven ice sheet melting (9). Our goal in this study is thus to quantify the uncertainty in projected ice sheet state that is caused by uncertainty in ocean-induced ice sheet melt, although the principles involved are extendable to uncertainty in other climate forcing (or uncertainty in glaciological parameters). We start by mathematically and numerically analyzing the uncertainty in ice sheet state simulated by a minimal model of grounding-line migration for a glacier under climate forcing (10, 11)
where L is the distance of the grounding line from the glacier onset, and hg=−ρwρibghg=−ρwρibg is the thickness of ice at the grounding line, which depends on the ratio of seawater (ρwρw) and ice (ρiρi) densities and the local bedrock depth (bgbg). This model, which is derived and discussed in more detail in Robel et al. (11), tracks the total mass balance of the glacier, captured in 3 processes. The first term captures ice entering as snowfall over the glacier surface at accumulation rate P (averaged through glacier geometry: L and hghg). The second term captures ice leaving the glacier due to ice flow through the grounding line (γhβ−1gγhgβ−1). The third term captures ocean-induced melt at the grounding line (η). The parameters β and γ are related to the balance of glaciological processes which contribute to setting the velocity of ice at the grounding line (e.g., gravitational driving stress, basal sliding, and ice shelf buttressing). Observations (12), mathematical analyses (1⇓–3, 13), and numerical simulations (11, 14, 15) have all shown that grounding-line velocity is generally a nonlinear function of grounding-line ice thickness (as we assume in Eq. 1), even during periods of transient grounding-line migration, although there is perhaps some variation in the exact value of β that applies in such a situation. Still, this minimal model is meant as a tool to understand the processes which drive uncertainty in simulations of marine ice sheet instability, not a means for making actual predictions of ice sheet change. As we show later on, the conclusions drawn from this minimal model are reproduced in a state-of-the-art ice sheet model which does not make the same simplifying assumptions.
In Eq. 1, the rate at which the grounding line migrates in response to ocean-induced melting (or freezing) is η=η¯+η′(t)η=η¯+η′(t), consisting of a time-averaged component (η¯η¯) and a time-variable component (η′(t)η′(t)). The time-averaged ocean forcing may be uncertain and so is drawn from a Gaussian distribution with SD σPσP. The time-variable ocean forcing is a first-order autoregressive Gaussian noise process with interannual SD σFσF, and decorrelation timescale τFτF. Other studies have shown using a complex spatially resolved model that ocean-induced grounding-line variability is filtered through the frequency-dependent response of the ice shelf to ocean forcing (16). In this minimal model, we assume a simpler form for η in which all ocean-induced grounding-line migration is the result of melting directly at the grounding line and neglects effects from sub-ice shelf melt and buttressing. While this assumption will likely produce some quantitative difference than that of a model which includes sub-ice shelf melt beyond the grounding line, the more complicated ice-shelf–resolving simulations in the next section show that the qualitative aspects of our mathematical analysis do not appear to be changed by such detailed considerations.
Fig. 2 shows ensembles (with 10,000 simulations each) of simulated grounding-line migration over a bed of constant slope, calculated using Eq. 1 (details in Materials and Methods). The only forcing during the simulation period shown is ocean-induced grounding-line migration (η). The ensemble spread (represented in Fig. 2 by the interquartile range) captures the uncertainty in projected grounding-line position due to uncertainty in ocean forcing. On a forward-sloping bed (green shading/lines), small interannual forcing in the grounding-line position (σF=100σF=100 m/y, η¯=0η¯=0) produces an ensemble spread that remains small, bounded, and symmetric. For the same stochastic forcing on a reverse-sloping bed (orange shading/lines), all ensemble members retreat, as the ensemble spread grows rapidly without bound and becomes skewed (negatively) toward more retreat.
Evolution of a 10,000-member ensemble of minimal model (Eq. 1) simulations of grounding-line retreat over idealized constant-slope bed topography and variability in ocean forcing. (A) Ensemble interquartile range (shading spans 25th percentile to 75th percentile). (B) SD derived from numerically calculated ensemble statistics (solid lines) and analytic predictions from stochastic perturbation theory (circles). (C) Skewness derived from numerically calculated ensemble statistics (solid lines) and analytic predictions from stochastic perturbation theory (circles). Negative skew indicates more retreated grounding line. There is no analytic approximation available for skewness under autocorrelated forcing (see SI Appendix for discussion of stochastic perturbation theory). Pink shading and lines are simulations on a reverse-sloping bed (bx=4×10−3bx=4×10−3) with constant ocean forcing, selected from a Gaussian distribution. Blue shading and lines are simulations on a reverse-sloping bed (bx=4×10−3bx=4×10−3) with interdecadal variability in ocean forcing (τF=10τF=10 y). Orange shading and lines are simulations on a reverse-sloping bed (bx=3.5×10−3bx=3.5×10−3) with interannual variability in ocean forcing (τF=1τF=1 y). Green shading and lines are simulations on a forward-sloping bed (bx=−10−3bx=−10−3) with interannual variability in ocean forcing (τF=1τF=1 y). In all simulations, P=0.35P=0.35 m/y, γ=7.8×10−9γ=7.8×10−9 m−2.75⋅y−1, and β=4.75β=4.75. In simulations with variable ocean forcing (blue, orange, green), η¯=0η¯=0 and σF=100σF=100 m/y. In simulations with uncertainty in constant ocean forcing (pink), σP=50σP=50 m/y.
The growth in ensemble spread (i.e., uncertainty) occurs because the marine ice sheet instability amplifies (rather than damps) small perturbations from stochastic ocean forcing. These growing perturbations accumulate over time, leading to a divergence between ensemble members, which each experience a different series of perturbations from ocean forcing. The skewness of the ensemble can be understood physically and from an analysis of Eq. 1. For a retreating ice sheet, the rate of retreat is set by the difference between two fluxes: The accumulation flux and the grounding-line flux. If the grounding-line flux is more sensitive to the position of the grounding line than the accumulation (which it is for sufficiently nonlinear grounding-line flux), the net effect will be that the rate of retreat of more-retreated ensemble members will be greater than the rate of retreat of the less-retreated ensemble members. The result is that the retreat of the ensemble becomes progressively more negatively skewed with time. In ensembles where all simulations are advancing, the most advanced ensemble members accelerate faster, producing a positive skew.
Observations indicate that climate forcing of glaciers in Antarctica (and elsewhere) exhibits strong variability on decadal timescales (17, 18). In our minimal model, when stochastic forcing has decadal persistence, the ensemble spread and skewness grow considerably faster (blue shading/lines in Fig. 2). Such an amplified glacier response to temporal persistence in forcing agrees with previous model studies of mountain glaciers (19) and periodically forced ice streams (16, 20, 21).
For temporal ocean variability, stochastic perturbation theory (22) (SI Appendix) provides a theoretical framework for determining the physical processes which control the amplification and skewing of uncertainty in ice sheet projections. Analytic approximations for the spread and skewness of ensembles derived from stochastic perturbation theory (circles in Fig. 2 B and C) match well with numerically calculated ensemble statistics. This theoretical framework shows that ensemble spread grows exponentially with a rate that is proportional to the bed slope and the nonlinearity in grounding-line ice flux (β in Eq. 1). Thus, when the bed is forward sloping (negative), the ensemble spread remains bounded. When the bed is reverse sloping (positive), the marine ice sheet instability causes the ensemble spread to grow exponentially without bound. The ensemble variance is also proportional to the decorrelation timescale of the forcing, implying greater uncertainty in projections when climate forcing is persistent on longer timescales.
As alluded to above, the skewness of the ensemble is caused by the changing rate of grounding-line migration over a reverse-sloping bed. It can be shown analytically (see SI Appendix for details) that when the grounding-line ice flux is sufficiently nonlinear with respect to ice thickness (β>3β>3 in Eq. 1), then ensembles of a retreating grounding line will tend to be skewed toward more retreat. Conversely, when grounding-line ice flux is linear or weakly nonlinear (β<3β<3), then ensembles will tend to be skewed toward less retreat. In a wide range of realistic settings, we expect ensembles to skew toward more retreat during the retreating phase of the marine ice sheet instability because of the high-degree nonlinearity of grounding-line ice flux (β=4.75β=4.75 in ref. 1, β=5β=5 in ref. 2, β=4β=4 in ref. 3). In other words, the fact that the probability distribution is skewed in the direction of more sea-level rise is a fundamental consequence of the strong nonlinearity inherent in grounding-line dynamics.
Uncertainty in the time-averaged ocean forcing (η¯η¯; pink shading/lines in Fig. 2) produces even more ensemble spread (for relatively less uncertainty, σP=50σP=50 m/y) and further indicates the importance of the marine ice sheet instability for amplifying and skewing uncertainty in ice sheet projections. Uncertainty in the time-averaged climate forcing can be thought of as a limiting case of the response to an initial impulse with an infinite decorrelation time (τF→∞τF→∞). However, for such a nonstochastic case, there is no formal limit from stochastic perturbation theory in which the ensemble spread can be predicted.
Large Ensembles of Thwaites Glacier Instability.
To demonstrate that the intuition gained from the theoretical framework developed in the previous section applies to realistic glacier models, we simulate ensembles of the future retreat of Thwaites Glacier in West Antarctica using the Ice Sheet System Model (ISSM), a state-of-the-art finite-element model of ice sheet flow (23). Thwaites Glacier rests on a reverse-sloping bed and is currently retreating rapidly, which is argued to be the result of the marine ice sheet instability (24, 25). In ISSM, as in other models, ocean-induced ice sheet melting is parameterized with a depth-dependent melt rate, with maximum melt rate, MmaxMmax, prescribed at some depth (25). We treat MmaxMmax as a first-order autoregressive noise process that varies monthly with a prescribed decorrelation timescale (τFτF), a mean of 80 m/y, no long-term trend, and no variation in space. Many observations and models indicate that subice shelf melt rates at glaciers in the Amundsen Sea, and elsewhere in Antarctica, exhibit strong variability on decadal (and longer) timescales (17, 26, 27). A short run of a regional ocean model simulation for the Amundsen Sea region (SI Appendix) produces variability in MmaxMmax with interannual SD of 1.4 m/y. This estimate of variability is likely an underestimate since the ocean simulation was run for only 15 y (the time period over which reanalysis forcing is available) and did not include coupled ocean–atmosphere feedbacks. Thus, for our baseline ensemble of Thwaites Glacier, our conservative estimate for the statistics of ocean-induced melt variability is τF=10τF=10 y and σM=1.4σM=1.4 m/y. In reality, we also expect that MmaxMmax varies in space, due to (for example) the Coriolis effect on ocean circulation in the subshelf cavity, which would quantitatively (but not necessarily qualitatively) affect our results.
Fig. 3A shows the evolution of the probability distribution of a 500-member ensemble of ISSM-simulated ice volume at Thwaites Glacier in response to decadal variability in subice shelf melt rate. All ensemble members initialized with the modern state of Thwaites Glacier eventually reach complete deglaciation (Fig. 3B), in agreement with previous studies (24, 25). The rate of grounding-line migration (Fig. 3C) experiences significant variability over the course of the retreat due to the stochastic ocean forcing and the presence of forward-sloping “speed bumps” in the bed topography, both of which can slow the rate of retreat or even cause advance for short durations (28). Even with the relatively conservative assumption that there is no variability in surface mass balance and a small amplitude of subshelf melt variability (representing <2%<2% of the time-averaged subshelf melt), the spread in the ensemble spans ∼20 cm of uncertainty in projected sea-level rise during periods of fast retreat (i.e., the green probability distribution functions [PDFs] in Fig. 3A), with a probability distribution skewed in the direction of lower ice volume (greater contribution to sea level). This uncertainty is over 25% of the entire sea-level rise due to deglaciation of Thwaites Glacier and 50% of the median sea-level rise achieved during those periods of fast retreat. This spread between simulations amounts to instantaneous differences of hundreds of kilometers in the grounding-line position (Fig. 3D). Following this growth of uncertainty during the centuries of most rapid retreat, the ensemble then contracts and skews in the opposite direction as individual ensemble members achieve complete deglaciation of Thwaites Glacier, due to the limited model domain used in our simulations. In simulations of the entire Antarctic Ice Sheet in which the marine ice sheet instability spreads to other glaciers (5, 6), we would expect even faster amplification of uncertainty as multiple glaciers become involved in deglaciation.
Evolution of a 500-member ensemble of ISSM simulations of Thwaites Glacier evolution over 500 y (where year 0 in model time is the modern glacier state) in response to decadal variability and constant average in maximum subice shelf melt rate. (A) Evolution of ensemble PDF over time, plotted every 25 y, with probability on the y axis and Thwaites Glacier ice volume (in cm sea-level equivalent [SLE]) on the x axis. (B) Black lines are simulated ice volume contained in Thwaites Glacier catchment in cm SLE for all ensemble members. (C) Black dots are evolving grounding-line migration rates for all ensemble members (based on the centroid of the 2D grounding line). (D) Snapshots (red, orange, and pink lines) of grounding-line positions at year 635 in model time, from 5th percentile, 50th percentile, and 95th percentile ice volume ensemble members.
In Fig. 4, we compare Thwaites Glacier ensemble statistics, given a comparable amplitude (σM=1.4σM=1.4 m/y) of variability in MmaxMmax, but differing degrees of temporal persistence. As predicted by theory, ensemble spread (Fig. 4A) increases with longer persistence in forcing variability (proportional to τF−−√τF; SI Appendix). During the century of fastest retreat, multidecadal ocean variability (yellow line; τF=30τF=30 y) produces skewed uncertainty that is nearly 50% of the total ice loss from Thwaites glacier or ∼40 cm of uncertainty in projected sea-level rise. Some studies have suggested that Antarctic glaciers may be subject to such multidecadal variability in forcing through low-frequency coupled modes of the ocean–atmosphere system (26) or sporadic detachment of very large tabular icebergs (29).
Evolution of uncertainty and skewness of uncertainty in four Thwaites Glacier ensembles (500 simulations each). Three of the ensembles have variability in ocean forcing specified using a first-order autoregressive model: Including variability at interannual (τF=1.1τF=1.1 y, blue line), interdecadal (τF=10τF=10 y, red line; Fig. 3), and multidecadal (τF=30τF=30 y, yellow line) timescales. One ensemble has no temporal variability, but the constant maximum subshelf melt rate is uncertain and so drawn from a Gaussian distribution (with σM=5σM=5m/y and the same mean as other ensembles, purple line). (A) “Fractional projection uncertainty” given by the ratio of ensemble spread (measured by ±2σ±2σ of ensemble) to total ice loss at the end of simulation: 4σvol/μvloss4σvol/μvloss. (B) Ensemble skewness, with negative skewness representing a distribution skewed toward lower total ice volume (more ice loss and more sea-level rise).
Poorly constrained subice shelf properties [such as roughness (30)] and the small scale of the turbulent ice–ocean boundary layer make it difficult to accurately simulate even the time-averaged subice shelf melt rate given some change in global climate. Consequently, we also consider uncertainty in the time-averaged subshelf basal melt rate (which may also result from uncertainties in future anthropogenic emissions) by keeping MmaxMmax constant in time, but varying it between ensemble members (drawing from a Gaussian distribution with SD of 5 m/y). As in the minimal model, this ensemble (purple line in Fig. 4) has a very strong amplification of skewed uncertainty due to the accumulation of differences in subshelf basal melt rate among ensemble members over the course of the instability. For several centuries, the spread in this ensemble amounts to nearly the entire signal of ice loss from Thwaites Glacier (i.e., some ensemble members have retreated completely while others have lost almost no ice at all), skewed in the direction of more ice loss throughout most of the early period of the simulation.
Discussion and Conclusions
Studies of the future evolution of the Antarctic Ice Sheet have estimated the uncertainty in future sea-level rise due to poorly constrained model parameters (5, 6, 31⇓⇓–34). Other studies (35) have investigated the role of internal climate variability in the Greenland Ice Sheet contribution to sea-level rise, but with simulations that were too short to capture much of the marine ice sheet instability that may occur in the future. No study has provided a theoretical framework explaining the role of ice sheet dynamics in setting the amount and structure of uncertainty in sea-level rise projections. We provide such a theoretical framework in this study and find that ice sheet instabilities are amplifiers of uncertainty, which is a common mathematical property of unstable nonlinear systems (22). Although there are processes not considered here that might stabilize (36) or further destabilize (6) an ice sheet, our analysis shows that we should expect more rapid instability (of any kind) to cause more rapid uncertainty growth. Indeed, the theoretical framework developed in this study applies to a sufficiently broad set of assumptions regarding ice sheet dynamics, such that we expect that any type of ice sheet instability, regardless of the processes involved, will experience rapid growth in the ice sheet projection uncertainty during periods of most rapid instability. Integrating the contribution of marine ice sheet instability over many glaciers also integrates the uncertainty of each glacier’s future evolution, potentially leading to considerable uncertainty in sea-level projections, as has been seen in ensemble studies of total ice sheet contribution to future sea-level rise (5, 6, 32, 34, 35). We have shown that model ensembles can be used to quantify a range of possible scenarios for future sea-level rise, including potentially catastrophic scenarios of rapid sea-level rise. However, large model ensembles can be prohibitively expensive when extended to the entire Antarctic Ice Sheet. To fully capture the complete range of possible Antarctic futures, we will need efficient methods for uncertainty quantification (32, 37) and model order reduction that captures the complexities of ice sheet dynamics (31, 34). Such sophisticated methods will ensure that we can make the most useful sea-level projections beyond 2100 for those stakeholders who depend on them.
The study, published in the scientific journal PNAS, notes that the Thwaites Glacier is at a proverbial “tipping point” that could cause a neverending flow of ice into the world’s oceans.
“If you trigger this instability, you don’t need to continue to force the ice sheet by cranking up temperatures. It will keep going by itself, and that’s the worry,” said the study’s lead author and Georgia Tech professor Alex Robel, in a statement. “Climate variations will still be important after that tipping point because they will determine how fast the ice will move.”
The Thwaites Glacier is seen above. (NASA/OIB/Jeremy Harbeck)
NASA JPL scientist Helene Seroussi, who worked on the study along with Robel, said that the glacier could lose all of its ice over the next 150 years. “That would make for a sea level rise of about half a meter (1.64 feet),” Seroussi added in the statement.
The Thwaites Glacier is “the largest single source of uncertainty in projections of future sea-level rise,” according to the study’s abstract. If it were to collapse, it would make “worst-case scenarios of rapid sea-level rise more likely in future projections,” the abstract added.
“If you trigger this instability, you don’t need to continue to force the ice sheet by cranking up temperatures. It will keep going by itself, and that’s the worry.”
— Georgia Tech professor Alex Robel
The Antarctic ice sheet has more than 50 times the amount of ice than the mountain glaciers in the world combined, and eight times as much ice in the Greenland ice sheet, Robel added in the statement.
If and when the glacier becomes unstable, the after-effects would be considered “catastrophic.”
Thwaites Glacier acts like a giant cork that holds back the West Antarctic Ice Sheet. (NASA/James Yungel)
“Once [the] ice is past the grounding line and only over water, it’s contributing to sea level because buoyancy is holding it up more than it was before,” Robel said. “Ice flows out into the floating ice shelf and melts or breaks off as icebergs.”
The grounding line is the line between where the ice sheet rests on the seafloor and where it extends over the water.
As is common for most sea-level studies, the time scale for the study was in centuries and simulations showed that the ice loss for the Thwaites Glacier started after 600 years. However, the researchers warn that if ocean temperatures continue to rise, the instability in the glacier could occur much faster than many expect.
The huge cavity – which is approximately 1,000 feet tall, about as tall as New York City’s Chrysler Building – is growing at the bottom of the glacier and is large enough to have once contained 14 billion tons of ice, according to NASA. Most of that ice has melted over the past three years.
Images of vanishing Arctic ice and mountain glaciers are jarring, but their potential contributions to sea level rise are no match for Antarctica’s, even if receding southern ice is less eye-catching. Now, a study says that instability hidden within Antarctic ice is likely to accelerate its flow into the ocean and push sea level up at a more rapid pace than previously expected.
In the last six years, five closely observed Antarctic glaciers have doubled their rate of ice loss, according to the National Science Foundation. At least one, Thwaites Glacier, modeled for the new study, may be in danger of succumbing to this instability, a volatile process that pushes ice into the ocean fast.
How much ice the glacier will shed in coming 50 to 800 years can’t exactly be projected due to unpredictable fluctuations in climate and the need for more data. But researchers at the Georgia Institute of Technology, NASA Jet Propulsion Laboratory, and the University of Washington have factored the instability into 500 ice flow simulations for Thwaites with refined calculations.
The scenarios diverged strongly from each other but together pointed to the eventual triggering of the instability, which will be described in the question and answer section below. Even if global warming were to later stop, the instability would keep pushing ice out to sea at an enormously accelerated rate over the coming centuries.
And this is if ice melt due to warming oceans does not get worse than it is today. The study went with present-day ice melt rates because the researchers were interested in the instability factor in itself.
Glacier tipping point
“If you trigger this instability, you don’t need to continue to force the ice sheet by cranking up temperatures. It will keep going by itself, and that’s the worry,” said Alex Robel, who led the study and is an assistant professor in Georgia Tech’s School of Earth and Atmospheric Sciences. “Climate variations will still be important after that tipping point because they will determine how fast the ice will move.”
“After reaching the tipping point, Thwaites Glacier could lose all of its ice in a period of 150 years. That would make for a sea level rise of about half a meter (1.64 feet),” said NASA JPL scientist Helene Seroussi, who collaborated on the study. For comparison, current sea level is 20 cm (nearly 8 inches) above pre-global warming levels and is blamed for increased coastal flooding.
The researchers published their study in the journal the Proceedings of the National Academy of Sciences on Monday, July 8, 2019. The research was funded by the National Science Foundation and NASA.
The study also showed that the instability makes forecasting more uncertain, leading to the broad spread of scenarios. This is particularly relevant to the challenge of engineering against flood dangers.
“You want to engineer critical infrastructure to be resistant against the upper bound of potential sea level scenarios a hundred years from now,” Robel said. “It can mean building your water treatment plants and nuclear reactors for the absolute worst-case scenario, which could be two or three feet of sea level rise from Thwaites Glacier alone, so it’s a huge difference.”
Why is Antarctic ice the big driver of sea level rise?
Arctic sea ice is already floating in water. Readers will likely remember that 90% of an iceberg’s mass is underwater and that when its ice melts, the volume shrinks, resulting in no change in sea level.
But when ice masses long supported by land, like mountain glaciers, melt, the water that ends up in the ocean adds to sea level. Antarctica holds the most land-supported ice, even if much of that land is seabed holding up just part of the ice’s mass, while water holds up part of it. Also, Antarctica is an ice leviathan.
“There’s almost eight times as much ice in the Antarctic ice sheet as there is in the Greenland ice sheet and 50 times as much as in all the mountain glaciers in the world,” Robel said.
What is that ‘instability’ underneath the ice?
The line between where the ice sheet rests on the seafloor and where it extends over water is called the grounding line. In spots where the bedrock underneath the ice behind the grounding line slopes down, deepening as it moves inland, the instability can kick in.
On deeper beds, ice moves faster because water is giving it a little more lift. Also, warmer ocean water hollows out the bottom of the ice, adding a little more water to the ocean. More importantly, the ice above the hollow loses land contact and flows faster out to sea.
“Once ice is past the grounding line and just over water, it’s contributing to sea level because buoyancy is holding it up more than it was,” Robel said. “Ice flows out into the floating ice shelf and melts or breaks off as icebergs.”
“The process becomes self-perpetuating,” Seroussi said, describing why it is called “instability.”
How did the researchers integrate instability into sea level forecasting?
The researchers borrowed math from statistical physics that calculate what random variables do to predictability in a physical system, like ice flow, acted upon by outside forces, like temperature changes. They applied the math to simulations of possible future fates of marine glaciers like Thwaites Glacier.
They made an added surprising discovery. Normally, when climate conditions fluctuate strongly, Antarctic ice evens out the effects. Ice flow may increase but gradually, not wildly, but the instability produced the opposite effect in the simulations.
“The system didn’t damp out the fluctuations, it actually amplified them. It increased the chances of rapid ice loss,” Robel said.
How rapid is ‘rapid’ sea level rise and when will we feel it?
The study’s time scale was centuries, as is common for sea level studies. In the simulations, Thwaites Glacier colossal ice loss kicked in after 600 years, but it could come sooner.
“It could happen in the next 200 to 600 years. It depends on the bedrock topography under the ice, and we don’t know it in great detail yet,” Seroussi said.
So far, Antarctica and Greenland have lost a small fraction of their ice, but already, shoreline infrastructures face challenges from increased tidal flooding and storm surges. Sea level is expected to rise by up to two feet by the end of this century.
For about 2,000 years until the late 1800s, sea level held steady, then it began climbing, according to the Smithsonian Institution. The annual rate of sea level rise has roughly doubled since 1990.
Living in a warming world means experiencing a litany of unexpected events.
From an increase in the population of iguanas in Florida and super nests of wasps in Alabama, to world-class soccer stars competing in record-breaking heat in France and torrential rainfall in India, this week has seen a slew of unprecedented and unexpected climate impacts.
New analysis out this week by scientists trying to decipher the degree to which climate change played a role in these soaring temperatures revealed that global warming may indeed have made the heat wave “at least five times” more likely.
Areas in Switzerland, Germany, the Czech Republic and Spain also experienced record-breaking heat, and Austria logged its warmest June on record, which was “in large part due to the heat wave,” researchers said.
As a result, there were wildfires in Spain and 4,000 schools closed early in France. And in Toulouse, France, a conference on extreme weather and climate change was also disrupted.
Deadly rainfall in drought-stricken India
This week, at least 35 people died due to heavy rainfall in the Indian state of Maharashtra. On Tuesday, nearly 15 inches of rain fell in just 24 hours — the worstMumbai had experienced in 14 years. Flights and trains were cancelled and around 1,000 people were left stranded in the city awaiting rescue.
India’s monsoon season lasts from June until September. Typically, the country gets about 70% of its annual rainfall during this season — water on which farmers rely.
The deadly rainfall this week, however, comes after a drier-than-normal start to the monsoon season. June ended with a third less rainfall than the 50-year average, according to the India Meteorological Department. This has sparked concerns about access to adequate drinking water as well as fears over crop production; 9.5% less land has been cultivated this year for summer crops so far.
Meanwhile, a report by the United Nations’ International Labor Organization warns that India’s agriculture and construction sectors are expected to be hard-hit by climate change. Global warming, it states, will likely lead to a productivity loss equivalent to 34 million full-time jobs by 2030.
Warmer winters producing wasp ‘super nests’
Warmer winters could be leading to emergence of wasp ‘super nests’ as The New York Times reported recently.
In Alabama, at least four super nests — huge colonies made up of the aggressive yellow jacket wasps that survive for a second year rather than dying-off in winter — have been spotted so far. Typically, only about one or two such nests are spotted in a year, during June and July. However, the Alabama Cooperative Extension System issued a news release warning residents to expect more this year.
“Imagine a colony of yellow jackets the size of a Volkswagen Beetle, filled with 15,000 of the stinging insects. Now, imagine more than 90 of these super nests in Alabama,” the news release states.
That’s what the state experienced in 2006 and this year could be shaping up to be another record-breaker.
Yellow jacket wasps usually don’t survive in the cold — only the queens have an antifreeze compound in their blood that allows them to start a new colony in the spring. But with warmer winters and more queens surviving, that means more wasps are hatching.
Rapid sea ice loss in Antarctica
New satellite data reveals rapid sea ice loss in Antarctica. According to researchers, the continent has seen a “precipitous” fall in sea ice since 2014 with the rate of loss much faster than that experienced in the Arctic; as much sea ice was lost in four years in Antarctica as was lost in the Arctic over 34 years.
Scientists are still determining exactly what caused the dramatic loss in sea ice. In fact, the steep drop comes after 40 years of steady growth in Antarctica’s sea ice, further puzzling researchers as it reached a record low in 2017.
Unlike melting land ice, sea ice loss does not contribute to sea level rise. However, the loss of the highly-reflective white ice does contribute to global warming — darker surfaces such as open water absorb more heat than they reflect. The more sea ice is lost, the more heat is trapped, thereby leading to more ice loss in a vicious circle.
As Andrew Shepherd, a professor at Leeds University in the U.K., told The Guardian, “The rapid decline has caught us by surprise and changes the picture completely. Now sea ice is retreating in both hemispheres and that presents a challenge because it could mean further warming.”
Melting glaciers in Greenland are creating sand
Everyone knows that Greenland’s glaciers are melting. But with that comes a lot of erosion — and a lot of sand.
According to scientists, 8% of the annual sediment delivered to the world’s oceans comes from the Greenland ice sheet, and they expect that to increase with climate change.
And as The New York Times reported this week, scientists are starting a research project to see whether the “erosive power of ice” — one that is set to continue with climate change as glaciers melt — is enough to produce the highly sought after resource; sand is vital to the construction industry but it’s increasingly hard to come by as demand grows with urbanization.
More iguanas in Florida
Iguanas thrive in warmer weather. And now Florida’s Fish and Wildlife Conservation Commission has issued a notice encouraging homeowners to “kill green iguanas on their own property whenever possible.”
As one local resident who used to love seeing the reptiles around his home told The Washington Post, “They aren’t cute anymore…. They’re a menace.”
A proliferation of iguanas comes with a host of problems biologists say, including erosion, degradation of infrastructure (such as canal banks, sea walls, building foundations), and harm to landscaping and ornamental plants. They can also carry salmonella.
According to scientists, climate change is helping iguanas spread further north and more quickly. Between 2000 and 2018, for example, Grand Cayman island saw its iguana population expand from almost none to an estimated 1.6 million. Now, Florida is trying to take control before things in the state become similarly explosive.
It is palpable now. Even the most ardent deniers of human-caused climate disruption can feel the convulsions wracking the planet.
I truly believe this, given that, essentially, we are all of and from the Earth. Deep down inside all of us is the “fight or flight” instinct. Like any other animal, our very core knows when we are in danger, as the converging crises descend ever closer to home, wherever we may find ourselves on the globe.
This anxiety that increases by the day, this curious dread of what our climate-disrupted future will bring, is difficult to bear. Even those who have not already lost homes or loved ones to climate disruption-fueled extreme weather events have to live with the burden of this daily tension.
A recently published study showed that Earth’s glaciers are now melting five times more rapidly than they were in the 1960s.
“The glaciers shrinking fastest are in central Europe, the Caucasus region, western Canada, the U.S. Lower 48 states, New Zealand and near the tropics,” lead author Michael Zemp, director of the World Glacier Monitoring Service at the University of Zurich told Time Magazine. Glaciers in those places are losing an average of more than 1 percent of their mass each year, according to the study. “In these regions, at the current glacier loss rate, the glaciers will not survive the century,” added Zemp.
Meanwhile, the World Meteorological Organization announced that extreme weather events impacted 62 million people across the world last year. In 2018, 35 million people were struck by flooding, and Hurricanes Florence and Michael were just two of 14 “billion-dollar disasters” in 2018 in the U.S. More than 1,600 deaths were linked to heat waves and wildfires in Europe, Japan and the U.S. The report also noted the last four years were the warmest on record.
As an example of this last statistic, another report revealed that Canada is warming at twice the global rate. “We are already seeing the effects of widespread warming in Canada,” Elizabeth Bush, a climate science adviser at Environment Canada, told TheGuardian. “It’s clear, the science supports the fact that adapting to climate change is an imperative.”
Another recent report showed that the last time there was this much CO2 in the atmosphere (412 ppm), in the Pliocene Epoch 5.3 to 2.6 million years ago, sea levels were 20 meters higher than they are right now, trees were growing at the South Pole, and average global temperatures were 3 to 4 degrees Centigrade (3°-4° C) warmer, and even 10°C warmer in some areas. NASA echoed the report’s findings.
And if business as usual continues, emissions will only accelerate. The International Energy Agency announced that global carbon emissions set a record in 2018, rising 1.7 percent to a record 33.1 billion tons.
The impact of runaway emissions is already upon us. Several cities in the northern U.S., such as Buffalo, Cincinnati and Duluth, are already preparing to receive migrants from states like Florida, where residents are beset with increasing flooding, brutal heat waves, more severe and frequent hurricanes, sea level rise, and a worse allergy season. City planners in the aforementioned cities are already preparing by trying to figure out how to create jobs and housing for an influx of new residents.
Indications of the climate disruption refugee crisis are even more glaring in some other countries.
Large numbers of Guatemalan farmers already have to leave their landdue to drought, flooding, and increasingly severe extreme weather events.
In low-lying Bangladesh, hundreds of thousands of people are already in the process of being displaced from coastal homes, and are moving into poverty-stricken areas of cities that are already unprepared to receive the influx of people. Given that 80 percent of the population of the country already lives in a flood plain, the crisis can only escalate with time as sea level rise continues to accelerate.
Meanwhile, diseases spread by mosquitoes are also set to worsen in our increasingly warm world. A recently published study on the issue shows that over the next three decades, half a billion more people could be at risk of mosquito-delivered diseases.
Other migrations are occurring as well. In Canada’s Yukon, Indigenous elders told the CBC that caribou and moose are moving further north than ever before in order to escape the impacts of climate disruption like warmer summers, lakes and rivers that don’t freeze, and adjusting their migrations to find more food. This has deep impacts on the survival and culture of the area’s Indigenous residents.
In economic news, a researcher for the Federal Reserve Bank recently penned a letter urging central banks to note the financial risks, and possibly an impending financial crisis, brought about by climate disruption. “Without substantial and sustained global mitigation and regional adaptation efforts,” read the letter, “climate change is expected to cause growing losses to American infrastructure and property and impede the rate of economic growth over this century.”
Another report showed that climate disruption is already negatively impacting fruit breeders, and consumers will soon feel the pain of higher prices. “We are seeing industries that may not survive if we don’t find a solution, and we are only just seeing the consequences of climate change,” Thomas Gradziel, of the University of California at Davis, told The Washington Post.
Underscoring all of this, the Global Seed Vault in Svalbard, Norway, known as the “Doomsday Vault,” has already been altered by climate disruption impacts. The primary impacts thus far have been floodingaround the vault, given how warm temperatures have become across the Arctic. The Doomsday Vault holds nearly one million seeds from around the globe, and functions as a backup in case climate disruption, war, famine, or disease wipes out certain crops. In other words, it’s a backup plan to backup plans. A recent report showed that climate change’s impacts on the seed vault could get worse as snow season shortens, heavier and more frequent rainfalls escalate, and avalanches and mudslides near the vault become more common.
Lastly in this section, researchers recently warned that the Arctic has now entered an “unprecedented state” that is literally threatening the stability of the entire global climate system. Their paper, “Key Indicators of Arctic Climate Change: 1971–2017,” with both American and European climate scientists contributing, warned starkly that changes in the Arctic will continue to have massive and negative impacts around the globe.
“Because the Arctic atmosphere is warming faster than the rest of the world, weather patterns across Europe, North America, and Asia are becoming more persistent, leading to extreme weather conditions,” Jason Box, the lead author of the paper said.
As usual, there continue to be ample examples of the impacts of climate disruption in the watery realms of the planet.
In oceans, most of the sea turtles now being born are female; a crisis in sea turtle sex that is borne from climate disruption. This is due to the dramatically warmer sand temperatures where the eggs are buried. At a current ratio of 116/1 female/male, clearly this trend cannot continue indefinitely if sea turtles are to survive.
An alarming study showed recently that the number of new corals on the Great Barrier Reef has crashed by 89 percent after the mass bleaching events of 2016 and 2017. With coral bleaching events happening nearly annually now across many of the world’s reefs, such as the Great Barrier, we must remember that it takes an average of a decade for them to recover from a bleaching event. This is why some scientists in Australia believe the Great Barrier Reef to be in its “terminal stage.”
The UN recently sounded the alarm that urgent action is needed if Arab states are to avoid a water emergency. Water scarcity and desertification are afflicting the Middle East and North Africa more than any other region on Earth, hence the need for countries there to improve water management. However, the per capita share of fresh water availability there is already just 10 percent of the global average, with agriculture consuming 85 percent of it.
Another recent study has linked shrinking Arctic sea ice to less rain in Central America, adding to the water woes in that region as well.
In Alaska, warming continues apace. The Nenana Ice Classic, a competition where people guess when a tripod atop the frozen Nenana River breaks through the ice each spring, has resulted in a record this year of the earliest river ice breakup. It broke the previous record by nearly one full week.
Meanwhile, the pace of warming and the ensuing change across the Bering Sea is startling scientists there. Phenomena like floods during the winter and record low sea ice are generating great concern among scientists as well as Indigenous populations living there. “The projections were saying we would’ve hit situations similar to what we saw last year, but not for another 40 or 50 years,” Seth Danielson, a physical oceanographer at the University of Alaska Fairbanks, told The Associated Press of the diminishing sea ice.
In fact, people in the northernmost community of the Canadian Yukon, the village of Old Crow, are declaring a climate disruption State of Emergency. The chief of the Vuntut Gwitchin First Nation in the Yukon, Chief Dana Tizya-Tramm, has stated that his community’s traditional way of life is at stake, including thawing permafrost and rivers and lakes that no longer freeze deeply enough to walk across in the winter, making hunting and fishing difficult and dangerous. He said that declaring the climate emergency is his community’s responsibility to the rest of the planet.
Other signs of the dramatic warming across the Arctic abound. On Denali, North America’s highest mountain (20,310 feet), more than 66 tons of frozen feces left by climbers on the mountain are expected to begin thawing out of the glaciers there as early as this coming summer.
Another study found that tall ice cliffs around Greenland and the Antarctic are beginning to “slump,” behaving like soil and rock in sediment do before they break apart from the land and slide down a slope. Scientists believe the slumping ice cliffs may well be an ominous sign that could lead to more acceleration in global sea level rise, as far more ice is now poised to melt into the seas than previously believed.
In New Zealand, following the third hottest summer on record there, glaciers have been described by scientists as “sad and dirty,” with many of them having disappeared forever. Snow on a glacier protects the ice underneath it from melting, so this is another way scientists measure how rapidly a glacier can melt — if the snow is gone and the blue ice underneath it is directly exposed to the sun, it’s highly prone to melting. “Last year, the vast majority of glaciers had snowlines that were off the top of the mountain, and this year, we had some where we could see snowlines on, but they were very high,” NIWA Environmental Science Institute climate scientist Drew Lorrey told the New Zealand Herald. “On the first day of our survey, we observed 28 of them, and only about six of them had what I would call a snowline.”
Lastly in this section, another study warned that if emissions continue to increase at their current rate, ice will have all but vanished from European Alpine valleys by 2100. The study showed that half of the ice in the Alps’ 4,000 glaciers will be gone by 2050 with only the warming that is already baked into the system from past emissions. The study warned that even if we ceased all emissions at this moment, two-thirds of the ice will still have melted by 2100.
Washington State, in the traditionally damp and moist Pacific Northwest, has already had 50 wildfires this year. The state normally doesn’t see this number until the end of summer from late August through October, which is normally the peak of wildfire season.
Record-high temperatures continue to be set globally, especially in the Arctic.
High temperatures in March across the state of Alaska obliterated records. The statewide temperature for the entire month smashed the previous record by a whopping 4°F. Most rivers are melting out early, the town of Deadhorse in northern Alaska was 23 degrees above normal for the entire month of March, and for many days that month the industrial settlement near the Prudhoe Bay oil fields was 30 to 40 degrees above normal. Anchorage saw seven days with a record-high temperature for March, Juneau saw 10, Utquiagvik (formerly Barrow) saw six, as did Yakutat. Warmer temperature anomalies there have now become the norm.
Distressingly, another study revealed that melting permafrost across the Arctic could now be releasing 12 times as much nitrous oxide as previously thought. Nitrous oxide is an extremely powerful greenhouse gas, 300 times more potent than carbon dioxide, and can remain in the atmosphere for 114 years.
Recent research shows that Canada’s Arctic is now the warmest it has been in 10,000 years, and the temperatures are continuing to climb. Duane Froese, a professor at the University of Alberta and a co-author of the recent study on the topic, told the CBC,
“I would guess we’re getting back over 100,000 years since we’ve seen temperatures at least this warm.”
Another study has warned that climate disruption is set to raise Pittsburgh temperatures to the level of those of the southern U.S. states by 2080 … meaning the city of Pennsylvania will feel more like Jonesboro, Arkansas. That means Pittsburgh will be 10°F warmer, with summers 18 percent drier, and winters 45 percent wetter.
Scientists have warned that extreme hemispheric heat waves like that which occurred during 2018 are becoming more common due to climate disruption. They warn that these massive heatwaves will cover wider areas, and with just 2°C of warming (we are currently at 1.1°C) most summers will look like that of 2018. “From May to July, the heat waves affected 22 percent of the agricultural land and populated areas in the mid-latitudes of the Northern Hemisphere, from Canada and the United States to Russia, Japan and South Korea, killing hundreds of people, devastating crops and curtailing power production,” Inside Climate Newswrote of the study. “On an average day during those heat waves, 5.2 million square kilometers (about 2 million square miles) were affected by extreme heat, [Martha Vogel, an extreme-temperature researcher with ETH Zürich Institute for Atmospheric and Climate Science] said. At its peak extent in July, the affected area was twice as big.”
Another report has warned that warming temperatures across the globe could release into the atmosphere long-frozen radiation — from atomic bombs, Chernobyl and Fukushima. Radioactive particles are very light, and therefore, were transported very long distances across the atmosphere after nuclear detonations or radiological accidents. When the radioactive particles fall as snow, they can be stored in ice fields and glaciers for decades. If climate disruption melts the ice, the radiation is washed downstream and spreads throughout ecosystems.
Caroline Clason, a lecturer in physical geography at the University of Plymouth affiliated with the study, said an example of how this is already playing out came from Sweden, when wild boar there were found to have 10 times the levels of normal radiation in 2017. The radiation is likely to have come from Chernobyl, although radiation from all of these nuclear accidents is capable of spreading globally.
Denial and Reality
While this certainly comes as no surprise, yet another report came out highlighting how oil and gas giants are spending millions of dollars in their ongoing effort to lobby their paid politicians to block policies aimed at addressing climate disruption. The giant fossil fuel companies are spending an average of $200 million annually to weaken and/or oppose legislation aimed at addressing climate disruption. BP led the way in spending with $53 million, followed by Shell ($49 million), ExxonMobil ($41 million), Chevron and Total ($29 million each).
Meanwhile, as per usual, President Donald Trump has signed executive orders to speed up oil and gas pipeline projects, making it harder for states to block construction projects due to environmental concerns.
Yet, as the White House is actively denying climate disruption and working as hard as it can to promote fossil fuel use, the U.S. military is planning and preparing for dealing with the vast impacts of ongoing climate disruption. “People are acting on climate not for political reasons, but [because] it really affects their mission,” Jon Powers, an Iraq War veteran who served as the federal chief sustainability officer who is now president and chief executive of the investment firm CleanCapital, told The Washington Post. “With the military, it’s now ingrained in the culture and mission there, which I think is the biggest change over the last 10 years.”
Meanwhile, a federal climate disruption study panel and advisory group that was disbanded by the Trump administration due to it not having enough members “from industry,” recently released a report warning that the muddled political response to very clear climate science is putting Americans at risk.
“We were concerned that the federal government is missing an opportunity to get better information into the hands of those who prepare for what we have already unleashed,” Richard Moss, a visiting scientist at Columbia University, who previously chaired the federal panel and is a member of the group who released the report, told The Guardian. “We’re only just starting to see the effects of climate change, it’s only going to get much worse. But we haven’t yet rearranged our daily affairs to adapt to science we have.”
With each passing month, the impacts of runaway climate disruption continue to intensify. And as they do, so must our awareness of what is happening across the planet, and our resolve to take action to address it – especially since most governments around the world are failing to meet these challenges.
Glaciers are moody things with a myriad of personalities. Some are pretty stubborn, refusing to melt too much as Earth’s climate warms. But others are quite sensitive, with the potential to shrink more than you might expect if you push them too far.
Much of this has to do with the shape of the bedrock beneath. Some glaciers that touch the ocean have bedrock bases that slope downward as you head inland. If the glacier starts retreating downhill, seawater can flow in and float the ice more and more easily, destabilizing it so it retreats faster.
Each marine glacier has a “grounding line”—the point where ice stops resting on solid ground and starts floating, instead, like a canoe shoving off from shore. When you hear about an “ice shelf,” that’s the floating portion of the glacier. The position of the grounding line along the bedrock is where topography plays such a big role. But a new study from a team led by NASA’s Eric Larour shows how the bedrock can move, too, making these sensitive glaciers a little less sensitive.
The idea isn’t new. The retreat of these glaciers can be accelerated or slowed by a number of processes, including changing sea level out front. As sea level rises, the floating effect obviously increases, accelerating ice loss. And there are weirder factors: glaciers actually exert a gravitational attraction on the seawater around them, pulling a mound of water in close. If the glacier shrinks, that gravitational pull also shrinks, which actually lets water slosh away—lowering sea level at the coast.
Bedrock also responds to changes in the mass of ice on top. Increasing ice acts to slowly depress the land surface (which is why the land beneath Greenland’s ice sheet is roughly bowl-shaped). Losing ice allows the bedrock to rebound upwards. And in this case, that means that the bedrock at the grounding line beneath a sensitive glacier can spring upwards to meet the ice, helping to maintain the friction that slows retreat.
The question is, how much of an effect does this have? Many models that are used to simulate changing glaciers try to include these processes but are limited to coarser resolutions. In this new study, the researchers modeled Antarctica down to a resolution of 1 kilometer. It turns out that makes a pretty big difference.
The study is focused on Antarctica’s Thwaites Glacier, which is among the continent’s most sensitive and vulnerable—and therefore a major wildcard when it comes to how quickly future sea level rise will accumulate. Several versions of the model were run to simulate the next 500 years, each time adding another process to see what impact it had.
The two largest effects were rebounding bedrock followed by the gravitational attraction, both of which slowed Thwaites Glacier’s shrinkage. The higher model resolution showed that these processes were stronger in the immediate vicinity of the glacier than you would see in coarser models that average over larger areas. Together, they reduced the movement of the glacier’s grounding line by almost 40 percent in the year 2350, reducing its contribution to sea level rise by 25 percent.
While that result indicates that these processes could be important and helpful in the long run for glaciers like Thwaites, there was unfortunately very little difference this century. Around 2100, there was only a 1% change in sea level rise contribution. Larger changes in mass were required before rebounding bedrock or weaker gravitational attraction could become significant factors.
One of the more sobering facts about sea level rise is that it will continue long into the future, even if we successfully halt global warming. Ice sheets simply take a long time to fully respond to a warmer world. This study shows that complex factors like moving bedrock may not have a big impact on sensitive glaciers over the coming decades, but they have to be properly accounted for if you want to project those changes out a few centuries—where they can provide some rare good news.
Researchers say what was once the world’s second-largest colony of emperor penguins has “now all but disappeared” after changes in sea-ice conditions made their typical breeding grounds highly unstable.
A group of researchers from the British Antarctic Survey (BAS) published their findings in the Antarctic Science journal on Thursday. The team said in a statement that they studied “very high resolution satellite imagery to reveal the unusual findings.”
According to their research, satellite imagery showed that the emperor penguin colony at Halley Bay in Antarctica had drastically decreased over the past three years on account of breeding failures caused by severe changes in local environmental conditions.
“For the last 60 years the sea-ice conditions in the Halley Bay site have been stable and reliable,” the team said. “But in 2016, after a period of abnormally stormy weather, the sea-ice broke up in October, well before any emperor chicks would have fledged.”
The group said the conditions were repeated the following two years, leading to “the death of almost all the chicks at the site each season.”
“The colony at Halley Bay colony has now all but disappeared, whilst the nearby Dawson Lambton colony has markedly increased in size, indicating that many of the adult emperors have moved there, seeking better breeding grounds as environmental conditions have changed,” the researchers said.
Peter Fretwell, the lead author of the report and a remote sensing specialist at BAS, said the team has been studying the population of penguins at the Halley Bay colony and other nearby colonies for years using the high resolution satellite imagery.
“These images have clearly shown the catastrophic breeding failure at this site over the last three years,” Fretwell said. “Our specialized satellite image analysis can detect individuals and penguin huddles, so we can estimate the population based on the known density of the groups to give reliable estimate of colony size.”
Phil Trathan, a penguin expert with BAS who co-authored the report, said “it is impossible to say whether the changes in sea-ice conditions at Halley Bay are specifically related to climate change, but such a complete failure to breed successfully is unprecedented at this site.”
“Even taking into account levels of ecological uncertainty, published models suggest that emperor penguins numbers are set to fall dramatically,” he said, adding that the penguins are likely to lose between 50 percent and 70 percent “of their numbers before the end of this century as sea-ice conditions change as a result of climate change.”
The researchers said they plan to continue to study the colony’s response to the changing sea-ice conditions to help other scientists gain “vital information about how this iconic species might cope with future environmental change.”
Now we just got a new metric showing the severity of the situation.
A group of scientists have came together to discuss what we can learn about the environment by peering back into Earth’s history.
Looking back to the last time Earth’s atmosphere had this much carbon dioxide in it, the scene is rather dramatic: there were trees growing at the South Pole, sea levels were up to 20 metres (66 feet) higher, and global temperatures were 3-4°C above what they are today.
That paints a worrying picture about how much CO2 we’ve got in our air, and how our world might continue to change as temperatures go up.
Scientists from across the UK came together in a Royal Meteorological Society meeting on April 3 to discuss the most recent research in climate change, and how our distant past may soon come back to repeat itself.
One of the researchers, Jane Francis from the British Antarctic Survey, based her analysis on a finding of plant fossils and sedimentary records dating from the Pliocene epoch, between 5.3 million and 2.6 million years ago.
“This is an amazing discovery,” she told The Guardian. “They found fossil leaves of southern beech. I call them the last forests of Antarctica.”
“They were growing at 400 ppm [parts-per-million] CO2, so this may be where we are going back to, with ice sheets melting at times, which may allow plants to colonise again.”
Last year the amount of carbon dioxide in our atmosphere reached 410 ppm, thought to be the highest level in the last 800,000 years. We’re carrying on burning fossil fuels, and carbon dioxide keeps on building up.
So far we haven’t seen the sea level and temperature rises of the Pliocene, or much in the way of vegetation at the South Pole, but that’s the way we’re heading – these new findings are another stark warning about our future, as if we needed one.
“If you put your oven on at home and set it to 200C, the temperature doesn’t get to that level immediately,” said Martin Siegert from Imperial College London in the UK, who chaired the discussion. “It takes a bit of time.”
“And it’s the same with Earth’s climate. If you ratchet up the level of CO2 at 400 parts-per-million, it won’t suddenly get to an equilibrium overnight. It will take maybe 300 years or something.”
Polar regions are the most sensitive to climate change, and show the effects first – it’s like an early warning system for our planet.
When it comes to the discovery of South Pole forests, the indications are that when these fossilised leaves were growing, there were no ice sheets in Greenland and west Antarctica.
Summertime temperatures in Antarctica would have been around 5 degrees Celsius (41 degrees Fahrenheit), compared with the -15 to -20 degrees Celsius (5 to -4 degrees Fahrenheit) they are today.
At the current rate of emissions, the researchers suggest, we could be up to 1,000 ppm of CO2 in the atmosphere. Drastic steps are needed to stop that from happening, otherwise we’ll be back to the Pliocene era – or maybe even further.
And scientists are staring down the barrel of this new climate reality, as emphasised by palaeoclimate scientist Alan Haywood from the University of Leeds.
“After studying the Pliocene for 21 years, and all things being equal in the decades ahead, I will experience first hand a climate state that has not existed for more than three million years,” he said.
You can watch a recording of the meeting and view presentation abstracts here.
Earth’s sea levels should be nine meters higher than they are — and dramatic melting in Antarctica may soon plug the gap, scientists warn.
They say global temperatures today are the same as they were 115,000 years ago, a time when modern humans were only just beginning to leave Africa.
Research shows during this time period, known as the Eemian, scorching ocean temperatures caused a catastrophic global ice melt. As a result, sea levels were six to nine meters higher than they are today.
But if modern ocean temperatures are the same as they were during the Eemian, that means our planet is “missing” a devastating sea rise.
If oceans were to rise by just 1.8 meters, large swathes of coastal cities would find themselves underwater, turning streets into canals and completely submerging some buildings.
Scientists think sea levels made this jump 115,000 years ago because of a sudden ice collapse in Antarctica.
The continent’s vulnerable West Antarctic ice sheet — which is already retreating again today — released a lot of sea level rise in a hurry.
“There’s no way to get tens of meters of sea level rise without getting tens of meters of sea level rise from Antarctica,” said Dr. Rob DeConto, an Antarctic expert at the University of Massachusetts in the U.S.
His team created state-of-the-art computer models that showed how Antarctic ice responded to warm ocean temperatures during the Eemian.
They showed two processes, called marine ice cliff collapse and marine ice sheet instability, rapidly melted the West Antarctic ice sheet.
They exposed thick glaciers that formed part of the ice sheet to the ocean, meaning the ice blocks floated out to sea more quickly. Here they quickly melted, adding thousands of tonnes of water to the world’s oceans.
Scientists warn if ice shelves in Antarctica undergo similar processes, it could spell disaster for Earth. Combined with melting in Greenland, we could see sea levels rise by almost two meters this century.
In the next century, ice loss would get even worse.
“What we pointed out was if the kind of calving that we see in Greenland today were to start turning on in analogous settings in Antarctica — Antarctica has way thicker ice, it’s a way bigger ice sheet — the consequences would be potentially really monumental for sea level rise,” Dr. DeConto said.
Last month, NASA warned Antarctica’s Thwaites glacier could collapse within decades and “sink cities” after the discovery of a 300-meter doomsday cavity lurking below the ice block.
If you fancy a fright, check out this sea level “doomsday” simulator if you’d like to know whether your home would be wiped out by rising oceans.