Sea Ice Melt Research Articles

Observations of preferential summer melt of Arctic sea-ice ridge keels from repeated multibeam sonar surveys

Abstract. Sea-ice ridges constitute a large fraction of the total Arctic sea-ice area (up to 40 %–50 %); nevertheless, they are the least studied part of the ice pack. Here we investigate sea-ice melt rates using rare, repeated underwater multibeam sonar surveys that cover a period of 1 month during the advanced stage of sea-ice melt. Bottom melt increases with ice draft for first- and second-year level ice and a first-year ice ridge, with an average of 0.46, 0.55, and 0.95 m of total snow and ice melt in the observation period, respectively. On average, the studied ridge had a 4.6 m keel bottom draft, was 42 m wide, and had 4 % macroporosity. While bottom melt rates of ridge keel were 3.8 times higher than first-year level ice, surface melt rates were almost identical but responsible for 40 % of ridge draft decrease. Average cross-sectional keel melt ranged from 0.2 to 2.6 m, with a maximum point ice loss of 6 m, showcasing its large spatial variability. We attribute 57 % of the ridge total (surface and bottom) melt variability to keel draft (36 %), slope (32 %), and width (27 %), with higher melt for ridges with a larger draft, a steeper slope, and a smaller width. The melt rate of the ridge keel flanks was proportional to the draft, with increased keel melt within 10 m of its bottom corners and the melt rates between these corners comparable to the melt rates of level ice.

Separating Direct Heat Flux Forcing and Freshwater Feedback on AMOC Change Under Global Warming

AbstractThe Atlantic meridional overturning circulation (AMOC) is predicted to weaken under global warming. Whether it is caused by heat flux or freshwater flux is under debate. Here we separate these two processes in changing the AMOC under global warming. The simulated AMOC is weakened during the first 600 years and then gradually recovered to its initial state, with heat flux and freshwater feedback dominating at different timescales. Global warming immediately puts freshwater into the Southern Ocean, which triggers the initial AMOC weakening via altering surface temperature. Concurrently, the extensive heat into the ocean surface increases the temperature over the subpolar North Atlantic, reducing the deep convection and thus the AMOC in the subsequent 50–150 years. Meanwhile, the Arctic sea ice melt leads to the AMOC shutdown. Subsequently, the salinity accumulation in the subtropical North Atlantic propagating northward to restart the North Atlantic deep convection is responsible for the AMOC recovery.

Prevention and control of ship-source pollution in the Arctic shipping routes: challenges and countermeasures

Ship-source pollution is one of the important contributors to marine environment pollution. Because the legal status of the Arctic shipping routes is not clear, there is a considerable degree of dispute in the application of the rules on the prevention and control of ship-source pollution. The increased melting of sea ice undermines the legal legitimacy of the “ice-covered areas” clause under the United Nations Convention on the Law of the Sea. The conflict between the application of the Polar Code and “ice-covered areas” will also reach an initial conclusion in the context of melting sea ice. However, the inadequacy of ship-source pollution rules in the Polar Code hampers its application, which has led to a negative impact on the more active role in the governance of pollution from Arctic shipping. For replying to the Challenges in the prevention of ship-source pollution in Arctic shipping routes, the relevant rules of the Polar Code need to be further improved, while a more binding HFO ban according to ship types needs to be applied. Therefore, a more important role in the future Arctic governance mechanism will be played by the enhanced enforcement of the Polar Code, meanwhile, the target for uniform international regulation of preventing and controlling ship-source pollution in Arctic shipping routes should be achieved.

Physical Links from Atmospheric Circulation Patterns to Barents–Kara Sea Ice Variability from Synoptic to Seasonal Timescales in the Cold Season

Abstract Previous findings show that large-scale atmospheric circulation plays an important role in driving Arctic sea ice variability from synoptic to seasonal time scales. While some circulation patterns responsible for Barents–Kara sea ice changes have been identified in previous works, the most important patterns and the role of their persistence remain unclear. Our study uses self-organizing maps to identify nine high-latitude circulation patterns responsible for day-to-day Barents–Kara sea ice changes. Circulation patterns with a high pressure center over the Urals (Scandinavia) and a low pressure center over Iceland (Greenland) are found to be the most important for Barents–Kara sea ice loss. Their opposite-phase counterparts are found to be the most important for sea ice growth. The persistence of these circulation patterns helps explain sea ice variability from synoptic to seasonal time scales. We further use sea ice models forced by observed atmospheric fields (including the surface circulation and temperature) to reproduce observed sea ice variability and diagnose the role of atmosphere-driven thermodynamic and dynamic processes. Results show that thermodynamic and dynamic processes similarly contribute to Barents–Kara sea ice concentration changes on synoptic time scales via circulation. On seasonal time scales, thermodynamic processes seem to play a stronger role than dynamic processes. Overall, our study highlights the importance of large-scale atmospheric circulation, its persistence, and varying physical processes in shaping sea ice variability across multiple time scales, which has implications for seasonal sea ice prediction. Significance Statement Understanding what processes lead to Arctic sea ice changes is important due to their significant impacts on the ecosystem, weather, and shipping, and hence our society. A well-known process that causes sea ice changes is atmospheric circulation variability. We further pin down what circulation patterns and underlying mechanisms matter. We identify multiple circulation patterns responsible for sea ice loss and growth to different extents. We find that the circulation can cause sea ice loss by mechanically pushing sea ice northward and bringing warm and moist air to melt sea ice. The two processes are similarly important. Our study advances understanding of the Arctic sea ice variability with important implications for Arctic sea ice prediction.

Improvement of sea ice thermodynamics with variable sea ice salinity and melt pond parameterizations in an OGCM

Enhanced representation of sea ice processes in ocean modeling studies is required for advancing our understanding and prediction of the climate variability. In the present study, we improved the sea ice thermodynamics in an OGCM by introducing processes for variable sea ice salinity and melt ponds on sea ice. The former affects the latent heat and conductivity of sea ice as well as the salt budget in the ocean–sea ice system. We formulated salinification and desalination processes based on previous observational studies. Melt ponds enhance summertime surface melting by reducing the surface albedo. In our formulation of the melt pond thermodynamics, the shortwave radiation absorbed in the pond was partly released to the air and partly conducted to the underlying sea ice. By adopting these parameterizations, seasonal cycles of the sea ice salinity distributions in both hemispheres were generally reproduced. Simulated seasonal and interannual variations in the Arctic melt pond area and associated surface albedo reductions were basically consistent with observational estimates. The melt pond effect reduced the Arctic sea ice volume by about 1.5 × 103 km3 in the summer; half of this impact remained throughout the year. Our results suggest that the new parameterizations have the potential to improve the seasonal evolution of the sea ice thickness and concentration distributions, which would contribute to prediction studies.

The Pacific water flow branches in the eastern Chukchi Sea

The flow of Pacific-origin water across the Chukchi Sea shelf impacts the regional ecosystem in profound ways, yet the two current branches on the eastern shelf that carry the water from Bering Strait to Barrow Canyon – the Alaskan Coastal Current (ACC) and Central Channel (CC) Branch – have not been clearly distinguished or quantified. In this study we use an extensive collection of repeat hydrographic sections occupied at three locations on the Chukchi shelf, together with data from a climatology of shipboard velocity data, to accomplish this. The data were collected predominantly between 2010 and 2020 during the warm months of the year as part of the Distributed Biological Observatory and Arctic Observing Network. The mean sections show that mass is balanced for both currents at the three locations: Bering Strait, Point Hope, and Barrow Canyon. The overall mean ACC transport is 0.34 ± 0.04 Sv, and that of the CC Branch is 0.86 ± 0.11 Sv. The dominant hydrographic variability at Bering Strait is seasonal, but this becomes less evident to the north. At Barrow Canyon, the dominant hydrographic signal is associated with year-to-year variations in sea-ice melt. Farther south there is pronounced mesoscale variability: an empirical orthogonal function analysis at Bering Strait and Point Hope reveals a distinct ACC mode and CC Branch mode in hydrography and baroclinic transport, where the former is wind-driven. Finally, the northward evolution in properties of the two currents is investigated. The poleward increase in salinity of the ACC can be explained by lateral mixing alone, but solar heating together with wind mixing play a large role in the temperature evolution. This same atmospheric forcing also impacts the northward evolution of the CC Branch.

Decadal Changes in the Antarctic Sea Ice Response to the Changing ENSO in the Last Four Decades

Sea ice fraction (SIF) over the Ross/Amundsen/Bellingshausen Sea (RAB) are investigated using the Modern-Era Retrospective Analysis for Research and Application, Version 2 (MERRA-2), focusing on the differences in time-lagged response to ENSO between the late 20th (1980–2000, L20) and the early 21st century (2001–2021, E21). The findings suggest that the typical Antarctic response to ENSO is influenced by changes in ENSO type/intensity, highlighting the need for caution when investigating the Antarctic teleconnection. Time-lagged regressions onto the mature phase of El Niño reveal that the SIF decrease and SST increase over the RAB is relatively weaker in E21 and most pronounced at 0–4 months lag. Conversely, the SIF in L20 continues to decline and reaches its peak at two-season lag (5–7 months). Tropospheric wind, pressure, and wave activity in response to El Niño in L20 show a zonally oriented high/low-pressure areas with two-season lag, enhancing the poleward flow that plays a key role in sea ice melt in the RAB, while this pattern in E21 is insignificant at the same lag. This study suggests that stronger (weaker) and more eastern (central) Pacific ENSOs on average in L20 (E21) are associated with this decadal change in the SIF response to ENSO.

The Role of Local and Remote Processes for Wintertime Surface Energy Budget Extremes over Arctic Sea Ice

Abstract Arctic warm extremes and anomalous sea ice melting have been linked to episodic injections of warm and moist air from midlatitudes, as well as airmass transformations inside the Arctic. However, the relative importance of remote and local processes for such events remains unclear. Here, we focus on events with extreme positive daily-mean surface energy budget (SEB) anomalies over Arctic sea ice in ERA5 data during extended winters (November–March during 1979–2020). Kinematic backward trajectories from the tropospheric column collocated with the SEB anomalies show that near-surface air is of Arctic origin, whereas air farther aloft is transported poleward from the midlatitudes and ascends. Despite the different origin of the air, the entire tropospheric column shows pronounced potential temperature anomalies (on the order of 10 K) building up along air-parcel trajectories over 2–4 days. Quantifying the contributions of horizontal and vertical transport as well as diabatic processes to the generation of these potential temperature anomalies emphasizes the relevance of horizontal advection across the climatological potential temperature gradient for the generation of the anomalies at all levels. Anomalies aloft are further enhanced by latent heating and those near the surface by subsidence, respectively. Surface heat fluxes over subpolar and polar oceans are key for warming and moistening the near-surface air of predominantly Arctic origin and maintaining a positive potential temperature anomaly, which due to its proximity to the surface unfolds the strongest impact on the SEB. This suggests that Arctic airmasses and their local transformations are crucial for generating the most extreme SEB anomalies.

Impacts of glacial and sea-ice meltwater, primary production, and ocean CO2 uptake on ocean acidification state of waters by the 79 North Glacier and northeast Greenland shelf

The waters adjacent to the Nioghalvfjerdsbræ (79 North Glacier, 79NG) are influenced by Greenland Ice Sheet (GrIS) melt, sea-ice meltwater, and waters on the adjacent northeast Greenland shelf (NEGS). We investigated ocean acidification (OA) variables and the role of freshening, primary production, and air-sea CO2 exchange in Dijmphna Sound (DS) and on the NEGS in the summers of 2012 and 2016. The upper 150 m consisted of Polar Water with Arctic origin that was divided into a fresh surface layer (SL<50 m) and a cold halocline layer (CHL, 50 to 150 m). The layer below 150 m was of Atlantic origin. The SL freshwater was larger in 2012 than in 2016, mainly originated from local 79NG (and GrIS) runoff in DS, whereas on the NEGS in both years, it was mainly from sea-ice melt. The lowest aragonite saturation state (ΩAr) of 1.13 was found in the SL in 2012. Biological CO2 drawdown at primary production caused increased ΩAr in SL, which compensated for most of the ΩAr decrease due to the freshwater dilution of carbonate ions reducing total alkalinity, hence preventing corrosive conditions. This was most pronounced near the 79NG front in 2012, where surface stratification was most pronounced coinciding with large glacial meltwater fractions. Freshening decreased ΩAr by 0.4 at the 79NG front was compensated by biological CO2 drawdown by ~0.5. In 2016, a well-mixed water column in DS and NEGS, with dilution by sea-ice meltwater, caused less compensation on ΩAr by biological CO2 drawdown than in 2012. In future with changing climate and changing ocean chemistry, the increased meltwater effects may overcome the alleviating effects of biological CO2 drawdown on OA with unfavorable conditions for calcifying organisms. However, our study also suggests that primary production may be stimulated by stratification from surface meltwater. In addition, Atlantification and subglacial discharge may result in upwelling of inorganic nutrients that could promote primary production.

Sources and melt flux of methylmercury in sea ice on the Chukchi Plateau, Arctic Ocean

To identify the major source and melt flux of Hg in sea ice, we measured total Hg (THg) and methylmercury (MeHg) concentrations from sea ice cores collected from the Chukchi Plateau, Arctic Ocean. The THg maxima were found in the surface section (0–40 cm) of the cold cores (−2.3 ± 0.19 °C) and middle section (30–75 cm) of the warm cores (−1.9 ± 0.38 °C), whereas MeHg concentrations were nearly constant by core depth in the cold and warm cores. Using the enrichment factor mixing model, we estimated seawater to be the dominant source of THg over atmospheric deposition, both in the cold (89.1–99.6 %) and warm cores (98.4–99.7 %). The preliminary input estimation for MeHg showed that in situ methylation, instead of seawater input, was the potential source of MeHg in sea ice. The sea ice melt flux of MeHg in the Arctic Ocean was estimated to be 231 ± 77 kg yr−1 in the period of 2010–2020, which is insignificant compared with other external sources, such as atmospheric deposition, river discharge, and coastal erosion. Based on the results of the present study, the ongoing decline of sea ice extent related to polar amplification is likely to enhance MeHg production in sea ice in late spring and summer as a result of the improved light availability and consequent promotion of algal and microbial activities.

Climate change and seismic resilience: Key considerations for Alaska's infrastructure and built environment.

Alaska is one of the most seismically active regions of the world. Coincidentally, the state has also experienced dramatic impacts of climate change as it is warming at twice the rate of the rest of the United States. Through mechanisms such as permafrost thaw, water table fluctuation, and melting of sea ice and glaciers, climatic-driven changes to the natural and built-environment influence the seismic response of infrastructure systems. This paper discusses the challenges and needs posed by earthquake hazards and climate change to Alaska's infrastructure and built environment, drawing on the contributions of researchers and decision-makers in interviews and a workshop. It outlines policy, mitigation, and adaptation areas meriting further attention to improve the seismic resilience of Alaska's built environment from the perspectives of engineering and complementary coupled human-environmental systems.

Coastal Morphodynamics and Climate Change: A Review of Recent Advances

The shape of the coast and the processes that mold it change together as a complex system. There is constant feedback among the multiple components of the system, and when climate changes, all facets of the system change. Abrupt shifts to different states can also take place when certain tipping points are crossed. The coupling of rapid warming in the Arctic with melting sea ice is one example of positive feedback. Climate changes, particularly rising sea temperatures, are causing an increasing frequency of tropical storms and “compound events” such as storm surges combined with torrential rains. These events are superimposed on progressive rises in relative sea level and are anticipated to push many coastal morphodynamic systems to tipping points beyond which return to preexisting conditions is unlikely. Complex systems modeling results and long-term sets of observations from diverse cases help to anticipate future coastal threats. Innovative engineering solutions are needed to adapt to changes in coastal landscapes and environmental risks. New understandings of cascading climate-change-related physical, ecological, socioeconomic effects, and multi-faceted morphodynamic systems are continually contributing to the imperative search for resilience. Recent contributions, summarized here, are based on theory, observations, numerically modeled results, regional case studies, and global projections.

Potential Predictability of the Spring Bloom in the Southern Ocean Sea Ice Zone

AbstractEvery austral spring when Antarctic sea ice melts, favorable growing conditions lead to an intense phytoplankton bloom, which supports much of the local marine ecosystem. Recent studies have found that Antarctic sea ice is predictable several years in advance, suggesting that the spring bloom might exhibit similar predictability. Using a suite of perfect model predictability experiments, we find that November net primary production (NPP) is potentially predictable 7 to 10 years in advance in many Southern Ocean regions. Sea ice extent predictability peaks in late winter, followed by absorbed shortwave radiation and NPP with a 2 to 3 months lag. This seasonal progression of predictability supports our hypothesis that sea ice and light limitation control the inherent predictability of the spring bloom. Our results suggest skillful interannual predictions of NPP may be achievable, with implications for managing fisheries and the marine ecosystem, and guiding conservation policy in the Southern Ocean.

The weakening AMOC under extreme climate change

Changes in the Atlantic Meridional Overturning Circulation (AMOC) in the quadrupled CO2 experiments conducted under the sixth Coupled Model Intercomparison Project (CMIP6) are examined. Increased CO2 triggers extensive Arctic warming, causing widespread melting of sea ice. The resulting freshwater spreads southward, first from the Labrador Sea and then the Nordic Seas, and proceeds along the eastern coast of North America. The freshwater enters the subpolar gyre north of the separated Gulf Stream, the North Atlantic Current. This decreases the density gradient across the current and the current weakens in response, reducing the inflow to the deepwater production regions. The AMOC cell weakens in tandem, first near the North Atlantic Current and then spreading to higher and lower latitudes. This contrasts with the common perception that freshwater caps the convection regions, stifling deepwater production; rather, it is the inflow to the subpolar gyre that is suppressed. Changes in surface temperature have a much weaker effect, and there are no consistent changes in local or remote wind forcing among the models. Thus an increase in freshwater discharge, primarily from the Labrador Sea, is the precursor to AMOC weakening in these simulations.

Do Salinity Variations Along the East Greenland Shelf Show Imprints of Increasing Meltwater Runoff?

AbstractAccelerated melting of the Greenland Ice Sheet is considered a tipping element in the freshwater balance of the subpolar North Atlantic (SPNA). The East Greenland Current (EGC) and Coastal Current (EGCC) are the major conduits for transporting Arctic‐sourced and Greenland glacial freshwater. Understanding freshwater changes in the EGC system and drivers thereof is crucial for connecting tipping elements in the SPNA. Using the eddy‐rich model VIKING20X (1/20°) and Copernicus GLORYS12 (1/12°), we find that from 1993 to 2019 freshwater remains close to the shelf with interannual extremes in freshwater content (FWC) attributable to the imprint of Greenland melt only in years 2010 and 2012. Runoff increased significantly from 1995 to 2005 and Arctic freshwater export after 2005. Overall, regional wind patterns, sea ice melt and increasingly glacial ice and snow meltwater runoff along with the Arctic‐sourced Polar Water set interannual FWC variations in the EGC system. We emphasize that these freshwater sources have different seasonal timing. South of 65°N sea ice melts year round and retreats to north of 65°N, where melt in summer prevails. Greenland runoff peaks in June–August with only some locations of year round discharge. Alongshore winds intensify in fall and winter where reduced onshore Ekman transport allows for freshwater to spread laterally in the EGC. We show that sea ice melt, runoff and wind can cause interannual variations of comparable magnitude. All of which makes attributing ocean freshening events to Greenland meltwater inflow at current magnitudes a major challenge.

Enhanced Mixing at the Edges of Mesoscale Eddies Observed From High‐Resolution Seismic Data in the Western Arctic Ocean

AbstractIn recent years, the Arctic Ocean has experienced a dramatic decrease in sea ice cover, leading to enhanced turbulent mixing and eddy activity. Due to the scarcity of high‐resolution observations, our understanding of turbulent mixing in the Arctic is incomplete. Using three seismic reflection transects with high spatial resolution (∼O (10) m) and concurrent ADCP‐derived current velocity, this study identified 11 mesoscale eddies on the ice‐free Chukchi Borderlands of the western Arctic Ocean. 82% of them are intra‐halocline anticyclones. The total length of horizontal scales of these 11 eddies occupies ∼40% of the total length of three seismic lines. Diapycnal diffusivities estimated from seismic data were enhanced and can be up to 10−4 m2 s−1 at the edges of these eddies, compared with the average values (∼10−6 m2 s−1) at the Chukchi Borderlands. Seismic‐estimated diffusivities were validated by fine‐scale parameterization using ADCP‐derived velocity data and historical hydrographic data. Enhanced diffusivities at the edges of eddies may be attributed to shear instabilities at the top and bottom edges and to submesoscale motions at the lateral edges of these eddies. We highlight the enhanced mixing at the edges of eddies in the halocline can increase the upward heat flux. This upward heat flux can transfer the heat of the warm Atlantic water below to the surface, which may further promote the melting of surface sea ice.

Potential for natural attenuation of crude oil hydrocarbons in benthic microbiomes near coastal communities in Kivalliq, Nunavut, Canada

Oil spilled in marine environments can settle to the seafloor through aggregation and sedimentation processes. This has been predicted to be especially relevant in the Arctic due to plankton blooms initiated by melting sea ice. These conditions exist in the Kivalliq region in Nunavut, Canada, where elevated shipping traffic has increased the risk of accidental spills. Experimental microcosms combining surface sediment and crude oil were incubated at 4 °C over 21 weeks to evaluate the biodegradation potential of seabed microbiomes. Sediments sampled near the communities of Arviat and Chesterfield Inlet were assessed for biodegradation capabilities by combining hydrocarbon geochemistry with 16S rRNA gene and metagenomic sequencing, revealing decreased microbial diversity but enrichment of oil-degrading taxa. Alkane and aromatic hydrocarbon losses corresponded to detection of genes and genomes that encode enzymes for aerobic biodegradation of these compounds, pointing to the utility of marine microbiome surveys for predicting the fate of oil released into Arctic marine environments.

Freshwater Displacement Effect on the Weddell Gyre Carbon Budget

AbstractThe Weddell Gyre mediates carbon exchange between the abyssal ocean and atmosphere, which is critical to global climate. This region also features large and highly variable freshwater fluxes due to seasonal sea ice, net precipitation, and glacial melt; however, the impact of these freshwater fluxes on the regional carbon cycle has not been fully appreciated. Using a novel budget analysis of dissolved inorganic carbon (DIC) mass in the Biogeochemical Southern Ocean State Estimate, we highlight two freshwater‐driven transports. Where freshwater with minimal DIC enters the ocean, it displaces DIC‐rich seawater outwards, driving a lateral transport of 75 ± 5 Tg DIC/year. Additionally, sea ice export requires a compensating import of seawater, which carries 48 ± 11 Tg DIC/year into the gyre. Though often overlooked, these freshwater displacement effects are of leading order in the Weddell Gyre carbon budget in the state estimate and in regrouped box‐inversion estimates, with implications for evaluating basin‐scale carbon transport.

AMOC decline and recovery in a warmer climate

This study presents novel insight into the mechanisms of Atlantic Meridional Overturning Circulation (AMOC) reduction and its recovery under a warmer climate scenario. An one-thousand-year-long numerical simulation of a global coupled ocean–ice–atmosphere climate model, subjected to a stationary atmospheric radiative forcing, depict a coherent picture of the Arctic sea ice melting as a trigger for the initial AMOC reduction, along with decreases in the northward fluxes of salt and heat. Further atmospheric-driven ocean processes contribute to an erosion of the stable stratification of the fresher, yet colder waters in the surface layers of the North Atlantic, contributing to the recovery of a permanently altered AMOC.

Microbial metabolomic responses to changes in temperature and salinity along the western Antarctic Peninsula.

Seasonal cycles within the marginal ice zones in polar regions include large shifts in temperature and salinity that strongly influence microbial abundance and physiology. However, the combined effects of concurrent temperature and salinity change on microbial community structure and biochemical composition during transitions between seawater and sea ice are not well understood. Coastal marine communities along the western Antarctic Peninsula were sampled and surface seawater was incubated at combinations of temperature and salinity mimicking the formation (cold, salty) and melting (warm, fresh) of sea ice to evaluate how these factors may shape community composition and particulate metabolite pools during seasonal transitions. Bacterial and algal community structures were tightly coupled to each other and distinct across sea-ice, seawater, and sea-ice-meltwater field samples, with unique metabolite profiles in each habitat. During short-term (approximately 10-day) incubations of seawater microbial communities under different temperature and salinity conditions, community compositions changed minimally while metabolite pools shifted greatly, strongly accumulating compatible solutes like proline and glycine betaine under cold and salty conditions. Lower salinities reduced total metabolite concentrations in particulate matter, which may indicate a release of metabolites into the labile dissolved organic matter pool. Low salinity also increased acylcarnitine concentrations in particulate matter, suggesting a potential for fatty acid degradation and reduced nutritional value at the base of the food web during freshening. Our findings have consequences for food web dynamics, microbial interactions, and carbon cycling as polar regions undergo rapid climate change.