Burned out
Kyoto and Carbon Leakage: An Empirical Analysis of the Carbon Content of Bilateral Trade
Rahel Aichele & Gabriel Felbermayr
Review of Economics and Statistics, forthcoming
Abstract:
Has the Kyoto Protocol induced carbon leakage? We conduct the first empirical ex-post evaluation of the Protocol. We derive a theoretical gravity equation for the CO2 content of trade, which accounts for intermediate inputs, both domestic and imported. The structure of our new panel database of the carbon content of sectoral bilateral trade flows allows controlling for the endogenous selection of countries into the Kyoto Protocol. Binding commitments under Kyoto have increased committed countries' embodied carbon imports from non-committed countries by around 8% and the emission intensity of their imports by about 3%. Hence, Kyoto has indeed led to leakage.
----------------------
Carbon Emissions from the Commercial Building Sector: The Role of Climate, Quality, and Incentives
Matthew Kahn, Nils Kok & John Quigley
Journal of Public Economics, May 2014, Pages 1–12
Abstract:
Commercial buildings play a major role in determining U.S. greenhouse gas emissions, yet surprisingly little is known about the environmental performance of different buildings at a point in time or how the same buildings perform over time. By exploiting a unique panel of commercial buildings from a major electric utility, we study the association between a building’s electricity consumption and the physical attributes of buildings, lease incentive terms, indicators of human capital, and climatic conditions. We find that buildings that are newer and of higher quality consume more electricity, contrasting evidence for the residential sector. However, using our panel data set, we document that newer buildings are most resilient when exposed to hotter weather. Those buildings that have a building manager on site and whose tenants face a positive marginal cost for electricity also demonstrate a better environmental performance.
----------------------
Lucas Chancel
Ecological Economics, April 2014, Pages 195–207
Abstract:
Proper understanding of the determinants of household CO2 emissions is essential for a shift to sustainable lifestyles. This paper explores the impacts of date of birth and income on household CO2 emissions in France and in the USA. Direct CO2 emissions of French and American households are computed from consumer budget surveys, over the 1980–2000 time period. Age Period Cohort estimators are used to isolate the generational effect on CO2 emissions — i.e. the specific effect of date of birth, independent of the age, the year and other control variables. The paper shows that French 1935–55 cohorts have a stronger tendency to emit CO2 than their predecessors and followers. The generational effect is explained by the fact that over their lifespan, French baby boomers are better off than other generations and live in energy and carbon inefficient dwellings. In the USA, the absence of a generational effect on CO2 emissions can be explained by the fact that intergenerational income inequalities are weaker than in France. Persistence of the generational effect once income and housing type is controlled for in France can be explained by the difficulty for French 1935–55 cohorts to adapt to sober energy consumption patterns.
----------------------
Extreme Weather and Civil War: Does Drought Fuel Conflict in Somalia through Livestock Price Shocks?
Jean-François Maystadt & Olivier Ecker
American Journal of Agricultural Economics, forthcoming
Abstract:
A growing body of evidence shows a causal relationship between extreme weather events and civil conflict incidence at the global level. We find that this causality is also valid for droughts and local violent conflicts in a within-country setting over a short time frame in the case of Somalia. We estimate that a one standard deviation increase in drought intensity and length raises the likelihood of conflict by 62%. We also find that drought affects conflict through livestock price changes, establishing livestock markets as the primary channel of transmission in Somalia.
----------------------
Scientific uncertainty and climate change: Part I. Uncertainty and unabated emissions
Stephan Lewandowsky et al.
Climatic Change, forthcoming
Abstract:
Uncertainty forms an integral part of climate science, and it is often used to argue against mitigative action. This article presents an analysis of uncertainty in climate sensitivity that is robust to a range of assumptions. We show that increasing uncertainty is necessarily associated with greater expected damages from warming, provided the function relating warming to damages is convex. This constraint is unaffected by subjective or cultural risk-perception factors, it is unlikely to be overcome by the discount rate, and it is independent of the presumed magnitude of climate sensitivity. The analysis also extends to “second-order” uncertainty; that is, situations in which experts disagree. Greater disagreement among experts increases the likelihood that the risk of exceeding a global temperature threshold is greater. Likewise, increasing uncertainty requires increasingly greater protective measures against sea level rise. This constraint derives directly from the statistical properties of extreme values. We conclude that any appeal to uncertainty compels a stronger, rather than weaker, concern about unabated warming than in the absence of uncertainty.
----------------------
Unilateral Climate Policy: Harmful or Even Disastrous?
Hendrik Ritter & Mark Schopf
Environmental and Resource Economics, May 2014, Pages 155-178
Abstract:
This paper deals with possible foreign reactions to unilateral carbon demand reducing policies. It differentiates between demand side and supply side reactions as well as between intra- and inter-temporal shifts in greenhouse gas emissions. In our model, we integrate a stock-dependent marginal physical cost of extracting fossil fuels into Eichner and Pethig’s (Int Econ Rev 52(3):767–805, 2011) general equilibrium carbon leakage model. The results are as follows: Under similar but somewhat tighter conditions than those derived by Eichner and Pethig (Int Econ Rev 52(3):767–805, 2011), a weak green paradox arises. Furthermore, a strong green paradox can arise in our model under supplementary constraints. That means a “green” policy measure might not only lead to a harmful acceleration of fossil fuel extraction but to an increase in the cumulative climate damages at the same time. In some of these cases there is even a cumulative extraction expansion, which we consider disastrous.
----------------------
Nitrate assimilation is inhibited by elevated CO2 in field-grown wheat
Arnold Bloom et al.
Nature Climate Change, forthcoming
Abstract:
Total protein and nitrogen concentrations in plants generally decline under elevated CO2 atmospheres. Explanations for this decline include that plants under elevated CO2 grow larger, diluting the protein within their tissues; that carbohydrates accumulate within leaves, downregulating the amount of the most prevalent protein Rubisco; that carbon enrichment of the rhizosphere leads to progressively greater limitations of the nitrogen available to plants; and that elevated CO2 directly inhibits plant nitrogen metabolism, especially the assimilation of nitrate into proteins in leaves of C3 plants. Recently, several meta-analyses have indicated that CO2 inhibition of nitrate assimilation is the explanation most consistent with observations. Here, we present the first direct field test of this explanation. We analysed wheat (Triticum aestivum L.) grown under elevated and ambient CO2 concentrations in the free-air CO2 enrichment experiment at Maricopa, Arizona. In leaf tissue, the ratio of nitrate to total nitrogen concentration and the stable isotope ratios of organic nitrogen and free nitrate showed that nitrate assimilation was slower under elevated than ambient CO2. These findings imply that food quality will suffer under the CO2 levels anticipated during this century unless more sophisticated approaches to nitrogen fertilization are employed.
----------------------
Toward a better understanding and quantification of methane emissions from shale gas development
Dana Caulton et al.
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
The identification and quantification of methane emissions from natural gas production has become increasingly important owing to the increase in the natural gas component of the energy sector. An instrumented aircraft platform was used to identify large sources of methane and quantify emission rates in southwestern PA in June 2012. A large regional flux, 2.0–14 g CH4 s−1 km−2, was quantified for a ∼2,800-km2 area, which did not differ statistically from a bottom-up inventory, 2.3–4.6 g CH4 s−1 km−2. Large emissions averaging 34 g CH4/s per well were observed from seven well pads determined to be in the drilling phase, 2 to 3 orders of magnitude greater than US Environmental Protection Agency estimates for this operational phase. The emissions from these well pads, representing ∼1% of the total number of wells, account for 4–30% of the observed regional flux. More work is needed to determine all of the sources of methane emissions from natural gas production, to ascertain why these emissions occur and to evaluate their climate and atmospheric chemistry impacts.
----------------------
Volha Roshchanka & Meredydd Evans
Earth's Future, forthcoming
Abstract:
Reducing methane losses is a concern for climate change policy and energy policy. The energy sector is the major source of anthropogenic methane emissions into the atmosphere in Ukraine. Reducing methane emissions and avoiding combustion can be very cost-effective, but various barriers prevent such energy-efficiency measures from taking place. To date, few examples of industry-wide improvements exist. One example of substantial investments into upgrading natural gas transmission system comes from Ukraine's natural gas transmission company, Ukrtransgaz. The company's investments into system upgrades, along with a 34 percent fall in throughput, resulted in reduction of Ukrtransgaz system's own consumption of natural gas by 68 percent in 2011 compared to the level in 2005. Evaluating reductions in methane emissions is challenging because of lack of accurate data and gaps in accounting methodologies. At the same time, Ukraine's transmission system has undergone improvements that, at the very least, have contained methane emissions, if not substantially reduced them. In this paper, we describe recent developments in Ukraine's natural gas transmission system and analyze the incentives that forced the sector to pay close attention to its methane losses. Ukraine is one of the most energy-intensive countries, among the largest natural gas consumers in the world, and a significant emitter of methane. The country is also dependent on imports of natural gas. A combination of several factors has created conditions for successful reductions in methane emissions and combustion. These factors include: an eightfold increase in the price of imported natural gas; comprehensive domestic environmental and energy policies, such as the Laws of Ukraine on Protecting the Natural Environment and on Air Protection; policies aimed at integration with European Union's energy market and accession to the Energy Community Treaty; and the country's participation in international cooperation on environment, such as through the Joint Implementation mechanism and the voluntary Global Methane Initiative. Learning about such case studies can help policymakers and sustainability professionals design better policies elsewhere.
----------------------
Loss of cultural world heritage and currently inhabited places to sea-level rise
Ben Marzeion & Anders Levermann
Environmental Research Letters, March 2014
Abstract:
The world population is concentrated near the coasts, as are a large number of Cultural World Heritage sites, defined by the UNESCO. Using spatially explicit sea-level estimates for the next 2000 years and high-resolution topography data, we compute which current cultural heritage sites will be affected by sea-level rise at different levels of sustained future warming. As indicators for the pressure on future cultural heritage we estimate the percentage of each country's area loss, and the percentage of current population living in regions that will be permanently below sea level, for different temperature levels. If the current global mean temperature was sustained for the next two millennia, about 6% (40 sites) of the UNESCO sites will be affected, and 0.7% of global land area will be below mean sea level. These numbers increase to 19% (136 sites) and 1.1% for a warming of 3 K. At this warming level, 3–12 countries will experience a loss of more than half of their current land surface, 25–36 countries lose at least 10% of their territory, and 7% of the global population currently lives in regions that will be below local sea level. Given the millennial scale lifetime of carbon dioxide in the atmosphere, our results indicate that fundamental decisions with regard to mankind's cultural heritage are required.
----------------------
Yuan Wang et al.
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
Atmospheric aerosols affect weather and global general circulation by modifying cloud and precipitation processes, but the magnitude of cloud adjustment by aerosols remains poorly quantified and represents the largest uncertainty in estimated forcing of climate change. Here we assess the effects of anthropogenic aerosols on the Pacific storm track, using a multiscale global aerosol–climate model (GCM). Simulations of two aerosol scenarios corresponding to the present day and preindustrial conditions reveal long-range transport of anthropogenic aerosols across the north Pacific and large resulting changes in the aerosol optical depth, cloud droplet number concentration, and cloud and ice water paths. Shortwave and longwave cloud radiative forcing at the top of atmosphere are changed by −2.5 and +1.3 W m−2, respectively, by emission changes from preindustrial to present day, and an increased cloud top height indicates invigorated midlatitude cyclones. The overall increased precipitation and poleward heat transport reflect intensification of the Pacific storm track by anthropogenic aerosols. Hence, this work provides, for the first time to the authors’ knowledge, a global perspective of the effects of Asian pollution outflows from GCMs. Furthermore, our results suggest that the multiscale modeling framework is essential in producing the aerosol invigoration effect of deep convective clouds on a global scale.
----------------------
Vulnerability to the mortality effects of warm temperature in the districts of England and Wales
James Bennett et al.
Nature Climate Change, April 2014, Pages 269–273
Abstract:
Warm temperatures adversely affect disease occurrence and death, in extreme conditions as well as when the temperature changes are more modest1, 2. Therefore climate change, which is expected to affect both average temperatures and temperature variability, is likely to impact health even in temperate climates. Climate change risk assessment is enriched if there is information on vulnerability and resilience to effects of temperature. Some studies have analysed socio-demographic characteristics that make individuals vulnerable to adverse effects of temperature1, 2, 3, 4. Less is known about community-level vulnerability. We used geo-coded mortality and environmental data and Bayesian spatial methods to conduct a national small-area analysis of the mortality effects of warm temperature for all 376 districts in England and Wales. In the most vulnerable districts, those in London and south/southeast England, odds of dying from cardiorespiratory causes increased by more than 10% for 1 °C warmer temperature, compared with virtually no effect in the most resilient districts, which were in the far north. A 2 °C warmer summer may result in 1,552 (95% credible interval 1,307–1,762) additional deaths, about one-half of which would occur in 95 districts. The findings enable risk and adaptation analyses to incorporate local vulnerability to warm temperature and to quantify inequality in its effects.
----------------------
Global warming and 21st century drying
Benjamin Cook et al.
Climate Dynamics, forthcoming
Abstract:
Global warming is expected to increase the frequency and intensity of droughts in the twenty-first century, but the relative contributions from changes in moisture supply (precipitation) versus evaporative demand (potential evapotranspiration; PET) have not been comprehensively assessed. Using output from a suite of general circulation model (GCM) simulations from phase 5 of the Coupled Model Intercomparison Project, projected twenty-first century drying and wetting trends are investigated using two offline indices of surface moisture balance: the Palmer Drought Severity Index (PDSI) and the Standardized Precipitation Evapotranspiration Index (SPEI). PDSI and SPEI projections using precipitation and Penman-Monteith based PET changes from the GCMs generally agree, showing robust cross-model drying in western North America, Central America, the Mediterranean, southern Africa, and the Amazon and robust wetting occurring in the Northern Hemisphere high latitudes and east Africa (PDSI only). The SPEI is more sensitive to PET changes than the PDSI, especially in arid regions such as the Sahara and Middle East. Regional drying and wetting patterns largely mirror the spatially heterogeneous response of precipitation in the models, although drying in the PDSI and SPEI calculations extends beyond the regions of reduced precipitation. This expansion of drying areas is attributed to globally widespread increases in PET, caused by increases in surface net radiation and the vapor pressure deficit. Increased PET not only intensifies drying in areas where precipitation is already reduced, it also drives areas into drought that would otherwise experience little drying or even wetting from precipitation trends alone. This PET amplification effect is largest in the Northern Hemisphere mid-latitudes, and is especially pronounced in western North America, Europe, and southeast China. Compared to PDSI projections using precipitation changes only, the projections incorporating both precipitation and PET changes increase the percentage of global land area projected to experience at least moderate drying (PDSI standard deviation of ≤−1) by the end of the twenty-first century from 12 to 30 %. PET induced moderate drying is even more severe in the SPEI projections (SPEI standard deviation of ≤−1; 11 to 44 %), although this is likely less meaningful because much of the PET induced drying in the SPEI occurs in the aforementioned arid regions. Integrated accounting of both the supply and demand sides of the surface moisture balance is therefore critical for characterizing the full range of projected drought risks tied to increasing greenhouse gases and associated warming of the climate system.
----------------------
Methanogenic burst in the end-Permian carbon cycle
Daniel Rothman et al.
Proceedings of the National Academy of Sciences, 15 April 2014, Pages 5462–5467
Abstract:
The end-Permian extinction is associated with a mysterious disruption to Earth’s carbon cycle. Here we identify causal mechanisms via three observations. First, we show that geochemical signals indicate superexponential growth of the marine inorganic carbon reservoir, coincident with the extinction and consistent with the expansion of a new microbial metabolic pathway. Second, we show that the efficient acetoclastic pathway in Methanosarcina emerged at a time statistically indistinguishable from the extinction. Finally, we show that nickel concentrations in South China sediments increased sharply at the extinction, probably as a consequence of massive Siberian volcanism, enabling a methanogenic expansion by removal of nickel limitation. Collectively, these results are consistent with the instigation of Earth’s greatest mass extinction by a specific microbial innovation.
----------------------
Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming
Shfaqat Khan et al.
Nature Climate Change, April 2014, Pages 292–299
Abstract:
The Greenland ice sheet has been one of the largest contributors to global sea-level rise over the past 20 years, accounting for 0.5 mm yr−1 of a total of 3.2 mm yr−1. A significant portion of this contribution is associated with the speed-up of an increased number of glaciers in southeast and northwest Greenland. Here, we show that the northeast Greenland ice stream, which extends more than 600 km into the interior of the ice sheet, is now undergoing sustained dynamic thinning, linked to regional warming, after more than a quarter of a century of stability. This sector of the Greenland ice sheet is of particular interest, because the drainage basin area covers 16% of the ice sheet (twice that of Jakobshavn Isbræ) and numerical model predictions suggest no significant mass loss for this sector, leading to an under-estimation of future global sea-level rise. The geometry of the bedrock and monotonic trend in glacier speed-up and mass loss suggests that dynamic drawdown of ice in this region will continue in the near future.
----------------------
J. Mouginot, E. Rignot & B. Scheuchl
Geophysical Research Letters, 16 March 2014, Pages 1576–1584
Abstract:
We combine measurements of ice velocity from Landsat feature tracking and satellite radar interferometry, and ice thickness from existing compilations to document 41 years of mass flux from the Amundsen Sea Embayment (ASE) of West Antarctica. The total ice discharge has increased by 77% since 1973. Half of the increase occurred between 2003 and 2009. Grounding-line ice speeds of Pine Island Glacier stabilized between 2009 and 2013, following a decade of rapid acceleration, but that acceleration reached far inland and occurred at a rate faster than predicted by advective processes. Flow speeds across Thwaites Glacier increased rapidly after 2006, following a decade of near-stability, leading to a 33% increase in flux between 2006 and 2013. Haynes, Smith, Pope, and Kohler Glaciers all accelerated during the entire study period. The sustained increase in ice discharge is a possible indicator of the development of a marine ice sheet instability in this part of Antarctica.
----------------------
Global crop yield response to extreme heat stress under multiple climate change futures
Delphine Deryng et al.
Environmental Research Letters, March 2014
Abstract:
Extreme heat stress during the crop reproductive period can be critical for crop productivity. Projected changes in the frequency and severity of extreme climatic events are expected to negatively impact crop yields and global food production. This study applies the global crop model PEGASUS to quantify, for the first time at the global scale, impacts of extreme heat stress on maize, spring wheat and soybean yields resulting from 72 climate change scenarios for the 21st century. Our results project maize to face progressively worse impacts under a range of RCPs but spring wheat and soybean to improve globally through to the 2080s due to CO2 fertilization effects, even though parts of the tropic and sub-tropic regions could face substantial yield declines. We find extreme heat stress at anthesis (HSA) by the 2080s (relative to the 1980s) under RCP 8.5, taking into account CO2 fertilization effects, could double global losses of maize yield (ΔY = −12.8 ± 6.7% versus − 7.0 ± 5.3% without HSA), reduce projected gains in spring wheat yield by half (ΔY = 34.3 ± 13.5% versus 72.0 ± 10.9% without HSA) and in soybean yield by a quarter (ΔY = 15.3 ± 26.5% versus 20.4 ± 22.1% without HSA). The range reflects uncertainty due to differences between climate model scenarios; soybean exhibits both positive and negative impacts, maize is generally negative and spring wheat generally positive. Furthermore, when assuming CO2 fertilization effects to be negligible, we observe drastic climate mitigation policy as in RCP 2.6 could avoid more than 80% of the global average yield losses otherwise expected by the 2080s under RCP 8.5. We show large disparities in climate impacts across regions and find extreme heat stress adversely affects major producing regions and lower income countries.
----------------------
Greater ecosystem carbon in the Mojave Desert after ten years exposure to elevated CO2
R.D. Evans et al.
Nature Climate Change, forthcoming
Abstract:
Carbon dioxide is the main greenhouse gas inducing climate change. Increased global CO2 emissions, estimated at 8.4 Pg C yr−1 at present, have accelerated from 1% yr−1 during 1990–1999 to 2.5% yr−1 during 2000–2009. The carbon balance of terrestrial ecosystems is the greatest unknown in the global C budget because the actual magnitude, location and causes of terrestrial sinks are uncertain; estimates of terrestrial C uptake, therefore, are often based on the residuals between direct measurements of the atmospheric sink and well-constrained models of ocean uptake of CO2. Here we report significant terrestrial C accumulation caused by CO2 enhancement to net ecosystem productivity in an intact, undisturbed arid ecosystem following ten years of exposure to elevated atmospheric CO2. Results provide direct evidence that CO2 fertilization substantially increases ecosystem C storage and that arid ecosystems are significant, previously unrecognized, sinks for atmospheric CO2 that must be accounted for in efforts to constrain terrestrial and global C cycles.
----------------------
Potential Effects of Climate Change on the Productivity of U.S. Dairies
Nigel Key & Stacy Sneeringer
American Journal of Agricultural Economics, forthcoming
Abstract:
In the United States, climate change is likely to increase average daily temperatures and the frequency of heat waves, which can reduce meat and milk production in animals. Methods that livestock producers use to mitigate thermal stress — including modifications to animal management or housing — tend to increase production costs. We use operation-level economic data coupled with finely-scaled climate data to estimate how the local thermal environment affects the technical efficiency of dairies across the United States. We then use this information to estimate the possible decline in milk production in 2030 resulting from climate change-induced heat stress under the simplifying assumptions that the production technology, location of production, and other factors are held constant. For four climate model scenarios, the results indicate modest heat-stress-related production declines by 2030, with the largest declines occurring in the southern states.
----------------------
Distinct effects of anthropogenic aerosols on tropical cyclones
Yuan Wang et al.
Nature Climate Change, forthcoming
Abstract:
Long-term observations have revealed large amplitude fluctuations in the frequency and intensity of tropical cyclones (TCs), but the anthropogenic impacts, including greenhouse gases and particulate matter pollution, remain to be elucidated. Here, we show distinct aerosol effects on the development of TCs: the coupled microphysical and radiative effects of anthropogenic aerosols result in delayed development, weakened intensity and early dissipation, but an enlarged rainband and increased precipitation under polluted conditions. Our results imply that anthropogenic aerosols probably exhibit an opposite effect to that of greenhouse gases, highlighting the necessity of incorporating a realistic microphysical–radiative interaction of aerosols for accurate forecasting and climatic prediction of TCs in atmospheric models.
----------------------
The European climate under a 2 °C global warming
Robert Vautard et al.
Environmental Research Letters, March 2014
Abstract:
A global warming of 2 °C relative to pre-industrial climate has been considered as a threshold which society should endeavor to remain below, in order to limit the dangerous effects of anthropogenic climate change. The possible changes in regional climate under this target level of global warming have so far not been investigated in detail. Using an ensemble of 15 regional climate simulations downscaling six transient global climate simulations, we identify the respective time periods corresponding to 2 °C global warming, describe the range of projected changes for the European climate for this level of global warming, and investigate the uncertainty across the multi-model ensemble. Robust changes in mean and extreme temperature, precipitation, winds and surface energy budgets are found based on the ensemble of simulations. The results indicate that most of Europe will experience higher warming than the global average. They also reveal strong distributional patterns across Europe, which will be important in subsequent impact assessments and adaptation responses in different countries and regions. For instance, a North–South (West–East) warming gradient is found for summer (winter) along with a general increase in heavy precipitation and summer extreme temperatures. Tying the ensemble analysis to time periods with a prescribed global temperature change rather than fixed time periods allows for the identification of more robust regional patterns of temperature changes due to removal of some of the uncertainty related to the global models' climate sensitivity.
----------------------
Cessation of deep convection in the open Southern Ocean under anthropogenic climate change
Casimir de Lavergne et al.
Nature Climate Change, April 2014, Pages 278–282
Abstract:
In 1974, newly available satellite observations unveiled the presence of a giant ice-free area, or polynya, within the Antarctic ice pack of the Weddell Sea, which persisted during the two following winters. Subsequent research showed that deep convective overturning had opened a conduit between the surface and the abyssal ocean, and had maintained the polynya through the massive release of heat from the deep sea. Although the polynya has aroused continued interest, the presence of a fresh surface layer has prevented the recurrence of deep convection there since 1976, and it is now largely viewed as a naturally rare event. Here, we present a new analysis of historical observations and model simulations that suggest deep convection in the Weddell Sea was more active in the past, and has been weakened by anthropogenic forcing. The observations show that surface freshening of the southern polar ocean since the 1950s has considerably enhanced the salinity stratification. Meanwhile, among the present generation of global climate models, deep convection is common in the Southern Ocean under pre-industrial conditions, but weakens and ceases under a climate change scenario owing to surface freshening. A decline of open-ocean convection would reduce the production rate of Antarctic Bottom Waters, with important implications for ocean heat and carbon storage, and may have played a role in recent Antarctic climate change.