Due to the large heat capacity of the ocean and amount of time it takes for water to circulate there is a delay before the full effects of warming can be seen. This also means that there would be a delay between a reduction in atmospheric temperature and the cooling of the oceans. Tokarska and Zickfeld modeled sea level response to several scenarios of atmospheric CO 2 concentrations. pdf , Accessed July 12, Clark, A. Cazenave, J. Gregory, S. Jevrejeva, A. Levermann, M. Merrifield, G. Milne, R. Nerem, P. Nunn, A. Payne, W. Pfeffer, D. Stammer and A. Sea Level Change. In: Climate Change The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T. Qin, G. Plattner, M.

Tignor, S. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. Midgley eds. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Over the 20th century, the atmospheric concentrations of key greenhouse gases increased due to human activities. While some irreversible climate changes such as ice sheet collapse are possible but highly uncertain 1 , 4 , others can now be identified with greater confidence, and examples among the latter are presented in this paper. It is not generally appreciated that the atmospheric temperature increases caused by rising carbon dioxide concentrations are not expected to decrease significantly even if carbon emissions were to completely cease 5 — 7 see Fig.

Future carbon dioxide emissions in the 21st century will hence lead to adverse climate changes on both short and long time scales that would be essentially irreversible where irreversible is defined here as a time scale exceeding the end of the millennium in year ; note that we do not consider geo-engineering measures that might be able to remove gases already in the atmosphere or to introduce active cooling to counteract warming. For the same reason, the physical climate changes that are due to anthropogenic carbon dioxide already in the atmosphere today are expected to be largely irreversible. Such climate changes will lead to a range of damaging impacts in different regions and sectors, some of which occur promptly in association with warming, while others build up under sustained warming because of the time lags of the processes involved.

Here we illustrate 2 such aspects of the irreversibly altered world that should be expected. These aspects are among reasons for concern but are not comprehensive; other possible climate impacts include Arctic sea ice retreat, increases in heavy rainfall and flooding, permafrost melt, loss of glaciers and snowpack with attendant changes in water supply, increased intensity of hurricanes, etc. A complete climate impacts review is presented elsewhere 8 and is beyond the scope of this paper. We focus on illustrative adverse and irreversible climate impacts for which 3 criteria are met: i observed changes are already occurring and there is evidence for anthropogenic contributions to these changes, ii the phenomenon is based upon physical principles thought to be well understood, and iii projections are available and are broadly robust across models.

Carbon dioxide and global mean climate system changes relative to preindustrial conditions in from 1 illustrative model, the Bern 2. Results have been smoothed using an year running mean. The year variation seen in the carbon dioxide time series is introduced by the climatology used to force the terrestrial biosphere model Top Falloff of CO 2 concentrations following zero emissions after the peak. Middle Globally averaged surface warming degrees Celsius for these cases note that this model has an equilibrium climate sensitivity of 3. Warming over land is expected to be larger than these global averaged values, with the greatest warming expected in the Arctic 5.

Bottom Sea level rise meters from thermal expansion only not including loss of glaciers, ice caps, or ice sheets. Advances in modeling have led not only to improvements in complex Atmosphere—Ocean General Circulation Models AOGCMs for projecting 21st century climate, but also to the implementation of Earth System Models of Intermediate Complexity EMICs for millennial time scales. These 2 types of models are used in this paper to show how different peak carbon dioxide concentrations that could be attained in the 21st century are expected to lead to substantial and irreversible decreases in dry-season rainfall in a number of already-dry subtropical areas and lower limits to eventual sea level rise of the order of meters, implying unavoidable inundation of many small islands and low-lying coastal areas.

As has long been known, the removal of carbon dioxide from the atmosphere involves multiple processes including rapid exchange with the land biosphere and the surface layer of the ocean through air—sea exchange and much slower penetration to the ocean interior that is dependent upon the buffering effect of ocean chemistry along with vertical transport 9 — On the time scale of a millennium addressed here, the CO 2 equilibrates largely between the atmosphere and the ocean and, depending on associated increases in acidity and in ocean warming i. Carbon isotope studies provide important observational constraints on these processes and time constants. On multimillenium and longer time scales, geochemical and geological processes could restore atmospheric carbon dioxide to its preindustrial values 10 , 11 , but are not included here.

This is not intended to be a realistic scenario but rather to represent a test case whose purpose is to probe physical climate system changes. A more gradual reduction of carbon dioxide emission as is more likely , or a faster or slower adopted rate of emissions in the growth period, would lead to long-term behavior qualitatively similar to that illustrated in Fig. The example of a sudden cessation of emissions provides an upper bound to how much reversibility is possible, if, for example, unexpectedly damaging climate changes were to be observed. Carbon dioxide is the only greenhouse gas whose falloff displays multiple rather than single time constants see Fig.

Current emissions of major non-CO 2 greenhouse gases such as methane or nitrous oxide are significant for climate change in the next few decades or century, but these gases do not persist over time in the same way as carbon dioxide Assuming given cumulative emissions, EMI, the peak concentration, CO 2 peak increase over the preindustrial value CO 2 0 , and the resulting 1,year quasi-equilibrium concentration, CO 2 equi can be expressed as. Additional carbon cycle feedbacks could reduce the efficiency of the ocean and biosphere to remove the anthropogenic CO 2 and thereby increase these CO 2 values 15 , Further, a longer decay time and increased CO 2 concentrations at year are expected for large total carbon emissions This important result is due to a near balance between the long-term decrease of radiative forcing due to CO 2 concentration decay and reduced cooling through heat loss to the oceans.

It arises because long-term carbon dioxide removal and ocean heat uptake are both dependent on the same physics of deep-ocean mixing. Sea level rise due to thermal expansion accompanies mixing of heat into the ocean long after carbon dioxide emissions have stopped. For larger carbon dioxide concentrations, warming and thermal sea level rise show greater increases and display transient changes that can be very rapid i. Paleoclimatic evidence suggests that additional contributions from melting of glaciers and ice sheets may be comparable to or greater than thermal expansion discussed further below , but these are not included in Fig. time, while Fig. After emissions cease, the temperature change approaches equilibrium with respect to the slowly decreasing carbon dioxide concentrations cyan lines in Fig.

Related changes in fast-responding atmospheric climate variables such as precipitation, water vapor, heat waves, cloudiness, etc. Comparison between calculated time-dependent surface warming in the Bern2. Left The actual and equilibrium temperature changes based upon the model's climate sensitivity at equilibrium. The cyan lines in Right show the ratio of actual and equilibrium temperatures or realized fraction of the warming for the time-dependent CO 2 concentrations , while the magenta lines show the ratio of actual warming to the equilibrium temperature for the peak CO 2 concentration. Warming is expected to be linked to changes in rainfall 20 , which can adversely affect the supply of water for humans, agriculture, and ecosystems.

Precipitation is highly variable but long-term rainfall decreases have been observed in some large regions including, e. Confident projection of future changes remains elusive over many parts of the globe and at small scales. However, well-known physics the Clausius—Clapeyron law implies that increased temperature causes increased atmospheric water vapor concentrations, and changes in water vapor transport and the hydrologic cycle can hence be expected 26 — Attribution studies suggest that such a drying pattern is already occurring in a manner consistent with models including anthropogenic forcing 23 , particularly in the southwestern United States 22 and Mediterranean basin 24 , We use a suite of 22 available AOGCM projections based upon the evaluation in the IPCC report 5 , 29 to characterize precipitation changes.

Changes in precipitation are expected 5 , 20 , 30 to scale approximately linearly with increasing warming see Fig. On the other hand, the observed 20th century changes follow a similar latitudinal pattern but presently exceed those calculated by AOGCMs Models that include more complex representations of the land surface, soil, and vegetation interactively are likely to display additional feedbacks so that larger precipitation responses are possible. Here we evaluate the relationship between temperature and precipitation averaged for each month and over a decade at each grid point. One ensemble member is used for each model so that all AOGCMs are equally weighted in the multimodel ensemble; results are nearly identical if all available model ensemble members are used.

Some of these grid points occur in desert regions that are already very dry, but many occur in currently more temperate and semiarid locations. We find that model results are more robust over land across the available models over wider areas for drying of the dry season than for the annual mean or wet season see Fig. The Insets in Fig. Although given particular years would show exceptions, the long-term irreversible warming and mean rainfall changes as suggested by Figs. While some relief can be expected in the wet season for some regions Fig. The spatial changes in precipitation as shown in Fig. Such changes occurring not just for a few decades but over centuries are expected to have a range of impacts that differ by region.

These include, e. Expected decadally averaged changes in the global distribution of precipitation per degree of warming percentage of change in precipitation per degree of warming, relative to — as the baseline period in the dry season at each grid point, based upon a suite of 22 AOGCMs for a midrange future scenario A1B, see ref. White is used where fewer than 16 of 22 models agree on the sign of the change. Data are monthly averaged over several broad regions in Inset plots. Red lines show the best estimate median of the changes in these regions, while the red shading indicates the ±1-σ likely range i.

We use 3 °C as the best estimate of climate sensitivity across the suite of AOGCMs for a doubling of carbon dioxide from preindustrial values 5 along with the regional drying values depicted in Fig. Illustrative irreversible climate changes as a function of peak carbon dioxide reached. Upper Best estimate of expected irreversible dry-season precipitation changes for the regions shown in Fig. The precipitation change per degree is derived for each region as in Fig. Lower Corresponding irreversible global warming black line. Also shown is the associated lower limit of irreversible sea level rise because of thermal expansion only based upon a range of 0.

Anthropogenic carbon dioxide will cause irrevocable sea level rise. There are 2 relatively well-understood processes that contribute to this and a third that may be much more important but is also very uncertain. Warming causes the ocean to expand and sea levels to rise as shown in Fig. Loss of land ice also makes important contributions to sea level rise as the world warms. Mountain glaciers in many locations are observed to be retreating due to warming, and this contribution to sea level rise is also relatively well understood. Additional rapid ice losses from particular parts of the ice sheets of Greenland and Antarctica have recently been observed 40 — One recent study uses current ice discharge data to suggest ice sheet contributions of up to 1—2 m to sea level rise by 42 , but other studies suggest that changes in winds rather than warming may account for currently observed rapid ice sheet flow 43 , rendering quantitative extrapolation into the future uncertain.

In addition to rapid ice flow, slow ice sheet mass balance processes are another mechanism for potential large sea level rise. Paleoclimatic data demonstrate large contributions of ice sheet loss to sea level rise 1 , 4 but provide limited constraints on the rate of such processes. Some recent studies suggest that ice sheet surface mass balance loss for peak CO 2 concentrations of — ppmv may be even slower than the removal of manmade carbon dioxide following cessation of emissions, so that this loss could contribute less than a meter to irreversible sea level rise even after many thousands of years 44 , It is evident that the contribution from the ice sheets could be large in the future, but the dependence upon carbon dioxide levels is extremely uncertain not only over the coming century but also in the millennial time scale.

An assessed range of models suggests that the eventual contribution to sea level rise from thermal expansion of the ocean is expected to be 0. For lower values of warming, partial remnants of glaciers might be retained, but this has not been examined in detail for realistic representations of glacier shrinkage and is not quantified here. Sea level rise can be expected to affect many coastal regions While sea walls and other adaptation measures might combat some of this sea level rise, Fig. It is sometimes imagined that slow processes such as climate changes pose small risks, on the basis of the assumption that a choice can always be made to quickly reduce emissions and thereby reverse any harm within a few years or decades.

We have shown that this assumption is incorrect for carbon dioxide emissions, because of the longevity of the atmospheric CO 2 perturbation and ocean warming. Irreversible climate changes due to carbon dioxide emissions have already taken place, and future carbon dioxide emissions would imply further irreversible effects on the planet, with attendant long legacies for choices made by contemporary society. Discount rates used in some estimates of economic trade-offs assume that more efficient climate mitigation can occur in a future richer world, but neglect the irreversibility shown here.

Similarly, understanding of irreversibility reveals limitations in trading of greenhouse gases on the basis of year estimated climate changes global warming potentials, GWPs , because this metric neglects carbon dioxide's unique long-term effects. In this paper we have quantified how societal decisions regarding carbon dioxide concentrations that have already occurred or could occur in the coming century imply irreversible dangers relating to climate change for some illustrative populations and regions. These and other dangers pose substantial challenges to humanity and nature, with a magnitude that is directly linked to the peak level of carbon dioxide reached. The AOGCM simulation data presented in this paper are part of the World Climate Research Program's WCRP's Coupled Model Intercomparison Project phase 3 CMIP3 multimodel data set 29 and are available from the Program for Climate Model Diagnosis and Intercomparison PCMDI www-pcmdi.

php , where further information on the AOGCMs can also be obtained. The EMIC used in this study is the Bern2. It is a coupled climate—carbon cycle model of intermediate complexity that consists of a zonally averaged dynamic ocean model, a 1-layer atmospheric energy—moisture balance model, and interactive representations of the marine and terrestrial carbon cycles. We gratefully acknowledge the modeling groups, the Program for Climate Model Diagnosis and Intercomparison, and the World Climate Research Program's Working Group on Coupled Modeling for their roles in making available the Working Group on Coupled Modeling's Coupled Model Intercomparison Project phase 3 multimodel data set.

Support of this data set is provided by the Office of Science, U. Department of Energy. We also appreciate helpful comments from 3 reviewers. The authors declare no conflict of interest. This article contains supporting information online at www. Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation. Proc Natl Acad Sci U S A. Published online Jan doi: PMCID: PMC Susan Solomon , a, 1 Gian-Kasper Plattner , b Reto Knutti , c and Pierre Friedlingstein d. Susan Solomon a Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO ; Find articles by Susan Solomon. Gian-Kasper Plattner b Institute of Biogeochemistry and Pollutant Dynamics and Find articles by Gian-Kasper Plattner.

Reto Knutti c Institute for Atmospheric and Climate Science, ETH CH, Zurich, Switzerland; and Find articles by Reto Knutti. Author information Article notes Copyright and License information Disclaimer. c Institute for Atmospheric and Climate Science, ETH CH, Zurich, Switzerland; and. E-mail: vog. aaon nomolos. Received Nov Copyright © by The National Academy of Sciences of the USA. Associated Data Supplementary Materials Supporting Information. html bytes. pdf K. Abstract The severity of damaging human-induced climate change depends not only on the magnitude of the change but also on the potential for irreversibility. Keywords: dangerous interference, precipitation, sea level rise, warming. Open in a separate window. Results Longevity of an Atmospheric CO 2 Perturbation. Irreversible Climate Change: Atmospheric Warming.

Irreversible Climate Change: Precipitation Changes. Irreversible Climate Change: Sea Level Rise. Discussion: Some Policy Implications It is sometimes imagined that slow processes such as climate changes pose small risks, on the basis of the assumption that a choice can always be made to quickly reduce emissions and thereby reverse any harm within a few years or decades. Materials and Methods The AOGCM simulation data presented in this paper are part of the World Climate Research Program's WCRP's Coupled Model Intercomparison Project phase 3 CMIP3 multimodel data set 29 and are available from the Program for Climate Model Diagnosis and Intercomparison PCMDI www-pcmdi.

Supplementary Material Supporting Information: Click here to view. Footnotes The authors declare no conflict of interest. References 1. Hansen J, et al.

The new PMC design is here! Learn more about navigating our updated article layout. The PMC legacy view will also be available for a limited time. Federal government websites often end in. gov or. The site is secure. a Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO ;. Author contributions: S. designed research; S. performed research; G. and R. analyzed data; and S. wrote the paper. The severity of damaging human-induced climate change depends not only on the magnitude of the change but also on the potential for irreversibility. This paper shows that the climate change that takes place due to increases in carbon dioxide concentration is largely irreversible for 1, years after emissions stop.

Following cessation of emissions, removal of atmospheric carbon dioxide decreases radiative forcing, but is largely compensated by slower loss of heat to the ocean, so that atmospheric temperatures do not drop significantly for at least 1, years. Thermal expansion of the warming ocean provides a conservative lower limit to irreversible global average sea level rise of at least 0. Additional contributions from glaciers and ice sheet contributions to future sea level rise are uncertain but may equal or exceed several meters over the next millennium or longer. Over the 20th century, the atmospheric concentrations of key greenhouse gases increased due to human activities. While some irreversible climate changes such as ice sheet collapse are possible but highly uncertain 1 , 4 , others can now be identified with greater confidence, and examples among the latter are presented in this paper.

It is not generally appreciated that the atmospheric temperature increases caused by rising carbon dioxide concentrations are not expected to decrease significantly even if carbon emissions were to completely cease 5 — 7 see Fig. Future carbon dioxide emissions in the 21st century will hence lead to adverse climate changes on both short and long time scales that would be essentially irreversible where irreversible is defined here as a time scale exceeding the end of the millennium in year ; note that we do not consider geo-engineering measures that might be able to remove gases already in the atmosphere or to introduce active cooling to counteract warming. For the same reason, the physical climate changes that are due to anthropogenic carbon dioxide already in the atmosphere today are expected to be largely irreversible.

Such climate changes will lead to a range of damaging impacts in different regions and sectors, some of which occur promptly in association with warming, while others build up under sustained warming because of the time lags of the processes involved. Here we illustrate 2 such aspects of the irreversibly altered world that should be expected. These aspects are among reasons for concern but are not comprehensive; other possible climate impacts include Arctic sea ice retreat, increases in heavy rainfall and flooding, permafrost melt, loss of glaciers and snowpack with attendant changes in water supply, increased intensity of hurricanes, etc.

A complete climate impacts review is presented elsewhere 8 and is beyond the scope of this paper. We focus on illustrative adverse and irreversible climate impacts for which 3 criteria are met: i observed changes are already occurring and there is evidence for anthropogenic contributions to these changes, ii the phenomenon is based upon physical principles thought to be well understood, and iii projections are available and are broadly robust across models. Carbon dioxide and global mean climate system changes relative to preindustrial conditions in from 1 illustrative model, the Bern 2. Results have been smoothed using an year running mean. The year variation seen in the carbon dioxide time series is introduced by the climatology used to force the terrestrial biosphere model Top Falloff of CO 2 concentrations following zero emissions after the peak.

Middle Globally averaged surface warming degrees Celsius for these cases note that this model has an equilibrium climate sensitivity of 3. Warming over land is expected to be larger than these global averaged values, with the greatest warming expected in the Arctic 5. Bottom Sea level rise meters from thermal expansion only not including loss of glaciers, ice caps, or ice sheets. Advances in modeling have led not only to improvements in complex Atmosphere—Ocean General Circulation Models AOGCMs for projecting 21st century climate, but also to the implementation of Earth System Models of Intermediate Complexity EMICs for millennial time scales. These 2 types of models are used in this paper to show how different peak carbon dioxide concentrations that could be attained in the 21st century are expected to lead to substantial and irreversible decreases in dry-season rainfall in a number of already-dry subtropical areas and lower limits to eventual sea level rise of the order of meters, implying unavoidable inundation of many small islands and low-lying coastal areas.

As has long been known, the removal of carbon dioxide from the atmosphere involves multiple processes including rapid exchange with the land biosphere and the surface layer of the ocean through air—sea exchange and much slower penetration to the ocean interior that is dependent upon the buffering effect of ocean chemistry along with vertical transport 9 — On the time scale of a millennium addressed here, the CO 2 equilibrates largely between the atmosphere and the ocean and, depending on associated increases in acidity and in ocean warming i. Carbon isotope studies provide important observational constraints on these processes and time constants. On multimillenium and longer time scales, geochemical and geological processes could restore atmospheric carbon dioxide to its preindustrial values 10 , 11 , but are not included here.

This is not intended to be a realistic scenario but rather to represent a test case whose purpose is to probe physical climate system changes. A more gradual reduction of carbon dioxide emission as is more likely , or a faster or slower adopted rate of emissions in the growth period, would lead to long-term behavior qualitatively similar to that illustrated in Fig. The example of a sudden cessation of emissions provides an upper bound to how much reversibility is possible, if, for example, unexpectedly damaging climate changes were to be observed. Carbon dioxide is the only greenhouse gas whose falloff displays multiple rather than single time constants see Fig.

Current emissions of major non-CO 2 greenhouse gases such as methane or nitrous oxide are significant for climate change in the next few decades or century, but these gases do not persist over time in the same way as carbon dioxide Assuming given cumulative emissions, EMI, the peak concentration, CO 2 peak increase over the preindustrial value CO 2 0 , and the resulting 1,year quasi-equilibrium concentration, CO 2 equi can be expressed as. Additional carbon cycle feedbacks could reduce the efficiency of the ocean and biosphere to remove the anthropogenic CO 2 and thereby increase these CO 2 values 15 , Further, a longer decay time and increased CO 2 concentrations at year are expected for large total carbon emissions This important result is due to a near balance between the long-term decrease of radiative forcing due to CO 2 concentration decay and reduced cooling through heat loss to the oceans.

It arises because long-term carbon dioxide removal and ocean heat uptake are both dependent on the same physics of deep-ocean mixing. Sea level rise due to thermal expansion accompanies mixing of heat into the ocean long after carbon dioxide emissions have stopped. For larger carbon dioxide concentrations, warming and thermal sea level rise show greater increases and display transient changes that can be very rapid i. Paleoclimatic evidence suggests that additional contributions from melting of glaciers and ice sheets may be comparable to or greater than thermal expansion discussed further below , but these are not included in Fig.

time, while Fig. After emissions cease, the temperature change approaches equilibrium with respect to the slowly decreasing carbon dioxide concentrations cyan lines in Fig. Related changes in fast-responding atmospheric climate variables such as precipitation, water vapor, heat waves, cloudiness, etc. Comparison between calculated time-dependent surface warming in the Bern2. Left The actual and equilibrium temperature changes based upon the model's climate sensitivity at equilibrium. The cyan lines in Right show the ratio of actual and equilibrium temperatures or realized fraction of the warming for the time-dependent CO 2 concentrations , while the magenta lines show the ratio of actual warming to the equilibrium temperature for the peak CO 2 concentration.

Warming is expected to be linked to changes in rainfall 20 , which can adversely affect the supply of water for humans, agriculture, and ecosystems. Precipitation is highly variable but long-term rainfall decreases have been observed in some large regions including, e. Confident projection of future changes remains elusive over many parts of the globe and at small scales. However, well-known physics the Clausius—Clapeyron law implies that increased temperature causes increased atmospheric water vapor concentrations, and changes in water vapor transport and the hydrologic cycle can hence be expected 26 — Attribution studies suggest that such a drying pattern is already occurring in a manner consistent with models including anthropogenic forcing 23 , particularly in the southwestern United States 22 and Mediterranean basin 24 , We use a suite of 22 available AOGCM projections based upon the evaluation in the IPCC report 5 , 29 to characterize precipitation changes.

Changes in precipitation are expected 5 , 20 , 30 to scale approximately linearly with increasing warming see Fig. On the other hand, the observed 20th century changes follow a similar latitudinal pattern but presently exceed those calculated by AOGCMs Models that include more complex representations of the land surface, soil, and vegetation interactively are likely to display additional feedbacks so that larger precipitation responses are possible. Here we evaluate the relationship between temperature and precipitation averaged for each month and over a decade at each grid point.

One ensemble member is used for each model so that all AOGCMs are equally weighted in the multimodel ensemble; results are nearly identical if all available model ensemble members are used. Some of these grid points occur in desert regions that are already very dry, but many occur in currently more temperate and semiarid locations. We find that model results are more robust over land across the available models over wider areas for drying of the dry season than for the annual mean or wet season see Fig. The Insets in Fig. Although given particular years would show exceptions, the long-term irreversible warming and mean rainfall changes as suggested by Figs.

While some relief can be expected in the wet season for some regions Fig. The spatial changes in precipitation as shown in Fig. Such changes occurring not just for a few decades but over centuries are expected to have a range of impacts that differ by region. These include, e. Expected decadally averaged changes in the global distribution of precipitation per degree of warming percentage of change in precipitation per degree of warming, relative to — as the baseline period in the dry season at each grid point, based upon a suite of 22 AOGCMs for a midrange future scenario A1B, see ref.

White is used where fewer than 16 of 22 models agree on the sign of the change. Data are monthly averaged over several broad regions in Inset plots. Red lines show the best estimate median of the changes in these regions, while the red shading indicates the ±1-σ likely range i. We use 3 °C as the best estimate of climate sensitivity across the suite of AOGCMs for a doubling of carbon dioxide from preindustrial values 5 along with the regional drying values depicted in Fig. Illustrative irreversible climate changes as a function of peak carbon dioxide reached. Upper Best estimate of expected irreversible dry-season precipitation changes for the regions shown in Fig.

The precipitation change per degree is derived for each region as in Fig. Lower Corresponding irreversible global warming black line. Also shown is the associated lower limit of irreversible sea level rise because of thermal expansion only based upon a range of 0. Anthropogenic carbon dioxide will cause irrevocable sea level rise. There are 2 relatively well-understood processes that contribute to this and a third that may be much more important but is also very uncertain. Warming causes the ocean to expand and sea levels to rise as shown in Fig. Loss of land ice also makes important contributions to sea level rise as the world warms. Mountain glaciers in many locations are observed to be retreating due to warming, and this contribution to sea level rise is also relatively well understood.

Additional rapid ice losses from particular parts of the ice sheets of Greenland and Antarctica have recently been observed 40 — One recent study uses current ice discharge data to suggest ice sheet contributions of up to 1—2 m to sea level rise by 42 , but other studies suggest that changes in winds rather than warming may account for currently observed rapid ice sheet flow 43 , rendering quantitative extrapolation into the future uncertain. In addition to rapid ice flow, slow ice sheet mass balance processes are another mechanism for potential large sea level rise. Paleoclimatic data demonstrate large contributions of ice sheet loss to sea level rise 1 , 4 but provide limited constraints on the rate of such processes.

Some recent studies suggest that ice sheet surface mass balance loss for peak CO 2 concentrations of — ppmv may be even slower than the removal of manmade carbon dioxide following cessation of emissions, so that this loss could contribute less than a meter to irreversible sea level rise even after many thousands of years 44 ,

You cannot download interactives. Then the heat stored in the mixed layer is diffused to the deep layer through thermocline. Assessment of coastal impacts What impacts will result from a further increase in mean sea level? Time series for the World Ocean of ocean heat content for the 0— m red and — m black layers based on pendatal five year running mean analyses. When we refer to sea-level change rise in this paper, it means the change increase in mean sea level, including both global and local, in a general sense. James Hansen: sea level rise [audio].

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