Global Climate Change Impacts In The United States – Atmospheric greenhouse gas concentrations will continue to rise unless the billions of tons of our annual emissions are significantly reduced. Increased concentrations are expected to:
Many greenhouse gases remain in the atmosphere for long periods of time. As a result, even if emissions stopped rising, the concentration of greenhouse gases in the atmosphere would continue to rise and remain at elevated levels for hundreds of years. Moreover, if we stabilize concentrations and the composition of today’s atmosphere remains constant (which would require radical reductions in current greenhouse gas emissions), surface air temperatures will continue to rise. This is because the oceans, which store heat, take many decades to fully respond to higher concentrations of greenhouse gases. The ocean’s response to higher greenhouse gas concentrations and warmer temperatures will continue to influence climate for the next several decades and even hundreds of years.[2]
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Global Climate Change Impacts In The United States
To learn more about greenhouse gases, visit the “Greenhouse Gas Emissions” page and the “Greenhouse Effect” section on the Causes of Climate Change page.
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Because it is difficult to predict distant future emissions and other human factors influencing climate, scientists use a range of scenarios, making different assumptions about future economic, social, technological and environmental conditions.
This figure shows projected greenhouse gas concentrations for four different emission pathways. The most important path assumes that greenhouse gas emissions will continue to rise throughout this century. The lower path assumes emissions will peak between 2010 and 2020 and decline thereafter. Source: Chart created using data from the Representative Concentration Pathways database (version 2.0.5)http://www.iiasa.ac.at/web-apps/tnt/RcpDb Click on the image to view a larger version.
We have already seen global warming over the last few decades. Future temperatures are expected to continue to change. Climate models predict the following key temperature-related changes.
Projected changes in global average temperatures across four emission pathways (rows) for three different periods (columns). Temperature changes are related to averages from 1986-2005. The pathways are from the IPCC Fifth Assessment Report: RCP2.6 is the very low emissions pathway, RCP4.5 is the medium emissions pathway, RCP6.0 is the medium-high emissions pathway, and RCP8.5 is the high emissions pathway (emissions are assumed to will continue to grow throughout the century). Source: IPCC, 2013Output Click on the image to view a larger version.
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Observed and projected changes in global mean temperature across four emission pathways. The vertical bars on the right show likely temperature ranges by the end of the century, while the lines show forecasts averaged across climate models. The changes refer to the average from 1986-2005. Source: IPCC, 2013 Exit, FAQ 12.1, Figure 1. Click on the image to view a larger version.
Projected mid-century (left) and end-of-century (right) temperature change in the United States under higher (top) and lower (bottom) emissions scenarios. The brackets on the thermometers show the likely range of the model’s predictions, although lower or higher results are possible. Source: USGCRP (2009)
Precipitation and storm patterns, including rain and snow, are also likely to change. However, some of these changes are less certain than temperature-related changes. Forecasts show that future changes in rainfall and storm patterns will vary by season and region. Some regions may experience less rainfall, others may experience more rainfall, and in others there may be little or no change. Rainfall amounts from heavy rainfall are likely to increase in most regions, while storm tracks are expected to shift poleward.[2] Climate models predict the following changes in rainfall and storms.
Projected changes in global mean annual precipitation for the low emissions scenario (left) and the high emissions scenario (right). By the end of the century, blue and green areas are expected to see an increase in rainfall, while yellow and brown areas will see a decrease. Source: IPCC, 2013Output Click on the image to view a larger version.
Global Climate Change Impacts In The United States: Highlights
The maps show projected future changes in precipitation at the end of this century compared to 1970-1999, under a higher emissions scenario. For example, during winter and spring, climate models agree that northern areas of the United States are likely to become wetter and southern areas drier. It is less certain exactly where the transition between wetter and drier areas will occur. The certainty of forecast changes is highest in the areas marked with diagonal lines. Changes in white areas are not expected to be greater than would be expected based on natural variability. Source: US National Climate Assessment, 2014. Click on image to view larger version.
Arctic Sea ice cover is already decreasing.[2] Snow cover in the Northern Hemisphere has decreased since around 1970.[2] Permafrost temperatures in Alaska and much of the Arctic[2] have increased over the past century.[1] To learn more about recent changes in snow and ice, visit the Snow and Ice page in the Indicators section.
Over the next century, sea ice is expected to continue to decline, glaciers will continue to shrink, snow cover will continue to decline, and permafrost will continue to thaw. Potential changes to ice, snow and permafrost are described below. These maps show projected sea ice losses in the Arctic and Antarctica. The maps in a) show the average ice concentration (relative area covered by sea ice) from 1986 to 2005. The maps in b) and c) show climate model simulations of sea ice thickness in February and September in the late 21st century under low (b) and high (c) emission scenarios. There will be less ice (more blue) in the Arctic in February; September is expected to be almost ice-free (almost all blue). Projected changes in Antarctic sea ice are more subtle. Source: IPCC, 2013 Click on the image to view a larger version.
Meltwater flowing from the Greenland Ice Sheet Source: NASA Rising temperatures contribute to sea level rise by: expanding ocean water; melting of mountain glaciers and ice caps; and causing parts of the Greenland and Antarctic ice sheets to melt or leak into the ocean.[3]
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Since 1870, global sea levels have risen by approximately 7.5 inches.[2] Estimates of future sea level rise vary for different regions, but global sea level is expected to rise at a faster rate in the next century than in the last 50 years.
Studies predict that global sea levels will rise another 1-4 feet by 2100, with an uncertainty range of 0.66-6.6 feet.[1]
The contributions of thermal expansion, ice caps and small glaciers to sea level rise are relatively well-studied, but the impact of climate change on the Greenland and Antarctic ice sheets is less understood and is an active area of research. Changes in ice sheets are currently expected to cause sea levels to rise by 1.2 to 8 inches by the end of this century.[3]
Past and projected sea level rise from 1800 to 2100. The orange line on the right shows the currently projected range of sea level rise from 1 to 4 feet by 2100; the wider range (0.66 feet to 6.6 feet) reflects uncertainty about how glaciers and ice sheets will respond to climate change. Source: NCA, 2014. Click on image to view larger version. Regional and local factors will influence future relative sea level rise for specific coastlines around the world. For example, relative sea level rise depends on changes in land elevation that occur through subsidence (sinking) or uplift (uplift). Assuming these historic geological forces continue, a 2-foot rise in global sea level by 2100 will result in the following relative sea level rise:
Report On Climate Change Impacts In The United States: The Third National Climate Assessment, U.s. Global Change Research Program (highlights)
Relative sea level rise also depends on local changes in currents, winds, salinity and water temperature, as well as the proximity of thinning ice sheets.
Ocean acidification adversely affects many marine species, including plankton, molluscs, crustaceans and corals. As ocean acidification increases, the availability of calcium carbonate will decrease. Calcium carbonate is a key building block of the shells and skeletons of many marine organisms. If atmospheric CO
Coral concentrations continue to increase at current rates, the combination of global warming and ocean acidification could slow coral growth by almost 50% by 2050 [5].
The oceans become more acidic as carbon dioxide (CO2) emissions from the atmosphere dissolve into the ocean. This change is measured on the pH scale, with lower values being more acidic. The pH level of the oceans has decreased by about 0.1 pH unit since pre-industrial times, which corresponds to an increase in non-acidity of about 30%. As shown in the chart and map above, ocean pH levels are expected to decline even further by the end of the century as CO2 concentrations increase in the foreseeable future.[1] [2]Source: IPCC, 2013, Chapter 6. Click on image to view larger version.
Climate Change Adaptation
[1] USGCRP (2014) Melillo, Jerry M., Teresa (T.C.) Richmond, and Gary W. Yohe, eds., 2014: Climate Change Impacts in the United States: Third National Climate Assessment. American Global Change Research Program.
[2] IPCC (2013). Climate change 2013: Moving beyond the basics of physical science. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex, and P.M. Midgley (ed.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA.
[3] NRC (2011). Climate stabilization targets: emissions, concentrations and impacts over decades to millennia. National Research Council. National Academies Press, Washington, DC, USA.
[4] USGCRP (2009). Global effects of climate change in
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