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Federal Advisory Committee Draft Climate Assessment Report Released for Public Review
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Draft for Public Comment Chapter 1 ? Executive Summary
(v. 11 Jan 2013)
DRAFT FOR PUBLIC COMMENT
Executive Summary
Climate change is already affecting the American people. Certain types of weather events have become more frequent and/or intense, including heat waves, heavy downpours, and, in some regions, floods and droughts. Sea level is rising, oceans are becoming more acidic, and glaciers and arctic sea ice are melting. These changes are part of the pattern of global climate change, which is primarily driven by human activity.
Many impacts associated with these changes are important to Americans? health and livelihoods and the ecosystems that sustain us. These impacts are the subject of this report. The impacts are often most significant for communities that already face economic or health-related challenges, and for species and habitats that are already facing other pressures. While some changes will bring potential benefits, such as longer growing seasons, many will be disruptive to society because our institutions and infrastructure have been designed for the relatively stable climate of the past, not the changing one of the present and future. Similarly, the natural ecosystems that sustain us will be challenged by changing conditions. Using scientific information to prepare for these changes in advance provides economic opportunities, and proactively managing the risks will reduce costs over time.
Evidence for climate change abounds, from the top of the atmosphere to the depths of the oceans. This evidence has been compiled by scientists and engineers from around the world, using satellites, weather balloons, thermometers, buoys, and other observing systems. The sum total of this evidence tells an unambiguous story: the planet is warming.
U.S. average temperature has increased by about 1.5?F since 1895; more than 80% of this increase has occurred since 1980. The most recent decade was the nation?s hottest on record. Though most regions of the U.S. are experiencing warming, the changes in temperature are not uniform. In general, temperatures are rising more quickly at higher latitudes, but there is considerable observed variability across the regions of the U.S.
U.S. temperatures will continue to rise, with the next few decades projected to see another 2?F to 4?F of warming in most areas. The amount of warming by the end of the century is projected to correspond closely to the cumulative global emissions of greenhouse gases up to that time: roughly 3?F to 5?F under a lower emissions scenario involving substantial reductions in emissions after 2050 (referred to as the ?B1 scenario?), and 5?F to 10?F for a higher emissions scenario assuming continued increases in emissions (referred to as the ?A2 scenario?) (Ch. 2).
The chances of record-breaking high temperature extremes will continue to increase as the climate continues to change. There has been an increasing trend in persistently high nighttime temperatures, which have widespread impacts because people and livestock get no respite from the heat. In other places, prolonged periods of record high temperatures associated with droughts contribute to conditions that are driving larger and more frequent wildfires. There is strong evidence to indicate that human influence on the climate has already roughly doubled the probability of extreme heat events like the record-breaking summer of 2011 in Texas and Oklahoma (Ch. 2,3,6,9,20).
Human-induced climate change means much more than just hotter weather. Increases in ocean and freshwater temperatures, frost-free days, and heavy downpours have all been documented. Sea level has risen, and there have been large reductions in snow-cover extent, glaciers, permafrost, and sea ice. Winter storms along the west coast and the coast of New England have increased slightly in frequency and intensity. These changes and other climatic changes have affected and will continue to affect human health, water supply, agriculture, transportation, energy, and many other aspects of society (Ch. 2,3,4,5,6,10,12,16,20,24,25).
Some of the changes discussed in this report are common to many regions. For example, very heavy precipitation has increased over the past century in many parts of the country. The largest increases have occurred in the Northeast, Midwest, and Great Plains, where heavy downpours have exceeded the capacity of infrastructure such as storm drains, and have led to flooding events and accelerated erosion. Other impacts, such as those associated with the rapid thawing of permafrost in Alaska, are unique to one U.S. region (Ch. 2,16,18,19,20,21,22,23).
Some impacts that occur in one region have more wide-ranging effects. For example, the dramatic decline of summer sea ice in the Arctic ? a loss of ice cover roughly equal to half of the continental U.S. ? exacerbates global warming by reducing the reflectivity of Earth?s surface and increasing the amount of heat the Arctic absorbs. There is some evidence that this affects weather patterns farther south in the United States. Similarly, wildfires in one region can trigger poor air quality in far-away regions, and new evidence suggests the particulate matter in the atmosphere affects global circulation, leading to more persistent periods of anomalous weather. Major storms that hit the Gulf Coast affect the entire country through their cascading effects on oil and gas production and distribution (Ch. 2,4,16,17,18,19,20,22).
Sea level rise, combined with coastal storms, has increased the risk of erosion, storm-surge damage, and flooding for coastal communities, especially along the Gulf of Mexico, the Atlantic seaboard, and Alaska. In the Southeast, coastal infrastructure including roads, rail lines, energy infrastructure, and port facilities including naval bases, are at risk from storm surge that is exacerbated by rising sea level. Over the past century, global sea level has risen by about 8 inches. Since 1992, the rate of global sea level rise measured by satellites has been roughly twice the rate observed over the last century. Sea level is projected to rise by another 1 to 4 feet in this century. A wider range of scenarios, ranging from 8 inches to 6.6 feet of rise by 2100, has been suggested for use in risk-based analyses. In general, higher emissions scenarios that lead to more warming would be expected to lead to sea level rise toward the upper end of the projected range. The stakes are high, as nearly five million Americans live within four feet of the local high-tide level (Ch. 2,4,10,16,17,20, 22,25).
In addition to changing climate, carbon dioxide from fossil fuel burning has a direct effect on the world?s oceans. Carbon dioxide interacts with ocean water to form carbonic acid, lowering the ocean?s pH. Ocean surface waters have become 30% more acidic as they have absorbed large amounts of carbon dioxide from the atmosphere. This ocean acidification reduces the capacity of marine organisms with shells or skeletons made of calcium carbonate (such as corals, krill, oysters, clams, and crabs) to survive, grow, and reproduce, which in turn will affect the entire marine food chain (Ch. 2,8,23,24,25).
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Draft for Public Comment Chapter 1 ? Executive Summary
(v. 11 Jan 2013)
DRAFT FOR PUBLIC COMMENT
Executive Summary
Climate change is already affecting the American people. Certain types of weather events have become more frequent and/or intense, including heat waves, heavy downpours, and, in some regions, floods and droughts. Sea level is rising, oceans are becoming more acidic, and glaciers and arctic sea ice are melting. These changes are part of the pattern of global climate change, which is primarily driven by human activity.
Many impacts associated with these changes are important to Americans? health and livelihoods and the ecosystems that sustain us. These impacts are the subject of this report. The impacts are often most significant for communities that already face economic or health-related challenges, and for species and habitats that are already facing other pressures. While some changes will bring potential benefits, such as longer growing seasons, many will be disruptive to society because our institutions and infrastructure have been designed for the relatively stable climate of the past, not the changing one of the present and future. Similarly, the natural ecosystems that sustain us will be challenged by changing conditions. Using scientific information to prepare for these changes in advance provides economic opportunities, and proactively managing the risks will reduce costs over time.
Evidence for climate change abounds, from the top of the atmosphere to the depths of the oceans. This evidence has been compiled by scientists and engineers from around the world, using satellites, weather balloons, thermometers, buoys, and other observing systems. The sum total of this evidence tells an unambiguous story: the planet is warming.
U.S. average temperature has increased by about 1.5?F since 1895; more than 80% of this increase has occurred since 1980. The most recent decade was the nation?s hottest on record. Though most regions of the U.S. are experiencing warming, the changes in temperature are not uniform. In general, temperatures are rising more quickly at higher latitudes, but there is considerable observed variability across the regions of the U.S.
U.S. temperatures will continue to rise, with the next few decades projected to see another 2?F to 4?F of warming in most areas. The amount of warming by the end of the century is projected to correspond closely to the cumulative global emissions of greenhouse gases up to that time: roughly 3?F to 5?F under a lower emissions scenario involving substantial reductions in emissions after 2050 (referred to as the ?B1 scenario?), and 5?F to 10?F for a higher emissions scenario assuming continued increases in emissions (referred to as the ?A2 scenario?) (Ch. 2).
The chances of record-breaking high temperature extremes will continue to increase as the climate continues to change. There has been an increasing trend in persistently high nighttime temperatures, which have widespread impacts because people and livestock get no respite from the heat. In other places, prolonged periods of record high temperatures associated with droughts contribute to conditions that are driving larger and more frequent wildfires. There is strong evidence to indicate that human influence on the climate has already roughly doubled the probability of extreme heat events like the record-breaking summer of 2011 in Texas and Oklahoma (Ch. 2,3,6,9,20).
Human-induced climate change means much more than just hotter weather. Increases in ocean and freshwater temperatures, frost-free days, and heavy downpours have all been documented. Sea level has risen, and there have been large reductions in snow-cover extent, glaciers, permafrost, and sea ice. Winter storms along the west coast and the coast of New England have increased slightly in frequency and intensity. These changes and other climatic changes have affected and will continue to affect human health, water supply, agriculture, transportation, energy, and many other aspects of society (Ch. 2,3,4,5,6,10,12,16,20,24,25).
Some of the changes discussed in this report are common to many regions. For example, very heavy precipitation has increased over the past century in many parts of the country. The largest increases have occurred in the Northeast, Midwest, and Great Plains, where heavy downpours have exceeded the capacity of infrastructure such as storm drains, and have led to flooding events and accelerated erosion. Other impacts, such as those associated with the rapid thawing of permafrost in Alaska, are unique to one U.S. region (Ch. 2,16,18,19,20,21,22,23).
Some impacts that occur in one region have more wide-ranging effects. For example, the dramatic decline of summer sea ice in the Arctic ? a loss of ice cover roughly equal to half of the continental U.S. ? exacerbates global warming by reducing the reflectivity of Earth?s surface and increasing the amount of heat the Arctic absorbs. There is some evidence that this affects weather patterns farther south in the United States. Similarly, wildfires in one region can trigger poor air quality in far-away regions, and new evidence suggests the particulate matter in the atmosphere affects global circulation, leading to more persistent periods of anomalous weather. Major storms that hit the Gulf Coast affect the entire country through their cascading effects on oil and gas production and distribution (Ch. 2,4,16,17,18,19,20,22).
Sea level rise, combined with coastal storms, has increased the risk of erosion, storm-surge damage, and flooding for coastal communities, especially along the Gulf of Mexico, the Atlantic seaboard, and Alaska. In the Southeast, coastal infrastructure including roads, rail lines, energy infrastructure, and port facilities including naval bases, are at risk from storm surge that is exacerbated by rising sea level. Over the past century, global sea level has risen by about 8 inches. Since 1992, the rate of global sea level rise measured by satellites has been roughly twice the rate observed over the last century. Sea level is projected to rise by another 1 to 4 feet in this century. A wider range of scenarios, ranging from 8 inches to 6.6 feet of rise by 2100, has been suggested for use in risk-based analyses. In general, higher emissions scenarios that lead to more warming would be expected to lead to sea level rise toward the upper end of the projected range. The stakes are high, as nearly five million Americans live within four feet of the local high-tide level (Ch. 2,4,10,16,17,20, 22,25).
In addition to changing climate, carbon dioxide from fossil fuel burning has a direct effect on the world?s oceans. Carbon dioxide interacts with ocean water to form carbonic acid, lowering the ocean?s pH. Ocean surface waters have become 30% more acidic as they have absorbed large amounts of carbon dioxide from the atmosphere. This ocean acidification reduces the capacity of marine organisms with shells or skeletons made of calcium carbonate (such as corals, krill, oysters, clams, and crabs) to survive, grow, and reproduce, which in turn will affect the entire marine food chain (Ch. 2,8,23,24,25).
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