January 15, 2013
A 60-person Federal Advisory Committee (The "National Climate Assessment and Development Advisory Committee" or NCADAC) has overseen the development of this draft climate report.
The Executive Summary begins with climate change 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 26 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 36 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 38 Oklahoma (Ch. 2,3,6,9,20).
Continue reading the report at the National Climate Assessment Development Advisory Committee website.
Provide comments to the report between January 14th and April 12th only. Please go to the Review and Comment System to provide comments on the draft. Visit the National Climate Assessment Development Advisory Committee website.