Droughts, heavy downpours, excessive heat and intense hurricanes are likely to become more common as humans continue to increase the atmospheric concentrations of heat-trapping greenhouse gases (GHG), according to a scientific assessment of observed and projected changes in weather and climate extremes in North America and U.S. territories.
The report, released Thursday by the National Oceanic and Atmospheric Administration's (NOAA) U.S. Climate Change Science Program and the Subcommittee on Global Change Research, concluded "that we are now witnessing and will increasingly experience more extreme weather and climate events," said Tom Karl, director of NOAA's National Climatic Data Center in Asheville, NC.
Global warming over the past 50 years is due primarily to human-induced increases in heat-trapping gases, according to the report.
Extreme weather changes predicted by the report for coming decades include abnormally hot weather, decreasing or disappearing sea ice in the Arctic Ocean, more frequent and severe droughts, less frequent but more intense precipitation, hurricanes with increased precipitation and wind, as well as stronger winds and higher extreme wave heights during cold-season storms in the Atlantic and Pacific oceans.
Studies of the projected effects of rising GHG levels have delivered a variety of results. Just last month NOAA scientists said they had determined that global warming would not lead to an increase in Atlantic Basin hurricanes, and, in fact, might lead to fewer tropical storms and hurricanes. In a paper published online by Nature Geoscience, the NOAA scientists explained how they simulated Atlantic hurricane activity in 21st century conditions -- during periods of an expected rise in GHG emissions. The simulations indicated 27% fewer tropical storms and 18% fewer hurricanes. The strongest hurricanes had slightly higher wind speeds.
Last year a study by National Aeronautics and Space Administration (NASA) scientists suggested that GHG emissions could raise average summer temperatures in the eastern part of the United States nearly 10 degrees Fahrenheit by the 2080s (see NGI, May 14, 2007). The NASA research found that eastern U.S. summer daily high temperatures that currently average in the low to mid 80s Fahrenheit will most likely soar into the low to mid 90s during typical summers by the 2080s. In extreme seasons, for example, if a drought occurred, July and August daily high temperatures could average between 100 and 110 degrees in Washington, DC, Atlanta and as far west as Chicago.
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