California drought: Scientists to probe cause
Carolyn Lochhead | San Francisco Chronicle
Updated 8:31 am, Wednesday, January 22, 2014
Washington -- California's drought will be one of the extreme weather events that the American Meteorological Society will examine later this year to determine whether the cause is natural variability or human-caused climate change, a federal official said Tuesday.
The American Meteorological Society's study will be similar to one the group undertook of extreme weather events of 2012. In September, the Bulletin of the American Meteorological Society released a report finding that a 2012 Midwestern drought was mainly due to natural variation in weather, but that climate change was a factor in U.S. heat waves that spring and summer.
Scientists have not yet linked the California drought directly to climate change, Thomas Karl, head of the National Oceanic and Atmospheric Administration's National Climatic Data Center, said Tuesday in announcing the latest study. "I'm sure there's a way, but we haven't done it yet," he said.
Last year's peer-reviewed study was conducted by 18 research teams from around the world, and examined the causes of a dozen extreme events that occurred on five continents and in the Arctic during 2012. Three of the four lead editors on the report were NOAA scientists. The next report is due in September.
Karl made his comments during a conference call on new findings by NOAA and NASA that last year was tied with 2003 as the fourth-warmest year globally since record-keeping began in 1880.
Gavin Schmidt, deputy director of NASA's Goddard Institute for Space Studies in New York, noted that the rate of warming has slowed in the past decade. He said that may be due to poorly understood effects of air pollution, chiefly from burning coal.
Such so-called aerosols, which are also produced by volcanoes, may help reflect solar radiation and prevent some warming, Schmidt said.
However, the long-term warming trend is "extremely robust," Schmidt said. It may be snowing on the East Coast, he said, but "the long-term trends are very clear."
The new report from NOAA and NASA said ice continues to decrease in the Arctic but increase in Antarctica. Schmidt said the increase in Antarctica varies considerably by region and may be affected by the ozone hole over the South Pole, which in turn could be affecting wind currents.
Asked about charges by climate-change skeptics that scientists are attributing a loss of Arctic ice to global warming and an increase in Antarctic ice to natural variability, Schmidt said, "All of us are skeptics because we are scientists."
The report found that the 2013 global average land surface temperature was 1.78 degrees Fahrenheit above the 20th century average. "Including 2013, nine of the 10 warmest years in the 134-year period of record have occurred in the 21st century," the report said. "Only one year during the 20th century - 1998 - was warmer than 2013."
Precipitation changes are particularly difficult to predict, Karl said. While California is experiencing a record drought, he said, "that's juxtaposed in just the U.S. with some of wettest weather we've seen," with North Dakota setting an all-time record for precipitation.
"Normally, what we would expect as the world continues to warm is that the high latitudes generally get wetter and the subtropics get drier," Karl said. For midlatitude countries such as the United States, he said, "it's difficult to say exactly what the long term projection is."
Source: http://www.sfgate.com/science/article/California-drought-Scientists-to-probe-cause-5163948.php
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