Sunday, October 24, 2010

High latitude havens in global drought

Climate change: Drought may threaten much of globe within decades
UCAR: Heavily populated countries face a growing threat of severe and prolonged drought in coming decades, according to a new study by National Center for Atmospheric Research (NCAR) scientist Aiguo Dai. The detailed analysis concludes that warming temperatures associated with climate change will likely create increasingly dry conditions across much of the globe in the next 30 years, possibly reaching a scale in some regions by the end of the century that has rarely, if ever, been observed in modern times...

Using an ensemble of 22 computer climate models and a comprehensive index of drought conditions, as well as analyses of previously published studies, the paper finds most of the Western Hemisphere, along with large parts of Eurasia, Africa, and Australia, may be a threat of extreme drought this century. In contrast, higher-latitude regions from Alaska to Scandinavia are likely to become more moist...

A climate change expert not associated with the study, Richard Seager of Columbia University's Lamont Doherty Earth Observatory, adds:... "The term 'global warming' does not do justice to the climatic changes the world will experience in coming decades. Some of the worst disruptions we face will involve water, not just temperature.'

Reuters: To get an idea of how severe the drought might get, scientists use a measure called the Palmer Drought Severity Index, or PDSI. A positive score is wet, a negative score is dry... An an example, the most severe drought in recent history, in the Sahel region of western Africa in the 1970s, had a PDSI of -3 or -4. By contrast, the new study indicates some areas with high populations could see drought in the -15 or -20 range by the end of the century.

Areas likely to experience significant drying include:
  • the western two-thirds of the United States;
  • much of Latin America, especially large parts of Mexico and Brazil;
  • regions bordering the Mediterranean Sea;
  • large parts of southwest Asia;
  • southeast Asia, including China and neighboring countries, and
  • most of Africa and Australia.
While Earth is expected to get dryer overall, some areas will see a lowering of the drought risk. These include:
  • much of northern Europe;
  • Russia;
  • Canada;
  • Alaska, and
  • some areas of the Southern Hemisphere.
That doesn't necessarily mean that agriculture will migrate from the drought areas to these places in the high latitudes, Dai wrote. 'The high-latitude land areas will experience large changes in terms of warmer temperatures and more precipitation, and thus may indeed become more habitable than today,' he wrote. 'However, limited sunshine, short growing season, and very cold nighttime temperature will still prevent farming over most of these high-latitude regions.'
Source of this image here, plus others projecting to the end of the century.