New York / Heidelberg, 9 September 2011
In an article in the current issue of the journal Climatic Change Letters, Boston University researchers have estimated the impact near-term increases in global-mean temperatures will have on summertime temperatures in the U.S. and around the globe.
The “2°C global warming target” is in reference to the current international efforts to reduce emissions of heat-trapping gases and limit human-induced global-mean near-surface temperature increases to 2°C (3.5°F) relative to the pre-industrial era, three-fifths of which has already occurred.
Anderson’s research indicates that if the 2°C increase were to come to pass 70–80% of the land surface will experience summertime temperature values that exceed observed historical extremes (equivalent to the top 5% of summertime temperatures experienced during the second half of the 20th century) in at least half of all years. In other words, even if an increase in the global mean temperature is limited to 2°C, current historical extreme values will still effectively become the norm for 70-80% of the earth’s land surface.
“Many regions of the globe—including much of Africa, the southeastern and central portions of Asia, Indonesia, and the Amazon—are already committed to reaching this point, given current amounts of heat-trapping gases in the atmosphere” said Anderson. Global-mean temperatures are expected to increase an additional 0.6°C (1°F) over the coming decades even if no more carbon dioxide, methane, or other heat-trapping gases are added to the atmosphere.
In the United States, the impacts are expected to be most severe over the western third of the country. “In these regions, if the 2°C threshold is passed, it is more likely than not that every summer will be an extreme summer compared with today,” said Anderson. Further, the region is expected to follow soon after Africa, Asia, and the Amazon as one in which summertime temperature extremes will become the norm. “While the western third of the U.S. is not committed to reaching such a situation, it is certainly on the brink,” said Anderson.