In an article in the current issue of the journal Climate Change, Boston University researchers have estimated the impact meeting a 2°C global warming target will have on global, seasonal mean temperatures (“Near-term increase in frequency of seasonal temperature extremes prior to the 2°C global warming target,” Climate Change, [pub data]).
The 2°C global warming target is the focus of current international efforts to reduce greenhouse gas emissions and limit human-induced global-mean near-surface temperature increases relative to the pre-industrial era. “We wanted to determine the impact such a temperature increase might have upon the frequency of seasonal-mean temperature extremes,” said Bruce Anderson, associate professor of geography and environment and the study’s principal author. “We also wanted to determine if meeting a global-mean temperature increase target would prevent extreme temperature values from becoming the norm.”
Anderson’s research indicates that given a 2°C global mean temperature increase, seasonal-mean temperature values will exceed historical extremes (as determined from the 95th percentile threshold value over the second half of the 20th Century) for 70–80% of the land surface in at least half of all years. In other words, even if the 2°C global mean temperature increase target is achieved, current historical extreme values will effectively become the norm.
“Many regions of the globe—including much of Africa, the southeastern and central portions of Asia, Indonesia, and the Amazon—will reach this point,” said Anderson. These results suggest substantial fractions of the globe could experience seasonal-mean temperature extremes with high regularity, even if the global-mean temperature increase remains below the 2°C target.
In addition, the project that the seasonal-mean temperature extremes will become the norm for large portions of the land-surface even before global-mean surface temperature changes reach the 2°C threshold. In certain locations—again, much of Africa, the southeastern and central portions of Asia, the Amazon, and western North America—such a situation could arise given a future 0.6°C increase in global-mean temperature; given a future 0.8°C global-mean temperature increase, it is possible that a third to half of the land surface grids will have median yearly-maximum seasonal-mean temperatures that are greater than the 95% exceedence threshold.
“We find that the results are sensitive to both the observational dataset used to determine the range of historical variability and the numerical model data used to determine the grid-point increases in future temperatures,” said Anderson. Despite these caveats, the findings suggest that near-term increases in global-mean temperatures will regularly produce seasonal-mean temperature extremes for substantial fractions of the Earth’s land surface well before the 2°C global-warming target is reached.