Friday, October 28, 2011

Human-caused climate change a major factor in more frequent Mediterranean droughts

NOAA: Wintertime droughts are increasingly common in the Mediterranean region, and human-caused climate change is partly responsible, according to a new analysis by NOAA scientists and colleagues at the Cooperative Institute for Research in Environmental Sciences (CIRES). In the last 20 years, 10 of the driest 12 winters have taken place in the lands surrounding the Mediterranean Sea.

“The magnitude and frequency of the drying that has occurred is too great to be explained by natural variability alone,” said Martin Hoerling, Ph.D. of NOAA’s Earth System Research Laboratory in Boulder, Colo., lead author of a paper published online in the Journal of Climate this month. “This is not encouraging news for a region that already experiences water stress, because it implies natural variability alone is unlikely to return the region’s climate to normal.”

The Mediterranean region accumulates most of its precipitation during the winter, and Hoerling’s team uncovered a pattern of increasing wintertime dryness that stretched from Gibraltar to the Middle East. Scientists used observations and climate models to investigate several possible culprits, including natural variability, a cyclical climate pattern called the North Atlantic Oscillation (NAO), and climate change caused by greenhouse gases released into the atmosphere during fossil fuel use and other human activities.

Climate change from greenhouse gases explained roughly half the increased dryness of 1902-2010, the team found. This means that other processes, none specifically identified in the new investigation, also have contributed to increasing drought frequency in the region. The team also found agreement between the observed increase in winter droughts and in the projections of climate models that include known increases in greenhouse gases. Both observations and model simulations show a sudden shift to drier conditions in the Mediterranean beginning in the 1970s. The analysis began with the year 1902, the first year of a recorded rainfall dataset....

Reds and oranges highlight lands around the Mediterranean that experienced significantly drier winters during 1971-2010 than the comparison period of 1902-2010. Map from NOAA

1 comment:

Dan Pangburn said...

A simple equation based on the physical phenomena involved, with inputs of only sunspot number and ppmv CO2, calculates the average global temperatures (agt) since 1895 with 88.4% accuracy (87.9% if CO2 is assumed to have no influence). The equation, links to the source data, an eye-opening graph of the results and how they are derived are in the pdfs at (see especially the pdfs made public on 4/10/10, 3/10/11 and 9/24/11). As shown in the 9/24/11 pdf, the equation accurately predicted the temperature trends for the last 20 years.

The future average global temperature trend that this equation calculates is down. The huge effective thermal capacitance of the oceans (about 30 times everything else) will cause the decline to be only about 0.13°C per decade. The decline may be as much as 0.22°C per decade if the sun goes really quiet.

This trend is corroborated by the growing separation between the rising CO2 and not-rising agt. From 2001 through September, 2011 the atmospheric CO2 increased by 23.7% of the total increase from 1800 to 2001 while the average global temperature has not increased. The 23.7% CO2 increase is the significant measurement, not the comparatively brief time period.

Without human caused global warming there can be no human caused climate change.