Global warming already causes some droughts, scientists say tagged: , , , , , ,

Global warming already causes some droughts, scientists say

Posted by in Biology, Climate change, Life, Science in Society

Courtesy of NOAA and World Science staff

Wintertime droughts are increasingly common in the Mediterranean region, partly because of human-caused climate change, according to a new analysis by US government scientists.

If correct, the findings would mean that some of the droughts predicted by models of global warming and its consequences have already occurred, something that had not been clear.

In the last two decades, 10 of the driest 12 winters have taken place in the lands surrounding the Mediterranean Sea, the researchers found. ‘The magnitude and frequency of the drying… is too great to be explained by natural variability alone,’ said Martin Hoerling of the US National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colorado, 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,’ added Hoerling, who worked with colleagues at the Cooperative Institute for Research in Environmental Sciences in Boulder, Colorado.

Weather drought leads to financial trouble?

The researchers published a map of Europe highlighting which countries were increasingly dry in winter. A striking aspect of the map was that some of the countries awash in red splotches representing dryness were the same ones – including Greece, Portugal, Italy and Spain – whose unpaid debts are currently threatening the global financial system.

The Mediterranean region accumulates most of its precipitation during the winter. Hoerling’s team identified a pattern of increasing wintertime dryness stretching 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, 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 other processes not specifically identified would also have contributed to increasing drought frequency in the region.

Mediterranean is a climate change ‘hot spot’

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.

The Mediterranean has long been identified as a ‘hot spot’ for substantial impact from climate change in the latter decades of this century because of water scarcity in the region, a rapidly increasing population, and climate modelling that projects increased risk of drought.

‘The question has been whether this projected drying has already begun to occur in winter, the most important season for water resources,’ Hoerling said. ‘The answer is yes.’

In the Mediterranean, winter drought is a ‘new normal’ that could threaten food security, the researchers said. Lessons learned from studying climate in that region may also be relevant for the US West Coast, they added, which has a similar climate to the Mediterranean region of Europe and North Africa.

Reds and oranges highlight lands around the Mediterranean that experienced significantly drier winters during 1971-2010 than a comparison period of 1902-2010. (Image: NOAA)

Source: World Science, http://www.world-science.net