Human-Caused Climate Change Already a Major Factor in More Frequent Mediterranean Droughts

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NOAA Bombshell: Human-Caused Climate Change Already a Major Factor in More Frequent Mediterranean Droughts

By Joe Romm on Oct 27, 2011 at 8:00 pm

NOAA reports that global warming is harming humans right now in a dramaƟc way:

WinterƟme droughts are increasingly common in the Mediterranean region, and human-caused climate change is partly responsible, according to a new analysis by NOAA scienƟsts and colleagues at the CooperaƟve InsƟtute 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 MarƟn 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 precipitaƟon during the winter….

Reds and oranges highlight lands around the Mediterranean that experienced signiﬁcantly drier winters during 1971-2010 than the comparison period of 1902-2010. [Click to enlarge.]

The above is from a news release from the NaƟonal Oceanic and Atmospheric AdministraƟon, “NOAA study: Human-caused climate change a major factor in more frequent Mediterranean droughts.”

It’s a bombshell for three reasons. First, this NOAA team has not always found a human cause for extreme weather events, as Climate Progress discussed here. Second, the study found that global warming is already driving drought in a key region of the world: Climate change is harming a great many people now. Third, the analysis provides important conﬁrmaƟon of climate predicƟons that human-caused emissions would lead to drying: “The team also found agreement between the observed increase in winter droughts and in the projecƟons of climate models that include known increases in greenhouse gases.”

This comes on the heel of the USGS study, that, despite its flaws sƟll found, “The decrease of floods in the southwestern region is consistent with other research findings that this region has been geƫng drier and experienced less precipitaƟon as a likely result of climate change.”

And these studies amplify the piece I had in the journal Nature this week that argued drying and Dust-BowliﬁcaƟon driven by climate change — and the impact on food insecurity — are probably the gravest threats the human race faces in the coming decades.

The fact that the NOAA analysis conﬁrmed the climate models predicƟons of drying is especially worrisome because the climate models project a very dry future for large parts of the planet’s currently habited and arable land in the coming decades:

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1 of 2 12/12/2011 12:26 PM NOAA Bombshell: Human-Caused Climate Change Already a Major Facto... http://thinkprogress.org/romm/2011/10/27/355639/noaa-climate-change-...

The NaƟonal Center for Atmospheric Research ﬁgure [click to enlarge] charts the Palmer Drought Severity Index [PDSI] where “a reading of -4 or below is considered extreme drought.” The PDSI in the Great Plains during the Dust Bowl spiked very brieﬂy to -6, but otherwise rarely exceeded -3 for the decade (see here).

The 2010 NCAR study, which Climate Progress reported on here, notes “By the end of the century, many populated areas, including parts of the United States, could face readings in the range of -8 to -10, and much of the Mediterranean could fall to -15 to -20. Such readings would be almost unprecedented.”

Indeed, the new NOAA study should be especially sobering to those in the Mediterranean since they clearly face some of the most extreme drying in the enƟre world:

The Mediterranean has long been idenƟﬁed as a “hot spot” for substanƟal impact from climate change in the laƩer decades of this century because of water scarcity in the region, a rapidly increasing populaƟon, and climate modeling that projects increased risk of drought.

“The quesƟon 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.”

Here is the trend so far, from NOAA [click to enlarge]:

Winter precipitaƟon trends in the Mediterranean region for the period 1902 – 2010.

NOAA further reports:

The Mediterranean region accumulates most of its precipitaƟon during the winter, and Hoerling’s team uncovered a paƩern of increasing winterƟme dryness that stretched from Gibraltar to the Middle East. ScienƟsts used observaƟons and climate models to invesƟgate several possible culprits, including natural variability, a cyclical climate paƩern called the North AtlanƟc OscillaƟon (NAO), and climate change caused by greenhouse gases released into the atmosphere during fossil fuel use and other human acƟviƟes.

Climate change from greenhouse gases explained roughly half the increased dryness of 1902-2010, the team found. This means that other processes, none speciﬁcally idenƟﬁed in the new invesƟgaƟon, 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 projecƟons of climate models that include known increases in greenhouse gases. Both observaƟons and model simulaƟons show a sudden shiŌ to drier condiƟons in the Mediterranean beginning in the 1970s. The analysis began with the year 1902, the ﬁrst year of a recorded rainfall dataset.

In this analysis, sea surface temperature paƩerns emerged as the primary reason for the relaƟonship between climate change and Mediterranean drought. In recent decades, greenhouse-induced climate change has caused somewhat greater warming of the tropical oceans compared to other ocean regions. That paƩern acts to drive drought-conducive weather paƩerns around the Mediterranean. The Ɵming of ocean temperature changes coincides closely with the Ɵming of increased droughts, the scienƟsts found….

Climate is a global phenomenon with global impacts on food prices and water security, and NOAA researchers are engaged in understanding changes in climate across many regions of the world. In the Mediterranean, winter drought has emerged as a new normal that could threaten food security. Lessons learned from studying climate in that region may also be relevant for the U.S. West Coast, which has a similar climate to the Mediterranean region of Europe and North Africa.

Dust-BowliﬁcaƟon is coming. The only quesƟon now is whether we are going to act quickly to reduce emissions and avoid the very worst of the consequences. As I’ll discussed in a future post, the kind of drying that is project is not something that you can adapt to in any meaningful sense of the word.

USGS on Dust-BowliﬁcaƟon: Drier condiƟons projected to accelerate dust storms in the U.S. Southwest

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