30/10/2016

Rapidly Warming Mediterranean Headed for Desertification, Study Warns

InsideClimate News - Sabrina Shankman

Even with 2 degrees of global warming, the current global goal, desertification would overtake parts of this lush and vibrant region.
People rush to the beach during heat waves in the Mediterranean region, which will get more extreme as the globe warms. Credit: Getty Images
If the Earth warms much more than it already has, the climate and ecosystems of the Mediterranean region might suddenly become unrecognizable, according to a new study.
The study, published Thursday in the journal Science, found that even if warming is constrained to 2 degrees Celsius above preindustrial times—which is the central goal of the Paris climate agreement—the Mediterranean region would see changes never experienced during recorded history.
With 2 degrees of warming, Morocco, for instance, would see increased temperatures and drought that would drive the southern deserts further north, displacing forests. Deserts would expand in the Middle East, too, pushing temperate forests higher into the mountains.
If warming continues unabated, the results would be significantly worse. The study found that all of southern Spain would become desert and most of the deciduous forests in the region would be replaced by shrubs and bushes.
These changes are already close at hand.
The Mediterranean is already warming faster than much of the rest of the world. Globally, temperatures have risen an average of .85 degrees Celsius since 1880-1920, while the Mediterranean basin has seen 1.3 degrees Celsius of warming. Historically, the Mediterranean has been characterized by mild, wet winters and warm, dry summers. The area is home to roughly 466 million people, and, in addition to its rich biodiversity, its ecosystems provide clean water, flood protection and carbon storage.
The study's authors—Joel Guiot and Wolfgang Cramer, both directors of research at France's National Center of Scientific Research—analyzed pollen locked in layers in sediment over the past 10,000 years. They then compared the ancient conditions with projections about climate and vegetation from the Intergovernmental Panel on Climate Change.
Is the looming change "close to what we have known before or is it very far?" said Guiot. "It's really to put the future in the context of the past."
Calling the study's findings "highly significant," Stephen Jackson, the director of the Department of the Interior's Southwest Climate Science Center, said the past 10,000 years are a critical comparison point. "Western civilization developed in and around the Mediterranean Basin within that period, and we risk going into new climatic territory within a very short time in the absence of emission reductions," said Jackson, who is not affiliated with the study.
The past 10,000 years have seen some periods of extended drought, according to the study. Roughly 3,000 years ago, a drought lasted several centuries, which researchers have cited as a possible factor in the fall of ancient Bronze Age societies before the rise of Classical Greece. The Science study points to two other extended periods of drought, both also associated with declines or collapses of civilizations in the region.
Those droughts were different from the region's current state, and what is projected in the future, in one significant way: They were not accompanied by extended rises in temperature.
A more recent example is the widespread crop failures in Syria in 1998 and 2010 that were attributed to extreme heat and drought. That is widely cited as a reason for that country's political upheaval and civil war.
"It's not just climate—political organization is important as well," said Guiot. "But if you amplify a problem of war with the problem of climate, the consequence can be more important."
The study is one of many these days emphasizing the importance of keeping temperatures well below 2 degrees of warming.
When the Paris Agreement was signed in December 2015, its primary goal read:
"To hold the increase in the global average temperature to below 2°C above preindustrial levels and pursue efforts to limit the temperature increase to 1.5°C."
That would mean reducing net emissions of carbon dioxide to zero some time in the mid to late century.
Guiot and Cramer found that holding warming to 1.5 degrees Celsius is the only way to keep a recognizable Mediterranean ecosystem.
"The difference is really important," said Guiot. "With 2 degrees of warming, for the Mediterranean we will have a change in the vegetation which has never been known in the past 10,000 years. 1.5 degrees corresponds to the variability of 10,000 years."

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