An anonymous reader quotes a report from The Guardian: Southern Spain will be reduced to desert by the end of the century if the current rate of greenhouse gas emissions continue unchecked, researchers have warned. Anything less than extremely ambitious and politically unlikely carbon emissions cuts will see ecosystems in the Mediterranean change to a state unprecedented in the past 10 millennia, they said. The study, published in the journal Science, modeled what would happen to vegetation in the Mediterranean basin under four different paths of future carbon emissions, from a business-as-usual scenario at the worst end to keeping temperature rises below the Paris climate deal target of 1.5C at the other. Temperatures would rise nearly 5C globally under the worst case scenario by 2100, causing deserts to expand northwards across southern Spain and Sicily, and Mediterranean vegetation to replace deciduous forests. Even if emissions are held to the level of pledges put forward ahead of the Paris deal, southern Europe would experience a “substantial” expansion of deserts. The level of change would be beyond anything the region’s ecosystems had experienced during the holocene, the geological epoch that started more than 10,000 years ago. The real impact on Mediterranean ecosystems, which are considered a hotspot of biodiversity, could be worse because the study did not look at other human impacts, such as forests being turned over to grow food. The researchers fed a model with 10,000 years of pollen records to build a picture of vegetation in the region, and used that to infer previous temperatures in the Mediterranean. They then ran the model to see what would happen to the vegetation in the future, using four different scenarios of warming, three of them taken from the UN’s climate science panel, the IPCC. Only the most stringent cut in emissions — which is roughly equivalent to meeting the Paris aspiration of holding warming to 1.5C — would see ecosystems remain within the limits they experienced in the Holocene.

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