The Greenland ice sheet is melting. If you live in nearby Norway, Germany or the UK how worried should you be about that sudden influx?
It turns out, not nearly as worried as you should be if you live in North Africa or Chile. People tend to imagine that when an ice sheet melts, it adds water to all of the world's ocean uniformly, like a bathtub filling up. "That isn't even close," Harvard University geophysicist Jerry Mitrovica explained at the annual meeting of AAAS (which publishes Science) in Washington, D.C. "Each ice sheet has its own pattern of sea level rise. Previous studies have shown that a “green Sahara” is linked to changes in the intensity and location of the West African monsoon. That major wind system blows hot, dry air southwestward across northern Africa during the cooler months and brings slightly wetter conditions northeastward during the hotter months. Climate change could make this season of monsoons much larger and impact the dessert by creating huge lakes and rivers again in the Sahara!
In the future, the Sahara and Sahelian regions could experience more rainfall than today as a result of climate change. Wetter periods, termed African humid periods, occurred in the past and witnessed a mesic landscape in place of today’s hyperarid and semiarid environment. Such large past changes raise the question of whether the near future might hold in store similar environmental transformations, particularly in view of the growing human-induced climate, land-use, and land-cover changes. In the last decades, geoengineering initiatives (in the form of active re-greening projects of the Sahara and Sahel) have been proposed and could have significant effects on the climate of the region. Here, we synthesize the literature on past and projected changes in the hydroclimate of the Sahelian-Saharan region and the associated feedbacks. We further address the current state of knowledge concerning Saharan and Sahelian afforestation projects and their consequences.
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