This story is actually quite fascinating and it obviously has something to do with changes in the climate, but just how to explain it all remains a subject of contention. You would think that increasing temperatures would make things worse in the deserts of the world, but in a rather counterintuitive instance of planet watching, it appears that the Sahara desert may actually be shrinking.
A few thousand years ago, a mighty river flowed through the Sahara across what is today Sudan. The Wadi Howar—now just a dried-out riverbed for most of the year—sustained not just fish, crocodiles, and hippopotamuses, but also agriculture and human settlement. As late as 1,000 B.C., a powerful fortress stood on its shores. But then the Sahara dried out, turning from a green savannah into an inhospitable desert. The culprit: climate change. According to desert geologist Stefan Kröpelin, who has studied geological data for the eastern Sahara going back 6,000 years, the desert spread as temperatures dropped. Global cooling meant that the air had less capacity to hold moisture from the oceans, leading to fewer rains and more arid climes.
Now, that same process is happening in reverse. As temperatures rise, the Sahara and other dry areas are greening on the edges. “I’ve been studying the Sahara for 30 years and can definitely say that it’s getting greener,” says Kröpelin, who specializes in desert archaeology and climate history at the University of Cologne. Where there used to be nothing but desert, he says, there is now not just grass but shrubs and acacia trees–and he has the photos from 30 years of extensive field study to prove it. “The nomads are taking their camels to graze in areas where they’ve never been able to graze before.” Satellite data showing more green on the southern edge of the Sahara also bear him out. “There are always winners and losers if weather patterns change,” he says. “But as a general rule, warmer temperatures inevitably mean that the air picks up more moisture from the oceans, which will lead to more rainfall. If you look at the geological records in the Sahara, there have been repeated periods where the Sahara was greener when temperatures were warmer than today.”
So the desert was originally created around six thousand years ago under this theory. (Clearly caused by the hydraulic fracturing taking place in the Garden of Eden. Darned industrialist snakes…) But now the warmer temperatures are causing more rain at the edges of the desert? The subject is endlessly fascinating. Over the years I’ve heard all sorts of theories being tossed out in the scientific community regarding the planet’s biggest, baddest desert. One of the most recent ones – and for some reason I thought this was generally accepted, but perhaps not – is that the planet’s orbital tilt drifts over time. Around the same time period they’re talking about in this article, the tilt began to change, shifting the planet into a less inclined tilt from then until now.
The widely-held belief is that the Sahara dried up due to a change in the Earth’s orbit, which affects solar insolation, or the amount of electromagnetic energy the Earth receives from the Sun. In simpler terms, insolation refers to the amount of sunlight shining down on a particular area at a certain time, and depends on factors such as the geographic location, time of day, season, landscape and local weather.
Climate scientist Gavin Schmidt, of NASA’s Goddard Institute for Space Studies, explained that around 8,000 years ago, the Earth’s orbit was slightly different to how it is today. The tilt changed from around 24.1 degrees to the present-day 23.5 degrees.
“Additionally, the Earth had its closest approach to the Sun in the northern hemisphere (with) summer in August,” Schmidt said. “Today, that closest approach is in January. So, summertime in the north was warmer back then than it is now.”
Earlier theories speculated that there was a growing “rain shadow” effect caused by the continually rising Himalayan Mountains, disrupting weather patterns and stopping the rainfall in some areas. Still other have said that eccentricities in the earth’s orbit around the sun (a different consideration than the orbital tilt) have periodically thrown things off kilter in either direction which also contributed to the growth or recession of major deserts.
In either event, even if we can’t nail down exactly what’s causing it and to what degree the effects are felt, this must at least be some good news for farmers and herders in Africa. Party on, folks.