Stretching 3.5 million square miles across northern Africa, the vast sand dunes and rocky plateaus of the Sahara cover more ground than the continental United States. Now, a pair of scientists is making a provocative claim that the world’s largest desert has expanded 10 percent since the early 20th century, effectively adding another Texas-sized chunk.
It sounds bad! But some outside experts contacted by Earther expressed serious doubts about study’s findings, suggesting more research on the Sahara, and better data collection across northern Africa, are sorely needed.
To track changes to the Sahara’s boundaries over time, the University of Maryland researchers used a global precipitation dataset that includes a network of rainfall gauges across Africa. Defining desert conditions as about four inches or less of rainfall per year, they found that from 1920 to 2013, the Sahara expanded by about 270,000 square miles.
According to their paper published Thursday in the Journal of Climate, a combination of the Atlantic Multidecadal Oscilllation (AMO), a shift from warmer to cooler waters over the North Atlantic that occurs every 50 to 80 years, and human-caused climate change, are the most likely culprits.
“Both effects are actually superimposed on each other, and both are leading to the expansion of the Sahara, particularly on the southern edge,” study co-author Sudam Nigam told Earther. He noted that as the AMO transitioned into a cool phase in the 1950s, rainfall in the savannah-covered Sahel just south of the Sahara “precipitously declined.”
Since the late 1990s, when the AMO shifted back into a warm phase, the Sahel has featured a warmer, wetter climate overall, according to NASA’s Earth Observatory. But the study also concluded that climate change is probably responsible for some amount of the regional dry-out—and climate change, of course, isn’t going away anytime soon.