Scientists say they have pinpointed the cause of medieval megadroughts that stretched for decades at a time, and they warn climate change could soon cause them to return to the American Southwest. From the 9th through the 16th centuries, the Southwest experienced about a dozen megadroughts. These extreme droughts were caused by a combination of three factors, according to a new study by researchers at Columbia University's Lamont-Doherty Earth Observatory.Two of the factors were warming sea surface temperatures in the Atlantic Ocean and high radiative forcing, which occurs when the atmosphere traps more energy from the sun than it radiates back into space, according to the study published this week in Science Advances. The third, and most important factor, was severe and frequent La Niña events, periods when tropical Pacific Ocean temperatures are cooler and storms are pushed toward the Northwest. “Both a warm Atlantic and a cold Pacific change where storms go,” Nathan Steiger, the study's lead author, told Vice. “They both result in fewer storms going to the Southwest.” On top of having less rainfall because of fewer storms, the radiative forcing caused any moisture that was there to evaporate more quickly. Beginning in 1600, volcanic eruptions that spewed particles into the atmosphere blocked some of the sun's energy and decreased the effect of radiative forcing, thereby greatly reducing the number of megadroughts. However, the increased burning of fossil fuels that started with the Industrial Age pumped more carbon dioxide into the atmosphere, which is again trapping the sun's energy...MORE
No comments:
Post a Comment