Washington:
Arctic warming weakens the temperature difference between the tropics and the poles, resulting in less precipitation, weaker cyclones and mid-latitude westerly wind flow -- a recipe for prolonged droughts, a study has found. The temperature difference between the tropics and the poles drives a lot of weather, according to the study published in the journal Nature.
When those opposite temperatures are wider, the result is more precipitation, stronger cyclones and more robust wind flow. However, due to the Arctic ice melting and warming up the poles, those disparate temperatures are becoming closer, researchers said.
"Our analysis shows that, when the Arctic is warmer, the jet stream and other wind patterns tend to be weaker," said Bryan Shuman, a professor at the University of Wyoming in the US.
"The temperature difference in the Arctic and the tropics is less steep. The change brings less precipitation to the mid-latitudes," Shuman said. "Importantly, when temperatures have changed in similar ways to today (warming of the Arctic), the mid-latitudes -- particularly places like Wyoming and other parts of central North America -- dried out," he said.
"Climate models anticipate similar changes in the future," said Shuman. Currently, the northern high latitudes are warming at rates that are double the global average.
This will decrease the equator-to-pole temperature gradient to values comparable with the early to middle Holocene Period, that began 12,000 to 11,500 years ago, according to the researchers.
Shuman said his research, using geological evidence, was helping to estimate how dry conditions have been in the past 10,000 years.
"Lakes are these natural recorders of wet and dry conditions. When lakes rise or lower, it leaves geological evidence behind," Shuman said.
The analysis included 236 records from 219 sites. During the past 10,000 years, many of the lakes studied were lower earlier in history than today, he said.
The research group looked at the evolution of the tropic-to-pole temperature difference from three time periods: 100 years ago, 2,000 years ago and 10,000 years ago.
