Blocking patterns: How global warming might have worsened US drought
Two teams of researchers find that subtle changes brought about by global warming might be amplifying atmospheric blocking patterns, which keep weather conditions in place for a long time.
(Page 2 of 2)
Another study, by scientists at NCAR, looked at the reasons behind a prolonged heat wave and drought in Russia, drought in Brazil, and heavy rains and flooding in Pakistan, Colombia, and northeastern Australia in 2010.
Skip to next paragraph
It identified four expanses of tropical oceans – the northern Indian Ocean, the Gulf of Mexico as well as Caribbean Sea, and the tropical Pacific – where sea-surface temperatures either broke or approached record levels at various times between May and September. In the meantime, the shift from El Niño to La Nina – the seesaw cycle in ocean temperatures and wind patterns in the tropical Pacific – shifted the center of thunderstorm action in the tropical oceans to these unusually-warm regions.
An atmosphere already warmed by climate change and capable of holding more moisture built vigorous storms that provided the heavy rains. The release to the atmosphere of heat as the water vapor feeding these storms cooled and condensed triggered a chain of changes in circulation patterns.
Over the tropical Atlantic, it led to the establishment of a stubbornly persistent high-pressure system over southern Europe and the western part of the Russia, bringing with it the heat wave, which set the stage for wildfires the country experienced. The blocking pattern also kept steering amped-up monsoon storms to flood Pakistan.
Meanwhile, intensified convection over the Caribbean also brought heavy rains to Colombia, where flooding displaced an estimated 1.5 million people.
The study, led by NCAR's Kevin Trenberth, was published earlier this month in the Journal of Geophysical Research.
The direct effect of global warming on features such as Russia's heat wave and drought is small, acknowledges Dr. Fasullo, who teamed up with Dr. Trenberth on the study. But that small contribution appears to have triggered processes that amplified the warming, he adds.
Over time, as climates change plant species change and soils lose moisture. In the US Midwest this summer, scant winter snowfall left soils with little moisture on hand to evaporate and serve as an air conditioner when spring and summer arrived. These conditions can help reinforce the blocking pattern that keeps at bay storms that otherwise might reach the area.
The same thing happened in Russia, according to the study. The warming it has undergone has been greater than warming implied by the 1-degree Fahrenheit increase in the global average temperature since the 1950s, Fasullo says. This set the stage for feedbacks that amplified the warming the country experienced when the heatwave arrived.
Previous
Become part of the Monitor community