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Cornell researcher: Melting Arctic helped make monster Houston hurricane

In the wake of heavy rains from Storm Harvey, the National Weather Service added a color to its precipitation map to include accumulations of more than 30 inches. This is the map before the addition. Photo: National Weather Service

ALBANY — While the Arctic is a long way from Houston, the continuing loss of polar ice from man-made climate change likely helped make Hurricane Harvey into a record-setting killer that dumped trillions of gallons of rain, according to a researcher from Cornell University.

"What happens in the Arctic does not stay in the Arctic," said Charles Greene, a professor of earth and atmospheric sciences. He said the loss of Arctic sea ice is weakening high-altitude jet stream winds, which makes it more likely that powerful storms like Harvey can "stall" in place.

Greene also studied Superstorm Sandy, which in 2012 slammed New York and the Northeast in 2012, and found that storm lingered after being blocked by a stalled weather system in the northern Atlantic. Sandy was the second-costliest storm in U.S. history.

"Arctic warming likely played an important role in making Hurricane Harvey such an extreme killer storm. With sea ice loss and Arctic amplification of greenhouse warming, the jet stream slows down, meanders more, and frequently results in stalled weather systems," he said.

"This week, we are seeing the effects of another stalled weather system," said Greene. "Houston would have suffered much less damage if the storm had just crashed through the city and petered out in west Texas. But instead, the storm system stalled in place and continued to dump record amounts of rainfall from the Gulf of Mexico on the city."

Over the course of about three days before ending Tuesday, Harvey dumped more than 50 inches of rain on Houston, which is about what the city gets for an entire year.

Also, said Greene, the hurricane carried much more rain because of the much warmer waters of the Gulf of Mexico, which are now about 3 degrees warmer compared to the decades before the 1990s. Warmer water releases more water vapor into the air, which results in more rain from storms.

Altogether, Houston was hit by about 19 trillion gallons, or roughly equivalent to the Hudson River flowing into New York Harbor for 225 years.

Greene said if that much water fell in the Great Lakes region at once, it would raise the level of all five lakes by a foot. Greene, who holds a doctorate in oceanography and is a fellow at the Woods Hole Oceanographic Institution, has been at Cornell since 1986.

High-level jet stream winds in the Northern Hemisphere are influenced by the temperature difference between the Arctic, which in recent decades has been warming at twice the global average, and more temperate regions to the south.

Arctic sea ice has been shrinking for several decades as temperatures climb. In March 2017, scientists at NASA announced that ice cover had declined to an all-time record low for the winter season.

As the Arctic warms and loses more of its sea ice, that temperature difference with southerly regions has been narrowing, which causes the jet stream to weaken and wobble. This weakening also allows high-pressure systems to remain in place longer, which can block storms from moving off, said Greene.

Declining Arctic ice has also influenced winter weather in the New York state and the Northeast by weakening high-altitude winds that circle the North Pole, known as the polar vortex. The winds act as a kind of barrier to keep frigid temperatures from spilling southward.

In years when the polar vortex weakens and slows, it can become misshapen and dip further south than normal, bringing extreme cold and winter conditions with it, according to Andrea Lang, an assistant professor of atmospheric and environmental science at the University at Albany who studies the vortex.

A weakened polar vortex brought extreme winter conditions to the Capital Region and the Northeast in 2013 and 2014.

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