Wednesday, July 12, 2017

Why a Warming Arctic May Be Causing Colder U.S. Winters

[National Geographic] When a U.S. Republican senator threw a snowball onto the Senate floor in late February of 2015, he used it to underscore his belief that human-made climate change was an alarmist conclusion. The snowball had been rolled from the Capitol grounds in Washington D.C., which, at the time, was experiencing an uncharacteristically cold winter.
If global warming was real, he posited, how could the nation's capital experience such severe cold?
Uncharacteristically cold winters, however, just might be one of the most hard felt effects of climate change, according to a study published in Nature Geoscience by a team of researchers.
The study found that unusually cold temperatures in northern North America and lower precipitation in the south central U.S. all coincided with periods of warmer Arctic weather.
To reach this conclusion, the researchers analyzed how teleconnections in the Arctic cause cooler winters in North America. Teleconnections are largescale weather anomalies that influence weather across continents and span large portions of the atmosphere. The most commonly watched teleconnection weather patterns are El Ninos/as, but teleconnections are observed around the globe.
Anna Michalak, a researcher at the Carnegie Institution for Science, was involved in creating an ensemble of models used to support the study's findings. She explained that the massive system of climate models, called MsTMIP, creates a large dataset that allows researchers to study the changes in the Earth terrestrial biosphere.

In order to reach their conclusions, the study's authors looked at how the terrestrial biosphere (all the plants and soil on the Earth's surface) contributed to or pulled carbon from the atmosphere. They found that over the past three decades, plants pulled less carbon from the Earth's atmosphere during periods of warmer weather in the arctic.
"Even though we're talking about the Arctic, it has immediate impacts on what we experience at lower latitudes," said Michalak. Read More