From: ETH Zurich via ScienceDaily
Published March 28, 2015 06:59 AM

Climate change doesn't cause severe winters after all

Cold snaps like the ones that hit the eastern United States in the past winters are not a consequence of climate change. Scientists at ETH Zurich and the California Institute of Technology have shown that global warming actually tends to reduce temperature variability.

Repeated cold snaps led to temperatures far below freezing across the eastern United States in the past two winters. Parts of the Niagara Falls froze, and ice floes formed on Lake Michigan. Such low temperatures had become rare in recent years. Pictures of icy, snow-covered cities made their way around the world, raising the question of whether climate change could be responsible for these extreme events.

It has been argued that the amplified warming of the Arctic relative to lower latitudes in recent decades has weakened the polar jet stream, a strong wind current several kilometres high in the atmosphere driven by temperature differences between the warm tropics and cold polar regions. One hypothesis is that a weaker jet stream may become more wavy, leading to greater fluctuations in temperature in mid-latitudes. Through a wavier jet stream, it has been suggested, amplified Arctic warming may have contributed to the cold snaps that hit the eastern United States.

Scientists at ETH Zurich and at the California Institute of Technology, led by Tapio Schneider, professor of climate dynamics at ETH Zurich, have come to a different conclusion. They used climate simulations and theoretical arguments to show that in most places, the range of temperature fluctuations will decrease as the climate warms. So not only will cold snaps become rarer simply because the climate is warming. Additionally, their frequency will be reduced because fluctuations about the warming mean temperature also become smaller, the scientists wrote in the latest issue of the Journal of Climate.

Snow covered road in forest image via Shutterstock.

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