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
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
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.
0 comments:
Post a Comment