Scientists
attribute extreme weather to man-made climate change
Researchers
have for the first time attributed recent floods, droughts and
heatwaves, to human-induced climate change
10
July, 2012
Climate
change researchers have been able to attribute recent examples of
extreme weather to the effects of human activity on the planet's
climate systems for the first time, marking a major step forward in
climate research.
The
findings make it much more likely that we will soon – within the
next few years – be able to discern whether the extremely wet and
cold summer and spring so far experienced in the UK this year are
attributable to human causes rather than luck, according to the
researchers.
Last
year's record warm November in the UK – the second hottest since
records began in 1659 – was at least 60 times more likely to happen
because of climate change than owing to natural variations in the
earth's weather systems, according to the peer-reviewed studies by
the National Oceanic and Atmospheric Administration in the US, and
the Met Office in the UK. The devastating heatwave that blighted
farmers in Texas in the US last year, destroying crop yields in
another record "extreme weather event", was about 20 times
more likely to have happened owing to climate change than to natural
variation.
Attributing
individual weather events, such as floods, droughts and heatwaves, to
human-induced climate change – rather than natural variation in the
planet's complex weather systems – has long been a goal of climate
change scientists. But the difficulty of separating the causation of
events from the background "noise" of the variability in
the earth's climate systems has until now made such attribution an
elusive goal.
To
attribute recent extreme weather events – rather than events 10
years ago or more – to human-caused climate change is a big
advance, and will help researchers to provide better warnings of the
likely effects of climate change in the near future. This is likely
to have major repercussions on climate change policy and the ongoing
efforts to adapt to the probable effects of global warming.
Peter
Stott, of the UK's Met Office, said: "We are much more confident
about attributing [weather effects] to climate change. This is all
adding up to a stronger and stronger picture of human influence on
the climate."
But
the researchers also said that not every extreme weather event could
be attributed to climate change. For instance, the extremely cold
British winter of 2010-11 – starkly exemplified by the satellite
picture of the UK and Ireland covered in white on Christmas Eve, as
snow gripped the nations – was owing to variations in the systems
of ocean and air circulation. Although such cold winters are now only
half as likely as they were several decades ago, owing to a generally
warming climate across the world, extremely low temperatures of this
type are still possible depending on circulation effects – in this
case, a negative North Atlantic Oscillation, the circulation system
that is a key determinant of European weather.
Floods
in Thailand last year, another example studied in the research, were
also not judged to be due to climate change but to other factors such
as changes in the management of local river systems.
Following
and predicting temperature rises tends to be much less complex than
predicting – and attributing the causes of – changes in
precipitation patterns.
This
year's weather in the UK is an example. The Met Office has said the
record wet conditions, which have brought serious flooding to regions
from Yorkshire to the south-west, were owing to "a particularly
disturbed jet stream". That is the weather system across the
north Atlantic that normally lies at higher latitudes during the
British summer, but has been lower in latitude than usual for several
years running, bringing wet and sometimes cold conditions. Some
research has suggested that the massive melting of Arctic ice has
been responsible for this effect – by changing the patterns of
warmer and colder winds in the upper atmosphere.
But
the key question – of whether man-made global warming is putting a
dampener on British summers – will take several years to solve,
according to Stott. "This is an open question in terms of
research – it is too early days to be able to say," he said.
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