Flood, drought, fire = extreme weather = climate change?
The United States based
National Oceanic and Atmospheric Administration (NOAA) released
research on Wednesday which found that the 2010 Russian heatwave
was primarily due to a natural atmospheric process called
"atmospheric blocking". It suggested that while a contribution from
climate change could not be ruled out, natural variability played a
much larger role.
The study was the latest to have examined the relationship
between a specific extreme weather event and increasing greenhouse
gases in the atmosphere.
Climate scientists are well aware of the pitfalls inherent in
this kind of work - and the statement that "a single event cannot
be attributed to climate change" is almost axiomatic in the public
discussion around climate science. As the science blog Real Climate
put it in 2005, following Hurricane Katrina:
"For a single event, regardless of how extreme, such attribution
is fundamentally impossible. We only have one Earth, and it will
follow only one of an infinite number of possible weather
sequences. It is impossible to know whether or not this event would
have taken place if we had not increased the concentration of
greenhouse gases in the atmosphere as much as we have."
This argument, however, has come under increasing pressure in
2010, as media interest in a series of unusual weather events
around the world intensifies.
2010 was the joint warmest year on record. Australia experienced
cyclones and flooding; Pakistan saw flooding; there was drought in
the Amazon; the Northern hemisphere had an unusually cold winter
whilst countries around the world set
new record temperature highs.
The problems inherent in looking at particular events does not
mean that science has nothing to say. Climatologist
Francis Zwiers put the answer well in his
written evidence to the US Senate earlier this week:
"… individual extreme events cannot be ascribed to human
influence on the climate system in the sense that the event could
not have occurred if it were not for human influence. It is,
however, possible to assess how human influence on climate may be
"loading the weather dice", making some events more likely, and
others less likely."
Zwiers cited two studies published in Nature last month, both of
which took the "loaded dice" approach to addressing the link
change and flooding.The first (Min et al 2011) found that the
probability of intense rainfall on any given day has increased by
7% over the last 50 years, across the whole of the Northern
The second (Pall et al 2011) found that the likelihood of a
single event - the UK flooding of 2000 - was significantly
increased by human-induced climate change. Zwiers also discussed
research by the same Oxford team in 2004, which estimated that
it is highly likely that human influence had at least doubled the
risk of a heatwave like the one that occurred in Europe in
Predictably, the NOAA study into the Russian heatwave has
prompted some triumphalism from climate sceptics, with the
Watts Up With That stating
"Maybe this will be a lesson to those in the MSM and eco
blogland who immediately jump on every newsworthy weather event,
with no supporting evidence, attributing it to "global warming",
"climate change" or "climate disruption"…"
It is true that statements made immediately after any extreme
weather event should be treated with caution. Producing scientific
research is a slow process (the two papers on flooding were
submitted to Nature in March 2010), and this is a tricky area.
The WUWT statement ignores the second conclusion from the NOAA
research - that while the scientists could not attribute the
intensity of this particular heat wave to climate change, they
found that extreme heat waves are likely to become increasingly
frequent in the region in coming decades - with the risk rising
"from less than one percent in 2010, to 10 percent or more by the
end of this century."
It looks as though conversations like this may be continuing
into the future.