by Steve Connor
1 July 2011
Scientists to End 20-Year
Reluctance With Study Into Global Warming and
Exceptional Weather Events
Scientists are to end their 20-year reluctance to link climate
change with extreme weather - the heavy storms, floods and droughts
which often fill news bulletins - as part of a radical departure
from a previous equivocal position that many now see as increasingly
Climate researchers from Britain, the
United States and other parts of the world have formed a new
international alliance that aims to investigate exceptional weather
events to see whether they can be attributable to global warming
caused by greenhouse gas emissions.
They believe that it is no longer plausible merely to claim that
extreme weather is “consistent” with climate change. Instead, they
intend to assess each unusual event in terms of the probability that
it has been exacerbated or even caused by the global temperature
increase seen over the past century.
The move is likely to be highly controversial because the science of
“climate attribution” is still in the early stages of development
and so is likely to be pounced on by climate “skeptics” who question
any link between industrial emissions of carbon dioxide and rises in
global average temperatures.
In this April 19,
2011 file photo, smoke rises from
wildfire burning near Possum Kingdom, Texas.
It was a spring to
remember, with America pummeled by
wildfire, snowmelt, thunderstorms and drought.
AP Photo/LM Otero,
In the past scientists have been extremely reluctant to link a
single extreme weather event with climate change, arguing that the
natural variability of the weather makes it virtually impossible to
establish any definitive association other than a possible general
consistency with what is expected from studies based on computer
However, a growing number of climate scientists are now prepared to
adopt a far more aggressive posture, arguing that the climate has
already changed enough for it to be affecting the probability of an
extreme weather event, whether it is an intense hurricane, a major
flood or a devastating drought.
“We’ve certainly moved beyond the
point of saying that we can’t say anything about attributing
extreme weather events to climate change,” said Peter Stott, a
leading climate scientist at the Met Office Hadley Centre in
“It’s very clear we’re in a changed climate now which means
there’s more moisture in the atmosphere and the potential for
stronger storms and heavier rainfall is clearly there.”
Kevin Trenberth, a distinguished
senior scientist at the US National Center for Atmospheric Research
(NCAR) in Boulder, Colorado, also believes the time has come to
emphasize the link between extreme weather and the global climate in
which it develops.
“The environment in which all storms
form has changed owing to human activities, in particular it is
warmer and more moist than it was 30 or 40 years ago,” Dr
“We have this extra water vapor lurking around waiting for
storms to develop and then there is more moisture as well as
heat that is available for these storms [to form]. The models
suggest it is going to get drier in the subtropics, wetter in
the monsoon trough and wetter at higher latitudes. This is the
pattern we're already seeing.”
The Met Office and NCAR have joined
forces with other climate organizations, including the influential
US National Oceanic and Atmospheric Organization (NOAA), to
carry out detailed investigations of extreme weather events, such as
the vast flooding in Pakistan last year, to see whether they can
detect a climate change “signal” as a likely cause.
A group of their researchers has formed a coalition called the
Attribution of Climate-Related Events which is preparing a report on
the subject to be published later this year at a meeting of the
World Climate Research Program in Denver.
They hope in future to assess each
extreme weather phenomenon in terms of its probability of being
linked with global warming and then to post the result on the
“There is strong evidence if you
look across the world that we are seeing an increase in
heat-waves and floods and droughts and extreme rainfall and
extreme temperatures,” Dr Stott said.
“The evidence is clear from looking at the observational records
globally that extreme temperatures and extreme rainfall are
changing. But you can’t jump from that and say that a specific
event is straightforwardly attributable because we know that
natural variability could have played a part.
“We’ve been developing the science to be increasingly more
quantitative about the links and make more definitive statements
about how the risk has changed. You look sensibly about these
things by talking about changing risk, or changing probability
of these events.”
Dr Stott had his colleagues have
already carried out studies of the 2003 heat-wave in Europe, in
which up to 35,000 people died of heat-related illnesses, as well as
the devastating UK floods in 2000 which cost £1.3bn in insurance
claims and destroyed 10,000 homes following the wettest autumn in
England and Wales since records began in 1766.
In both cases, the scientists found that the contribution of man-made greenhouse gases to global warming substantially increased
the risk of such extreme events occurring.
The group is also investigating the
exceptional warm April in Britain this year, which was the warmest
since central England records were kept in 1659 and 0.5°C warmer on
average than the previous warmest April.
Also this year, an unprecedented number of tornadoes across the
southeastern US and the flooding of major rivers such as the
Mississippi and Missouri led many people to question whether they
were exacerbated by global warming.
In the past scientists would have been
reluctant to link single weather events such as these with climate
change, but Dr Trenberth believes this is wrong.
“I will not say that you cannot link
one event to these things. I will say instead that the
environment in which all of these storms are developing has
changed,” Dr Trenberth told The Independent.
“It’s not so much the instantaneous result of the greenhouse
effect, it’s the memory of the system and the main memory is in
the oceans and the oceans have warmed up substantially, at
depth, and we can measure that.
I will assert that every event has
been changed by climate change and the main time we perceive it
is when we find ourselves outside the realms of the previous
natural variability, and because natural variability is so large
this is why we don't notice it most of the time.
“When we have things that occur usually 4 per cent of the time
start to occur 10 per cent of the time, that’s when we begin to
notice. The main way we perceive climate change is in changes in
the extremes? this is when we break records.”
A report by the insurance company Munich
Re found that 2010 was one of the worst years on record for natural
disasters, nine-tenths of which were related to extreme weather,
such as the floods in Pakistan and eastern Australia and heat-wave
in Russia, which is estimated to have killed at least 56,000 people,
making it the most deadly natural disaster in the country’s history.
“This long-term trend can no longer
be explained by natural climate oscillations alone. No, the
probability is that climate change is contributing to some of
the warming of the world’s oceans,” said Peter Höppe, author of
the Munich Re report.
Making the connection
Tornadoes, US, 2011 More than
220 people were killed by tornadoes and violent storms that
ripped through south-eastern United States in April; 131
were killed in Alabama alone. Fifteen people died in
Tuscaloosa and sections of the city were destroyed.
Heat-wave, UK, 2011April was the
warmest since 1659, when records in England began.
Sun-lovers flocked to St Ives, above, but fears of drought
were raised. Rainfall in the UK that month was only 52 per
cent of the long-term average.
Drought, Brazil, 2005 The Amazon
region suffered the worst drought in more than a century.
The floodplains dried up and people were walking or using
bicycles on areas where canoes and river boats had been the
only means of transport.
Floods, USA, 2005 Katrina was
one of the five deadliest hurricanes in the history of the
US, and it caused the destruction of New Orleans when levees
were overwhelmed. Some 90 per cent of residents of
south-east Louisiana were evacuated.