But do
people have influence on extreme weather?.
Well, some say yes and some say no. One organization who says that
humans tend to have an influence is the Intergovernmental Panel on Climate
Change (IPCC) http://www.ipcc.ch/ They
say that Anthropogenic Climate Change
not only influences the climate but also the weather and more specific extreme
weather. In their latest report about weather
and climate they state the following:
A changing climate can be expected to lead to
changes in climate and weather extremes. But it is challenging to associate a
single extreme event with a specific cause such as increasing greenhouse gases
because a wide range of extreme events could occur even in an unchanging climate,
and because extreme events are usually caused by a combination of factors.
Despite this, it may be possible to make an attribution statement about a
specific weather event by attributing the changed probability of its occurrence
to a particular cause. For example, it has been estimated that human influences
have more than doubled the probability of a very hot European summer like that
of 2003.
IPCC (2012) report: Changes in Climate
Extremes and their Impacts on the Natural Physical Environment
Chapter 3 page 126
But they also say that it is very
difficult to determine what exactly causes an extreme weather event. There are
so many different components which interact with each other. And that means
that there is not one single cause for an extreme weather event but many which
interact with each other in many ways. The IPCC report explains it with an
example:
The hot 2003 European summer was associated with a persistent
high-pressure system (which led
to clear skies and thus more solar energy received at the surface) and too-dry
soil (which meant that less solar energy was used for evaporation, leaving more
energy to heat the soil). Another example is that hurricane genesis requires
weak vertical wind shear, as well as very warm sea surface temperatures. Since
some factors, but not others, may be affected by a specific cause such as
increasing greenhouse gas concentrations, it is difficult to separate the human
influence on a single, specific extreme event from other factors influencing
the extreme.
IPCC(2012) report: Changes in Climate Extremes and their Impacts on the
Natural Physical Environment
Chapter 3 page 126
This makes it hard to distinguish ‘’normal’’
extreme weather from extreme weather that has been made worse by humans. And
there is still discussion going about what extreme weather events actually are.
Cited from the IPCC (2012) report: Some literature reserve the term ‘extreme
event’ for initial meteorological phenomena (Easterling et al., 2000; Jentsch
et al., 2007), some include the consequential physical impacts, like flooding
(Young, 2002), and some the entire spectrum of outcomes for humans, society, and
ecosystems (Rich et al., 2008).
The IPCC says that it’s likely that
humans have influence on extreme weather events but also says that there is
still uncertainty about this
relationship and that more research needs to be done.
All the reports from the IPCC are
free accessible and can be downloaded from their website. The report I used is
594 pages long, I used only the part in which they spoke about their position
on extreme weather and Climate Change. This
is the full report:
But not everyone agrees with the
views of IPCC . The editorial board of the famous journal Nature writes in its
journal that there is not enough evidence to link ‘’extremer’’ extreme weather with Climate Change at this moment. According to them we just don’t understand
the complex processes that cause extreme weather well enough to say even that it is likely.
‘’Solid understanding of these factors is crucial if researchers are to
improve the performance of, and confidence in, the climate models on which
event attribution and longer-term climate projections depend’’.
Nature (2012) volume 489 page 336
They want more knowledge about extreme weather
before they link extreme weather with climate change.
“To make this emerging science of ‘climate attribution’ fit to inform
legal and societal decisions will require enormous research effort.”
Nature (2012) volume 489 page 336
The current climate models which are used to predicted
climate change are not yet suitable for measuring the human impact on extreme
weather. Before you can say anything
about human influence on extreme weather you need good models and these are not
yet available.
Besides that they also question the usefulness
of understanding the relationship between climate change and extreme weather:
Especially in poor countries, the losses arising from extreme weather
have often as much to do with poverty, poor health and government corruption as
with a change in climate.
Nature (2012) volume 489 page 336
But both IPCC and Nature agree on
the fact that more research is required.
Link to the Nature Editorial writing: http://www.nature.com/polopoly_fs/1.11428!/menu/main/topColumns/topLeftColumn/pdf/489335b.pdf
In the next posts I will
review two studies. The first study has become very famous in recent days
because it studies the possibility that New York City will be hit by a hurricane. And that’s
exactly what happened one week ago. The second study is called EXPLAINING
EXTREME EVENTS OF 2011 FROM A CLIMATE PERSPECTIVE and argues that climate
change had an influence on recent extreme weather events. Both the studies have
made headlines: http://www.nytimes.com/2012/07/11/science/earth/global-warming-makes-heat-waves-more-likely-study-finds.html?ref=global-home&_r=0
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