Tornadoes and climate change - what does the science say?
- 22 May 2013, 16:15
- Freya Roberts
Monday's tornado in Oklahoma highlights the
threat extreme weather poses to human life, and has prompted some
to ask if human-caused climate change is partly to blame.
Unfortunately, that's a question scientists still can't
The overwhelming response in the
online in the wake of the tornado has done a
pretty good job of accurately reflecting the science, which is so
far unclear over whether theres a link between climate change and
This statement from scientist Michael Wehner sums
up the situation pretty well:
tornadoes, what we don't know is as much as what we do
Before we dig into the science in more detail,
here's a quick introduction to
what tornadoes are and how they
Tornadoes are narrow, spinning columns of air
reaching from a the base of a thunderstorm down to the ground. They
actually only account for a fraction of the energy released in a
thunderstorm, but that energy is concentrated on a small
As the video below shows, tornadoes need
two critical conditions to form: warm moist air and
high 'wind shear'.
Wind shear is the spinning motion caused
when winds at different heights blow at different speeds. It's the
moisture and high winds which cause most of the destruction when a
What does the science say?
Trying to establish whether tornadoes activity
will change as the climate warms is tricky for a number of reasons,
as a recent
report from the Intergovernmental Panel on Climate
Change (IPCC) highlights.
First, scientists don't have a complete, good
quality data set on tornadoes that have already occurred. Without a
long reliable record, scientists can't easily look to see how
tornadoes have changed since temperatures started
Second, computer models used to simulate the
climate can't tell scientists much about tornadoes either. That's
because these models work on large scales, simulating changes in
the ocean and the atmosphere on a global scale. In comparison,
tornadoes are small weather events. As Dr
Suzanne Gray, a meteorologist from Reading
are too small-scale for current climate models to simulate, so it
is not possible to say very much about how strength and occurrence
might alter under climate change."
Then, there's one final problem. Climate change
is likely to affect the two critical conditions for tornado
formation - atmospheric moisture and wind shear - in opposite ways.
The atmosphere is expected to hold more moisture as temperatures
rise, making tornadoes more likely. But wind shear will probably
decrease, having the opposite effect. Scientists can't say whether
one force will override the other.
Climate change and the Oklahoma
Given how hard it is to find any link between
climate change and tornadoes, it's no surprise scientists say
individual events, like the tornado which struck Oklahoma, cannot
be pinned to climate change. As IPCC chair Rajendra Pachauri
cannot relate an event of this nature to human-induced climate
change. It's just not possible. Scientifically, that's not
Scientists worldwide are continually researching tornadoes
to find out how their frequency and intensity might change in the
future. As time goes on, the record of past tornadoes will grow too
- providing a bigger set of data to spot trends in. It seems
logical that climate change will have some effect on tornadoes, but
for now it's very hard to say what that effect will be.