Global
warming may be far worse than thought, cloud analysis suggests
Researchers
find clouds contain more liquid – as opposed to ice – than was
previously believed, threatening greater increase in temperatures
Oliver Milman
Thursday 7 April
2016 19.00 BST
Climate change
projections have vastly underestimated the role that clouds play,
meaning future warming could be far worse than is currently
projected, according to new research.
Researchers said
that a doubling of carbon dioxide in the Earth’s atmosphere
compared with pre-industrial times could result in a global
temperature increase of up to 5.3C – far warmer than the 4.6C older
models predict.
The analysis of
satellite data, led by Yale University, found that clouds have much
more liquid in them, rather than ice, than has been assumed until
now. Clouds with ice crystals reflect more solar light than those
with liquid in them, stopping it reaching and heating the Earth’s
surface.
The underestimation
of the current level of liquid droplets in clouds means that models
showing future warming are misguided, says the paper, published in
Science. It also found that fewer clouds will change to a
heat-reflecting state in the future – due to CO2 increases – than
previously thought, meaning that warming estimates will have to be
raised.
Such higher levels
of warming would make it much more difficult for countries to keep
the global temperature rise to below 2C, as they agreed to do at the
landmark Paris climate summit last year, to avoid dangerous extreme
weather and negative effects on food security. The world has already
warmed by 1C since the advent of heavy industry, driven by CO2
concentrations soaring by more than 40%.
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A lack of data and
continuing uncertainty over the role of clouds is to blame for the
confusion about warming estimates, said Ivy Tan, a graduate student
at Yale who worked on the research with academics from Yale and the
Lawrence Livermore National Laboratory.
“Models have been
systematically underestimating the amount of liquid in clouds,
meaning that we aren’t fully appreciating the feedback,” she
said. “It could mean our higher limit of warming is now even
higher, depending on the model, which means serious consequences for
us in terms of climate change.
“This is one of
the largest uncertainties left in climate change. We need to
understand these feedbacks a lot better.”
Scientists have been
trying to get to grips with the extent clouds and water vapor will
influence the warming already under way. A paper published last year
found that short-term fluctuations in clouds have large impacts on
the net rate of heat gain by the Earth.
One of this paper’s
authors, Dr Kevin Trenberth, senior scientist at the National Center
for Atmospheric Research, said research has already shown “major
errors in climate simulations associated with clouds”.
Trenberth said there
is “some art” to working out the role of clouds, given their
annual cycles and distribution, with uncertainty over whether climate
sensitivity is significantly changed.
“I think the paper
is fine as a first step but it is not the last step, and much more is
needed to establish how clouds change as the climate changes,”
Trenberth said of the Yale study.
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