Half a degree doesn’t sound much. But if it gets any warmer, we will notice the difference soon enough.
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| Heavy rainfall is becoming more frequent across many parts of the world. Image: Roger Price from Hong Kong, via Wikimedia Commons |
LONDON – Researchers now know the difference half a degree can make. They can tell you why 1.5°C warming would be better than a 2°C climb in average global temperatures,
because even half a degree Celsius could mean greater extremes of heat,
more overwhelming rainfall, and longer spells of warm weather.
And they know all this because they’ve
seen it happen in the recent past. There is enough evidence, they say,
in the observational record for the last half century to underline the
importance of even half a degree.
Scientists from Germany and Switzerland outline the argument and identify the evidence in the journal Nature Climate Change.
In the last two centuries, the ratio of
carbon dioxide, the result of extravagant fossil fuel use since the
Industrial Revolution, has risen from around 280 parts per million to 400 ppm, and average global temperatures have risen around 1°C during that time.
The researchers matched temperature and
climate records for the years 1960 to 1979 and 1991 to 2010, a period
when the thermometer averages climbed by a whole half a degree.
They found that the intensity of extreme
rainfall had increased by 9% over that period. The coldest winters were
measurably less cold, and half of the global land mass had experienced
changes of what they called “warm spell duration” of more than six days.
It is not that perceptible global warming made these extremes happen – extremes happen anyway – but the researchers think it made them more likely. By raising the temperature, humans loaded the climate dice.
“The hottest summer temperatures
increased by more than 1°C in a quarter of global land areas, while the
coldest winter temperatures warmed by more than 2.5°C,” said Peter Pfleiderer, a scientist with the Potsdam Institute for Climate Impact Research and for Climate Analytics.
And his colleague Carl-Friedrich Schleussner said:
“As we’re moving increasingly outside of the range of natural climate
variability, we have to expect that impacts on agriculture, human and
biological systems will be more pronounced.”
The Intergovernmental Panel on Climate
Change has begun to prepare a special report on the impacts of a warming
of 1.5°C, the target set by the world’s nations in the Paris Agreement of 2015.
“With the warming the world has already experienced, we have an actual record of warming to study, and we can see very clearly that a difference of 0.5˚C of warming really does matter.”
There is no certainty that the world’s
nations can meet the Paris target and contain global warming, and limit
climate change, because enough carbon dioxide has been emitted to take air temperatures over land to that level already.
The next decade could be critical, which is why researchers feel they need the evidence in as clear a form as possible.
“One of the pressing questions for
scientists today is whether we know that limiting warming to 1.5°C
instead of 2°C would make a difference in the future. We have to rely on
climate models to predict the future, but given we now have
observational evidence of around 1˚C warming, we can also look at the
real life impacts this warming has brought,” Dr Schleussner said.
And the third signatory, Erich Fischer of ETH Zurich, said: “Communicating abstract quantities like differences in global mean temperature is difficult.
“With the warming the world has already
experienced, we have an actual record of warming to study, and we can
see very clearly that a difference of 0.5˚C of warming really does
matter.”
*Tim Radford, a founding editor of Climate News Network, worked for The
Guardian for 32 years, for most of that time as science editor. He has
been covering climate change since 1988.
Links
- Recent past shows half a degree of warming means more extreme weather
- In the observational record half a degree matters
- CO2 impacts taint pristine island
- Wildlife faces climate’s survival and sex problems
- Climate change may increase California’s rain
- Sahel monsoon may see African drylands bloom
- Human growth lessens wildfire risk
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