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World must adapt to unknown climate future, says IPCC

There is still great uncertainty about the impacts of climate change, according to the latest

report from the Intergovernmental Panel on Climate Change, released today. So if we are to

survive and prosper, rather than trying to fend off specific threats like cyclones, we must

build flexible and resilient societies.

Today's report is the second of three instalments of the IPCC's fifth assessment of climate

change. The first instalment, released last year, covered the physical science of climate

change. It stated with increased certainty that climate change is happening, and that it is the

result of humanity's greenhouse gas emissions. The new report focuses on the impacts of

climate change and how to adapt to them. The third instalment, on how to cut greenhouse gas

emissions, comes out in April.

The latest report backs off from some of the predictions made in the previous IPCC report, in

2007. During the final editing process, the authors also retreated from many of the more

confident projections from the final draft, leaked last year. The IPCC now says it often

cannot predict which specific impacts of climate change – such as droughts, storms or floods

– will hit particular places.

Instead, the IPCC focuses on how people can adapt in the face of uncertainty, arguing that

we must become resilient against diverse changes in the climate.

"The natural human tendency is to want things to be clear and simple," says the report's

co-chair Chris Field of the Carnegie Institution for Science in Stanford, California. "And one

of the messages that doesn't just come from the IPCC, it comes from history, is that the

future doesn't ever turn out the way you think it will be." That means, Field adds, that "being

prepared for a wide range of possible futures is just always smart".

Here New Scientist breaks down what is new in the report, and what it means for humanity's

efforts to cope with a changing climate. A companion article, "How climate change will

affect where you live", highlights some of the key impacts that different regions are facing.

What has changed in the new IPCC report?

In essence, the predictions are intentionally more vague. Much of the firmer language from

the 2007 report about exactly what kind of weather to expect, and how changes will affect

people, has been replaced with more cautious statements. The scale and timing of many

regional impacts, and even the form of some, now appear uncertain.

For example, the 2007 report predicted that the intensity of cyclones over Asia would

increase by 10 to 20 per cent. The new report makes no such claim. Similarly, the last report

estimated that climate change would force up to a quarter of a billion Africans into water

shortage by the end of this decade. The new report avoids using such firm numbers.

The report has even watered down many of the more confident predictions that appeared in

the leaked drafts. References to "hundreds of millions" of people being affected by rising sea

levels have been removed from the summary, as have statements about the impact of warmer

temperatures on crops.

"I think it's gone back a bit," says Jean Palutikof of Griffith University in Brisbane,

Queensland, Australia, who worked on the 2007 report. "That may be a good thing. In the

fourth [climate assessment] we tried to do things that weren't really possible and the fifth has

sort of rebalanced the whole thing."

So do we know less than we did before?

Not really, says Andy Pitman of the University of New South Wales in Sydney, Australia. It

is just more rigorous language. "Pointing to the sign of the change, rather than the precise

magnitude of the change, is scientifically more defensible," he says.

We also know more about what we don't know, says David Karoly at the University of

Melbourne. "There is now a better understanding of uncertainties in regional climate

projections at decadal timescales."

"If your system is vulnerable to the total amount of rainfall, I kind of think we're getting to

know that," says Pitman. "If however your system is vulnerable to the timing of rainfall,

that's hard. If your system is vulnerable to the intensity of rainfall, that is very hard."

Are we less confident about all the impacts of climate change?

Not quite. There are still plenty of confident predictions of impacts in the report – at least in

the draft chapters that were leaked last year, and which are expected to be roughly the same

when they are released later this week. These include more rain in parts of Africa, more

heatwaves in southern Europe, and more frequent droughts in Australia (see "How climate

change will affect where you live"). It also remains clear that the seas are rising.

How do we prepare in cases in which there is low confidence about the effects of climate

change?

That's exactly what this report deals with. In many cases, the uncertainty is a matter of

magnitude, so the choices are not hard. "It doesn't really matter if the car hits the wall at 70

or 80 kilometres an hour," says Karoly. "You should still wear your seat belt." So when it

comes to sea-level rise or heatwaves, the uncertainty does not change what we need to do;

build sea walls, use efficient cooling and so forth.