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. 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.
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.
But in some cases – such as African rainfall, which could go up or down – the models are not giving us great advice, so all we know is that things will change. "We are not certain about the precise nature of regional change, but we are absolutely certain there are going to be profound changes in many regions," says Pitman.
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