There’s a major new report on the state of the climate due next month from the Intergovernmental Panel on Climate Change.
This week has seen a sneak preview of some of the findings after journalists got their hands on a leaked summary. Here’s a rundown of what the papers had to say.
What’s been leaked?
Every five or six years, the Intergovernmental Panel on Climate Change (IPCC) produces an in-depth assessment of the state of research in all areas of climate science, from rainfall patterns to polar ice. It’s not new science as such, but a mega-summary of the state of the scientific literature on climate.
The fifth version of the IPCC’s report is due to be published in three parts, starting next month. The first part of the report is nearing the end of an involved process of review by experts and governments worldwide and is not yet in the public domain.
But a summary intended for policymakers appears to have been leaked to journalists, and Alister Doyle from Reuters broke the story first last week.
Clear on the causes of warming
Like a number of others that followed, the Reuters piece focuses on how new tools and ways to analyse data mean scientists are more confident about how and why the climate is changing than in the last report six years ago.
“Climate scientists are surer than ever that human activity is causing global warming â?¦ [The draft report says] it is at least 95 percent likely that human activities – chiefly the burning of fossil fuels – are the main cause of warming since the 1950s.”
Doyle describes how the 95 per cent figure is “up from at least 90 percent in the last report in 2007, 66 percent in 2001, and just over 50 in 1995”.
As for what we can expect this century, he says the report suggests warming somewhere between less than one degree and nearly five degrees by 2100, depending on how quickly we continue to emit carbon dioxide. On the reasoning behind the lower end of this range, Doyle adds:
“[This] is because the IPCC has added what diplomats say is an improbable scenario for radical government action – not considered in 2007 – that would require cuts in global greenhouse gases to zero by about 2070.”
Many of the news articles also highlight what the report says about sea level rise – the New York Times called it “one of the biggest single worries about climate change”.
The IPCC reportedly projects sea level rise between 29 and 82 cm by 2100, a considerably larger range than in the 2007 report. This comes from a better understanding of how much melting ice sheets contribute. This is a point The Independent and The Telegraph also pick up on, the latter saying “evidence of rising sea levels is ‘unequivocal'”.
On Tuesday, Bloomberg featured an interview with Kevin Trenberth, climate scientist at the US National Center for Atmospheric Research, who warned that “sea level is going to keep rising even if we stabilize other aspects of the climate system.”
Areas of uncertainty
Although scientists are growing in confidence about changes taking place at the global level, the impacts for specific regions is less certain. IPCC lead author Reto Knutti, who is quoted in the Reuters piece, puts this succinctly:
“We have got quite a bit more certain that climate change … is largely manmade … We’re less certain than many would hope about the local impacts.”
Reuters also does a good job of explaining that some types of extreme weather, notably heatwaves and heavy rainfall, are showing a clear link with rising global temperatures. But in some places, it appears newer science has actually lessened confidence about some conclusions. Doyle says:
“The new study will state with greater confidence than in 2007 that rising manmade greenhouse gas emissions have already meant more heatwaves. But it is likely to play down some tentative findings from 2007, such as that human activities have contributed to more droughts.”
Surface warming slowdown
Today’s Daily Mail stuck with the theme of areas of less certainty, choosing to focus on why surface temperatures – that’s the land and top of the ocean – haven’t risen as fast recently as in previous decades.
The Mail on Sunday has repeatedly suggested this means global warming has ‘stopped’. The Mail today takes a different line:
“Global temperatures have continued to rise, but at a slower rate since 1998, despite greenhouse gas concentrations peaking due to more emissions.”
“[M]ore heat being absorbed by oceans could explain why global warming seems to have decelerated in recent times.”
The Mail piece quotes Alistair Doyle’s take on what’s driving the slowdown:
“Scientists believe causes could include: greater-than-expected quantities of ash from volcanoes, which dims sunlight; a decline in heat from the sun during a current 11-year solar cycle; more heat being absorbed by the deep oceans; or the possibility that the climate may be less sensitive than expected to a build-up of carbon dioxide”.
It remains to be seen exactly what the new report will say about how sensitive the climate is to carbon dioxide when it’s released next month – although the New York Times suggests the lower range of the estimate could have come down a little since the last report.
But scientists don’t generally talk about climate sensitivity in the context of what’s driving the surface warming slowdown. The scientists we’ve spoken to tell us the most likely reason temperature rise has slowed is that heat is entering the oceans rather than staying in the atmosphere, which would make the slowdown we’re seeing a temporary thing.
Still, ongoing discussions among scientists allows the Mail to ask provocatively in a headline: “Why has global warming slowed? Scientists admit they don’t know why”. And the BBC takes a similar line, characterising recent temperatures as “a controversial slowdown that scientists have been struggling to explain.”
National Geographic and the New York Times take the time to explain that scientists are pretty confident the slowdown is likely down to “short term factors”, which won’t significantly impact the amount of warming we can expect in the long term.
Wait and see
The IPCC won’t comment on material in the reports before they are published, and so its response to the leak has been limited to cautioning against drawing conclusions from the draft, as the findings are still subject to change.
However, there’s not long left to wait now – the IPCC has just announced the official version of the summary for policymakers is set for release in just over a month’s time.