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IPCC draft report published online - suggests that the sun is not behind climate change

  • 14 Dec 2012, 15:30
  • Carbon Brief Staff

The argument that climate change is caused by solar activity has been described by an Intergovernmental Panel on Climate Change (IPCC) lead author as "completely ridiculous" and "exactly the opposite" of what the draft IPCC report concludes, after a climate skeptic blogger leaked a draft section of its next report onto the internet. Climate skeptic bloggers have claimed the IPCC's new report shows solar activity is causing global warming and the "jig is up" on climate science. But a closer look indicates that this is another case of cherry-picking.

The fifth version of the IPCC's report on the current state of climate science is due to be published in 2014, but individual parts of it are currently going through an involved process of review. The most recent draft of Working Group 1 (WG I) - which reports on the physical science of climate change - was published on the internet yesterday.

WG I's reports deal with the scientific basis for climate change - examining, for example, changing levels of greenhouse gases, temperature changes in the atmosphere and the oceans and impacts observed around the world, including melting glaciers, changes in rainfall and the carbon cycle. The last version of this report had nearly a thousand pages and the next one looks like it may be even bigger.

The latest draft has just gone through an open process of review. Anyone can sign up to be a reviewer, but individuals accepted as reviewers are asked not to "cite, quote or distribute" the draft reports. However, Alex Rawls, a climate skeptic blogger who signed up to the process posted the draft onto his website last night, arguing:

"...I regard [that the confidentiality agreement is made irrelevant] by the systematic dishonesty of the report... [in] the Second Order Draft ... the addition of one single sentence demands the release of the whole. That sentence is an astounding bit of honesty, a killing admission that completely undercuts the main premise and the main conclusion of the full report, revealing the fundamental dishonesty of the whole."

Rawls is talking about a section of the draft which discusses the theory that solar activity is causing climate change, rather than greenhouse gases from human activities.

Rawls has previously written about this theory, and claims that the new IPCC report supports it. Prominent skeptic website Watts Up With That agrees, saying that the leak contains a "game-changing admission". Daily Telegraph blogger James Delingpole says "even the IPCC admits the jig is up".

Solar down, temperature up?

The Australian website Skeptical science has already done a good job at looking at the argument that "it was the sun wot done it", so we'll be brief.

A handful of scientific studies propose that high energy particles from space, called galactic cosmic rays (GCRs), can influence global temperature by helping to form clouds, which reflect sunlight. At times of low solar activity, the theory suggests that more GCRs reach the atmosphere - causing more clouds to form, and amplifying the cooling effect.

The theory goes that this also works the other way round - more solar activity means less GCRs, fewer clouds and therefore even more warming. Rawls suggests this means the increase in global temperatures is due to GCRs, and not to human activity.

The leaked IPCC report acknowledges the studies suggesting this link in the following paragraph:

"Many empirical relationships have been reported between GCR or cosmogenic isotope archives and some aspects of the climate system (e.g., Bond et al., 2001; Dengel et al., 2009; Ram and Stolz, 1999). The forcing from changes in total solar irradiance alone does not seem to account for these observations, implying the existence of an amplifying mechanism such as the hypothesized GCR-cloud link."

Rawls argues that this paragraph shows the IPCC agrees with his belief that solar activity and GCRs play a far bigger role in the climate than scientists previously thought.

But there are two problems with this theory. First, as Professor Steve Sherwood, a lead author on the leaked report explained on ABC last night, only a small number of studies suggest the link between solar activity and GCRs. Most other studies disagree. Professor Sherwood told ABC:

"[T]here have been a couple of papers suggesting that solar forcing affects climate through cosmic ray/cloud interactions, but most of the literature on this shows that that doesn't actually work."

What's more, this conclusion is stated in the leaked IPCC report, just a few paragraphs later:

"Although there is some evidence that ionization from cosmic rays may enhance aerosol nucleation in the free troposphere, there is medium evidence and high agreement that the cosmic ray-ionization mechanism is too weak to influence global concentrations of CCN or their change over the last century or during a solar cycle  in any climatically significant way."

When Sherwood was asked on ABC whether Rawls' argument was a "case of cherry-picking a sentence", he replied:

"Yeah, it's a pretty severe case of that, because even the sentence doesn't say what they say and certainly if you look at the context, we're really saying the opposite."

Second, for the theory to explain current temperature rise, solar activity would have to be increasing now. As Skeptical Science have noted, it isn't - solar activity has been slowly decreasing since about 1980, and is in a period of low activity, as the graph below shows.

Were the GCR theory right, this should be having a cooling effect at the moment - and wouldn't explain current global temperature rise.

 Solaractivity _and _temperature

Solar activity has decreased over the last three decades, as global temperature has continued to rise. Source: Skeptical Science

Rawls suggests that global temperatures are showing a delayed response to an increase in solar activity in the early 20th century. But this argument makes "no physical sense", says Skeptical Science, since the graph above shows that fluctuations in solar activity are reflected in global temperature fairly quickly.

The draft IPCC report makes the point clearly that while the sun does have a small influence on earth's climate, scientists are confident that by comparison it is a "small fraction of the anthropogenic forcing". This echoes the last IPCC report from 2007, from which the chart below is taken. The bottom two bars suggest that all known effects of solar activity are minor compared to all human impacts (in the top box).

IPCC_radiative Forcing

Source: IPCC 4th Assessment Report (AR4) 2007

What will the media say?

As far as we can see, the leaked IPCC report doesn't show that the "jig is up" for climate science. In fact, a quick scan of the 1000 or so pages suggests that when it is finally published next year, many of the conclusions of the report will be fairly familiar to those who have read the last report from 2007.

If anything, it looks like the new draft firms up many of the top line conclusions, although there are likely to be some important differences - that is, after all, why this process has been repeated five times.

Of course, that the section on solar activity doesn't actually demonstrate what skeptics have said it does might not stop stories about the sun causing climate change. Newspapers which take a line that global warming isn't as bad as politicians think often find such stories too tempting to ignore.

We'll see. It is worth noting that a piece arguing that solar activity is leading to recent global warming might be difficult to reconcile with stories which argue that a decrease in solar activity is causing global cooling, and may be about to lead the world into a mini ice age. 

Here we are again

Finally, it's not the first time that an IPCC report has been leaked. Given the IPCC review process, which makes the draft text available to anyone who is interested, it probably won't be the last.

Some, including Andy Revkin at the New York Times, argue that this exposes weaknesses in the IPCC process. It's hard to avoid the conclusion that the slow pace of the IPCC leaves it unsuited to a media environment where information is ever-more freely available, open access to scientific information is a burgeoning phenomena, and embargoes are less solid than they used to be. Professor Piers Forster of Leeds university  sums up well in his quote to the Guardian:

"Although this may seem like a 'leak', the draft IPCC reports are not kept secret and the review process is open. The rationale in not disseminating the findings until the final version is complete, is to try and iron out all the errors and inconsistencies which might be inadvertently included. Personally, I would be happy if the whole IPCC process were even more open and public, and I think we as scientists need to explore how we can best match the development of measured critical arguments with those of the Twitter generation."

Updated 4.46pm - An earlier version incorrectly attributed the final quote.


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