Wednesday, July 11, 2007

The Sun and Climate Change

Whenever I blog about Climate Change, I almost inevitably get emails or comments arguing that it the Sun (not human activity) that is causing climate change. Not many scientists, however, accept that argument, and a new analysis of this claim should put the matter to rest. Here is a report from the Guardian:

It has been one of the central claims of those who challenge the idea that human activities are to blame for global warming. The planet's climate has long fluctuated, say the climate sceptics, and current warming is just part of that natural cycle - the result of variation in the sun's output and not carbon dioxide emissions.

But a new analysis of data on the sun's output in the last 25 years of the 20th century has firmly put the notion to rest. The data shows that even though the sun's activity has been decreasing since 1985, global temperatures have continued to rise at an accelerating rate.

The new analysis is designed to counter the main alternative scientific argument put forward by the programme - that solar activity may be to blame for global warming.

"The temperature record is simply not consistent with any of the solar forcings that people are talking about," said lead author Mike Lockwood at the Rutherford Appleton Laboratory in Oxfordshire.

"They changed direction in 1985, the climate did not ... [the temperature] increase should be slowing down but in fact it is speeding up."

Global temperatures are going up by 0.2 degrees per decade and the top 10 warmest years on record have happened in the past 12 years.

One way that the sun affects the climate is through clouds. The sun's magnetic field shields the Earth from its high energy particles called cosmic rays. The rays help form clouds that reflect the sun's energy back into space and cool the planet.

So if the sun's magnetic field is high, there should be a fall-off in cosmic rays, fewer clouds and more warming. But Prof Lockwood's data, published today in the Proceedings of the Royal Society, shows the sun's magnetic field has declined since 1985, even as the world heats up.

. . .

Nir Shaviv, an astrophysicist at the Hebrew University of Jerusalem and a proponent of the solar hypothesis, has tried to rescue the idea by invoking a time lag between changes in the sun and its effect on the Earth's climate. But Prof Lockwood dismissed this as "disingenuous".

"Nobody has invoked that kind of lag before. It's only been invoked now as a way out," he said. Even if the lag were 50 years then he believes we would begin to see the rise in global temperatures slowing down.

Read it all here.

David Adam, environment correspondent for the Guardian had these observations on the Guardian blog:

So it's official, the sun has nothing to do with recent global warming. Scientists have shown that changes in solar activity have nothing to do with the surge in global temperatures measured since the 1970s. Which is a problem for the climate change sceptics, who need something other than human emissions of greenhouse gases to blame it on. The study has been called the final nail in their coffin.

But what's really new here? The solar link to recent climate change has already been thoroughly examined and dismissed. Researchers already knew that changes in the amount of energy arriving from the sun couldn't be responsible. And the trend in cosmic rays - the darling "new" theory of the sceptics - is known to go in the wrong direction . Scientifically, this new paper does nothing new except correct some technical errors in a satellite record of solar irradiance - hardly headline stuff. And while recycling old claims as new may be routine for politicians and the media, it is much less common for scientific journals. The top journal Nature decided not to accept this new study for this reason. And the decision by the Royal Society to publish it appears to be as much about politics as science.

Britain's scientific elite were shaken by the public reaction to Channel 4's Great Global Warming Swindle. They thought they had won the argument on the causes of climate change. Several who give public lectures on the subject had even started to leave out that section. Mike Lockwood, the physicist behind the new study, admits he wrote the paper as a direct challenge to the programme's claims. The Royal Society appears to have published it for the same reason.

The problem with that approach is that the majority of arguments employed by the climate sceptics have their roots in a political dislike for curbs on emissions, rather than scientific enquiry. For those with a genuine interest in the latter, the answers are already out there. Just how secure does the Royal Society move leave the scientific record? Should we repackage important work on evolution by natural selection to counter creationists?

The new study may yet have a positive effect. It leaves little doubt (again) that human emissions are the culprit, and stamps on another of the snakes released by Channel 4's swindle. But does science really need the right presentation for it to be authoritative? And how many final nails does a coffin need before it can be buried?

Read it all here.

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