Sun’s cooling influence not a reason to relax

It is just possible that the current solar minimum will provide us with short-term relief from global warming. It will be our task to make sure this does not distract us from the long-term task at hand. [18 November 2008 | Peter Boyer]

In the world of science, debates are never really concluded. Science isn’t about answers; it’s about questions. Good scientists keep on asking questions, and that’s why science continues to debate global warming.

The International Space Station, a source of recent data on the amount of radiant energy from the Sun reaching Earth’s outer atmosphere. NASA photo

The International Space Station, a source of recent data on the amount of radiant energy from the Sun reaching Earth’s outer atmosphere. NASA photo

Such relentless self-examination might be seen as a weakness, but it’s actually science’s great strength and the reason we put such faith in its findings. We’ve learned that while scientists, like all of us, have their weaknesses, good science is robust, reliable and more credible than pretty well anything.

Being so concerned to get things right, science can’t provide the straight, simple answers that most people like. In studying human influence on Earth’s climate we’re continually having to deal with complexities that, if we’re not careful, can compromise our ability to act decisively.

Take the case of solar energy. The question of how much the changing energy output of the sun affects surface temperatures here on Earth lies at the heart of today’s climate debate.

A former head of CSIRO’s space science division, Dr Ken McCracken, believes there’s a fair chance that reduced solar energy output over the next decade or two will cause temperatures on Earth to stop rising – or even to drop a little.

Don’t be mistaken – Ken McCracken firmly believes that humans have caused a dangerous planet-wide warming and that we must reduce our fossil fuel emissions to halt this process.

But he also cites evidence that in its 2007 report the Intergovernmental Panel on Climate Change may have erred in assuming that a cyclical reduction in solar energy reaching Earth (TSI, or total solar irradiance) would not significantly influence mean global temperatures.

As he sees it, with the sun now entering a much less active phase in its cycle, a significantly lower TSI may neutralise the impact of greenhouse warming for up to 20 years, and cause people and governments to assume there’s no problem after all.

A result of this, he says, would be that the IPCC’s good work would be thrown into serious doubt and the necessary political will to act may evaporate.

“As I see it, scientists should be up-front about the possibility that there may be a cooling phase in the future, while stating firmly that when it ceases, the anthropogenic effects (effects of human emissions) will be 20 years worse than when it started,” Dr McCracken told me.

Needless to say, many leading climate scientists disagree that temperatures might actually drop in coming decades. Professor David Karoly of the University of Melbourne referred me to IPCC estimates, and supporting 2007 research, that the influence on Earth’s temperatures of changes to the sun’s energy output is about one-tenth that of increasing levels of long-lived greenhouse gases.

If Prof Karoly and the IPCC are right, we’ll likely hear no more of the McCracken thesis. But if not – if global warming seems to be slackening off over the next year or two – then we should be ready to explain why, and we should thank Ken McCracken for his good science.

Whichever way you look at it, science is the winner.

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