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You are in: In Depth: Climate change | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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![]() Viewpoint: The Sun and climate change
Satellites now monitor solar activity constantly
By Dr Paal Brekke from the European Space Agency
Natural processes involving changes in the Sun could have at least as powerful an effect on global temperature as increased emissions of carbon dioxide (CO2). Climate scientists have already looked at changes related to Sun spot activity - a cycle of approximately 11 years - and long-term changes in the Sun's brightness, which has a cycle that lasts for centuries. They have discounted the effect of both on the temperature increase over the last century because they either happen over too short a timescale, or they are too weak. But so far they have omitted to take two other factors into account:
Cloud cover One of the effects that cosmic rays have is to influence how cloudy the Earth is.
The amount of cloud affects the amount of radiation from the Sun reaching the planet surface, which in turn affects the global temperature. Data collected from satellites show that the amount of low clouds over the Earth closely follows the amount of cosmic rays reaching the Earth. The resulting warming due to this effect over the last century could be comparable to the amount of warming people think has been due to the greenhouse effect. Add to that the other effects due to the Sun, and greenhouse gases become less than 50% responsible for rising global temperatures. Little effect The other side of this coin is that reducing greenhouse emissions will have much less effect in halting rising temperatures than some people think, and it might have hardly any effect at all.
Thus, some people may ask: "So why bother worrying about greenhouse gases, and adding billions to the costs of industry to force them to cut emissions, when it could well be a pointless exercise?" If the Sun is indeed the main contributor to the recent climate change, the money may be better spent providing clean air in big cities and clean drinking water to the Third World. The author is a solar physicist serving as the European Space Agency's deputy project scientist for the Esa-Nasa Solar and Heliospheric Observatory (Soho)
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