PLANET-wide heating and cooling of the atmosphere during the 11-year sunspot cycle has been measured for the first time. Climate-change sceptics may seize on the findings as evidence that the sun's variability can explain global warming - but mathematician Ka-Kit Tung says quite the contrary is true.
New_scientist_sunspots_climate_change
Global warming and cooling linked to the sunspot cycle
- 09 August 2007
- NewScientist.com news service
- Fred Pearce
PLANET-wide heating and cooling of the atmosphere during the 11-year sunspot cycle has been measured for the first time. Climate-change sceptics may seize on the findings as evidence that the sun's variability can explain global warming - but mathematician Ka-Kit Tung says quite the contrary is true.
Tung and colleague Charles Camp, both of the University of Washington in Seattle, analysed satellite data on solar radiation and surface temperatures over the past 50 years, covering four-and-a-half solar cycles. They found that global average temperatures oscillated by almost 0.2 °C between high and low points in the cycle, nearly twice the amplitude of previous estimates (Geophysical Research Letters, DOI: 10.1029/2007GL030207).
The finding adds to the evidence that mainstream climate models are right about the likely extent of future human-generated warming, Tung says. It also effectively rules out some lower estimates in those models.
"The findings provide important real-world evidence that climate-model predictions of global warming are correct
Joanna Haigh of Imperial College London, an expert on solar influences on climate, says this is the first time a statistically significant global temperature signal has been found for the 11-year cycle. "Other people have previously found only regional responses," she says.
The 11-year cycle is the shortest of a number of known oscillations in the solar radiation reaching the Earth. Tung says the sun is currently at a low point in the 11-year cycle. Unless other influences like volcanic eruptions or El Niños intervene, we can expect strong warming of the atmosphere in the next five years, as an upturn in the cycle reinforces human-generated warming.
Tung says his findings provide important real-world evidence that climate model predictions of global warming are correct. For instance, they show that the temperature changes are two to three times as strong in polar regions. On the face of it this is surprising, because the variation in solar radiation is greatest in the tropics. But Tung says "it reinforces the idea of melting ice as an amplification mechanism in the climate-change models".
What will excite climate scientists most is that Tung and Camp are the first to measure directly how a given change in the amount of heat energy in the atmosphere translates into a change in temperature. Researchers call this the "climate sensitivity" of the atmosphere, and it is a vital factor in climate research because it determines how fast the planet will warm as a result of climate change.
All previous estimates of climate sensitivity have been based on models. Now Tung and Camp have used real figures to show that an extra 0.9 watts per square metre of heating at the Earth's surface, at the height of the 11-year cycle, produces an immediate warming of the atmosphere of 0.16 °C.
In an as yet unpublished paper posted on Tung's website, he and Camp say this shows that a doubling of carbon dioxide levels in the atmosphere would cause a warming of between 2.3 and 4.1 °C within about a year. They say this makes the lower estimates of some models of climate change "unlikely".
This immediate warming, Tung stresses, is almost certain to be an underestimate of the overall effect of greenhouse gases, because extra warming is delayed due to the deep ocean heating up only slowly. "But our findings give a lower bound to the atmosphere's climate sensitivity that we have not had before."
Climate modeller Peter Cox from the University of Exeter, UK, says Tung has shown, without recourse to climate models, that a doubling of carbon dioxide would cause at least 2 °C of warming, "which is considered by many to be the threshold of dangerous climate change."
Believe long-range weather forecasts at your own risk
Oliver Burkeman
Wednesday August 22, 2007
The Guardian
If one subject of conversation preoccupies the British more than the weather, it's the perceived uselessness of forecasts. So deeply is this conviction held that it extends to claims about the past, not just the future. For example, it's a verifiable fact that the first two weeks of August were significantly sunnier than on average, but the revelation was still greeted, in the media and elsewhere, with wounded anger, as if it couldn't possibly be true.
Part of the problem is that weather systems are inherently chaotic: unpredictability is built in, and rapidly magnified. The Met Office says its 24-hour forecasts are correct about six times out of seven, but further into the future, the accuracy rate falls precipitously. As a result, some forecasters argue that we should be receiving "probabilistic" bulletins on TV and radio, with percentage chances of rain or sun, along with an indication of how much confidence the meteorologists have in any given prediction.
This, the theory goes, would be empowering: if you knew what risk you were running of being caught without an umbrella, or waking up to a flooded tent, you could make a decision, depending on your attitude to risk. "I think we as an organisation would eventually want to move in that direction," says Barry Gromit at the Met Office. "But we're a way off getting a general public level of education about the concept of probability forecasts."
Meanwhile, you can get this kind of inside information today - if you're willing to pay for it. For £17, the Met Office will connect you for three minutes to a senior forecaster, who will give you a one-to-one forecast, tailored to your specifications. It's like phone sex, except about the weather. In other words: phone sex for British people.
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