Professor sheds light for climate sceptics

Australian
Thursday 4/12/2008 Page: 5

THE sun is a powerful player in the planet's climate as the energy it sends to Earth waxes and wanes. But the sun is not driving recent global warming as climate change sceptics claim. That is the message from atmospheric scientist Marvin Geller of Stony Brook University in New York state, a keynote speaker at this week's Australian Institute of Physics national congress in Adelaide.

"Solar physicists and climate scientists agree that while the sun affects climate (they) cannot account for the last several decades' warming trend without including human influences," he said. "There is no doubt humans are making the earth warmer by adding greenhouse gases (like carbon dioxide)." According to Professor Geller, solar radiation varies in an 11-year solar cycle but it has changed only one-tenth of 1 per cent since 1978 when solar satellite measurements began. "By any direct means, that would not have a very strong influence," he claimed.

In contrast, the rate of global warming has escalated rapidly, increasing on average by about 0.6C between 1956 and 2006. As of 2006, 11 of the previous 12 years were warmer than any others since 1850, said Professor Geller. He dismissed the claim by climate change sceptics such as Martin Durkin producer and director of the controversial film The Great Global Warming Swindle that global warming peaked in 1998 then declined slightly. "That was a year of a massive El Nino. It's well known that El Ninos cause a temporary increase in global temperature.

One has to distinguish between a steady and consistent (upward) trend and natural fluctuations in the internal system," said Professor Geller, pointing to a common confusion of "weather" and "climate". He noted that weather refers to current atmospheric phenomena like rain, temperature and wind. Climate is the average atmospheric conditions over years, decades or even millenniums. According to Professor Geller, sceptics are incorrect when they claim CO2, cannot cause warming as it comprises only a small, though increasing, fraction of the atmosphere.

In fact, CO2 is highly reactive in the atmosphere, he said: "Just because it's a small fraction doesn't mean it's unimportant. If you don't believe me, try surviving in a room with a small concentration of cyanide gas." It is also incorrect to argue that since CO2, levels only rose after the end of the ice ages over the past half a million years, it cannot cause global warming now despite the fact that human activity has released unprecedented amounts of CO2 and other greenhouse gases, such as methane and water vapour, into the atmosphere since the 1850s.

In fact, while the initial warming that ended the ice ages and released the CO2 was due to shifts in Earth's orbit, once the gas was released from the oceans, it accelerated the warming by absorbing solar radiation. And further back in geological time there were examples of warming triggered by rises on CO2, noted Professor Geller, who helped draft the American Geophysical Union position statement Human Impacts on Climate.

The AGU is the world's largest scientific society of Earth and space scientists. The statement said: "Many components of the climate system ... are now changing at rates and in patterns that are not natural and are best explained by the increased atmospheric abundance of greenhouse gases and aerosols generated by human activity during the 20th century".