Azara Blog: Earth absorbing solar energy

Blog home page | Blog archive

Google   Bookmark and Share

Date published: 2005/04/29

The BBC says:

The Earth is absorbing more energy from the Sun than it is giving back into space, according to a new study by climate scientists in the US.

They base their findings on computer models of climate, and on measurements of temperature in the oceans.

The group describes its results as "the smoking gun that we were looking for", removing any doubt that human activities are warming the planet.

The results are published in the journal Science this week.

The study attempts to calculate the Earth's "energy imbalance" - the difference between the amount of energy received at the top of the atmosphere from solar radiation, and the amount that is given back into space.

Rather than measuring the imbalance directly, the researchers draw on data from the oceans, in particular from the growing global flotilla of scientific buoys and floats, now numbered in the thousands, which monitor sea temperature.

"Measuring the imbalance directly is extremely difficult, because you are looking for a very small number on a background of very large numbers," Gavin Schmidt, one of the research team from the US space agency's (Nasa) Goddard Institute for Space Studies in New York, told BBC News.

"But we know how much energy is going into the oceans - that has been measured and over the last 10 years confirmed by satellites and in-situ measurements - and from our understanding of atmospheric physics, that has to be equal to the imbalance at the top of the atmosphere."

So data gathered from the oceans is plugged into a computer model representing the Earth's complex climate, including the atmosphere, oceans, winds, currents, greenhouse gases and other "pollutants". What emerges is that at the top of the atmosphere, our planet is absorbing 0.85 watts more energy per metre squared than it is emitting into space.

The reason the extra energy is trapped, the researchers say, is the human-produced greenhouse effect - elevated levels of gases such as carbon dioxide that absorb radiation from the Earth's surface which would otherwise disappear into space.
Not everyone agrees with these conclusions. One scientist who disagrees is William Kininmonth, a former head of Australia's National Climate Centre and a member of Australia's delegations at various rounds of United Nations climate treaty negotiations.

"The paper implies that it is possible to estimate quite accurately the global radiation imbalance," he told BBC News; other researchers, he says, have "explained why it is not possible to measure the imbalance with an accuracy better than several watts per metre squared".

The article is not yet published in the (paper) journal Science, but presumably will be next week. To know the significance of this result one needs to know the error bars, and hopefully some are quoted in the article. The blatantly political spin on the story by the group ("the smoking gun") is not encouraging. But presumably global warming must imply something like this, so it's chicken and egg.

All material not included from other sources is copyright For further information or questions email: info [at] cambridge2000 [dot] com (replace "[at]" with "@" and "[dot]" with ".").