Global warming 'proof' detected

BBCNews.com, April 29, 2005

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.

"This is almost unprecedented," said Gavin Schmidt. "The normal state of the atmosphere is that pretty much the same amount of energy that comes in leaves; and only when there are very large changes is that going to change.

"Historically, those changes have happened very slowly; but what we are doing now is we are changing that imbalance at a rate which appears to be unprecedented over at least a thousand years and possibly longer."

However, there is a time-lag between the absorption of energy at the top of the atmosphere and resultant heating of the oceans. The extra energy already trapped, according to the Nasa team, means that a global temperature rise of a further half a degree Celsius is inevitable, even if human production of greenhouse gases could be turned off tomorrow.

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".

Like other "climate change sceptics", Dr Kininmonth believes too much reliance is placed on computer models rather than hard data.

"I do not believe this research team has made a compelling case to suggest that their computer models are sufficiently realistic to justify the implications of anthropogenic (human-induced) global warming that they make," he said.

But Damian Wilson, manager of clouds and radiation parameterisation at the UK's Meteorological Office, was more enthusiastic.

"The computer model matches temperature changes at the Earth's surface quite well - but that alone doesn't prove it's right," he said.

"Having a model that also matches ocean heat uptake well suggests that the model is doing a pretty good job. I wouldn't like to say the research proves that 0.85 watts per metre squared is the right figure, but it does give us more confidence that the models are doing a good job of producing a reasonable simulation of the energy imbalance."

Computer climate models have grown much more sophisticated over the years. But there are still problems modelling some atmospheric processes, notably heat convection within clouds.

And any model can only be as accurate as the data which goes into it. There is still a need, most researchers agree, for more data from the oceans, and on the role of aerosols (small particles of dust, soot, soil and other substances) in the atmosphere; but gathering that data is easier said than done.

New data on climate change worries scientists

Earth absorbing more heat than it gives off

The Associated Press, April 29, 2005

NEW YORK -- Climate scientists armed with new data from the ocean depths and from space satellites have found that Earth is absorbing much more heat than it is giving off, which they say validates computer projections of global warming.

Lead scientist James Hansen, a prominent NASA climatologist, described the findings on the planet's out-of-balance energy exchange as a 'smoking gun" that should dispel doubts about forecasts of climate change. A climate specialist from Germany called it a valuable contribution to climate research.

Hansen's team, reporting yesterday in the journal Science, said they also determined that global temperatures will rise by 1 degree Fahrenheit this century even if emissions of greenhouse gases are capped tomorrow.

If carbon dioxide and other heat-trapping emissions instead continue to grow, as expected, things could spin 'out of our control," especially as ocean levels rise from melting Greenland and Antarctic ice sheets, the researchers said. International specialists predict a 10-degree leap in Fahrenheit readings in such a worst-case scenario.

The NASA-led researchers were able to measure Earth's energy imbalance because of more- precise ocean readings collected by 1,800 technology-packed floats deployed in seas worldwide beginning in 2000, in an international monitoring effort called Argo. The robots regularly dive as deep as a mile undersea to take temperature and other readings.

Their measurements are supplemented by better satellite gauging of ocean levels, which rise from meltwater and as the sea warms and expands.

With this data, the scientists calculated the oceans' heat content and the global energy imbalance. They found that for every square meter of surface area, the planet is absorbing almost 1 watt more of the sun's energy than it is radiating back to space as heat -- a historically large imbalance. Such absorbed energy will steadily warm the atmosphere.

The 0.85-watt figure corresponds well with the energy imbalance predicted by the researchers' supercomputer simulations of climate change, the report said.

The computer models factor in greenhouse gases in the atmosphere -- including carbon dioxide and methane -- which are produced by everything from automobiles to pig farms. Those gases keep heat from escaping into space. Significantly, greenhouse emissions have increased at a rate consistent with the detected energy imbalance, the researchers said.

'There can no longer be genuine doubt that human-made gases are the dominant cause of observed warming," said Hansen, director of NASA's Goddard Institute for Space Studies at Columbia University's Earth Institute. 'This energy imbalance is the 'smoking gun' that we have been looking for."

Fourteen other specialists from NASA, Columbia, and the Department of Energy coauthored the study.

Scientists have found other possible 'smoking guns" on global warming in recent years, but Klaus Hasselmann, a leading climatologist from Germany, praised the Hansen report for its innovative work on energy imbalance. 'This is valuable additional supporting evidence" of manmade climate change, he said.

In February, scientists at San Diego's Scripps Institution of Oceanography said their research -- not yet published -- also showed a close correlation between climate models and the observed temperatures of oceans, further defusing skeptics' criticism of uncertainties in modeling.

Average atmospheric temperatures rose by about 1 degree Fahrenheit in the 20th century. The Intergovernmental Panel on Climate Change, a UN-organized network of scientists, says computer modeling predicts temperatures rising between 2.5 degrees and 10.4 degrees Fahrenheit by the year 2100.

Besides raising ocean levels, global warming is expected to intensify storms, spread disease to new areas, and shift climate zones, possibly making farmlands drier and deserts wetter.