Has Global Warming Stopped?

By David Whitehouse
New Statesman, December 19, 2007

Edited by Andy Ross

With only few days remaining in 2007, the indications are the global temperature for this year is the same as that for 2006 – there has been no warming over the 12 months.

The global temperature of 2007 is statistically the same as 2006 as well as every year since 2001. Global warming has, temporarily or permanently, ceased. Temperatures across the world are not increasing as they should according to the fundamental theory behind global warming – the greenhouse effect.

In principle the greenhouse effect is simple. Gases like carbon dioxide present in the atmosphere absorb outgoing infrared radiation from the earth’s surface causing some heat to be retained. So an increase in the atmospheric concentration of greenhouse gases from human activities such as burning fossil fuels leads to an enhanced greenhouse effect. Thus the world warms and the climate changes.

The evidence for this hypothesis is the correlation of increasing global carbon dioxide concentration with rising global temperature. Carbon dioxide is clearly increasing in the Earth’s atmosphere. It’s a straight line upward. It is currently about 390 parts per million. Pre-industrial levels were about 285 ppm.

The period 1980-98 was one of rapid warming – a temperature increase of about 0.5 degrees C. But since then the global temperature has been flat. The global temperature today is about 0.3 degrees less than it would have been had the rapid increase continued.

Clearly the world of the past 30 years is warmer than the previous decades and there is abundant evidence (in the northern hemisphere at least) that the world is responding to those elevated temperatures. But the evidence shows that global warming as such has ceased.

The explanation for the standstill has been attributed to aerosols in the atmosphere produced as a by-product of greenhouse gas emission and volcanic activity. They would have the effect of reflecting some of the incidental sunlight into space thereby reducing the greenhouse effect.

But the fact that the global temperature has remained unchanged for a decade requires that the quantity of reflecting aerosols dumped put in our atmosphere must be increasing year on year at precisely the exact rate needed to offset the accumulating carbon dioxide that wants to drive the temperature higher. This precise balance seems highly unlikely.

It was a pity that the delegates at Bali didn’t discuss this or that the recent IPCC Synthesis report did not look in more detail at this recent warming standstill.

Some media commentators say that the science of global warming is now beyond doubt and those who advocate alternative approaches had lost the scientific argument. Not so.

We are fools if we think we have a sufficient understanding of such a complicated system as the Earth’s atmosphere’s interaction with sunlight to decide. We know far less than many think we do. We must explain why global warming has stopped.


David Whitehouse was BBC Science Correspondent 1988–1998, Science Editor BBC News Online 1998–2006 and the 2004 European Internet Journalist of the Year. He has a doctorate in astrophysics.
 

AR  This merits further investigation.

Freman Dyson on global warming