Media Release - 15 November 2002

Australians use September 11 data to solve climate “paradox”

The tragic events in New York and Washington of September 11 last year have, ironically, helped two Australian scientists solve a 50-year scientific mystery concerning climate change.

At the heart of the so-called “pan evaporation paradox” was the now accepted scientific fact that the world’s temperature has been rising by an average of 0.15 degrees centigrade per decade over the past 50 years.

It has been commonly assumed by scientists that rising temperatures would trigger increased evaporation rates over bodies of water, including “pans” (specially built devices to precisely measure evaporation which have been used around the world for many decades).

However, pan evaporation rate data from across the planet for the past 50 years shows there has been an accelerating overall decrease in evaporation rates.

This apparent paradox has been subject to widespread international study for several years but the Australian scientists’ breakthrough paper has today been published in the prominent US journal, Science, following intensive peer review of their work.

The paper, in effect, states that the massive extent of air pollution around the planet, combined with increasing levels of cloud, have helped to reduce evaporation rates despite rising global temperatures.

The particles of pollution and the clouds are diffusing sunlight - blocking some direct sunlight from reaching the surface of the water in the manner that it did before widespread pollution and increasing cloud became major factors.

The scientists, Dr Michael Roderick and Prof Graham Farquhar, are senior scientists at the Australian National University who work for Australia’s leading greenhouse research organisation, the Cooperative Research Centre for Greenhouse Accounting.

Their paper refers to data collected in the US last year when some 10,000 commercial aircraft were suddenly grounded for three days in the aftermath of the September 11 attacks.

This provided a unique opportunity to record any significant changes that might occur when those thousands of aircraft were temporarily prevented from pumping pollution particles high into the atmosphere.

US figures over those three days showed a “marked increase” in the diurnal temperature range on the ground – the difference between the maximum and minimum temperatures each day. (This gap has been reducing over the recorded period of planetary warming).

The CEO of the CRC for Greenhouse Accounting, Dr Chris Mitchell, said: “We are thrilled that two of our scientists have solved the pan evaporation paradox. This is a direct example of the world-leading climate change research our 110 scientists are undertaking at the CRC”.

Dr Roderick said: “This project was very satisfying because it ties together several previously reported trends, decreasing sunlight and decreasing diurnal temperature range with the actual decline in pan evaporation rates”.

Prof Farquhar said: “This project has underlined the importance of maintaining long-term climate and environmental records if we are to achieve sound results from Australia’s research efforts.

“Unfortunately we do not have proper records in Australia of daily sunlight levels – we now have access only to data recorded at airports following funding cuts several years ago which saw much of the previous system shutdown”, he said.

INFORMATION:

Prof Graham Farquhar (02 6125 5052)

Dr Mike Roderick (02 6125 5589)

Dr Chris Mitchell, CEO, CRC for Greenhouse Accounting(Mobile: 0419 992 914)

Dennis Ringrose, Communication Manager, CRC for Greenhouse Accounting . (02 6125 5593)