Troubled water helps climate forecasting

Water is one of the major absorbers of solar radiation (Roland Zumbühl, Arlesheim) Roland Zumbühl, Arlesheim, 03/04/2002

Climate prediction looks set to become more accurate thanks to a discovery at the Federal Institute of Technology in Lausanne.

Researchers have produced new estimates of how the sun’s energy is absorbed by water in the atmosphere.

The measurements vary considerably from current theoretical calculations.

Because water plays a key role in atmospheric absorption of the sun’s energy, the new estimates look set to serve as the basis for future models of global climate.

Andrea Callegari and a team of international colleagues used three different lasers and an electric field to help fill in the blanks about how water molecules behave when they are excited or highly energized.

New technique

“We measured a property of water called the dipole moment, which basically describes how electrical charge is distributed within the molecule and this is connected to how water molecules absorb radiation,” Callegari told swissinfo.

Water is one of the major absorbers of solar radiation but it’s been very difficult to measure this process accurately. Until now scientists have resorted to calculations rather than direct measurements.

The novel technique allows small quantities of water in an excited state to be prepared and their properties investigated with high sensitivity.

The estimates are used in climate models to calculate how solar energy is deposited in the atmosphere and specifically the role of water.

“Water has about 70 per cent of the total solar absorption so we are happy to get a major piece of the picture right,” said Callegari.

Wider application

His colleague, Professor Thomas Rizzo, said the research was a good example of how basic research can lead to interesting applications.

“Techniques we have developed over the years were really to increase our fundamental understanding of molecules and how they absorb light,” Rizzo told swissinfo.

“It’s a wonderful example of curiosity-driven research which at the end can have very important applications in very practical ways.”

The research continues to try to understand why there is disagreement between the new measurements and theoretical calculations.

The hope is that the new measurements will be incorporated into atmospheric models.

The work was carried out in collaboration with scientists in the United States, Britain and Russia.

by Vincent Landon

Key facts

Water absorbs 70 per cent of solar radiation
New techniques improve measurements for climate models
Collaboration in Switzerland, Britain, US and Russia