Study probes clouds' climate role

BBC, 22 October 2008 00:15 UK

The clouds' impact on the climate is relatively unknown to modellers

An international team of scientists is hoping to shed light on how clouds over the Pacific Ocean are affecting global climate and weather systems.

The clouds, some of which are bigger than the US, reflect sunlight back into space and cool the ocean below.

The team hopes to learn more about the clouds' properties and if pollution from activities such as mining affect the formation of these systems.

The month-long study will involve more than 200 experts from 10 countries.

A team of 20 climate and cloud experts from the UK's National Centre for Atmospheric Science (NCAS) are taking part in the expedition, which will be based in Chile.

Hugh Coe, the lead scientist for the British consortium, said the project would help improve the accuracy of climate change models.

"These are some of the largest cloud systems in the world and we know that they must play a very significant role in climate change, yet we know that climate models do not represent them very well," he explained.

"This campaign is a fantastic opportunity to make cutting-edge measurements in a unique environment and merge them with state-of-the-art climate models.

"We hope to finally hit some of the uncertainties in current climate models on the head."

Cloud catching

Professor Coe and his colleagues will gather data via cloud and dust probes fitted to two research aircraft, which will be flown through the low-lying cloud masses, in order to understand how the systems form, how reflective they are, and what factors determine how long the clouds last.

The type of cloud being investigated is known as a marine stratocumulus.

They usually occur near land where deep, cold, upwelling water reaches the surface of the sea.

This water cools the surface air, resulting in condensation and cloud formation.

The clouds do not exceed 2km in altitude, and they are present nearly all year round in the South-East Pacific region.

It is already understood that the clouds play a role in influencing the planet's climate because the vast formations act like massive mirrors that reflect sunlight back into space and limit the amount of solar energy that reaches the Earth's surface.

However, the UK team will also be hoping to establish whether pollution from mining actives along the Chilean and Peruvian coasts affect the clouds' properties.

Tiny particles emitted during the mining processes are carried up into the atmosphere and form droplets when they come into contact with water vapour within the atmosphere.

The NCAS researchers will also gather data to assess whether the particles affect the amount of rain produced and if the particle-filled clouds are more reflective than normal clouds.

The UK project - funded by NCAS, the Natural Environment Research Council (Nerc) and the UK Met Office - is one part of an international three-year project called VOCALS, which is exploring how complex interactions between clouds, oceans and land affect the world's climate.

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