How clouds influence our climate – satellites could provide new answers

A warmer climate could affect cloudiness on our planet. However, a change in cloudiness could in turn have repercussions on the climate. There are, however, still large gaps in knowledge of the link meaning that we cannot for sure say if the feedback is positive or negative in terms of the induced temperature change. Research to better monitor clouds is now being intensified using satellites.

Clouds, along with polar ice and desert surfaces, are major contributors to the fact that almost one-third of all solar radiation is reflected back to space. Less clouds, or altered cloudiness, could therefore in theory lead to the Earth being heated up even more.

“The warming effect is well-known when it comes to melting and shrinking polar ice caps. However, cloud changes could have an even greater effect on the global climate,” says Karl-Göran Karlsson, remote sensing scientist at SMHI.

Despite existing uncertainties, scientists are quite confident that changes in cloudiness do not explain the strong global increase in temperature during the past 30 years. Studies of available satellite data have shown that cloudiness remained largely constant over this period.

“We don’t know if this will change. However, many climate models indicate that changes in cloudiness actually appear to boost the warming process. It is therefore extremely important to continue monitoring global cloudiness to assess the reliability of climate scenarios.”

Understand the impact of clouds on climate

Within the framework of European collaboration, major investments are being made to better understand the impact of clouds on climate. The big challenge is to compile and interpret the enormous amounts of raw data collected by weather and research satellites over the years. SMHI scientists are taking part in several such programmes as experts.

One important milestone has recently been achieved: analysing the Earth’s average cloudiness and several other cloud properties for the past 20 years, based on data from American and European satellites orbiting the Earth’s poles.

The picture shows a preliminary compilation of average cloudiness for the month of July in 1989-2009. Dark blue indicates clear weather, while dark red indicates completely overcast. Enlarge Image

Work will now progress, partly by building on the various series of measurements with data from additional satellites and going even further back in time. The aim in a few years is to have time series from the late 1970s, when the first more advanced weather satellites started being used.

The cloud analyses are being conducted within two projects, ‘CM SAF’ and ‘ESA-CLOUD-CCI’, initiated by the organisations EUMETSAT and the European Space Agency. A raft of other programmes are also taking place in parallel for parameters other than cloudiness, with the aim of interpreting and making satellite information useable for assessment of climate projections.