Clouds around the world may be falling in response to rising global temperatures and having a cooling effect on global warming, according to analysis of satellite data by Auckland University scientists.
The first 10 years of data from the NASA Terra satellite, which uses nine cameras at different angles to produce a stereo image of the world's clouds, shows their average height has lowered by about 1 percent, or 30 to 40 metres.
Most of the reduction was due to fewer clouds occurring at very high altitudes, says the study, published in the journal Geophysical Research Letters.
"This is the first time we have been able to accurately measure changes in global cloud height and, while the record is too short to be definitive, it provides just a hint that something quite important might be going on," said lead researcher, Professor Roger Davies.
In a "negative feedback mechanism", lower cloud height would allow the Earth to cool to space more efficiently, reducing the surface temperature of the planet and potentially slowing the effects of global warming.
"We don't know exactly what causes the cloud heights to lower but it must be due to a change in the circulation patterns that give rise to cloud formation at high altitude," Prof Davies said.
The Terra satellite is scheduled to continue gathering data through the remainder of this decade.
"If cloud heights come back up in the next 10 years we would conclude that they are not slowing climate change," Prof Davies said.
"But if they keep coming down it will be very significant."
NZN