A new study says that falling levels of cloud height across the world may have a cooling impact on global warming.
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, revealed that their average height has come down by about 1 per cent, or 30 to 40 metres.
Most of the reduction was because of fewer clouds occurring at very high altitudes, according to the study by Auckland University scientists.
"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, the Age reported.
"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," Professor Davies said.
The Terra satellite is scheduled to go on with collecting 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," Professor Davies said.
"But if they keep coming down it will be very significant," Professor Davies added.
The study has been published in the journal Geophysical Research Letters.