The rising levels of water vapour in the upper troposphere - a key amplifier of global warming - owing to greenhouse gases will intensify climate change impacts over the next decades, scientists said.
"The study is the first to confirm that human activities have increased water vapour in the upper troposphere," said Brian Soden, professor of atmospheric sciences at University of Miami's Rosenstiel School of Marine and Atmospheric Science.
To investigate the potential causes of a 30-year moistening trend in the upper troposphere, a region 3-7 miles above the Earth's surface, Soden and colleagues measured water vapour in the upper troposphere collected by NOAA satellites.
Using the set of climate model experiments, researchers showed that rising water vapour in the upper troposphere cannot be explained by natural forces such as volcanoes and changes in solar activity but by increased greenhouse gases.
Greenhouse gases raise temperatures by trapping the Earth's radiant heat inside the atmosphere.
This warming also increases the accumulation of atmospheric water vapour, the most abundant greenhouse gas.
The atmospheric moistening traps additional radiant heat and further increases temperatures.
Climate models predict that as the climate warms from the burning of fossil fuels, the concentrations of water vapour will also increase in response to that warming.
This moistening of the atmosphere, in turn, absorbs more heat and further raises the Earth's temperature, the study noted.