Global warming is increasing the frequency of extremely high clouds in the Earth's tropics that cause severe storms and rainfall, according to a NASA study released Friday.

The space agency's Jet Propulsion Laboratory (JPL) said a study by its scientists "found a strong correlation between the frequency of these clouds and seasonal variations in the average sea surface temperature of the tropical oceans."

"For every degree Centigrade (1.8 degrees Fahrenheit) increase in average ocean surface temperature, the team observed a 45-percent increase in the frequency of the very high clouds," according to the study, recently published in Geophysical Research Letters.

"At the present rate of global warming of 0.13 degrees Celsius (0.23 degrees Fahrenheit) per decade, the team inferred the frequency of these storms can be expected to increase by six percent per decade."

JPL Senior Research Scientist Hartmut Aumann headed the study on five years of data from the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua spacecraft, an instrument that observes climate variations.

The link between global warming and the frequency and intensity of severe storms has long been a source of speculation for climate modelers, noted the Pasadena, California-based JPL.