Global warming isn't just about the increase in the world's temperatures anymore as a new climate study suggests that the event may have also caused drastic shifts in cloud patterns over a 20-year period.
Climate researchers at the University of California, San Diego (UCSD) examined satellite data on cloud patterns since the 1980s. They discovered that clouds typically found in the Earth's mid-latitudes had shifted toward the planet's poles throughout the course of two decades. This event coincided with the expansion of subtropical dry zones and the movement of clouds to higher altitudes.
UCSD scientist Joel Norris pointed out that despite certain differences in their treatment of cloud data, most climate models were still able to predict the dramatic shifts in cloud patterns outlined in the new study.
"I guess what was surprising is that a lot of times we think of climate change as something that's going to occur in the future," Norris said.
"This is happening right now. It's happened during my lifetime — it was a bit startling."
Understanding Clouds
Studying cloud patterns has not been an easy task for researchers, especially since clouds cover as much as 70 percent of the world at any given moment. These masses of liquid droplets or frozen crystals are also constantly moving and shifting shapes, making it difficult to understand their nature.
Scientists often have to track the behavior of liquid droplets in order to get a good reading of clouds. They also have to study clouds in large masses, which could sometimes reach sizes of up to several hundreds of miles wide.
Those who want to create climate models also have to consider the two distinct impacts of clouds on the Earth's temperatures.
Norris said thick cloud formations, especially during daytime, help keep the planet cooler since they tend to block sunlight more effectively.
However, these same thick clouds can also serve as a form of blanket that prevents heat from the Earth from escaping. Norris said this is why it is sometimes warmer during cloudy evenings than during clear nights.
Impact Of Global Warming On Clouds
To find out the impact of climate change on cloud patterns, the UCSD team made use of satellite imaging gathered since the 1980s.
Norris and his colleagues first had to eliminate various factors from the records, such as changes in instrument calibration, sensor degradation and satellite orbit, in order to get a more conclusive read of the cloud satellite data. This allowed them to identify large-scale shifts in cloud patterns that occurred during the 1980s up until the 2000s.
According to the researchers, these changes were consistent with predictions mentioned in climate models at the time, such as an expansion of subtropical dry zones, an increase in the altitude of high cloud tops and a movement of mid-latitude clouds toward the Earth's poles.
Such shifts in cloud patterns may result in an increase in the planet's solar radiation absorption as well as a reduction of its ability to emit thermal radiation to space. These could also lead to an increase in the Earth's greenhouse gas levels, effectively worsening the impacts of global warming.
The researchers said the behavior of clouds they were able to identify was in line with an increase in greenhouse gas levels associated with human activity as well as with the recovery of the planet from the volcanic eruptions of Mexico's El Chichón in 1982 and the Philippines' Mt. Pinatubo in 1991.
The team added that the aerosols released from these two major eruptions left the Earth with a net cooling effect that lasted for a few years after the events took place.
Norris and his colleagues believe that the shift in cloud patterns they observed will likely continue for the next few years as global warming progresses.
The findings (PDF) of the UCSD study are featured in the journal Nature.
