Scientists from Norway say they are now certain that radiation from space is not responsible for current changes in the global temperatures. They concluded a study of cosmic rays, cloud condensation nuclei and clouds using the best technology available. Their findings support various other studies conducted last year.
Climate change skeptics claim that a reduction of cosmic rays during the last decades has contributed to the global temperature rise. They say that fewer cosmic rays cause fewer cloud droplets and reduced droplet size, and that this in turn causes global warming, since reduced cloud droplets reflect less energy from the sun into the atmosphere and space.
The Norwegian scientist Dr. Jon Egill Kristjansson took the hypothesis to the test. He reasoned that if cosmic rays play a significant role in cloud formation, sudden changes in cosmic ray intensity should show also up, producing increases in cloud cover, changes in the size of droplets, and possibly in the total amount of water carried in the clouds.
“According to our research, it does not look like reduced cosmic rays leads to reduced cloud formation”, says Kristjansson, who is a professor at the University of Oslo. Kristjansson and his collegaes used observations from so-called Forbush decrease events. These events are sudden outbreaks of intense solar activity that lead to a strong reduction of cosmic rays, lasting for a couple of days.
The Norwegian scientists identified 22 such events between 2000 and 2005. They investigated whether any of the events affected cloud formation in the skies.
Reduced cosmic rays did not lead to reduced cloud formation, either during the outbreaks or during the days that followed. Indeed, following some of the events we could see a reduction, but following others there was an increase in cloud formation. We did not find any patterns in the way the clouds changed”, Kristjansson explains.
He and his team of researchers used data from a space-borne measuring instrument known as MODIS and focused their efforts on the pristine Southern Hemisphere ocean regions, areas where a cosmic ray signal would be easier to detect than elsewhere. The scientists say the data MODIS sent back to the scientists were a lot more detailed than the information previous studies relied on. For instance, the high spatial and spectral resolution of the data allowed for a more thorough study of micro physical parameters such as cloud droplet size, cloud water content and cloud optical depth. Previous research looked at cloud cover only.
Kristjansson’s findings tie in with most other recent research findings. He asserts that to date no studies have proved a correlation between reduced cosmic rays and reduced cloud formation. “No statistically significant correlations were found between any of the four cloud parameters and galactic cosmic rays”, he says.
The researchers published their study in the journal Atmospheric Chemistry and Physics. Sponsors are University of Oslo, Norwegian Institute for Air Research (NILU), CICERO Center for Climate and Environmental Research, and the University of Iceland.