Washington: A new study has suggested that changes in solar activity have contributed no more than 10 per cent to global warming in the 20th century.
The findings, made by Professor Terry Sloan at the University of Lancaster and Professor Sir Arnold Wolfendale at the University of Durham, find that neither changes in the activity of the Sun, nor its impact in blocking cosmic rays, can be a significant contributor to global warming.
In their attempt to quantify the effect that solar activity-whether directly or through cosmic rays-may have had on global temperatures in the twentieth century, Sloan and Wolfendale compared data on the rate of cosmic rays entering the atmosphere, which can be used as a proxy for solar activity, with the record of global temperatures going back to 1955.
They found a small correlation between cosmic rays and global temperatures occurring every 22 years; however, the changing cosmic ray rate lagged behind the change in temperatures by between one and two years, suggesting that the cause may not be down to cosmic rays and cloud formation, but may be due to the direct effects of the Sun.
By comparing the small oscillations in cosmic ray rate, which was taken from data from two neutron monitors, and temperature with the overall trends in both since 1955, Sloan and Wolfendale found that less than 14 per cent of the global warming seen during this period could be attributable to solar activity.
Furthermore, the researchers reviewed their own previous studies and surveyed the relevant literature to find other evidence of a link between solar activity and increasing global temperatures existing.
Their findings indicated that overall, the contribution of changing solar activity, either directly or through cosmic rays, was even less cannot have contributed more than 10 per cent to global warming in the twentieth century.
The results have been published in IOP Publishing`s journal Environmental Research Letters.