LONDON — Changes in solar activity, sunspots and cosmic rays, and their effects on clouds have contributed no more than 10 percent to global warming, according to two British scientists.

The findings, published in the journal Environmental Research Letters, reconfirm the basic science that increasing carbon dioxide and other greenhouse gases are causing most climate change. They also reexamine the alternative case made by climate deniers: that it is the Sun’s changing activity and not us that is causing the Earth to heat up.

The two scientists, Terry Sloan at the University of Lancaster and Sir Arnold Wolfendale at the University of Durham, conclude that neither changes in the activity of the sun, nor its impact in blocking cosmic rays, can be a significant contributor to global warming.

Clouds and their role in keeping the Earth’s surface cool by reflecting sunlight back into space have been one of the biggest uncertainties of climate change science.

The acknowledged role of sunspots and cosmic rays in forming clouds has been fertile ground for climate deniers, who have cast doubt on whether anthropogenic climate change (in other words, change caused by humans) is occurring at all.

Sunspot activity, which ebbs and flows on an 11-year cycle, decreases the […]