Researchers Attribute Global Warming to Humans, Not Nature

New measurements make it increasingly clear that people--and not a natural force such as sunspots or volcanoes--are responsible for global warming, U.S. researchers said Thursday.

Tom Wigley of the National Center for Atmospheric Research in Boulder, Colo., and colleagues analyzed 115 years of global temperature data and concluded the release of greenhouse gases such as carbon dioxide explains most of the 1-degree increase in the planet’s average temperature over the last century.

“These results provide another important piece in the jigsaw puzzle of climate change, strengthening yet further our confidence that there has been a discernible human influence on climate,” they wrote in a report in the journal Science.

They used a new kind of statistical analysis, looking at the average temperature for each year in both the Northern and Southern Hemispheres, and then comparing these measurements to readings taken up to 20 years earlier or later.

They also figured in the effects of volcanoes--which throw up dust that can affect the atmosphere and temperatures--and of changes in the sun’s radiation, including sunspots and solar flares.

They said the sun was probably responsible for some of the changes. But the Earth’s climate would have to be about six times as sensitive to the sun’s effects than it actually is for the sun alone to be responsible for global warming, they wrote.