DURHAM, N.C. -- At least 10 to 30 percent of global warming measured during the past two decades may be due to increased solar output rather than factors such as increased heat-absorbing carbon dioxide gas released by various human activities, two Duke University physicists report.
"The problem is that Earth's atmosphere is not in thermodynamic equilibrium with the sun," Scafetta said. "The longer the time period the stronger the effect will be on the atmosphere, because it takes time to adapt."
Using a longer 22 year interval also allowed the Duke physicists to filter out shorter range effects that can influence surface temperatures but are not related to global warming, their paper said. Examples include volcanic eruptions, which can temporarily cool the climate, and ocean current changes such as el Nino that affect global weather patterns.