WASHINGTON – A nagging difference in temperature readings that had raised questions about global warming has been resolved, a panel of scientists reported Tuesday.
"This significant discrepancy no longer exists because errors in the satellite and radiosonde data have been identified and corrected," researchers said in the first of 21 assessment reports planned by the U.S. Climate Change Science Program.
The findings show clear evidence of human influences on climate due to changes in greenhouse gases, aerosols and stratospheric ozone.
There has been increasing concern about global climate change being caused by human activity, in particular the release of gases such as carbon dioxide into the atmosphere by automobiles and industrial activity.
But while temperature readings at the surface showed this increase, readings in the atmosphere taken by satellites and radiosondes — instruments carried by weather balloons — had shown little or no warming.
There are still some questions about the rate of atmospheric warming in the tropics, but overall the issue has been settled, said Thomas R. Karl, director of the National Climatic Data Center.
Findings of the report include:
— Since the 1950s, all data show the Earth's surface and the low and middle atmosphere have warmed, while the upper stratosphere has cooled. Those changes were expected from computer models of the effects of greenhouse warming.
— Radiosonde readings for the midtroposphere — the nearest portion of the atmosphere — show it warming slightly faster than the surface, also an expected finding.
— The most recent satellite data also show tropospheric warming, though there is some disagreement among data sets. This may be caused by uncertainties in the observations, flaws in climate models or a combination. The researchers think it is a problem with the data collection.
— The observed patterns of change over the past 50 years cannot be explained by natural processes alone.
The report came a day after the government reported that the greenhouse gases widely blamed for raising the planet's temperature are still building up in the atmosphere.
The National Oceanic and Atmospheric Administration said Monday there was a continuing increase in carbon dioxide and nitrous oxide in the air last year, though methane leveled off. Overall, NOAA said, its annual greenhouse gas index "shows a continuing, steady rise in the amount of heat-trapping gases in the atmosphere."