A dispute over whether global warming is really happening may have been caused by the placement of sensors on weather balloons when studies were done in the 1970s, researchers said Thursday.
WASHINGTON A dispute over whether global warming is really happening may have been caused by the placement of sensors on weather balloons when studies were done in the 1970s, researchers said Thursday.
Very few scientists now dispute that the Earth's temperature is rising, and that this is caused by human activity, including burning fossil fuels such as coal and oil.
But there have been some discrepancies that have troubled experts. For instance, some measurements show that atmospheric temperatures have been unchanged since the 1970s, while temperatures at the Earth's surface are rising.
"Even though models predict a close link between atmospheric and surface temperatures, there has been a large difference in the actual measurements," said Steven Sherwood, an associate professor of geology and geophysics at Yale University in Connecticut, who led the study.
"This has muddied the interpretation of reported warming."
Working with a team at the National Oceanic and Atmospheric Administration, Sherwood and colleagues said they found the key to the differences lay in where the sensors were placed on equipment.
With exposed sensors used in earlier designs, measurements taken in daylight read too warm. Later equipment reduced this effect.
"It's like being outside on a hot day -- it feels hotter when you are standing in the direct sun than when you are standing in the shade," Sherwood said in a statement.
"We can't hang our hats on the old balloon numbers."
Writing in the journal Science, Sherwood and colleagues said this helps explain why temperatures in the troposphere -- the lower atmosphere -- appear not to have risen.
After taking this problem into account, they estimate there has been an increase of 0.2 degree Celsius (0.36 degree F) in the average global temperature per decade for the last thirty years.
"Unfortunately, the warming is in an accelerating trend -- the climate has not yet caught up with what we've already put into the atmosphere," Sherwood said. "There are steps we should take, but it seems that shaking people out of complacency will take a strong incentive."
Two other papers published in Science support this conclusion.