Weather balloons caused climate spat
Weather balloons released in the 1970s collected skewed data that some scientists have used to argue against climate change, says new research.
The research is one of three papers published in today's issue of the journal Science to look at temperature changes in the troposphere, the lowest layer of Earth's atmosphere.
Many scientists say that the Earth's temperature is rising, largely because of human activity, including burning fossil fuels such as coal and oil: the enhanced greenhouse effect.
But some discrepancies in the data have troubled experts.
For instance, some measurements show that atmospheric temperatures have not changed 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," says 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 say they found the key to the differences lay in where the sensors were placed on weather balloons in the 1970s.
They say that the exposed sensors used in earlier designs meant that measurements taken in daylight were too high. 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 says.
"We can't hang our hats on the old balloon numbers."
Sherwood and colleagues say this helps to explain why temperatures in the troposphere appear not to have risen.
After taking this problem into account, they estimate there has been an increase of 0.2°C in the average global temperature per decade for the past 30 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 says.
Two other papers published in Science support Sherwood's conclusion that the troposphere is warming.
One paper proposes correcting data collected from satellites to better account for microwave radiation in the lower troposphere, the other proposes a new way of analysing data from the tropics.