WASHINGTON — Global warming has not stopped or even slowed in the past 18 years, according to a new federal study that rebuts doubters who've claimed that heating trends have paused.
Scientists at the National Oceanic and Atmospheric Administration readjusted thousands of weather data points to account for different measuring techniques through the decades. Their calculations show that since 1998, the rate of warming is about the same as it has been since 1950: about two-tenths of a degree Fahrenheit a decade.
The so-called hiatus has been touted by non-scientists who reject mainstream climate science. Those claims have resonated; two years ago, the United Nation's Intergovernmental Panel on Climate Change felt the need to explain why the Earth was not heating up as expected, listing such reasons as volcanic eruptions, reduced solar radiation and the oceans absorbing more heat.
"The reality is that there is no hiatus," said Tom Karl, director of the National Centers for Environmental Information in Asheville, North Carolina. He is the lead author of a study published Thursday in the peer-reviewed journal Science
One key to claims of a hiatus is the start date: 1998. That year there was a big temperature spike; some of the following years were not as hot, though even hotter years followed in 2005, 2010 and 2014, according to NOAA, NASA and temperature records kept in England and Japan. This year is on pace to break last year's global heat record.
Scientists keep updating the way they measure Earth's temperatures. This study focuses on the effects of the way ocean temperatures are taken. The old way, going back generations, is with ships. Sometimes people would dip a bucket in the way; other times they'd measure water that came into the engine. They also did it at various times of day.
The new way is on buoys at the same time of day. Karl said the buoy measurements are more accurate, but can't be compared directly to the ship measurements for a trend without making adjustments, because that would be comparing apples and oranges. So to come up with a trend using comparable numbers, NOAA increases the buoy temperatures a bit.
A few years ago NOAA made similar adjustments to make land temperatures more comparable decade-to-decade. But that also caused some non-scientists who reject climate change to cry tampering.
Several outside scientists contacted by The Associated Press said the new and previous adjustments are sound. Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research, said the new work was "good and careful analysis" but only confirms what most scientists already knew, that there was no such hiatus.
A few years ago, a group out of University of California Berkeley — funded in part by the Charles Koch Foundation, whose founder is a major funder of climate doubter groups and the tea party— took what was initially billed as a skeptical look at the previous NOAA data. But they pronounced the earlier adjustments legitimate. The same scientists now say the new NOAA adjustments are also proper.
"NOAA is confirming what we have been saying for some time that the 'hiatus' in global warming is spurious," Berkeley team chief and physicist Richard Muller said in an email. Muller said global warming continues but in "many fits and spurts."
John Christy of the University of Alabama Huntsville, one of the minority of scientists who dispute the magnitude of global warming, said the Karl paper "doesn't make sense" because satellite data show little recent warming. "You must conclude the data were adjusted to get this result" of no warming pause, Christy wrote in an email. "Were the adjustments proper? I don't know at this point."
Others who reject warming, especially non-scientists, point to satellite records by Remote Sensing Systems that appear to show no change in temperature since 1998. Satellites measure a different part of Earth's atmosphere than ground and ocean monitors that NOAA, NASA and others use.
Carl Mears, senior research scientist for RSS, said those rejecting climate change based on his work or any one dataset are wrong and "seek to deny the reality of human-induced climate change by grasping at straws." Mears said the overall data consistently show long-term global warming and that it really hasn't stopped recently. The NOAA adjustments make sense, he said.
Karl said NOAA didn't adjust datasets in the Arctic, where it is warming even faster, because there is a lack of reliable long-term records to compare. Had NOAA made those adjustments, the recent warming trend would be slightly larger, he said.
NOAA National Centers for Environmental Information: http://www.ncdc.noaa.gov
Seth Borenstein can be followed at http://twitter.com/borenbears