NEWS & ANALYSIS

Incognita. The fastest warming part of the globe, the Arctic, lacks temperature stations in many areas.

C L I M AT E S C I E N C E

compared their method’s skill in interpolation with that of the NASA and Hadley approaches in the Arctic by systematically removing known data and using each of the three techniques to reconstruct the data set. Cowtan says his and Way’s approach proved the most reliable, and data from Arctic buoys and three weather models support it. The takeaway? A slowdown in warming that’s half as big as previously thought. “When you fill in the gaps, temperatures in recent years go up, and temperatures around 1998 go down,” Cowtan told the climate scientists in Potsdam. The planet has warmed most where scientists are watching least, enhancing the perceived size of the slowdown in warming. Cowtan and Way first drew attention to their methods in November 2013, when SkepticalScience.com. They learned that their paper focusing on HadCRUT was first researchers had been trying for years to published online in the Quarterly Journal of explain why global temperature data sets the Royal Meteorological Society. In Potsdam, show different rates of warming—and are Cowtan shared an unpublished result that below what many climate models have suggests a data-smoothing algorithm may be predicted. The British and NASA data sets, tuning down temperature measurements that along with others maintained by NOAA and NOAA’s Arctic climate stations supply to academic scientists in Berkeley, California, NASA. NOAA says it is adding new stations rely on data from thousands of weather to its network to address the Arctic data gap. stations around the globe along with satellite Philip Jones of the University of East Anglia in measurements of ocean temperatures. Norwich, U.K., which runs HadCRUT jointly Yet gaps in the network of stations exist with the U.K. Met Office, says HadCRUT is over Antarctica, Africa, and, crucially, the also seeking to add stations. A r c t i c — t h e r eg i o n Cowtan’s talk at that satellites, weather PIK and remarks the TEMPERATURE TRENDS models, and shrinking sea previous day to a Pots1997−2012 ice point to as the fastest dam meeting on the Source Warming (°C/decade) warming on the planet. temperature record were The various data sets deal his first ever talks before Climate models 0.102−0.412 with the gaps in different climate researchers. NASA data set 0.080 ways. The British one, He attributes his odd HadCRUT data set 0.046 known as HadCRUT, interest in climate to omits missing regions “an obsession with Cowtan/Way 0.119 from its calculations of solving computational global mean temperature Getting warmer. New method brings mea- problems.” He and Way trends; NASA extra- sured temperatures closer to projections. have done the work on polates temperatures nights and weekends, for those areas using data from their edges. raising $3000 from readers at Skeptical Both groups have previously warned that that Science to pay for open-access fees for their sparse coverage may lead to underestimates of November paper. global warming. “It’s impressive when someone outside the Cowtan and Way set out to quantify those field makes a useful contribution,” says Dim underestimates. They applied a new method Coumou, an atmospheric scientist at PIK. that fills in missing temperatures over sea Cowtan says he appreciates the recognition ice by combining satellite data for missing but that improving the data sets is what really areas with a method known as kriging, which matters: “The reason I started this is that I calculates missing data by checking nearby wanted the problem fixed.” temperature station readings. Then they –ELI KINTISCH

POTSDAM, GERMANY—Kevin Cowtan had a clear message to deliver earlier this month when he spoke to researchers here at the Potsdam Institute for Climate Impact Research (PIK): Standard data sets of worldwide surface temperatures underestimate recent global warming, and the much-publicized slowdown in warming isn’t as slow as it seems. Crystal clear, one might say: Unlike the 25 scientists and students listening to his talk, Cowtan is not a climate scientist—he’s a protein crystallographer at the University of York in the United Kingdom. Cowtan described how he and a graduate student had recently reanalyzed data underpinning key global temperature data sets. Among their findings: The two most prominent data sets, one maintained by a British collaboration and the other by NASA, have underestimated the pace of warming between 1997 and 2012 by an estimated 158% and 49%, respectively. That’s not a big difference in absolute temperature rise, says PIK climatologist Stefan Rahmstorf, given the relatively short period covered (see table). But it shows that the slowdown, or “hiatus,” has been less pronounced than previously described, he says. Correcting the data sets “should have been done ages ago,” Rahmstorf adds. In an e-mailed statement to Science, climatologists at the National Oceanic and Atmospheric Administration (NOAA) call the recent work “important contributions” to the climate field. Cowtan and his partner Robert Way, of the University of Ottawa, got drawn into the problem by participating in the climate-science advocacy website

348

25 APRIL 2014

VOL 344

SCIENCE

Published by AAAS

www.sciencemag.org

CREDITS: KEVIN COWTAN, HADCRUT4; (DATA) COWTAN/CMIP5

Climate Outsider Finds Missing Global Warming

Climate science. Climate outsider finds missing global warming.

Climate science. Climate outsider finds missing global warming. - PDF Download Free
115KB Sizes 2 Downloads 4 Views