New look at data finds no break in warm­ing trend

Los Angeles Times - - FRONT PAGE - By Monte Morin

A fresh look at the way sea tem­per­a­tures are mea­sured has led gov­ern­ment sci­en­tists to make a sur­pris­ing claim: The puz­zling ap­par­ent hia­tus in global sur­face warm­ing never re­ally hap­pened.

In a study pub­lished Thurs­day in the pres­ti­gious jour­nal Science, re­searchers from the Na­tional Oceanic and At­mo­spheric Ad­min­is­tra­tion wrote that Earth’s global av­er­age sur­face tem­per­a­ture had climbed 0.2 of a de­gree Fahren­heit each decade since 1950, with­out in­ter­rup­tion, due to the heat­trap­ping ef­fects of green­house gases.

That con­clu­sion seem­ingly negated an awk­ward piece of ev­i­dence in the de­bate over whether hu­man ac­tiv­ity is in­deed warm­ing the planet.

Main­stream sci­en­tists have strug­gled to ex­plain to the public how cli­mate change can be get­ting worse if the warm­ing of the planet’s sur­face slowed at the turn of the cen­tury. Their var­i­ous the­o­ries have chalked it up to dust and ash blasted into the sky by vol­canic erup­tions, a rare pe­riod of calm in the so­lar cy­cle, and heat ab­sorp­tion by the Pa­cific Ocean and other wa­ters.

Mean­while, cli­mate change skep­tics have em­braced the hia­tus as ev­i­dence that cli­ma­tol­o­gists have greatly mis­cal­cu­lated the warm­ing ef­fects of fos­sil­fuel emis­sions.

The new find­ings — which are based on mea­sure­ments from thou­sands of land sta­tions, ships and buoys at sea go­ing back to 1880 — drew crit­i­cism from peo­ple on both sides of the ran­corous de­bate over man-

made cli­mate change.

“I don’t find this anal­y­sis at all con­vinc­ing,” said Ju­dith Curry, a cli­ma­tol­o­gist at Ge­or­gia Tech who ar­gues that nat­u­ral vari­abil­ity in cli­mate cy­cles dom­i­nates the im­pact of industrial emis­sions and other hu­man ac­tions. “While I’m sure this lat­est anal­y­sis from NOAA will be re­garded as po­lit­i­cally use­ful for the Obama ad­min­is­tra­tion, I don’t re­gard it as a par­tic­u­larly use­ful con­tri­bu­tion to our sci­en­tific un­der­stand­ing of what is go­ing on.”

Re­searchers rep­re­sent­ing the sci­en­tific main­stream also re­jected the idea that global sur­face tem­per­a­tures never stopped ris­ing.

“It’s al­ways good to go back and look at the data as care­fully as pos­si­ble and make sure it’s cal­i­brated cor­rectly,” said Wil­liam Patzert, a cli­ma­tol­o­gist at NASA’s Jet Propul­sion Lab­o­ra­tory in La Cañada Flin­tridge. “But the hia­tus is his­tory and it was real.”

The idea that the omi­nous rise in Earth’s av­er­age sur­face tem­per­a­ture had be­gun to slow in 1998 was ac­knowl­edged by the In­ter­gov­ern­men­tal Panel on Cli­mate Change, or IPCC, in 2013. The panel determined that from 1998 to 2012, the warm­ing trend was just one-third to one-half what the trend was from 1951 to 2012.

Ac­knowl­edg­ment of the hia­tus, or pause, prompted a flurry of re­search into where all of the planet’s “miss­ing” heat could be hid­ing.

In the study, the NOAA re­searchers ar­gue that long­stand­ing prob­lems with the way tem­per­a­tures are mea­sured have masked years of sea sur­face warm­ing. Once those prob­lems are cor­rected for, “this hia­tus or slow­down sim­ply van­ishes,” said lead study au­thor Thomas Karl, direc­tor of NOAA’s Na­tional Cli­matic Data Cen­ter in Asheville, N.C.

The in­for­ma­tion that led Karl and his col­leagues to their con­tro­ver­sial con­clu­sion was con­tained in the new Ex­tended Re­con­structed Sea Sur­face Tem­per­a­ture data set, which helps sci­en­tists mon­i­tor and de­scribe the ef­fects of cli­mate change.

Karl said the new data were the re­sult of some re­cent rev­e­la­tions on the part of cli­ma­tol­o­gists.

Although re­searchers have long known that sea sur­face tem­per­a­tures mea­sured by au­ton­o­mous buoys run cooler than tem­per­a­tures mea­sured by ships, they have failed to ac­count for this as they ex­panded their use of buoy read­ings over the last two decades, the study au­thors ar­gued.

This, com­bined with the fact that ships now sam­ple a smaller area of the world’s oceans, have skewed the data to­ward cooler tem­per­a­tures, they say.

Also, though it had long been as­sumed that ships mea­sured sea­wa­ter tem­per­a­ture with en­gine in­take ther­mome­ters — an in­no­va­tion that be­gan af­ter World War II — that is not the case, Karl said. In­stead, some ships still scoop up sea­wa­ter in can­vas or metal buck­ets.

“The buck­ets, when you pull them up, tend to evap­o­rate their wa­ter, and if they’re can­vas there’s even more evap­o­ra­tion,” Karl said. “By the time peo­ple stick a ther­mis­tor in the bucket to mea­sure tem­per­a­ture, it’s al­ready slightly cool.”

To cor­rect for the dis­crep­ancy be­tween bucket and en­gine mea­sure­ments, Karl and his col­leagues used night­time air tem­per­a­ture read­ings taken from the deck of the ship to cal­i­brate the read­ings.

The re­searchers also ar­gued that the IPCC’s de­ci­sion to use 1998 as a start of the hia­tus skewed the re­sults. That year marked an ex­treme El Niño, a pe­riod of un­usu­ally warm sea sur­face tem­per­a­tures.

“If you start a short-time se­ries on an anoma­lous value, you tend to get an anoma­lous trend,” Karl said.

Since the IPCC ac­knowl- edged a warm­ing slow­down in 2013, global av­er­age tem­per­a­tures have re­sumed their up­ward trend. Re­searchers say 2014 was among the warm­est years on record, and 2015 may be even hot­ter.

Karl’s team and other sci­en­tists have noted that, iron­i­cally, a large swath of the in­dus­tri­al­ized world has en­joyed a pe­riod of land sur­face cool­ing since the start of the 21st cen­tury. This cool­ing has oc­curred in the mid­lat­i­tudes of the North­ern Hemi­sphere, in­clud­ing North Amer­ica, Europe and much of Asia, but the global av­er­age con­tin­ues to rise.

A grow­ing num­ber of cli­mate sci­en­tists have ar­gued that this phe­nom­e­non, as well as other hia­tus ef­fects, are ev­i­dence of a poorly un­der­stood pat­tern of wind, ocean cur­rent and tem­pera- ture vari­a­tions that have far­reach­ing ef­fects on global cli­mate. They say the oceans have ab­sorbed heat en­ergy from the sun, caus­ing Arc­tic ice to melt and sea lev­els to rise.

“One way to think about it is that global warm­ing con­tin­ued, but the oceans just jug­gled a bit of heat around and made the sur­face seem cooler for a while,” said Joshua Wil­lis, an­other cli­mate sci­en­tist at JPL.

One of th­ese pat­terns, called the Pa­cific Decadal Os­cil­la­tion, has a warm phase and a cool phase, each of which can last many years. The cur­rent cool phase may ac­count for the hia­tus noted by the IPCC and oth­ers, Wil­lis said.

Karl said he had been chal­lenged fre­quently by fel­low sci­en­tists but stood by the study’s con­clu­sion. He said he was of­ten asked whether he was deny­ing the cool­ing ef­fects of vol­canic aerosols, a cycli­cal dip in so­lar en­ergy or the heat-ab­sorb­ing ef­fects of the ocean.

“All of those fac­tors are real,” Karl said. “If those fac­tors had not oc­curred, the warm­ing rate would have been even greater. … If any­thing we may still be un­der­es­ti­mat­ing the trend.”

Al Seib Los An­ge­les Times

PRE­VI­OUS ANAL­Y­SIS had shown global warm­ing slowed in re­cent years, con­found­ing sci­en­tists. But new find­ings sug­gest no such hia­tus oc­curred.

Ge­naro Molina Los An­ge­les Times

THE NEW DATA on global warm­ing pat­terns re­sulted from rev­e­la­tions such as f laws seen in how the ocean’s tem­per­a­ture had been mea­sured, the study’s lead au­thor says. Above, a hot spring day at Venice Beach.

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