Hansen vs. the World on

the Greenhouse Threat

Scientists like the attention the greenhouse effect is getting on

Capitol Hill, but they shun the reputedly unscientific way theircolleague James Hansen went about getting that attention

Amherst, MassachusettsSCIENTISTS GATHERING at the Workshopon Greenhouse-Gas-Induced ClimaticChange here in early May were waiting invain for their unofficial guest of honor toappear. James Hansen, climate modeler andleading scientific spokesman for the green-house effect, was in Washington testifyingto Congress, again.

Last summer, Hansen made the headlinesof virtually every major newspaper, carriedhis message onto the network news shows... and irked practically everyone in thefield when, in the midst of a drought, hetold Congress that the greenhouse warmingis here. It was this sort of unconditionalclaim from Hansen and his group that hadprompted this meeting. The greenhousecommunity was determined to set the recordstraight with hard facts, but now, even asthey got their meeting under way, Hansenwas at it once more on Capitol Hill.

This time Hansen was in Washington tostress that climate models had become reli-able enough to conclude that rapid strength-ening of the greenhouse effect would lead to"drought intensification at most middle-and low-latitude land areas." But the Officeof Management and Budget (OMB), in itsrole as monitor offederal policy statements,was not buying Hansen's views outright.Over his objections, it attached a caveat toHansen's written testimony-"... thesechanges should be viewed as estimates fromevolving computer models and not as reli-able predictions."When Hansen complained, he touched

off a furor in Washington among the politi-cians but not among the greenhouse scien-tists in Amherst. "I can't say I agree withcensorship," observed Rick Katz, who stud-ies climate change impacts at the NationalCenter for Atmospheric Research in Boul-der, "but it seems OMB has better peoplethan I thought. I'd have to agree with theirangle."So Hansen, who is director of NASA's

Goddard Institute of Space Studies in NewYork City, was once again at loggerheadswith his colleagues in the climate communi-ty over how to speak to outsiders. That

2 JUNE 1989

Hansen's colleagues are taking pleasure inthe federal bureaucracy's meddling in scien-tific testimony illustrates the resentmentthese climatologists feel toward their nowfamous colleague.But there's an irony: had it not been for

Hansen and his fame, few in public office,

"It's just a logicalconclusion that thegreenhouse is here."

-James Hansen

and certainly not the public itself, wouldhave paid much attention to a problem thateveryone at Amherst agrees threatens socialand economic disruption around the globe.After all, experts had been hemming andhawing for a decade on the likely magnitudeof the problem, and hardly anyone hadlistened. Then came Hansen. Now green-house scientists have the attention they havewanted but for reasons they think unsound.By day two of the workshop, Hansen had

appeared and, in an interview with Science,recalled his testimony on that sweltering dayin Washington in the midst of last summer'sdrought. "I said three things. The first wasthat I believed the earth was getting warmerand I could say that with 99% confidence.The second was that with a high degree ofconfidence we could associate the warming

and the greenhouse effect. The third wasthat in our climate model, by the late 1980sand early 1990s, there's already a noticeableincrease in the frequency of drought. De-spite all the criticism, I wouldn't change anyof these."

His colleagues certainly wish he would.What really bothers them is not that theybelieve Hansen is demonstrably wrong, butthat he fails to hedge his conclusions withthe appropriate qualifiers that reflect theimprecise science of climate modeling.

Hansen's critics start with his statementthat he has 99% confidence in the reality ofthe global warming trend. At the workshop,as he already had in the New York Times,statistician Andrew Solow of Woods HoleOceanographic Institution picked on thefew quantitative facts involved. Hansen hadsaid in last year's testimony that 1987 hadbeen so hot, so much warmer than theaverage of the previous 30 years, that itswarmth had only a 1% chance of being arandom quirk of the climate system.

"That's not a test for the greenhouse inany way," Solow told the workshop. Theyear "1987 should be assessed against previ-ous data. The key thing is logic, and I thinkthere's a logical problem here." When statis-tician Solow calculated how unusual 1987had been, he found that it did not standmuch above an underlying upward trend,giving a confidence of just 70% that it wasan exceptional year. To statisticians, that ispractically no confidence at all.

Climatologist Tom Wigley of the Univer-sity of East Anglia, though critical, wasmore sympathetic. "I think his 99% confi-dence is not justified theoretically. But he'sjust saying that, relative to 1958, there'sbeen a warming." In his enthusiasm forproper statistical analysis, Wigley was argu-ing, Solow had removed the trend thatHansen was trying to point out.

Wigley's sympathetic point ofview mighthave some merit, responded Solow, but"this kind of giving a result and not tellingthe whole story, that's what I'm criticizing."

If many of Hansen's colleagues find hisfirst point about the warming trend regret-table, they view his second-that the warm-ing could, with "high confidence," be linkedto the greenhouse effect-as unforgivable.None of the select greenhouse researchers atthe meeting could agree with him. "Takentogether, his statements have given peoplethe feeling the greenhouse effect has beendetected with certitude," says Michael Schle-singer, himself a modeler at Oregon StateUniversity. "Our current understandingdoes not support that. Confidence in detec-tion [of the greenhouse] is now down nearzero."

Hansen's third point-that "the green-

RESEARCH NEWS 1041

on

Apr

il 2,

201

3w

ww

.sci

ence

mag

.org

Dow

nloa

ded

from

house effect will [cause] certain changes inclimate variability such as the intensity ofdroughts and storms"-elicits a less vituper-ative response. Climate modeler StephenSchneider of the National Center for Atmo-spheric Research in Boulder reflects theviews of others at the meeting, who wouldonly speak privately, when he observes that"where Jim has had some problems with hisfriends, and I count myself as one, is whenhe says that the location of specific areas ofdrought in his model are robust. I can'tmake the case as strongly as Jim does,"Schneider contends, because model particu-lars such as how the oceans are simulatedcould make a difference.

"He's not running a realistic ocean," saysSchneider. "You don't really know what it'sgoing to do. But he's probably right any-way. The odds are better than 50:50 that thedrought areas are robust."

Despite their sharpness, these criticismsdo not reflect on Hansen's research abilities,rather they tend to revolve around the inter-pretation of climate models. "Jim is not thevillain that people make him out to be," saysSchneider. "He's a state-of-the-art climatemodeler. Jim got bad press that was partlydeserved and partly envy of other scientistswho resent the way he went to Congress.The problem I have is that he has moreconfidence in his tools than I do."The primary tool in the greenhouse game

is the general circulation model (GCM) ofthe climate system. Like its cousin thatforecasts the daily weather, the climateGCM cranks through equations that calcu-late the behavior of climate as greenhousegases increase. Unlike weather forecastingmodels, a climate GCM must include asimulated ocean whose behavior-such asthe way it carries heat around the globe-bears a reasonable resemblance to that of thereal ocean. Last year Hansen was the first topublish the results of a GCM that has anykind of a realistic ocean and that also isdriven by realistically increasing greenhousegases. That work provided the best guess upuntil then ofhow climate might be respond-ing now and how it will respond in the nextfew decades.

Despite the relative sophistication ofHansen's model, other modelers remain un-convinced because they feel Hansen givesshort shrift to the remaining shortcomingsof even newer, more realistic models. "They[Hansen's group] have been coupling theiratmospheric model to a pretty hokeyocean," says Schneider, "we all have. Butyou have to have less confidence because ofthat."

Other uncertainties lessen confidence aswell. Researchers must have some idea ofthe degree to which climate is being

SCIENCE, VOL. 2441042

on

Apr

il 2,

201

3w

ww

.sci

ence

mag

.org

Dow

nloa

ded

from

changed by forces other than greenhousegases. For example, volcanic dust in thestratosphere probably cools Earth, changesin solar activity may change the climate, andclimate surely meanders a bit from one stateto another with no prompting whatever.

All the climatic variability generated bythese natural forces generates noise in theclimatic record that, Hansen's critics wouldargue, has drowned out the poorly knowngreenhouse warming signal. "The variabilityof climate from decade to decade is mon-strous," said Tim P. Barnett, an oceanogra-pher at Scripps Institution of Oceanogra-phy. "To say that we've seen the greenhousesignal is ridiculous. It's going to be a diffi-cult problem."The detection problem is one that may

take decades to solve. Barnett and Schlesing-er have their own approach, an objective,statistical test. Through the latest results, ithas found no signal.Hansen was in no position to argue. He

arrived at the 5-day meeting a day late andleft 3 days early. "That is his habit," notedworkshop organizer Schlesinger. "Hecomes, gives his talk, and he leaves." Evenwhile present, his quiet, retiring mannerputs him in the background. These habits

One of James Hansen's many critics. Micdcomputer greenhouse models too, but he does not shconfidence" that the greenhouse is here.

have not encouraged mutual understanding.Neither did the audience's polite reticenceduring Hansen's talk, which contrasted withpot shots from many quarters during hisabsence. Not that Hansen is unaware of hiscolleagues' complaints. Last fall, in his loneconfrontation with his critics, Hansen en-dured what one observer described as "a get-Jim-Hansen session" at a climate workshopin Washington. Hansen, as is his style, wasunperturbed. "When we're at this level ofsignal to noise, anyone can disagree withme. I don't argue with that."

What gives Hansen high confidence whenothers hesitate to make any claim is a varietyof supporting evidence. The globe haswarmed slightly during the past 100 years.His model roughly tracks the warming ofthe past 30 years. And analyses of polar icecores suggest that a reduction of the green-house effect due to a reduction in atmo-spheric carbon dioxide contributed to thechill of the last ice age 18,000 years ago."The one thing that has the greatest im-

pact on my thinking," says Hansen, "is theincrease in atmospheric carbon dioxide from280 parts per million in the 19th century toits present 350 parts per million. It's justinconceivable that that is not affecting ourclimate. There's no model that would notsay it's affecting it right now."

"It's just a logical, well-reasoned conclu-sion that the greenhouse is here now," hesays. "I think there are a lot of people whoagree the warming is probably due to thegreenhouse effect, but they are waiting tosee."

There's no arguing with Hansen on thatpoint. Stanley Grotch, who has been moni-toring the performance of the greenhousemodels from Lawrence Livermore NationalLaboratory, guessed that "if there were a

secret ballot at thismeeting on the ques-tion, most peoplewould say the green-house warming is prob-ably there."

Schneider, who wasnot in Amherst for themeeting but usually tes-tifies to Congressalongside Hansen, isone of those scarcegreenhouse researcherswho do not need a se-cret ballot to expresstheir gut feelings. "Weneed 10 or 20 years toget an absolutely clearsignal. I'll be surprisedhael Schlesinger runs

Ware Hansen's "high if it doesn't happen, buthow do you assign aprobability to some-

thing when you have no objective means ofdoing so? You base it on physical intuitionand then state your assumptions. By myintuitive reasoning, the greenhouse signalhas been detected at an 80% probability. Myfaith is based on the principle of heat trap-ping by greenhouse gases and the billions ofobservations that support it. All that objec-tive stuff rests on assumptions. The future isnot based on statistics, it's based on physics.Objectivity is overplayed."

Obviously, certitude sells on Capitol Hill,intuition less so. As a group, those at the

Amherst workshop offered neither, only alarge dose of uncertainty. On the last day,the 40 participants who stayed to the endgathered en masse to put the finishingtouches to a press release. They argued overjust about everything except this passage: "Itis tempting to attribute [the 0.5°C warmingof the past 100 years] to the increase ingreenhouse gases. Because of the naturalvariation of temperature, however, such anattribution cannot now be made with anydegree of confidence."

Like it or not, the greenhouse communityhas a spokesman who is not following theconsensus script coming out of Amherst."What bothers a lot of us," said modelerAlan Robock of the University ofMaryland,"is that we have a scientist telling Congressthings we are reluctant to say ourselves."

"Jim Hansen has crawled out on a limb,"said Danny Harvey of the University ofToronto. "A continuing warming over thenext 10 years might not occur." The centu-ry-long warming has not been continuous."If the warming didn't happen, policy deci-sions could be derailed."

Curiously enough, while researchers wor-ry about the possible down side of thegreenhouse's newfound popularity, they arestill awaiting the benefits from Hansen'sconfident testimony. Currently about a doz-en people run the four U.S. and one Britishgreenhouse GCMs considered state of theart. Time on supercomputers to run green-house simulations is scarce, and most mod-elers often have to scrounge time whereverthey can find it. Hansen ran his transientmodel nights and weekends on his institute's1975-vintage Amdahl computer-a relic ofthe dark ages of supercomputing.

"It's getting done at a rate that will take25 years to get it right," says Schneider. "I'mhoping we can get the modeling of regionalgreenhouse changes right before they actual-ly happen. What's depressing is that wearen't seeing more resources."

Will a rapidly changing climate leave re-searchers forever fiddling with their models,still waiting for a consensus detection of thegreenhouse? Hansen thinks so. "I'm confi-dent that we're going to see new globalrecords, but it may not be this year. It maybe in a few years. I think these issues will goaway in the next few years as the earth getswarmer. There will be no sudden change,there will be those who don't agree, but assoon as the man in the street notices, itwon't matter. If the model is correct, theincreased frequency of drought will be evi-dent in the 1990s, the early 1990s if there isno large volcanic eruption" to cool theclimate. If Hansen is right, an exceptionaltrust in physical intuition may have won theday. * RICHARD A. KERR

RESEARCH NEWS I0432 JUNE I989

A64'

AA

-1.A

I

on

Apr

il 2,

201

3w

ww

.sci

ence

mag

.org

Dow

nloa

ded

from