Bengtsson in 1990: “one cannot oversell the greenhouse effect”

Lennart Bengtsson recently joined the Academic Council of the GWPF. This generated quite some attention on blogs and in the media. I interviewed him, but also Hans von Storch on Klimazwiebel, Axel Bojanowski had a story in Der Spiegel (English version), and there was an article in the Basler Zeitung.

Bengtsson emphasized that he has always been a “sceptic”. In the interview with me he said:

I have always been sort of a climate sceptic. I do not consider this in any way as negative but in fact as a natural attitude for a scientist. I have never been overly worried to express my opinion and have not really changed my opinion or attitude to science.

We all know that in climate discussions climate scientists are quick to say “we are all sceptics” so such a remark says little about Bengtsson’s exact viewpoints. The renowned Dutch science writer Simon Rozendaal then sent me a copy of his interview with Bengtsson published on 27 October 1990 (!) in the Dutch weekly Elsevier (for which Rozendaal still works as a science writer).

We can now confirm that Bengtsson was pretty “sceptic” in 1990. Here is the full translated Elsevier article:

A cool blanket of clouds

Climate expert Bengtsson puts the threat of the greenhouse effect in perspective

Next week, a large conference on the global climate will be held in Geneva. The most important topic of discussion: the greenhouse effect. Many hold the opinion that our planet is warming by the increase in carbon dioxide and that a climate disaster is looming. Maybe so, says Lennart Bengtsson, Europe’s most important climate scientist. Or maybe not. Bengtsson doesn’t actually know for sure. It could go either way.

Lennart Bengtsson is so far not daunted by the looming climate disaster. He frowns when looking at the tierische Ernst with which the rest of the world embraces the prediction that the planet warms due to the increase in gases like carbon dioxide (CO2). ‘It would become serious if the atmospheric CO2 concentration would decrease. Thanks to the greenhouse effect Earth is a habitable place. Were its concentration to decrease, then mean temperatures would plummet far below freezing. That really would be a catastrophe.’

The Sweed, who appears and talks like Max von Sydow, is director of the European Center for Medium Range Weather Forecast in Reading (United Kingdom), which supports eighteen European national weather centers like Dutch KNMI with computer models and simulations. Soon he will become director of the Max Planck institute in Hamburg and thereby will be in charge of Europe’s most important greenhouse effect computer model. ‘Until now the greenhouse effect research has concentrated in the United States, but Europe is advancing.’

There is something strange about the greenhouse effect. Many scientists babble and publish about it, but few really understand its ins and outs. Most of them treat assumptions as were they facts. Suppose that it would become two degrees warmer, how much higher would the Dutch dikes have to become? Or: suppose that we want to reduce CO2 emissions and still maintain economic growth for not so strong economies of Poland, Greece, and China, how much would the emissions of the wealthy Netherlands have to decrease? For the question whether the underlying assumptions are actually correct, one has to ask climate experts like Bengtsson.

He emphasizes that the greenhouse excitement is founded in computer simulations. And that computer generated models are not complete nonsense. ‘If for example such a model starts with a globally uniform temperature, then within a few months of simulation one would start to see the tropics warming and polar regions cooling. Remove the Amazon and after some time it reappears due to the torrential tropical rains. Such general characteristics of the global climate are part of the models.’

However, the models provide insufficient insight. ‘They are too coarse. While weather predictions nowadays have grid sizes of 100 by 100 kilometer, climate models work on a 500 by 500 km grid. In addition, models have problems with clouds. They are not able to predict what effect clouds have and they cannot distinguish between high and low clouds, yet we know that this differentiation has important consequences.’ Many other important aspects are lacking. Some of those cannot be incorporated simply because they are not well understood. ‘For a large part of the emitted carbon dioxide we do not know where it stays.’


Would there be no clouds, everything would be simple. ‘With a clear sky, increasing carbon dioxide or methane would lead to a reduction of heat radiation from the earth to the atmosphere. In addition, water vapor would amplify the so-called greenhouse effect. If temperatures increase, more water evaporates and water vapor is a powerful greenhouse gas.’

However, clouds do exist. It is these fluffy tufts that diminish much of the commotion surrounding the climate disaster. Clouds cool because they reflect sunlight. On the ground we notice this when we’re in a shadow. At the same time clouds warm because they prevent heat radiation from directly escaping to space: ground frost nearly always occurs under cloud free conditions. The simple question as to whether clouds cool or warm the Earth was until recently unanswered, and this says a lot about the current state of meteorology.

Among climate experts the opinion that clouds cool Earth is gaining ground, Bengtsson observes. ‘There are recent satellite observations, as reported in the scientific magazine Nature, showing that clouds reduce the greenhouse effect. In particular low level clouds are efficient cooling agents.’

Theoretically, the greenhouse effect could even cause a cooling rather than a warming of Earth. ‘The cooling effect of clouds is five times as strong as the temperature increase due to a doubling of atmospheric CO2.’ There is even an amplification of this feedback. Bengtsson: ‘If it gets warmer, clouds become whiter and thereby reflect more solar radiation.’

Such feedbacks are hardly part of the computer models that predict the warming, according to Bengtsson. ‘Almost no model is capable of dealing with the behavior of clouds. The models builders claim they do, but when we redo the calculations that turns out not to be true.’

There are other problematic issues. Were climate to really warm, snow and ice would have to melt. That would result in additional warming because white surfaces reflect more sunlight. ‘This additional warming is not present.’ Maybe the largest omission in knowledge about climate are the oceans.’ In most models it is assumed that the ocean is fifty meters deep, which is an average. But there are parts of the oceans that are several kilometers deep. Those would slow any potential warming. You could hide thousand years of warming in the ocean.’

The one small meteorological detail from the enormous amount of uncertainties, ambiguities and question marks that has become better understood is that an increase of CO2 and some other gases potentially has a warming effect. And that is what politics is focusing on right now. Bengtsson: ‘What happens in the Atlantic Ocean could have bigger consequences, but nevertheless all attention is focusing on the greenhouse effect.’


Bengtsson believes that climate experts should not pretend to be more knowledgeable than they really are. ‘In case of the greenhouse effect there is an interaction between media, politics and science. Every group pushes the other groups. Science is under pressure because everyone wants our advice. However, we cannot give the impression that a catastrophe is imminent. The greenhouse effect is a problem that is here to stay for hundreds of years. Climate experts should have the courage to state that we are not yet sure. What is wrong with making that statement clear and loudly?’

The excitement of the last weeks has moved everything into high gear. A United Nations committee (the IPCC) has released a report at the end of August which suggests that there is a broad scientific consensus about the existence of the greenhouse effect. This already has had political ramifications in many countries. For example, halfway October hundreds of Dutch politicians, experts, civil servants and industrialists have been discussing in Rotterdam themes from the 1960s like whether and how the Netherlands could lead the way (again). And early November there will be a global conference in Geneva about the global climate.

Bengtsson thinks that the IPCC has been particularly actuated for political reasons. ‘The IPCC prediction that with a doubling of CO2 in the atmosphere the temperature on Earth would rise by two degrees should be taken with a grain of salt.’

Due to the lack of understanding a thermometer remains crucial. And it is not pointing in the direction of a doomsday. ‘The temperature over the Northern Hemisphere has decreased since about 1950. In some countries the eighties were very warm, but there are countries where this is not the case. On Greenland there is little to be seen of the greenhouse effect. It has been very cold during the last couple of years.’

‘If you talk to the greenhouse mafia about these observations, they provide some answers, but those are not real. There is no proper support for the claim that the greenhouse effect should already be visible. It is sometimes stated that the Southern Hemisphere is warming. But there are so few observational sites over there that it is very difficult to draw any definitive conclusions about the temperature in the Southern Hemisphere.’

Bengtsson is not the only climate expert who thinks that much of the excitement about the greenhouse effect is undue. Many of his colleagues have been rather uneasy about what happened after they opened Pandora’s box. They have become afraid, now that politicians, camera crews, pressure groups and environmental departments worldwide have thrown themselves at the climate disaster, to openly state that what they have declared may have been a bit premature.

Bengtsson: ‘Many of us feel rather uncomfortable with much of what has been claimed about the greenhouse effect. No one had been talking about it because temperatures had been slightly on the decline during the last 30 years. Only after Jim Hansen of NASA had put the issue back on the agenda after the warm summer of 1988 has it become part of the political agenda. In itself there is no problem with that. Looking hundreds of years ahead the greenhouse effect could become a serious problem. Some policies are obviously a clever thing to do: save energy, become less dependent on oil, those are good ideas. But one cannot oversell the greenhouse effect. There are many environmental problems that are much more urgent like that of the sulphur dioxide in Eastern Europe.’


De Ingenieur: effect CO2 kleiner dan gedacht

Technologietijdschrift De Ingenieur vroeg mij de rubriek Punt te schrijven naar aanleiding van het rapport over klimaatgevoeligheid. Het staat in De Ingenieur nr. 3 van 2014 en is nu ook online te lezen:

Effect CO2 kleiner dan gedacht

Expert-review van nieuwste klimaatrapport

Het werkelijke klimaat is aanzienlijk minder gevoelig voor broeikasgassen dan klimaatmodellen suggereren. Toekomstverwachtingen voor de opwarming dienen daarom naar beneden bijgesteld te worden, stelt wetenschapsjournalist en expert reviewer Marcel Crok.

Het goede nieuws is dit: metingen aan ons klimaat over de afgelopen 150 jaar en de bijgewerkte kennis over effecten van broeikasgassen en aerosolen (luchtverontreiniging) suggereren dat het klimaat aanzienlijk minder (ruim veertig procent) gevoelig is voor broeikasgassen dan de klimaatwetenschap al decennia denkt, zo blijkt uit het rapport Een gevoelige kwestie: hoe het IPCC goed nieuws over klimaatverandering verborg.
Het rapport is geschreven door de Britse onafhankelijke klimaatwetenschapper Nic Lewis en ondergetekende. Wij waren beiden expert reviewers van het eind vorig jaar verschenen vijfde rapport van het Intergovernmental Panel on Climate Change (IPCC). We constateerden dat het IPCC naar alle relevante literatuur verwijst maar het ‘goede nieuws’ niet bracht. Wij laten zien dat bij het een na hoogste emissiescenario van het IPCC twee graden opwarming pas rond 2100 bereikt hoeft te worden, en niet de komende 25 jaar, zoals het IPCC zelf concludeert.

Lees verder op


Roderik van de Wal: ‘het gaat slecht met de Groenlandse ijskap’

We hebben kunnen zien dat de media massaal de mist in gingen bij hun verslaggeving over de Groenlandse smelt. Dat gold niet alleen voor de NOS, maar zoals in de commentaren onder mijn bericht van gisteren te zien was ook voor RTL Nieuws, de VRT en de Nederlandse kranten sloegen online aanvankelijk ook de plank mis (vooral in hun koppen), maar corrigeerden dat stilletjes.

Vandaag wil ik bekijken hoe twee onderzoekers, die gevraagd werden commentaar te leveren op het nieuws, het deden in de media. Neven attendeerde me via zijn blog op dit interview van Nasa’s Tom Wagner met PBS.  Hij zat dicht op het vuur en was zelfs betrokken bij het persbericht van Nasa.

Het tweede interview, met glacioloog Roderik van de Wal van de Universiteit Utrecht, vond woensdagochtend plaats op radio 1. Dat interview vond dus plaats vóór de uitzending van het NOS Journaal en had de redacteur van het Journaal het gehoord dan zou de fout waarschijnlijk niet gemaakt zijn. Van de Wal legt namelijk prima uit wat er aan de hand is.

Ik wil vandaag vooral observeren en vergelijken. Het interview met Wagner is te lang om snel even uit te typen. Van het gesprek met Van de Wal heb ik de belangrijkste passages wel uitgeschreven. Bekijk en beluister vooral eerst beide fragmenten (totaal tien minuten) en laat straks in een commentaar weten wat je van beide interviews vond. Ik lette zelf op drie zaken: 1) leggen ze duidelijk uit wat er aan de hand was? 2) hoe alarmerend vinden ze deze gebeurtenis? 3) kan de gebeurtenis worden toegeschreven aan de opwarming van de aarde (alias de klimaatverandering)?

Lees verder…


Koutsoyiannis: temperature rise probably smaller than 0.8°C

Koutsoyiannis and Steirou analysed 163 time series. 2/3 of the stations are adjusted upwards leading to a warm bias in the global surface land temperature.

My last post (in Dutch) on the new paper of Dick McNider reminded me of a very interesting presentation I attended at the last EGU meeting in Vienna. The presentation was given by Eva Steirou, a scientist in the group of Demetris Koutsoyiannis.

The popular summary of the presentation is that the rise in global land temperatures is probably smaller than the generally accepted 0,7-0,8 °C. Steirou and Koutsoyiannis claim that the adjustments that are applied to the raw monthly GHCN data make the trend larger. Lees verder…


Opwarming door nachtelijke onrust

Er is een belangrijke paper verschenen die meer licht werpt op hoe we temperatuurmetingen moeten interpreteren. Eerste auteur Richard McNider blogde over het artikel op de blog van Roger Pielke sr. en ook Anthony Watts pikte het op. Coauteurs van de paper zijn Bert Holtslag en Gert-Jan Steeneveld van Wageningen Universiteit.

De grafiek hierboven is afkomstig uit de paper en zegt meer dan de spreekwoordelijke duizend woorden. Linksboven is te zien dat de minimum temperaturen (Tmin) boven land veel sterker zijn gestegen dan de maximum temperaturen (Tmax). Rechtsboven is te zien dat klimaatmodellen de verschillen in trends tussen Tmin en Tmax niet goed simuleren. In klimaatmodellen is er nauwelijks verschil tussen Tmin en Tmax.

De paper van McNider en collega’s onderzoekt nu wat de oorzaak kan zijn van die snellere opwarming in de nacht. Een van de belangrijkste conclusies van het artikel is: Lees verder…


Milieutop is oefening in vruchteloos debatteren

Tijdens de recente milieutop in Rio werd ik gebeld door een journalist van het Nederlands Dagblad. Ik wist niet of hij iets met het gesprek gedaan had, maar nu kwam ik inderdaad een stuk tegen. Het is alleen tegen betaling volledig te lezen, maar omdat het inmiddels een paar weken oud is meen ik het hier wel integraal te kunnen plaatsen. Lees verder…


De Jager: geen groot minimum in het verschiet

De Jager en Duhau verwachten dat de zon een reguliere fase ingaat, vergelijkbaar met de periode 1724 tot 1924.

Kees de Jager gaat ondanks zijn leeftijd rustig door met publiceren. Vandaag geeft hij een korte uitleg op zijn website over een nieuwe paper die hij publiceerde samen met Silvia Duhau. Er zijn enkele verrassende conclusies. Belangrijkste is dat De Jager niet langer verwacht dat we een Groot Minimum tegemoet gaan, die vergelijkbaar is met het Maunder Minimum.

Er is zojuist een nieuwe publicatie verschenen van Silvia Duhau (Argentinië) en mij, waarin we de verwachtingen voor de komende activiteit van de zon specificeren. Voor de nieuwe zonnecyclus die sinds ca. 2010  gaande is, berekenen we dat het maximum in het midden van 2013 zal optreden. We bevestigen onze eerdere verwachtingen dat dit maximum laag zal zijn. Specifiek verwachten we een maximaal lopend gemiddeld zonnevlekken getal van 62 met een onzekerheid van 12. De waarschijnlijkheidsverdeling van de onzekerheden is scheef; de hoge getallen zijn waarschijnlijker dan de lagere.

We konden ook vaststellen dat het zo extreme Grote Maximum van de vorige eeuw in 2008 zijn einde gevonden heeft. Een nieuwe grote episode, zoals we dat noemen, is begonnen. Verscheidene onderzoekers, ook wij, hebben in eerdere jaren de verwachting uitgesproken dat deze episode te vergelijken zou zijn met het Grote Minimum (het Maunder Minimum) van de 17e eeuw. Daarom waren we verrast te vinden dat dit niet het geval zal zijn. Deze komende grote episode zal eerder te vergelijken zijn met de periode van vrij regelmatige fluctuaties die optrad tussen 1740 en 1924.Zelfs hebben we de voor ons zeer verrassende conclusie moeten trekken dat in de komende duizend jaren geen Grote Minima zullen voorkomen.

De hele paper is hier te downloaden.


McKitrick: models inaccurate by ignoring socioeconomic effects

I referred (in Dutch) last week to an interesting op-ed of Ross McKitrick on the regional performance of climate models. In that post he mentions an upcoming paper. That paper as well as a press release are now put online on McKitrick’s webpage.

The paper is a logical next step following several papers in which McKitrick showed that surface temperatures on land have a warm bias due to socioeconomic effects. In the new paper he looks how good different climate models are in reproducing regional temperature changes. It won’t surprise many that the models are not so good. The paper shows that a very simple economic model made better predictions.

Below is the full press release of the University of Guelph: Lees verder…


McKitrick: klimaatmodellen falen op regionaal niveau

Ross McKitrick heeft een eerste van twee opiniestukken over klimaatmodellen gepubliceerd in de Canadese Financial Post (een versie met literatuurverwijzingen staat hier). Aanleiding is een aanstaande publicatie in een klimaattijdschrift waarin hij zal voortborduren op eerder werk, waarin McKitrick aantoonde dat temperatuurtrends op land goed te verklaren zijn met socio-economische factoren en dus minder klimaat-gerelateerd zijn dan het IPCC aanneemt.

De discussie hierover is al jaren gaande en een van de meest beruchte climategate-e-mails uit 2004 gaat erover. Phil Jones schreef toen dat hij een paper van McKitrick en Michaels uit het volgende IPCC-rapport zou houden:

I can’t see either of these papers being in the next IPCC report. Kevin and I will keep them out somehow – even if we have to redefine what the peer-review literature is!

Tot nu toe heeft Mckitrick vooral gekeken naar correlaties tussen temperatuurtrends op land en allerlei socio-economische factoren (GDP, mate van industrialisatie etc.). Die correlaties zijn sterk. In zijn nieuwe paper zal hij laten zien in hoeverre (regionale) klimaatmodellen in staat zijn deze patronen te simuleren:

Lees verder…


Phil Jones: ‘Contact NMS’s for raw data’

Over at Climate Audit there is renewed interest in data availability with McIntyre asking whether journals that don’t guarantee data archiving (The Holocene in this case) should be cited in IPCC reports.

It happened that yesterday Phil Jones of CRU gave a talk at KNMI in De Bilt, The Netherlands, where he also talked about availability of data, in this case the data behind the recently published Crutem4 and Hadcrut4 graphs. The talk itself was pretty neutral, just explaining what had been done to produce these two datasets. However at the end Jones made a statement that is relevant to the long lasting discussions about data availability:

For raw temperature data you have to contact the NMS’s.

Lees verder…




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