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Aerosols: The Last Frontier? Aerossóis: A Última Fronteira?

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Guest commentary from Juliane Fry, UC Berkeley

The recently released IPCC 2007 Fourth Assessment Report Summary for Policymakers reminds us that aerosols remain the least understood component of the climate system. Aerosols are solid or liquid particles suspended in the atmosphere, consisting of (in rough order of abundance): sea salt, mineral dust, inorganic salts such as ammonium sulfate (which has natural as well as anthropogenic sources from e.g. coal burning), and carbonaceous aerosol such as soot, plant emissions, and incompletely combusted fossil fuel. As should be apparent from this list, there are many natural sources of aerosol, but changes have been observed in particular, in the atmospheric loading of carbonaceous aerosol and sulphates, which originate in part from fossil fuel burning. While a relatively minor part of the overall aerosol mass, changes in the anthropogenic portion of aerosols since 1750 have resulted in a globally averaged net radiative forcing of roughly -1.2 W/m2, in comparison to the overall average CO2 forcing of +1.66 W/m2.
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Fraser Institute fires off a damp squib

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New addition: Download an annotated pdf of the Fraser report. An interactive pdf file, to be read on the screen, is here, and a printable version is here. Suggestions for further commenting are welcome. Additions to the pdf have to be short, and tied to particular pieces of text or figures. And of course we will only incorporate comments that we deem to be scientifically sound and cogent.

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While most of the world’s climate scientists were following the IPCC fest last week, a few contrarians left out in the cold were trying to to organize their own party.

An unofficial, “Independent Summary for Policymakers” (ISPM) of the IPCC Fourth Assessment report has been delivered by the Fraser Institute. It’s a long, imposing-looking document, resembling, come to think of it, the formatting of the real Summary for Policymakers (SPM) document that was released on Friday after final negotiations of the IPCC in Paris last week. The Fraser Institute has assembled an awesome team of 10 authors, including such RC favorites as tilter-against-windmills-and-hockey-sticks Ross McKitrick, and other luminaries such as William Kininmonth, MSc, M.Admin — whose most recent paper is “Don’t be Gored into Going Along” in the Oct-Nov issue of Power Engineer. To be fair, he did publish a paper on weather forecasting, back in 1973. According to the press release, the London kickoff event will be graced by the presence of “noted environmentalist” David Bellamy. It’s true he’s “noted,” but what he’s noted for is his blatant fabrication of numbers purporting to show that the world’s glaciers are advancing rather retreating, as reported here.

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The IPCC Fourth Assessment SPM Le Quatrième Rapport d’Evaluation du GIEC – Résumé à l’intention des décideursA Quarta Avaliação do IPCC – Sumário para Tomadores de DeciçãoUluslararası Iklim Değişikliği Görevgücü’nün 4. Değerlendirme Raporunun Politika Belirliyicileri Icin ÖzetiEl resumen para responsables de políticas del cuarto informe de evaluación del IPCC

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We’ve had a policy of (mostly) not commenting on the various drafts, misquotes and mistaken readings of the Fourth Assessment report (“AR4” to those in the acronym loop) of the IPCC. Now that the summary for policy makers (or “SPM”) has actually been published though, we can discuss the substance of the report without having to worry that the details will change. This post will only be our first cut at talking about the whole report. We plan on going chapter by chapter, hopefully explaining the key issues and the remaining key uncertainties over the next few months. This report will be referenced repeatedly over the next few years, and so we can take the time to do a reasonable job explaining what’s in it and why.

Nous avons choisi (la plupart du temps) de ne pas commenter les diverses ébauches, citations incorrectes et erreurs de lecture du Quatrième Rapport d’Evaluation (« AR4 » pour les amateurs d’acronymes anglais ou « QRE » en français – version officieuse en français ici (fichier .doc)) du GIEC. Maintenant que le résumé à l’intention des décideurs (ou le « SPM ») a été publié, nous pouvons discuter le contenu du rapport sans crainte de changements des détails. Cet article sera notre première discussion du rapport entier. Nous avons l’intention de l’analyser chapitre par chapitre, en espérant expliquer les questions clefs et les principales incertitudes restantes au cours des mois à venir. Ce rapport sera largement cité au cours des années à venir, et nous pouvons prendre ainsi le temps d’expliquer ce qui est dans ce rapport et quelles en sont les raisons.
[Read more…] about The IPCC Fourth Assessment SPM Le Quatrième Rapport d’Evaluation du GIEC – Résumé à l’intention des décideursA Quarta Avaliação do IPCC – Sumário para Tomadores de DeciçãoUluslararası Iklim Değişikliği Görevgücü’nün 4. Değerlendirme Raporunun Politika Belirliyicileri Icin ÖzetiEl resumen para responsables de políticas del cuarto informe de evaluación del IPCC

Stern Science La science de SternA ciência de Stern

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Halldór Björnsson, William Connolley and Gavin Schmidt

Late last year, the UK Treasury’s Stern Review of the Economics of Climate Change was released to rapturous reception from all sides of the UK political spectrum (i.e. left and right). Since then it has been subject to significant criticism and debate (for a good listing see Rabbett Run). Much of that discussion has revolved around the economic (and ethical) issues associated with ‘discounting’ (how you weight welfare in the future against welfare today) – particularly Nordhaus’s review. We are not qualified to address those issues, and so have not previously commented.

However, as exemplified by interviews on a recent Radio 4 program (including with our own William Connolley), some questions have involved the science that underlies the economics. We will try and address those.
Halldór Björnsson, William Connolley and Gavin Schmidt (traduit par Etienne Pesnelle)

A la fin de l’an dernier, le Trésor britannique a publié le rapport Stern sur les conséquences économiques du changement climatique, qui a été reçu avec enthousiasme par l’ensemble de la classe politique du Royaume-Uni, c’est à dire la gauche et la droite Depuis, il a fait l’objet de nombreux débats et critiques (voir la liste qu’a établie Rabbett Run). L’essentiel de la discussion a tourné autour des problèmes économiques (et éthiques) associés à “l’actualisation” (c’est-à-dire comment mesurer le bien-être futur à l’aune du bien-être actuel), ce dont traite notamment Nordhaus . Nous ne sommes pas qualifiés pour discuter de ces points, aussi ne les avons-nous pas commentés précédemment.

Toutefois, comme l’illustrent les interviews données lors d’une émission récente de Radio 4 (dont une avec notre William Connolley), certaines questions ont concerné la science qui sous-tend les calculs économiques. Nous allons essayer de les aborder.
Halldór Björnsson, William Connolley e Gavin Schmidt (traduzido por F. M. Ramos e I. B. T. Lima)

No fim do ano passado, o Tesouro britânico publicou o Relatório Stern sobre as conseqüências econômicas das mudanças climáticas, que foi recebido com entusiasmo pelo conjunto da classe política do Reino Unido, isto é a esquerda e a direita. Depois, ele foi objeto de inúmeros debates e críticas (ver a lista que preparou Rabbett Run). O essencial da discussão realizou-se em torno dos problemas econômicos (e éticos) associados à “atualização” (isto é, como medir o bem-estar futuro em comparação ao bem-estar atual) – particularmente o Relatório Nordhaus. Nós não estamos qualificados para comentar estes assuntos, assim como não comentamos no passado.

No entanto, como ilustram as entrevistas concedidas durante um recente programa de Radio
4 (das quais uma com William Connolley), certas questões diziam respeito à ciência que sustenta os cálculos econômicos. Vamos tentar abordá-las a seguir. Ao contrário de um relatório mais antigo da Câmara dos Lordes, Stern não perde tempo tentando trapacear, e essencialmente busca a ciência no relatório do IPCC, com algumas atualizações de trabalhos mais recentes. A maior parte da ciência está resumida no capítulo um, e um leitor casual familiarizado com o relatório IPCC encontrará poucas surpresas em seções que incluem afirmações como “Uma massa esmagadora de evidências científicas indica que o clima da Terra está mudando rapidamente, predominantemente pelo efeito do crescimento dos gases de efeito estufa causado pelas atividades humanas” etc. Entretanto, as possibilidades científicas em Stern são ponderadas de maneira levemente diferente que nos relatórios do IPCC uma vez que, como ele afirma, “os tomadores de decisão devem levar em conta os riscos extremos, além das previsões médias, por que seria muito grave se estes riscos viessem a se materializar” (Stern reply to Byatt et al).

Há três componentes científicas no relatório Stern: a sensibilidade climática, as emissões futuras dos gases de efeito estufa, e os impactos de uma dada mudança, expressas na forma de anomalia de temperatura global por razões de comodidade.

A sensibilidade climática (já discutida aqui anteriormente) foi considerada como provavelmente estando no intervalo de 1.5 a 4.5 C do IPCC TAR, e no intervalo de 2 a 5 C nos modelos utilizados no relatório Stern. No entanto, a probabilidade de valores maiores tem um papel importante no relatório. Especificamente, Meinshausen* (2006) [estabelece] que há “entre 2% a 20% de probabilidade que o aquecimento possa ser maior que 5 C”. Isto é verdade, mas o relatório esquece de mencionar que outros novos estudos (Annan and Hargreaves; Hegerl et al) sugerem que é insignificante a probabilidade que a sensibilidade climática seja superior a 5 C.

A incerteza sobre o aquecimento futuro não se reduz à incerteza sobre a sensibilidade, mas depende também daquela relacionada aos níveis futuros dos gases de efeito estufa (GEE). Existe uma ampla gama de cenários e de estimativas sobre níveis futuros de GEE que são utilizados nos relatórios do IPCC. O cenário utilizado pelo Relatório Stern é o A2, mas neste cenário, os níveis de GEE na segunda metade do século XXI são superiores àqueles do cenário A1b, por exemplo. A questão não é se o cenário A2 é menos sólido que o A1, mas simplesmente que o Relatório Stern escolheu trabalhar com um dos cenários de “fortes emissões”. Além disso, o relatório reconhece também a grande incerteza (mas não claramente quantificável) de feedbacks positivos nas emissões de CO2 e CH4 de origem natural.

Com relação aos impactos das mudanças climáticas, a estória é semelhante: a maior parte dos impactos são declarados mas sua probabilidade de ocorrência é sujeita à debate. Por exemplo: o enfraquecimento da corrente termohalina sob 1 grau de aquecimento, risco de colapso em 3 graus, risco de derretimento irreversível da calota de gelo da Groenlândia para um aquecimento de 2 graus, a elevação dos mares de 5 a 12 metros durante muitos séculos, – estas eventualidades são questionáveis, e deveriam ser consideradas como “o cenário adverso” dentre os possíveis impactos.

Em conclusão: Stern de um modo geral utiliza bem a ciência do clima, mas desvia-se para o lado das estimativas mais impactantes e as utiliza em seu sumário. Este viés altista faz com que o relatório seja vulnerável a acusações de “alarmismo”. O relatório é justo em apontar que os danos e seus custos crescem de maneira desproporcional com o aumento da mudança de temperatura e portanto, dada esta assimetria, os tomadores de decisão têm razão de levá-los em conta. Entretanto, parece que a maior crítica deste relatório será atribuída (em outros foros) à parte econômica.

NB: De modo previsível, alguns dos “céticos” habituais atacaram igualmente a ciência do relatório Stern. No entanto, uma indicação de sua falta fundamental de seriedade é que, quando há realmente importantes incertezas (por exemplo, a probabilidade de que a sensibilidade seja superior àquela geralmente estimada), eles as ignoram para fazer as mesmas repetitivas, desinteressantes e incorretas afirmações que sempre fazem.

*Meinshausen, M. (2006): ‘What does a 2C target mean for greenhouse gas concentrations? A brief analysis based on multi-gas emission pathways and several climate sensitivity uncertainty estimates’ (“O que significa um alvo de +2°C em termos de concentração de gás de efeito estufa? Uma rápida análise fundamentada em caminhos de emissão multi-gás e várias estimativas de incerteza da sensibilidade climática”), Avoiding dangerous climate change (Evitando uma perigosa mudança climática), in H.J. Schellnhuber et al. (eds.), Cambridge: Cambridge University Press, pp. 265 a 280.
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How much CO2 emission is too much?

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This post is available in Slovak here (courtesy of Alexander Ač)

This week, representatives from around the world will gather in Nairobi, Kenya for the latest Conference of Parties (COP) meeting of the Framework Convention of Climate Change (FCCC) which brought us the Kyoto Protocol. The Kyoto Protocol expires in 2012, and the task facing the current delegates is to negotiate a further 5-year extension. This is a gradual, negotiated, no doubt frustrating process. By way of getting our bearings, a reader asks the question, what should the ultimate goal be? How much CO2 emissions cutting would it take to truly avoid “dangerous human interference in the climate system”? [Read more…] about How much CO2 emission is too much?

Tropical SSTs: Natural variations or Global warming?

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by Michael Mann and Gavin Schmidt

Roughly a year ago, we summarized the state of play in the ongoing scientific debate over the role of anthropogenic climate change in the observed trends in hurricane activity. This debate (as carefully outlined by Curry et al recently) revolves around a number of elements – whether the hurricane (or tropical cyclone) data show any significant variations, what those variations are linked to, and whether our understanding of the physics of tropical storms is sufficient to explain those links.

Several recent studies such as Emanuel (2005 — previously discussed here) and Hoyos et al (2006 — previously discussed here) have emphasized the role of increasing tropical sea surface temperatures (SSTs) on recent increases in hurricane intensities, both globally and for the Atlantic. The publication this week of a comprehensive paper by Santer et al provides an opportunity to assess the key middle question – to what can we attribute the relevant changes in tropical SSTs? And in particular, what can we say about Atlantic SSTs where we have the best data? [Read more…] about Tropical SSTs: Natural variations or Global warming?

Chinese whispers in Australia

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We decided months ago that we would not comment on leaks of the draft of the upcoming IPCC report (due Feb 2007) but we are prepared to correct obvious errors. The ongoing revisions of the text and the numerous drafts make any such commentary, let alone conclusions drawn from it, pretty pointless. This is even more true when the leaks are obviously confused about a central point. The principle error in the latest ‘exclusive’ is that the writer confuses a tightening of the estimate of climate sensitivity to 2xCO2 (as discussed here) with projections of climate change in 2100. These projections obviously depend on the uncertainties in the scenarios of future technology, economic progress and population (etc.) plus uncertainties in feedbacks related to the carbon or methane cycles. Unfortunately these have not been reduced since the last assessment report (and in some cases have actually increased).

That occasional stories will come out that get basic things wrong is unfortunate but not surprising. What is more troubling is that they subsequently get picked up by Reuters and UPI, and republished in places (such as Scientific American, though in their defence, it is simply a posting of the wire report) where the editors should know better. Worse still, the wire service stories are too brief to make the source of the error obvious, and thus the error gets propagated in an ever more confused state. As usual the blogsphere is playing a key role in amplifying and further muddying the story. The advantage of blogs is that errors can be corrected quickly, and the comments on Prometheus for instance, quickly revealed the confusion and the potential agenda of the original story.

There will be plenty of time to discuss the new IPCC report when it comes out and where everyone can read for themselves what has and what hasn’t changed since 2001. Until then, we would counsel against journalists and editors jumping at supposed ‘exclusives’ and – more dangerously – going ahead with them without even a basic sanity check of the details.

IPCC draft: No comment.

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As everyone has now realised, the second-order draft of the new IPCC report has become very widely available and many of the contributors to this site, commenters and readers will have seen copies. Part of the strength of the IPCC process are the multiple stages of review – the report is already significantly improved (in clarity and scientific basis) from the first round of reviews, and one can anticipate further improvements from the ongoing round as well. Thus no statements from this draft report can be considered ‘official’. While most of the contents of the report will come as no surprise to frequent visitors here, we have decided that we are not going to discuss the report until it is finalised and released (sometime in February 2007). At that time, we’ll go chapter by chapter hopefully pulling out the interesting bits, but until then, we feel it’s more appropriate to respect the ‘Do not cite or quote’ injunctions that can be found on every page. We trust that our commenters will likewise respect the process. Patience, people, patience!

Lawson vs. the IPCC

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Nigel Lawson, one of Britain’s Chancellors of the Exchequer during the Thatcher Era (Secretary of the Treasury for those needing a US translation) and more recently known as the father of Nigella Lawson (a UK cooking diva), has weighed into the climate debate with a recent broadside calling for the abolition of the IPCC (Intergovernmental Panel on Climate Change). Based on a curious report by the UK House of Lords Economics Affairs committee (in which they made clear that they had no scientific expertise), Lawson demands that the only global scientific assessment process on climate change be shut down, and replaced with ….well what exactly? [Read more…] about Lawson vs. the IPCC

Make your own forecasts of future energy, carbon emissions, and climate

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Over the years, IPCC has issued numerous scenarios describing the trajectory of civilization and what they may mean for CO2 emissions and the like. The most famous of these is the “Business-as-Usual” scenario, also called IS92A, although this has been supplanted somewhat by the SRES familiy of storylines that have been discussed here often.

While the different storylines and assumptions can be a little confusing, the ingredients for making such a forecast can be fairly simple, and I have coded them up into an interactive web site which can be used to explore the world of possibilities. The prediction is based on an idea called the Kaya identity, using numbers published by Hoffert et al. in Nature 1998 [Hoffert et al., 1998]. You could just read the excellent Hoffert et al. paper, but you might also enjoy playing with your own “live” forecasting model, located here.

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