RealClimate

Climate science from climate scientists...

You are here: Home / Archives for Climate Science

Climate Science

Round up and thanks

by

A few tidbits from around that may be of interest:

  • Tom Yulsman is running a new blog (now linked in our blogroll) for the Center for Environmental Journalism at U. Colorado, Boulder, covering climate change as one of his ‘beats’.
  • The Global Roundtable on Climate Change (GROCC), made up of business leaders, NGOs and academics released a statement on climate change. (Coverage BBC, Reuters)
  • The UN Foundation (an independent NGO established to support the UN mission) has helped put together a site called ‘IPCC facts‘ to help with the outreach associated with the IPCC Fourth Assessment. We haven’t examined every page, so if there are any questions, this is as good a place as any to go over them.

On the lighter side, those people who are fond of the offsetting concept (usually applied to carbon emissions) may find this site interesting (hat tip to Yarrow).

Finally, the more multi-lingual of our readers may have noticed the proliferation of translations of RC posts in recent weeks. We now have regular contributors translating articles into French, Slovak, Swedish and Portugeuse (as denoted by the hybrid flags associated with relevant articles). We can offer them nothing more than our deep gratitude – recent contributions have been from: Valérie Masson-Delmotte, Fernando Manuel Ramos and Ivan Bergier Tavares de Lima (ClimaGaia), Alexander Ač, Olivier Daniélo, Etienne Pesnelle, Jacob Wallström and Yves Fouquart. Many thanks to all!

(And if anyone else would like to help out on an occasional basis translating posts to their native language, please let us know. )

Update: And now turkish! (thanks to Figen Mekik).

Climate Reporting in Physics World Reportagem sobre o Clima na Physics World

by

PhysicsWorld cover, Volume 20, no. 2, February 2007 The February 2007 issue of PhysicsWorld contains several articles relevant to climate research, with a main feature article on climate modelling written by Adam Scaife, Chris Folland, and John Mitchell, and a profile on Richard Lindzen as well as an article on geoengineering in the ‘News & Analyses’ section. The magazine also contains an article (‘Living in the greenhouse’) under ‘Lateral Thoughts’ that brings up a bunch of tentative analogies to a wide range of topics completely unrelated to the greenhouse effect in a technical sense, and an editorial comment ‘Hot topic‘, arguing that it would be wrong of PhysicsWorld to ignore those outside the mainstream. To be more precise, the editorial comment devotes a few lines justifying the profile on Lindzen and the report on geoengineering, with a reference to a Feynman quote: “There is no harm in doubt and scepticism, for it is through these that new discoveries are made”. Wise words! Nevertheless, I cannot resist making some reflections.

[Read more…] about Climate Reporting in Physics World Reportagem sobre o Clima na Physics World

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

by

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.
[Read more…] about Aerosols: The Last Frontier? Aerossóis: A Última Fronteira?

Save the World! Earn $25 million! Dünya’yı Kurtar! 25 Milyon Dolar Kazan!Sauvez la planète ! Gagnez 25 millions de dollars !

by

Guest commentary from Juliane Fry, UC Berkeley

On February 9, The Virgin Group chairman Sir Richard Branson announced a $25 million prize for anyone who can demonstrate “a commercially viable design which results in the removal of anthropogenic, atmospheric greenhouse gases so as to contribute materially to the stability of Earth’s climate.” At the press conference announcing this “Virgin Earth Challenge”, Branson was joined by Al Gore, and the panel of judges for the competition includes additional climate change celebrities: James Hansen, James Lovelock, Tim Flannery, and Sir Crispin Tickell.

The goal of the competition is to find a method that will remove at least 1 billion tons of carbon per year from the atmosphere. It will be very interesting to see what ideas come to the fore to scrub CO2 from the atmosphere. $25m should encourage some creativity! (and of course, once working should bring in a significant amount of carbon offset money). A ruckus was caused last year when discussion of injecting SO2 into the stratosphere to form reflective sulfate aerosols to mask global warming made scientists feel they needed to state their position on this controversial, poorly understood proposal. During the discussion, a New York Times feature (described here ) discussed various “geo-engineering” alternatives to exert a cooling effect to mask global warming. At least in this case, we are not seeking to add something new and uncertain to the atmosphere, but rather, remove something that we added.

Comentário convidado de Juliane Fry, UC Berkeley (tradução de F. M. Ramos e I. B. T. Lima)

No dia 9 de fevereiro, o presidente do Grupo Virgin, Sir Richard Branson, anunciou um prêmio de US$ 25 milhões para quem demonstrar “a viabilidade comercial de algum projeto para retirada da atmosfera de gases de efeito estufa de origem antropogênica, para contribuir materialmente para a estabilidade do clima da Terra”. Na coletiva de imprensa que lançou o desafio, batizado de “Virgin Earth Challenge“, Branson estava acompanhado de Al Gore, e o corpo de jurados da competição incluía outras celebridades das mudanças climáticas como James Hansen, James Lovelock, Tim Flannery, e Sir Crispin Tickell.

O objetivo da competição é encontrar um método que seja capaz de remover pelo menos 1 bilhão de toneladas de carbono por ano da atmosfera. Será muito interessante observar que idéias surgirão para varrer CO2 da atmosfera. US$ 25M devem suscitar alguma criatividade! (e naturalmente, uma vez implementado, proporcionar muito dinheiro na forma créditos de compensação de carbono). No ano passado, o barulho causado pela proposta de injeção de SO2 na estratosfera para formar uma camada refletiva de aerossóis de sulfato, de modo a neutralizar o aquecimento global, forçou muitos cientistas a tomar uma posição clara a respeito desta proposta controvertida e pouco compreendida. Durante os debates, uma matéria do New York Times (descrita aqui) discutiu várias alternativas de “geo-engenharia” para criar um mecanismo de resfriamento de mascarasse o aquecimento global. Pelo menos neste caso, não estamos procurando adicionar algo novo e incerto na atmosfera, mas ao contrário, retirar algo que foi adicionado.



Misafir yazar Juliane Fry, California Üniversitesi, Berkeley (Ingilizce’den çeviren: Figen Mekik)

9 Şubat gunu, The Virgin Group’un (Bakir Grup) başkanı, Sir Richard Branson 25 milyon dolar ödüllü bir yarışma açıklamasında bulundu. Yarışmanın amacı dünya’nın küresel iklimini dengeleyebilecek yeni bir tasarım üretmek. Insanlar tarafından atmosferdeki yoğunluğu artırılan sera gazlarını eksiltebilen ve bunu en ucuz şekliyle başarabilen tasarımcıya 25 milyon dolar ödül verilecek. Bu Bakir Dünya Yarışmasının açıklandığı basın toplantısına, Branson’a Al Gore eşlik ettiği gibi, yarışmada hakemlik yapacak panelde yer alan diğer iklim meşhurları da katıldılar: James Hansen, James Lovelock, Tim Flannery ve Sir Crispin Tickell.

Yarışmanın amacı yılda en az 1 milyar ton karbonu atmosferden çekebilen bir yöntem geliştirmek. Atmosferdeki fazla karbon dioksidi yok etmek için ne çeşit fikirlerin ortaya atılacağını görmek çok ilginç olacak. Eh, 25 milyon dolar biraz yaratıcılığı teşvik eder herhalde (ve tabii ki, bu yeni yöntemler uygulandığında kâr da artar). Geçen sene küresel ısınmayı maskelemek amacıyla stratosfere SO2 aktarılarak yaratılacak parlak sülfat taneciklerinin (aerosol) iklimi soğutma etkisi tartışıldığında bir hayli gürültü koptu. Bilimciler çok tartışmaya sebep olan ve pek iyi anlaşılamayan bu konu hakkındaki tutumlarını açıkça beyan etmek istediler. Bu tartışma dahilinde New York Times’da çıkan bir yazı (tarifi burada) küresel ısınmanın etkilerini azaltmayı amaçlayan başka jeo-teknik çözümler önerdi. En azından bu sefer, bu 25 milyon dolarlık yarışmayla atmosfere yeni ve etkisi henüz tam kestirilemeyen bir şey eklemeyen bir çözüm aranıyor.


Juliane Fry, UC Berkeley, Traduit par Etienne Pesnelle

Le 9 février dernier, Richard Branson, président du groupe Virgin, a annoncé qu’il offrait 25 millions de dollars à quiconque pourra présenter « une invention commercialement viable qui permette de retirer de l’atmosphère les gaz à effet de serre d’origine anthropique, de façon à contribuer sensiblement à la stabilisation du climat de la Terre ». A la conférence de presse où il annonçait son « « Défi Virgin pour la Terre » », Branson a été rejoint par Al Gore, et le comité des juges de ce concours comprend d’autres célébrités du réchauffement climatique : James Hansen, James Lovelock, Tim Flannery, et Sir Crispin Tickell.

L’objectif du concours est de trouver une méthode qui pourra retirer de l’atmosphère au moins un milliard de tonnes de carbone par an. Il va être très intéressant de voir quelles idées de nettoyage de l’atmosphère vont émerger. 25 millions de dollars devraient encourager la créativité ! (et bien sûr, quand ça fonctionnera, ça devrait rapporter une somme significative en crédits de compensations d’émissions de carbone). Il y eut du grabuge l’année dernière, quand le débat à propos de l’injection de SO2 dans la stratosphère, visant à produire des sulfates en aérosol réfléchissant la lumière solaire qui contreraient le réchauffement climatique, a donné l’impression aux scientifiques qu’ils avaient besoin d’exposer leur position sur cette proposition mal comprise et controversée.

Durant ce débat, un article de fond du *New York Times* (décrit ici) a commenté les différentes options de « géo-ingénierie » ayant un effet refroidisseur contrant le réchauffement climatique. Au moins cette fois-ci, on ne cherche pas à ajouter quelque chose de nouveau et d’incertain à l’atmosphère, mais bien à en retirer ce qu’on y a ajouté.

What triggers ice ages? O que Dispara as Eras Glaciais? Buzul Çağlarını Tetikleyen Nedir?Qu’est ce qui déclenche les glaciations?

by

by Rasmus Benestad, with contributions from Caspar & Eric

In a recent article in Climatic Change, D.G. Martinson and W.C. Pitman III discuss a new hypothesis explaining how the climate could change abruptly between ice ages and inter-glacial (warm) periods. They argue that the changes in Earth’s orbit around the Sun in isolation is not sufficient to explain the estimated high rate of change, and that there must be an amplifying feedback process kicking in. The necessity for a feedback is not new, as the Swedish Nobel Prize winner (Chemistry), Svante Arrhenius, suggested already in 1896 that CO2 could act as an amplification mechanism. In addition, there is the albedo feedback, where the amount of solar radiation that is reflected back into space, scales with the area of the ice- and snow-cover. And are clouds as well as other aspects playing a role.

por Rasmus Benestad, com contribuições de Caspar & Eric

Em um artigo recente da Climatic Change, D.G. Martinson e W.C. Pitman III discutem uma nova hipótese que explica como o clima pode mudar abruptamente entre eras glaciais e períodos interglaciais (quentes). Eles argumentam que as mudanças na órbita da Terra ao redor do Sol em isolado não são suficientes para explicar as altas taxas de mudanças estimadas, e que deve necessariamente haver a ação de um mecanismo de feedback (ou retro-alimentação) amplificando o processo. A necessidade de um feedback não é nova, pois o sueco ganhador do Prêmio Nobel (Química), Svante Arrhenius, já havia sugerido em 1896 que o CO2 deveria agir como um mecanismo de amplificação. Além do mais, existe o feedback do albedo, pelo qual a quantidade de radiação solar que é refletida de volta ao espaço é escalonável com a área de cobertura de gelo e neve. E existem nuvens bem como outros aspectos envolvidos.

Orbital forcing A hipótese de Martinson & Pitman III formula que a entrada de água doce funciona em consonância com o ciclo de Milankovitch e o feedback de albedo. Eles concluem que os ‘maiores’ términos podem somente acontecer após um acúmulo de gelo grande o suficiente para isolar o Artico, inibindo o fluxo de entrada de água doce até um ponto em que o aumento da salinidade na camada superficial, através de um vagaroso e contínuo crescimento do gelo marinho, causa uma inversão das águas marinhas do Ártico (pelo efeito na circulação atmosférica e nas correntes oceânicas). A inversão vertical traz água quente de baixo para cima, promovendo condições mais favoráveis ao degelo. A salinidade também tem um papel, mas a hipótese não menciona variações de gases de efeito estufa (GEE). Algumas questões: Martinson e Pitman III esqueceram disso? Ou os GEE representam somente uma pequena contribuição? E, não poderiam as mudanças nos GEE explicar boa parte da variabilidade? Por outro lado, parece plausível que mudanças na salinidade e na entrada de água doce poderiam afetar a formação de gelo marinho e a convecção profunda. Contudo, até o presente, a hipótese proposta por Martinson and Pitman III é meramente uma especulação, e estamos aguardando para ver se a hipótese pode ser testada através de experimentos de modelos numéricos (o que pode requerer modelos oceânicos e de gelo marinho com maior resolução que os atualmente usados em modelos climáticos globais). Seria interessante conduzir experimentos para avaliar a significância individual da água doce, dos GEE e o efeito combinado.

Uma reação ao trabalho de Martison e Pittman é: Onde está o cálculo de energia? Gases de efeito estufa contribuem somente com alguns W/m2, em contraste com uma forçante >40 do ciclo sazonal de Milankovich. Para esta nova idéia ter mérito, teria sido melhor ter no mínimo fluxos de calor em paralelo com a forçante radioativa do CO2. Estudos de modelagem anteriores encontraram que GEE produzem aproximadamente 50% de todo Último Máximo Glacial (inglês, LGM) para a resposta da temperatura atual (veja por exemplo Broccoli & Manabe), a outra parte sendo o albedo, etc., que respondem ao ciclo sazonal de irradiância. É muito difícil isolar completamente as causas individuais pois as mudanças nos GEE podem produzir alterações na distribuição de nuvens e gelo marinho. Mas a grosso modo, se você rodar um LGM e somente somente reduzir o nível do mar, introduzir as calotas de gelo, mudar a vegetação, adicionar alguma poeria (embora esta ainda seja grosseira), então você alcançaria ao redor de 50% do caminho que você quer ir. Mude a concentração de GEE e você chegaria mais próximo. Isso é mais ou menos o que Manabe e Stouffer mostraram há quinze anos atrás. A questão é se realmente precisamos de algo mais, e se esse ‘algo mais’ tem força suficiente.

traduzido por Ivan B. T. Lima e Fernando M. Ramos.


[Read more…] about What triggers ice ages? O que Dispara as Eras Glaciais? Buzul Çağlarını Tetikleyen Nedir?Qu’est ce qui déclenche les glaciations?

Cold Case vs. CSI

by

If you are a follower of TV crime shows, it is likely that you’ve come across one of the CSI offshoots (CSI stands for Crime Scene Investigation) and a slightly less well known show called ‘Cold Case‘. In both these shows, difficult crimes (usually murders) are solved using the most up-to-date forensic methods and incredible detective work. However, it will be obvious to even the most jaded TV watcher that the CSI crew get to have a lot more fun with the latest gadgets and methodologies. The reason for that is clear: with a fresh crime scene there is a lot more evidence around and a lot more techniques that can be brought to bear on the problem. In a ‘Cold Case’ (where the incident happened years before), options are much more limited.

Why bring this up here? Well it illustrates nicely how paleo-climate research fits in to our understanding of current changes. Let me explain….
A partial translation of this article in Slovak is available here (courtesy Alexander Ač).
[Read more…] about Cold Case vs. CSI

Nigel Calder in the Times

by

As a prelude to a new book, Nigel Calder (who was the editor of New Scientist for four years in the 1960s) has written an op-ed for the Times (UK) basically recapitulating the hype over the Svensmark cosmic ray/climate experiments we reported on a couple of month ago (see Taking Cosmic Rays for a spin). At the time we pointed out that while the experiments were potentially of interest, they are a long way from actually demonstrating an influence of cosmic rays on the real world climate, and in no way justify the hyperbole that Svensmark and colleagues put into their press releases and more ‘popular’ pieces. Even if the evidence for solar forcing were legitimate, any bizarre calculus that takes evidence for solar forcing of climate as evidence against greenhouse gases for current climate change is simply wrong. Whether cosmic rays are correlated with climate or not, they have been regularly measured by the neutron monitor at Climax Station (Colorado) since 1953 and show no long term trend. No trend = no explanation for current changes.

WSJ Editorial Board: Head Still Buried in the Sand

by

While the rest of the world has basically accepted the conclusion of the latest IPCC report, one small village still holds out against the tide – the Wall Street Journal editorial board. This contrasts sharply with the news section of the paper which is actually pretty good. They had a front-page piece on business responses to global warming issues which not only pointed out that business was taking an interest in carbon reduction, but the article more or less took as a given that the problem was real. However, as we have pointed out before, the editorial pages operate in a universe all their own.

This would not be of much concern if the WSJ wasn’t such an influential paper in the US. However, the extent of its isolation on this issue is evident from the amusing reliance on the error-prone Christopher Monckton. They quote him saying that the sea level rise predictions were much smaller than in IPCC TAR (no they weren’t), that the human contribution to recent changes has been ‘cut by a third’ (no it hasn’t), and that the Summary for Policy Makers (SPM) was written by politicians (no it wasn’t – the clue is in the name).

Even more wrong is the claim that “the upcoming report is also missing any reference to the infamous ‘hockey stick’ “. Not only are the three original “hockey stick” reconstructions from the IPCC (2001) report shown in the (draft) paleoclimate chapter of the new report, but they are now joined by 9 others. Which is why the SPM comes to the even stronger conclusion that recent large-scale warmth is likely to be anomalous in the context of at least the past 1300 years, and not just the past 1000 years.

Thus on any index of wrongness, this WSJ editorial scores pretty high. What puzzles us is why their readership, who presumably want to know about issues that might affect their bottom line, tolerate this rather feeble denialism. While we enjoy pointing out their obvious absurdities, their readers would probably be better off if the WSJ accepted Jeffery Sachs’ challenge. For if they can’t be trusted to get even the basic checkable facts right on this issue, why should any of their opinions be taken seriously?

Enquanto o resto do mundo tem aceitado a conclusão do último relatório do IPCC, uma pequena cidade ainda permanece contra a maré – o corpo editorial do Wall Street Journal. Isso contrasta nitidamente com a seção de notícias do jornal que é muito boa. Eles publicaram uma matéria sobre as respostas dos mercados para as questões de aquecimento global que não apenas apontava que os mercados estão cada vez mais interessados na redução de carbono, mas o artigo de certo modo tomava como certo que o problema é real. No entanto, como já apontamos anteriormente, as páginas do editorial operam em um universo próprio.

Isso não seria muito preocupante se o WSJ não fosse um jornal influente nos Estados Unidos. Contudo, a extensão de seu isolamento sobre essas questões é evidente pela divertida confiança que tem o propenso Christopher Monckton. Eles o citam dizendo que as previsões de aumento do nível do mar foram muito menores que aquelas do IPCC TAR (não eram), que a contribuição humana para as recentes mudanças foram ‘cortadas em um terço’ (não foram), e que o Sumário para Tomadores de Decisão (SPM) foi escrito por políticos (não foi, a dica está no seu próprio nome).

Ainda mais errado é a declaração de que “no futuro relatório falta qualquer referência à famosa curva ‘taco de róquei’. Não somente as três reconstruções originais dos ‘tacos de róquei’ do relatório IPCC (2001) são mostrados no capítulo (rascunho) de paleoclima do novo relatório, mas estas são agora fundidas com mais outras nove reconstruções. Essa é a razão para que o SPM venha com uma conclusão ainda mais contundente de que o recente aquecimento de larga escala é provavelmente anômalo no contexto de no mínimo 1300 anos atrás, e não somente nos últimos 1000 anos.

Assim, em qualquer índice de erro, este editorial do WSJ pontua muito alto. O que nos deixa intrigados é porque seus leitores, os quais presumidamente querem saber sobre as questões que podem afetar suas próprias bases, toleram um negacionismo tão fraco. Enquanto nos deleitamos em apontar seus óbvios absurdos, seus leitores deveriam provavelmente estar melhor servidos se o WSJ aceitasse o desafio de Jeffery Sachs. Se eles não podem ser confiáveis mesmo nos fatos mais básicos sobre essa questão, qual a razão para se acreditar seriamente em quaisquer de suas outras opiniões?

Por Ivan Bergier Tavares de Lima e Fernando Manuel Ramos

Fraser Institute fires off a damp squib

by

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.

*****************

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.

[Read more…] about Fraser Institute fires off a damp squib

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

by

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