There has been a lot in the news recently about current volcanic activity – Merapi in Indonesia and Bezymianny in the Kamchatka peninsula in Russia, but while most reports have focussed on the very real dangers to the local populace and air traffic, volcanoes can have important impacts on climate as well. However, there are a number of conditions that need to be fulfilled before an eruption will show up in the climate record. [Read more…] about Current volcanic activity and climate?
Aerosols
Global Dimming and climate models
Guest posting from Beate Liepert (LDEO)
On April 18th PBS will air the NOVA documentary “Dimming the Sun” which stirred up lively discussions among scientists and non-scientists when originally shown by BBC in the UK (under the name ‘Global Dimming’ – see our previous posts). [The NOVA version has been thoroughly re-edited and some of the more controversial claims have apparently been excised or better put into context [and we look forward to seeing it! – Ed.].
Global dimming is the phenomena of an observed reduction (about 1-2% per decade since ~1960) of sunlight reaching the surface of the Earth caused by air pollution (aerosols – small particles) and cloud changes. Some of this solar energy is reflected back out to space and this cooling effect is believed to have counteracted part of the greenhouse gas warming. The original version of the film focused mainly on the observational recognition of global dimming, but one aspect did not receive much attention in the film – namely the oft-claimed lack of global dimming in climate models. This led some to assume that climate modelers were ignoring air pollution other than greenhouse gases emissions from fossil fuel burning. Another implication was that climate models are not capable of adequately simulating the transfer of sunlight through the atmosphere and the role of clouds, sunlight extinction of aerosols and aerosol effects on clouds etc, and therefore model projections should not be trusted. The NOVA version will address this issue more prominently by adding an interview with Jim Hansen from NASA Goddard Institute for Space Studies. Along this line, I’d like to elaborate on aerosols in climate models in more detail. [Read more…] about Global Dimming and climate models
Richard Lindzen’s HoL testimony
Prof. Richard Lindzen (MIT) is often described as the most respectable of the climate ‘sceptics’ and is frequently cited in discussions here and elsewhere. Lindzen clearly has many fundamentally important papers under his belt (work on the QBO and basic atmospheric dynamics), and a number of papers that have been much less well received by the community (the ‘Iris’ effect etc.). Last year, he gave evidence to and answered questions from, a UK House of Lords Committee investigating the economics of climate change, in which he discoursed freely on the science. I’ll try here to sort out what he said. [Read more…] about Richard Lindzen’s HoL testimony
An Aerosol Tour de Forcing
Guest commentary from Ron Miller and Dorothy Koch (NASA GISS)
Scientists have confidence in a result to the extent that it can be derived by different investigators. Their confidence is increased if different techniques lead to the same conclusion. Concurrence provides evidence that the conclusion does not depend upon assumptions that occasionally are insufficiently supported. In contrast, two articles published last December on the same day arrive at very different and incompatible estimates of the effect of human-made aerosols on the radiative budget of the planet (Bellouin et al., 2005; Chung et al., 2005). They follow an earlier estimate published last year, (which included Dorothy as a co-author) that was in the middle (Yu et al., 2005). Aerosols are important to climate partly because their concentration is increased by the same industrial processes that increase the atmospheric concentration of greenhouse gases; yet aerosols generally oppose greenhouse warming. Because aerosols cause respiratory and other health problems and acid rain, they have been regulated more aggressively than greenhouse gases. Concentrations of some aerosols have decreased over the United States and Europe in recent decades as a result of environmental laws, although an increase has been observed in many thrid world regions, where economic development is a priority. In the twenty-first century, aerosol levels are anticipated to drop faster than greenhouse gases in response to future emission reductions, which will leave greenhouse warming unopposed and unmoderated.
Each published calculation of aerosol radiative forcing was a tour de force for integrating a wide variety of measurements ranging from absorption of radiation by individual particles to satellite estimates of aerosol amount. The disparate results emphasize the complexity and difficulty of the calculation. But let’s start at the beginning…. [Read more…] about An Aerosol Tour de Forcing
What is a first-order climate forcing?
Roger Pielke Sr. (Colorado State) has a blog (Climate Science) that gives his personal perspective on climate change issues. In it, he has made clear that he feels that apart from greenhouse gases, other climate forcings (the changes that affect the energy balance of the planet) are being neglected in the scientific discussion. Specifically, he feels that many of these other forcings have sufficient ‘first-order’ effects to prevent a clear attribution of recent climate change to greenhouse gases.
In general, I heartily agree – other forcings are important, even essential, for understanding observed climate variability and, as a community, we are only just starting to get to grips with some of the more complicated effects. Obviously, though, not all forcings are of the same magnitude (either globally or regionally) and so it is useful to separate the ‘first-order’ forcings from those that are relatively minor. But what exactly is ‘first-order’ and what is not? [Read more…] about What is a first-order climate forcing?
Climate sensitivity and aerosol forcings
In a new review paper in Nature this week, Andreae, Jones and Cox expand on the idea that uncertainty in climate sensitivity is directly related to uncertainty in present day aerosol forcing (see also this New Scientist commentary). This was discussed here a couple of months back in the Global Dimming and the climateprediction.net posts, and so it is worth revisiting the question in the light of their analysis.
Global Dimming may have a brighter future Un avenir brillant pour l’assombrissement global ?
A while ago, we wrote about Global Dimming – a reduction in downward solar radiation of about 4% or about 7W/m2 from 1961 to 1990 was found at stations worldwide. We said at the time that there were hints of a recovery underway post-1990; now research has been published showing this. From Dimming to Brightening: Decadal Changes in Solar Radiation at Earth’s Surface by Martin Wild et al. (Science 6 May 2005; 308: 847-850; subscription required for link) uses surface measurements; Do Satellites Detect Trends in Surface Solar Radiation? by Pinker et al., Science 2005 308: 850-854 uses satellites; both find a recovery of surface downward radiation since about 1990.
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[Read more…] about Global Dimming may have a brighter future
Pollution-Climate Connections Liens entre Pollution et Climat
Guest commentary by Loretta Mickley, Harvard University
Every summer over much of the United States, we brace ourselves for heat waves. During these periods, the air turns muggy and usually smoggy. After a few days, a cold front moves in, sweeping away the pollution and ending the heat. Given that we are on a path towards global warming, atmospheric chemists are asking how climate change could affect air quality. Will warmer temperatures mean more pollution during these episodes? Will episodes last longer? Most importantly, what effect will changes in air quality have on human health?
Tous les étés, dans la plupart des régions des USA, nous nous préparons aux vagues de chaleur. Pendant ces périodes, l’air devient très humide et généralement brumeux. Après quelques jours, un front froid survient, balayant la pollution et mettant fin à la chaleur. Etant donné que nous nous acheminons vers un réchauffement global, les spécialistes de la chimie de l’atmosphère se demandent de quelle façon le changement climatique pourrait affecter la qualité de l’air. Des températures plus élevées signifieront-elles plus de pollution durant ces épisodes ? Ces épisodes dureront-ils plus longtemps ? Plus important : quels sont les effets des changements dans la qualité de l’air sur la santé humaine ?
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[Read more…] about Pollution-Climate Connections
Global Dimming II Assombrissement Global II
Guest commentary on BBC documentary on “Global Dimming” aired on January 13th 2005 by Beate Liepert, LDEO, Columbia University
I haven’t yet seen the documentary. I have only read the transcript and hence was spared the pictures of the potential apocalypse and the invocation of biblical-scale famines. However, as one of the lead scientists on the topic [and who was interviewed by the BBC for the Horizon documentary (transcript, previous post)], I feel I should explain a few things about it without using religious analogies and stoking unnecessary fear.
First though, this is a nice example of the power of words: Gerry Stanhill coined the observed reduction in solar energy reaching the ground “global dimming”. He called it “global” dimming because the technical term for the radiative energy is called “global solar radiation” and it contrasts nicely with the more common “global warming”.
par Beate Liepert, LDEO, Columbia University (traduit par Pierre Allemand)
Je n’ai pas encore vu le documentaire. J’ai seulement lu la transcription, et je n’ai donc pas été touché par les images d’une apocalypse potentielle et par l’évocation de famines à l’échelle biblique. Cependant, en tant que l’un des scientifiques leader du sujet, [et qui a été interviewé par la BBC pour le documentaire de la série Horizon, (transcription et article précédent)], je me sens dans l’obligation d’approfondir quelques détails sans utiliser d’analogie religieuse ni déclencher d’inutiles inquiétudes.
Première idée : voici un bel exemple du pouvoir des mots : Gerry Stanhill qualifie la réduction observée de l’énergie solaire atteignant le sol, d’ “assombrissement global”. Il l’a appelé assombrissement “global” parce que le terme technique pour l’énergie de radiation est “rayonnement solaire global” et il s’oppose ainsi élégamment au terme plus courant de “réchauffement global”.
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[Read more…] about Global Dimming II
Global Dimming? Assombrissement global?
It just so happens that most of the posts on this site have tried to counteract arguments from those who would sow fake “uncertainty” in the climate debate. But lest our readers feel that we are unjustifiably certain about our knowledge, let us look at a recent example of the opposite tendency: too much certainty.
A recent BBC Horizon documentary (transcript) raised the issue of ‘global dimming’ and argued that this ‘killer’ phenomena’s newly-recognised existence would lead to huge re-assessments of future global warming. As part of the hyperbole, the process of global dimming was linked very clearly to the famines in Ethiopia in the 1980s and the implication was left that worse was to come. Media reports with headlines like “Fossil Fuel Curbs May Speed Global Warming” swiftly followed. So what’s the real story?
Il est un fait que la plupart des interventions sur ce site ont essayé de contrer les arguments de ceux qui voudraient semer une “incertitude” trompeuse dans le débat sur le climat. Mais, de peur que nos lecteurs pensent que nous sommes abusivement certains de nos connaissances, examinons un exemple récent de la tendance inverse : trop de certitude.
Un récent documentaire de la série “Horizon” de la BBC (transcription) a soulevé la question d’un “assombrissement global” et a indiqué que l’existence récemment reconnue d’un tel phénomène « tueur » pourrait amener à reconsidérer très fortement l’hypothèse d’un futur réchauffement global. Cet audacieux raisonnement faisait un lien très clair entre l’assombrissement global et les famines en Ethiopie durant les années 1980, le plus grave restant encore à venir. Des dépêches de presse avec des titres du genre « Le coup de frein sur les énergies fossiles pourrait accélérer le réchauffement global » suivaient dans la foulée. Mais, qu’en est-il exactement ?
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[Read more…] about Global Dimming?