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Greenhouse gases

What is a first-order climate forcing?

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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

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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.

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The Acid Ocean – the Other Problem with CO2 Emission

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The Royal Society has just issued a summary report on the effects of CO2 on the pH chemistry of seawater and aquatic organisms and ecosystems. In addition to its pivotal role in the atmosphere in the regulation of global climate, CO2 and its sister chemical species, HCO3– and CO32- comprise the carbonate buffer system which regulates the pH of seawater. The new report can be found here. Acidifying the ocean is particularly detrimental to organisms that secrete shell material made of CaCO3, such as coral reefs and a type of phytoplankton called coccolithophorids [Kleypas et al., 1999]. The ocean pH change will persist for thousands of years. Because the fossil fuel CO2 rise is faster than natural CO2 increases in the past, the ocean will be acidified to a much greater extent than has occurred naturally in at least the past 800,000 years [Caldeira and Wicket, 2003].

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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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How much of the recent CO2 increase is due to human activities?

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Translations: (Français) (English)

Contributed by Corinne Le Quéré, University of East Anglia.

This question keeps coming back, although we know the answer very well: all of the recent CO2 increase in the atmosphere is due to human activities, in spite of the fact that both the oceans and the land biosphere respond to global warming. There is a lot of evidence to support this statement which has been explained in a previous posting here and in a letter in Physics Today . However, the most convincing arguments for scientists (based on isotopes and oxygen decreases in the atmosphere) may be hard to understand for the general public because they require a high level of scientific knowledge. I present simpler evidence of the same statement based on ocean observations, and I explain how we know that not only part of the atmospheric CO2 increase is due to human activities, but all of it.

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2005 Record Arctic Ozone Loss

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You read it here first!


Update (09/05/05): Markus Rex was kind enough to send us the full figure from which Nature made their thumbnail, and which is a little clearer. He also cautions that the 2005 numbers are still preliminary, however there is a clear trend towards increasing potential for Arctic ozone loss, which is realised or not depending on the vagaries of each individual winter.

Planetary energy imbalance?

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The recent paper in Science Express by Hansen et al (on which I am a co-author) has garnered quite a lot of press attention and has been described as the ‘smoking gun’ for anthropogenic climate change. We have discussed many of the relevant issues here before, but it may be useful to go over the arguments again here.

The key points of the paper are that: i) model simulations with 20th century forcings are able to match the surface air temperature record, ii) they also match the measured changes of ocean heat content over the last decade, iii) the implied planetary imbalance (the amount of excess energy the Earth is currently absorbing) which is roughly equal to the ocean heat uptake, is significant and growing, and iv) this implies both that there is significant heating “in the pipeline”, and that there is an important lag in the climate’s full response to changes in the forcing.

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Pollution-Climate Connections

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Translations: (Français) (English)

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?

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Ozone depletion and global warming

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Translations: (Français) (Türkçe) (English)

One of the most common mistakes that we have observed in discussions of climate and atmospheric change is confusion between the rather separate concepts of ozone depletion and global warming. This isn’t necessarily surprising given the scant information that most people pick up from the media. However, for many years meteorologists have been fighting a rearguard action to persuade people that the globe isn’t warming because there is more sun coming through the ozone hole. There are however important connections between the two issues that complicate potential actions that we might take to alleviate the different problems. This week, for instance, a new IPCC report was released that looked at the greenhouse warming potential of many of the replacement chemicals (HFCs and HCFCs) that were used to replace CFCs in aerosol cans and refrigeration units under the Montreal Protocol (and subsequent amendments).

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Water vapour: feedback or forcing?

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Translations: (Deutsch) (English)

Whenever three or more contrarians are gathered together, one will inevitably claim that water vapour is being unjustly neglected by ‘IPCC’ scientists. “Why isn’t water vapour acknowledged as a greenhouse gas?”, “Why does anyone even care about the other greenhouse gases since water vapour is 98% of the effect?”, “Why isn’t water vapour included in climate models?”, “Why isn’t included on the forcings bar charts?” etc. Any mainstream scientist present will trot out the standard response that water vapour is indeed an important greenhouse gas, it is included in all climate models, but it is a feedback and not a forcing. From personal experience, I am aware that these distinctions are not clear to many, and so here is a more in-depth response (see also this other attempt).

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