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?
Greenhouse gases
Rasslin’ swamp gas
In the early 1990’s, in defiance of IPCC projections, the methane concentration in the atmosphere abruptly stopped rising, and has remained nearly constant since then. Methane is a crouching tiger in the carbon cycle, with potentially enough available as hydrates and from peats to really clobber the Earth’s heat budget. The big question is, will atmospheric methane start rising again? [Read more…] about Rasslin’ swamp gas
Attribution of 20th Century climate change to CO2
The discussion of climate change in public (on blogs, in op-eds etc.) is often completely at odds to the discussion in the scientific community (in papers, at conferences, workshops etc.). In public discussions there is often an emphasis on seemingly simple questions (e.g. the percentage of the current greenhouse effect associated with water vapour) that, at first sight, appear to have profound importance to the question of human effects on climate change. In the scientific community however, discussions about these ‘simple’ questions are often not, and have subtleties that rarely get publicly addressed.
One such question is the percentage of 20th Century warming that can be attributed to CO2 increases. This appears straightforward, but it might be rather surprising to readers that this has neither an obvious definition, nor a precise answer. I will therefore try to explain why.
(courtesy Alexander Ač).
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Tropical SSTs: Natural variations or Global warming?
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?
Why greenhouse gases heat the ocean
Guest commentary by Peter Minnett (RSMAS)
Observations of ocean temperatures have revealed that the ocean heat content has been increasing significantly over recent decades (Willis et al, 2004; Levitus et al, 2005; Lyman et al, 2006). This is something that has been predicted by climate models (and confirmed notably by Hansen et al, 2005), and has therefore been described as a ‘smoking gun’ for human-caused greenhouse gases.
However, some have insisted that there is a paradox here – how can a forcing driven by longwave absorption and emission impact the ocean below since the infrared radiation does not penetrate more than a few micrometers into the ocean? Resolution of this conundrum is to be found in the recognition that the skin layer temperature gradient not only exists as a result of the ocean-atmosphere temperature difference, but also helps to control the ocean-atmosphere heat flux. (The ‘skin layer‘ is the very thin – up to 1 mm – layer at the top of ocean that is in direct contact with the atmosphere). Reducing the size of the temperature gradient through the skin layer reduces the flux. Thus, if the absorption of the infrared emission from atmospheric greenhouse gases reduces the gradient through the skin layer, the flow of heat from the ocean beneath will be reduced, leaving more of the heat introduced into the bulk of the upper oceanic layer by the absorption of sunlight to remain there to increase water temperature. Experimental evidence for this mechanism can be seen in at-sea measurements of the ocean skin and bulk temperatures. [Read more…] about Why greenhouse gases heat the ocean
Amazonian drought
There has been a flurry of recent commentary concerning Amazon drought – some of it good, some of it not so good. The good stuff has revolved around a recently-completed interesting field experiment that was run out of the Woods Hole Research Center (not to be confused with the Woods Hole Oceanographic Institution), where they have been examining rainforest responses to drought – basically by using a very large rainproof tent to divert precipitation at ground level (the trees don’t get covered up). As one might expect, a rainforest without rain does not do well! But exactly what happens when and how the biosphere responds are poorly understood. This 6 year long field experiment may provide a lot of good new data on plant strategies for dealing with drought which will be used to improve the models and our understanding of the system.
The not-so-good part comes when this experiment is linked too directly to the ongoing drought in the southern Amazon. In the experiment, older tree mortality increased markedly after the third year of no rain at all (with around 1 in 10 trees dying). Since parts of the Amazon are now entering a second year of drought (possibly related to a persistent northward excursion of the ITCZ), the assumption in the Independent story (with the headline ‘One year to save the Amazon’) was that trees will start dying forest-wide next year should the drought continue. [Read more…] about Amazonian drought
Geo-engineering in vogue…
There was an interesting article in the NY Times this week on possible geo-engineering solutions to the global warming problem. The story revolves around a paper that Paul Crutzen (Nobel Prize winner for chemistry related to the CFC/ozone depletion link) has written about deliberately adding sulphate aerosols in the stratosphere to increase the albedo and cool the planet – analogous to the natural effects of volcanoes. The paper is being published in Climatic Change, but unusually, with a suite of commentary articles by other scientists. This is because geo-engineering solutions do not have a good pedigree and, regardless of their merit or true potential, are often seized upon by people who for various reasons do not want to reduce greenhouse gas emissions. However, these ideas keep popping up naturally since significant emission cuts continue to be seen as difficult to achieve, and so should be considered fairly. After all, if there was a cheaper way to deal with the CO2 problem, or even a way to buy time, shouldn’t we take it? [Read more…] about Geo-engineering in vogue…
Buying a stairway to heaven?
Just in the last year or so, a new type of scheme for reducing personal carbon emissions has appeared, the remarkably painless purchasing of “carbon offsets”. Carbonfund.org claims to neutralize a person’s CO2 footprint on the Earth for the low, low price of $99 per year, plus if you act now they will throw in an extra 5 tons for free! And you get a pen! Prices listed here range from $5-30 per ton of CO2 from a variety of similar organizations around the world. The average U.S. citizen is responsible for about 20 tons of CO2 release per year.
Compliance with Kyoto, a mere 5% reduction in carbon emissions, was forecast by Nordhaus [2001] to cost a few percent of GDP globally. The cost to stop emission completely and immediately may not even be calculable. Carbonfund.org promises zero net emissions, for a fraction of 1% of the average U.S. income. Can this possibly be real, or are we talking indulgences and snake oil?
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Positive feedbacks from the carbon cycle
Two papers appeared in Geophysical Research Letters today claiming that the warming forecast for the coming century may be underestimated, because of positive feedbacks in the carbon cycle. One comes from Torn and Harte, and the other from Scheffer, Brovkin, and Cox. Both papers conclude that warming in the coming century could be increased by carbon cycle feedbacks, by 25-75% or so. Do we think it’s time to push the big red Stop the Press button down at IPCC? [Read more…] about Positive feedbacks from the carbon cycle
Thank you for emitting
A recent movie, ‘Thank You for Smoking‘, amusingly highlighted the lengths that PR reps for the tobacco companies would go to distort the public discourse on the health effects of smoking. Lest you thought that was of merely historical relevance, we would like to draw your attention to two of the funniest videos around. Lifting a page straight out of the Nick Naylor playbook, the CEI (an industry-funded lobby group) has launched a new ad campaign that is supposed to counteract all those pesky scientific facts about global warming.
The first ad (both available here) deserves to become a classic of the genre. It contains the immortal lines ‘CO2: they call it pollution, we call it Life!’ – it is beyond parody and without content – and so you should definitely see it. The second ad has a little more substance – but is as misleading as you might expect.
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