Another open thread. OT comments from the Amazon drying thread have been moved over. As usual, substantive comments only please and no abuse.
Climate Science
Up is Down, Brown is Green (with apologies to Orwell)
In the alternate universe of Fox News, Anthony Watts, and many others, up is down. Now, it appears, brown is green. Following the total confusion over the retraction of a paper on sea level, claims of another “mistake” by the IPCC are making the rounds of the blogosphere. This time, the issue is the impact of rainfall changes on the Amazon rainforest.
A study in 2007 showed that the forest gets greener when it rains less. A new study, by Samanta et al. in Geophysical Research Letters shows that the earlier work was flawed. Aided by an apparently rather careless press release, this is being used as evidence that the Amazon is less sensitive to rainfall changes than the IPCC claimed. But the Samanta et al. paper actually does not address the central questions at all. It only addresses whether a single anomalous rainfall year had an impact that is measureable and interpretable from a satellite sensor. The conclusion is that they could not detect a change. As noted in a commentary from Simon Lewis, University of Leeds, “the critical question is how these forests respond to repeated droughts, not merely single-year droughts.”
Lewis – a broadly published expert on tropical forests – makes a number of additional important points in his commentary below. Bottom line: IPCC gets it right as usual.
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Guest Commentary by Simon Lewis, University of Leeds, UK
The new Samanta et al. study uses sensors on satellites to assess the colour of the rainforest canopy in the dry season of the year 2005, compared to the dry seasons of the years 2003 and 2004. More detected green colour in 2005 may suggest that the forest is being more productive (more green leaves photosynthesising), or more brown colours may suggest leaves dying and less productivity, than the previous years. The results show that 2005 was little different to the previous years, despite the strong drought.
This is important new information, as in 2007, a paper using broadly the same satellite-based method showed a strong ‘greening-up’ of the Amazon in 2005, suggesting tolerance to drought (Saleska et al. 2007, Science). The new study shows that those results were not reproducible, but also highlight the extreme caution that should be attached to satellite studies generally in this field, with instruments in space collecting data which is then used to infer subtle changes in the ecology of tropical forests.
In contrast to the 2007 paper, Oliver Phillips, myself, and others, published a paper in Science last year, using ground observations from across the Amazon, showing that while the 2005 drought did not dramatically change the growth of the trees compared to a normal year, as Samanta et al. also show, the deaths of trees did increase considerably. The new study of Samanta et al. does not contradict the Phillips et al. study, which itself shows the Amazon is vulnerable to drought via impacts on tree mortality. The Phillips et al. paper showed that remaining Amazon forest trees changed from absorbing nearly 2 billion tonnes of CO2 from the atmosphere annually over recent decades, as tree growth has been exceeding mortality, to being a large, but temporary, source of over 3 billion tonnes, from the elevated tree mortality associated with the 2005 drought event.
The evidence for the possibility of a major die-back of the Amazon rainforest is due to two factors,
1. That climate change induced decreases in rainfall in the dry season occur, and
2. The trees cannot tolerate these reductions in rainfall.
The Samanta paper does not directly address the first point; this is addressed using global circulation models (of which some, but not all, show a strong drying trend for the east of the Amazon over the 21st century). The second point is only addressed in a limited way. The critical question is how these forests respond to repeated droughts, not merely single-year droughts. The forests are of course able to withstand these single droughts (otherwise there would be no rainforest!) — it is their ability to survive an increased frequency of the most severe droughts that is critical to answer. Drought experiments, where a roof is built under the forest canopy to reduce rainfall, show that most forest trees survive a single year’s intense drought, in agreement with the ground observations in the 2005 drought, but can’t persist with repeated years of drought. The Samanta study does not address this point at all.
In conclusion, the new Samanta et al. study lends further weight to the emerging picture of the impact of the 2005 drought: that tree growth was relatively unaffected, but tree mortality increased, contributing temporarily to accelerating the rate of climate change, rather than as usual reducing it, via additions of carbon to the atmosphere from the dead trees. The mortality was far from catastrophic, but the impact on the carbon cycle was globally significant. This is hardly the ‘no impact’ of the 2005-drought on the forest suggested in various news reports.
I should add that there is considerable uncertainty associated with the models suggesting decreases in rainfall, and uncertainty as to how Amazon forests may react (especially when one considers the impacts of deforestation, logging, and fire combined with climate change impacts). But this uncertainty is being chipped away at by scientists, a task in which the Samanta et al. paper assists.
Oddly, the Boston University press release to accompany the paper was titled, “New study debunks myths about Amazon rain forests”. The opening line runs: “A new NASA-funded study has concluded that Amazon rain forests were remarkably unaffected in the face of once-in-a-century drought in 2005, neither dying nor thriving, contrary to a previously published report and claims by the Intergovernmental Panel on Climate Change.” So, have scientists, myself included, been peddling myths? Have respected journals being publishing them? Have the IPCC? The answer is no, no and no.
The reality is that the IPCC have largely ignored the papers on the model results of decreasing rainfall in the east of the Amazon, and the diverse evidence used to assess the sensitivity of these forests to such rainfall reductions. There are a couple of lines in IPCC Working Group I (“New coupled climate-carbon models (Betts et al., 2004; Huntingford et al., 2004) demonstrate the possibility of large feedbacks between future climate change and vegetation change, discussed further in Section 7.3.5 (i.e., a die back of Amazon vegetation and reductions in Amazon precipitation).”). And in Working Group II there is a now infamous single sentence:
“Up to 40% of the Amazonian forests could react drastically to even a slight reduction in precipitation; this means that the tropical vegetation, hydrology and climate system in South America could change very rapidly to another steady state, not necessarily producing gradual changes between the current and the future situation (Rowell and Moore, 2000).”
The statement is not as carefully worded as it should be, and incorrectly referenced, but basically scientifically correct and defensible with recourse to the peer-reviewed literature available at the time. Rainforest persists above a threshold of rainfall, below which one finds savanna. If this threshold is crossed a landscape dominated by rainforest can ‘flip’ to savanna. Therefore a ‘slight’ reduction can lead to a ‘dramatic’ reaction. Of course, evidence of a shift to a new lower rainfall climate regime is needed, and evidence of large areas of forest close to that rainfall threshold would be required for the IPCC statement to be reasonable; there is ample published evidence for both.
Overall the conclusions in the IPCC 2007 Fourth Assessment Report are strengthened (because the anomalous result of the Saleska et al. 2007 paper appear to be at fault), not weakened, by the new Samanta et al. study as their press release implies.
Update: Saleska responds, pointing out that a) their 2007 paper is not contradicted by Samanta et al. (2010); b) nor is the IPCC report weakened by either paper. Confused? Then read what he has to say: here.
Why we bother
A letter from a reader (reproduced with permission):
Dear RealClimate team:
I have a background in biology and studied at post-grad level in the area of philosophy of science. For the last few years, I have been working on a book about the logic of argument used in debates between creationists and evolutionists.
About a year ago I decided it was time to properly educate myself about climate science. Being perhaps a little too influenced by Harry M Collins’ “The Golem” (and probably too much modern French philosophy!), I was definitely predisposed to see group-think, political and cultural bias in the work of climatologists.
On the whole, though, I tried hard to follow the principles of genuine skepticism, as I understood them.
Obviously, there are plenty of ill-considered opinions to be found either side of any issue, but only the most ignorant person could fail to see the terrible intellectual gulf between the quality of so-called skeptic sites and those defending the science behind the AGW thesis.
What convinced me, though, is that the arguments made by a few sites like yours are explicit and testable. In particular, it is useful that RealClimate sticks to the science as much as possible. It has been a lot of hard work to get here, but I am now at a point where I understand the fundamentals of climate science well enough to articulate them to others.
For my part, I am grateful to you guys. I hope it gives you some small amount of satisfaction to know that your work can convert readers who really were skeptics in the beginning. I use the word ‘skeptic’ carefully – the one thing most commonly absent from the so-called ‘skeptics’ is authentic skepticism.
By the way, my book is an attempt to categorise the various logical errors people fall into when they search for arguments to support a conclusion to which they have arrived at a priori. It will now have a few chapters on global warming.
All the best,
Sealevelgate
) (
) Imagine this. In its latest report, the IPCC has predicted up to 3 meters of sea level rise by the end of this century. But “climate sceptics” websites were quick to reveal a few problems (or “tricks”, as they called it).
First, although the temperature scenarios of IPCC project a maximum warming of 6.4 ºC (Table SPM3), the upper limit of sea level rise has been computed assuming a warming of 7.6 ºC. Second, the IPCC chose to compute sea level rise up to the year 2105 rather than 2100 – just to add that extra bit of alarmism. Worse, the IPCC report shows that over the past 40 years, sea level has in fact risen 50% less than predicted by its models – yet these same models are used uncorrected to predict the future! And finally, the future projections assume a massive ice sheet decay which is rather at odds with past ice sheet behaviour.
Some scientists within IPCC warned early that all this could lead to a credibility problem, but the IPCC decided to go ahead anyway.
Now, the blogosphere and their great media amplifiers are up in arms. Heads must roll!
More on sun-climate relations
Four new papers discuss the relatiosnhip between solar activity and climate: one by Judith Lean (2010) in WIREs Climate Change, a GRL paper by Calogovic et al. (2010), Kulmala et al. (2010), and an on-line preprint by Feulner and Rahmstorf (2010). They all look at different aspects of how changes in solar activity may influence our climate.
Arctic Methane on the Move?
) () Methane is like the radical wing of the carbon cycle, in today’s atmosphere a stronger greenhouse gas per molecule than CO2, and an atmospheric concentration that can change more quickly than CO2 can. There has been a lot of press coverage of a new paper in Science this week called “Extensive methane venting to the atmosphere from sediments of the East Siberian Arctic Shelf”, which comes on the heels of a handful of interrelated methane papers in the last year or so. Is now the time to get frightened?
Climate change commitments
) () There is an interesting letter in Nature Geoscience this month on what climate changes we have actually already committed ourselves to. The letter, by Mathews and Weaver (sub. reqd.), makes the valid point that there are both climatic and societal inertias to consider.
Close Encounters of the Absurd Kind
Guest commentary from Ben Santer
Part 2 of a series discussing the recent Guardian articles
A recent story by Fred Pearce in the February 9th online edition of the Guardian (“Victory for openness as IPCC climate scientist opens up lab doors”) covers some of the more publicized aspects of the last 14 years of my scientific career. I am glad that Mr. Pearce’s account illuminates some of the non-scientific difficulties I have faced. However, his account also repeats unfounded allegations that I engaged in dubious professional conduct. In a number of instances, Mr Pearce provides links to these allegations, but does not provide a balanced account of the rebuttals to them. Nor does he give links to locations where these rebuttals can be found. I am taking this opportunity to correct Mr. Pearce’s omissions, to reply to the key allegations, and to supply links to more detailed responses.
[Read more…] about Close Encounters of the Absurd Kind
The Guardian disappoints
Over the last few weeks or so the UK Guardian (who occasionally reprint our posts) has published a 12-part series about the stolen CRU emails by Fred Pearce that are well below the normal Guardian standards of reporting. We delineate some of the errors and misrepresentations below. While this has to be seen on a backdrop of an almost complete collapse in reporting standards across the UK media on the issue of climate change, it can’t be excused on the basis that the Mail or the Times is just as bad. As a long-time Guardian reader and avid Guardian crossword puzzle solver, I’m extremely unhappy writing this post, but the pathologies of media reporting on this issue have become too big to ignore.
We highlight issues with three of the articles below, which revisit a number of zombie arguments that have been doing the rounds of the sceptic blogs for years. Two follow-up pieces will deal with two further parts of the series. Hopefully some of the more egregious factual errors can be fixed as part of a ‘group experiment‘ in improving the stories, though the larger misconceptions probably can’t be (and readers should feel free to use this information to comment on the articles directly). Why the Guardian is asking for group input after the stories were published instead of before is however a puzzle. Some of the other pieces in this series are fine, which makes the ones that get it so wrong all the more puzzling. The errors consist of mistakes in the basic science, misunderstandings of scientific practice, more out of context quotes and some specific issues that are relatively new. (In the text below, quotes from the articles are in italics).
[Read more…] about The Guardian disappoints
Throw your iPhone into the climate debate
Who says that the climate debate is not evolving? According to the daily newspaper the Guardian, a new application (‘app‘) has been written for iPhones that provides a list of climate dissidents’ arguments, and counter arguments based on more legitimate scientific substance. The app is developed by John Cook from ‘Skeptical Science‘. It’s apparently enough to have the climate dissidents up in arms – meaning that it’s likely to have some effect? Some dissidents are now thinking of writing their own app.
Here on RC, we have developed a wiki, to which I also would like to bring the reader’s attention. Furthermore, I want to remind the readers about other useful web sites, listed at our blog roll.