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about Gavin Schmidt

Gavin Schmidt is a climate modeler, working for NASA and with Columbia University.

Requiem for the Younger Dryas impact hypothesis?

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This is the strong conclusion of a new paper in the Earth Science Reviews by Pinter et al (via Scribd). From their abstract:

The Younger Dryas (YD) impact hypothesis is a recent theory that suggests that a cometary or meteoritic body or bodies hit and/or exploded over North America 12,900 years ago, causing the YD climate episode, extinction of Pleistocene megafauna, demise of the Clovis archaeological culture, and a range of other effects.
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The physical evidence interpreted as signatures of an impact event can be separated into two groups. The first group consists of evidence that has been largely rejected by the scientific community and is no longer in widespread discussion…. The second group consists of evidence that has been active in recent research and discussions:…. Over time, however, these signatures have also seen contrary evidence rather than support.
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In summary, none of the original YD impact signatures have been subsequently corroborated by independent tests. Of the 12 original lines of evidence, seven have so far proven to be non-reproducible. The remaining signatures instead seem to represent either (1) non-catastrophic mechanisms, and/or (2) terrestrial rather than extraterrestrial or impact-related sources.

The YD impact hypothesis made a big splash at AGU in 2007, and we’ve written about it a few times since. Our assessment was (in 2007), that this would need a lot of confirmatory evidence to get accepted, and even if it was, it did not provide much explanation for other, very similar, abrupt changes in the record. In 2009, we were still skeptical and noted that “the level of proof required for this extraordinary idea will need to be extraordinarily strong”. Unfortunately, as this paper makes clear, neither a lot of confirmatory evidence nor extraordinarily strong proofs have been forthcoming.

This paper is unlikely to the very last word on the subject, but it is likely to be the last time the mainstream paleo-climatologists are going to pay this much heed unless some really big new piece of evidence comes to light.

However, while the specifics of this particular hypothesis and its refutation are interesting in many ways…

The YD impact hypothesis provides a cautionary tale for researchers, the scientific community, the press, and the broader public.

Let’s be specific…
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Going to extremes

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There are two new papers in Nature this week that go right to the heart of the conversation about extreme events and their potential relationship to climate change. This is a complex issue, and one not well-suited to soundbite quotes and headlines, and so we’ll try and give a flavour of what the issues are and what new directions these new papers are pointing towards.
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From blog to Science

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There is a lot of talk around about why science isn’t being done on blogs. It can happen though, and sometimes blog posts can even end up as (part of) a real Science paper. However, the process is non-trivial and the relatively small number of examples of such a transition demonstrate clearly why blog science is not going to replace the peer-reviewed literature any time soon.

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Getting things right

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Last Monday, I was asked by a journalist whether a claim in a new report from a small NGO made any sense. The report was mostly focused on the impacts of climate change on food production – clearly an important topic, and one where public awareness of the scale of the risk is low. However, the study was based on a mistaken estimate of how large global warming would be in 2020. I replied to the journalist (and indirectly to the NGO itself, as did other scientists) that no, this did not make any sense, and that they should fix the errors before the report went public on Thursday. For various reasons, the NGO made no changes to their report. The press response to their study has therefore been almost totally dominated by the error at the beginning of the report, rather than the substance of their work on the impacts. This public relations debacle has lessons for NGOs, the press, and the public.
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Reflections on funding panels

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Despite what is often claimed, climate scientists aren’t “just in it for the money”. But what scientists actually do to get money and how the funding is distributed is rarely discussed. Since I’ve spent time as a reviewer and on a number of panels for various agencies that provide some of the input into those decisions, I thought it might be interesting to discuss some of the real issues that arise and the real tensions that exist in this process. Obviously, I’m not going to discuss specific proposals, calls, or even the agencies involved, but there are plenty of general insights worth noting.
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One year later

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I woke up on Tuesday, 17 Nov 2009 completely unaware of what was about to unfold. I tried to log in to RealClimate, but for some reason my login did not work. Neither did the admin login. I logged in to the back-end via ssh, only to be inexplicably logged out again. I did it again. No dice. I then called the hosting company and told them to take us offline until I could see what was going on. When I did get control back from the hacker (and hacker it was), there was a large uploaded file on our server, and a draft post ready to go announcing the theft of the CRU emails. And so it began.

From that Friday, and for about 3 weeks afterward, we were drafted into the biggest context setting exercise we’d ever been involved in. What was the story with Soon and Baliunas? What is the difference between tree ring density and tree ring width? What papers were being discussed in email X? What was Trenberth talking about? Or Wigley? Or Briffa or Jones? Who were any of this people anyway? The very specificity of the emails meant that it was hard for the broader scientific community to add informed comment, and so the burden on the people directly involved was high.

The posts we put up initially are still valid today – and the 1000’s of comment stand as testimony to the contemporary fervour of the conversation:

I think we did pretty well considering – no other site, nor set of scientists (not even at UEA) provided so much of the background to counter the inevitable misinterpretations that starting immediately spreading. While some commentators were predicting resignations, retractions and criminal charges, we noted that there had not been any scientific misconduct, and predicted that this is what the inquiries would find and that the science would not be affected. (Note, the most thorough inquiry, and one that will have to withstand judicial review, is the one by EPA which, strangely enough, has barely been discussed in the blogosphere).

Overall, reactions have seemed to follow predictable lines. The Yale Forum has some interesting discussions from scientists, and there are a couple of good overviews available. Inevitably perhaps, the emails have been used to support and reinforce all sorts of existing narratives – right across the spectrum (from ‘GW hoaxers’ to Mike Hulme to UCS to open source advocates).

Things have clearly calmed down over the last year (despite a bit of a media meltdown in February), but as we predicted, no inquiries found anyone guilty of misconduct, no science was changed and no papers retracted. In the meantime we’ve had one of the hottest years on record, scientists continue to do science, and politicians…. well, they continue to do what politicians do.

Solar spectral stumper

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It’s again time for one of those puzzling results that if they turn out to be true, would have some very important implications and upset a lot of relatively established science. The big issue of course is the “if”. The case in question relates to some results published this week in Nature by Joanna Haigh and colleagues. They took some ‘hot off the presses’ satellite data from the SORCE mission (which has been in operation since 2003) and ran it through a relatively complex chemistry/radiation model. These data are measurements of how the solar output varies as a function of wavelength from an instrument called “SIM” (the Spectral Irradiance Monitor).
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IPCC report card

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Update: Nature has just published a thoughtful commentary on the report

The Inter-Academy Council report on the processes and governance of the IPCC is now available. It appears mostly sensible and has a lot of useful things to say about improving IPCC processes – from suggesting a new Executive to be able to speak for IPCC in-between reports, a new communications strategy, better consistency among working groups and ideas for how to reduce the burden on lead authors in responding to rapidly increasing review comments.

As the report itself notes, the process leading to each of the previous IPCC reports has been informed from issues that arose in previous assessments, and that will obviously also be true for the upcoming fifth Assessment report (AR5). The suggestions made here will mostly strengthen the credibility of the next IPCC, particularly working groups 2 and 3, though whether it will make the conclusions less contentious is unclear. Judging from the contrarian spin some are putting on this report, the answer is likely to be no.