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New Ocean Heat Content Histories

Guest commentary from Laure Zanna (U. Oxford) and G. Jake Gebbie (WHOI)

Two recent papers, Zanna et al. (2019) (hereafter ZKGIH19) and Gebbie & Huybers (2019) (hereafter GH19), independently reconstructed ocean heat content (OHC) changes prior to the instrumentally-based records (which start ~1950). The goals (and methodologies) of the two papers were quite different – ZKGIH19 investigated regional patterns of ocean warming and thermal sea level rise, while GH19 analyzed the long-term memory of the deep ocean – but they both touch on the same key questions of climate forcing and response.

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  1. L. Zanna, S. Khatiwala, J.M. Gregory, J. Ison, and P. Heimbach, "Global reconstruction of historical ocean heat storage and transport", Proceedings of the National Academy of Sciences, pp. 201808838, 2019.
  2. G. Gebbie, and P. Huybers, "The Little Ice Age and 20th-century deep Pacific cooling", Science, vol. 363, pp. 70-74, 2019.

Bending low with Bated breath

Filed under: — gavin @ 22 December 2018

“Shall I bend low and in a bondman’s key,
With bated breath and whisp’ring humbleness…?”

Shylock (Merchant of Venice, Act 1, Scene 3)

As dark nights draw in, the venerable contrarians at the GWPF are still up late commissioning silly pseudo-rebuttals to mainstream science. The latest, which no-one was awaiting with any kind of breath, is by Dr. Ray Bates (rtd.) which purports to be a take-down of the recent #SR15 report. As Peter Thorne (an IPCC author) correctly noted, this report is a “cut-and-paste of long-debunked arguments”. I’ve grown a little weary of diving down to rebut every repetitive piece of nonsense, but this one has a few funny aspects that make it worthwhile to do so.

When they go low, we go “sigh…”.

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The long story of constraining ocean heat content

Filed under: — gavin @ 21 November 2018

Scientists predicted in the 1980s that a key fingerprint of anthropogenic climate change would be found in the ocean. If they were correct that increases in greenhouse gases were changing how much heat was coming into the system, then the component with the biggest heat capacity, the oceans, is where most of that heat would end up.

We have now had almost two decades of attempts to characterize this change, but the path to confirming those predictions has been anything but smooth…

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Cracking the Climate Change Case

I have an op-ed in the New York Times this week:

How Scientists Cracked the Climate Change Case
The biggest crime scene on the planet is the planet. We know the earth is warming, but who or what is causing it?
Emilia Miękisz

Many of you will recognise the metaphor from previous Realclimate pieces (this is earliest one I think, from 2007), and indeed, the working title was “CSI: Planet Earth”. The process description and conclusions are drawn from multiple sources on the attribution of recent climate trends (here, here etc.), as well the data visualization for surface temperature trends at Bloomberg News.

There have been many comments about this on Twitter – most appreciative, some expected, and a few interesting. The expected criticisms come from people who mostly appear not to have read the piece at all (“Climate has changed before!” – a claim that no-one disputes), and a lot of pointless counter-arguments by assertion. Of the more interesting comment threads, was one started by Ted Nordhaus who asked

My response is basically that it might be old hat for him (and maybe many readers here), but I am constantly surprised at the number of people – even those concerned about climate – who are unaware of how we do attribution and how solid the science behind the IPCC statements is. And judging by many of the comments, it certainly isn’t the case that these pieces are only read by the already convinced. But asking how many people are helped to be persuaded by articles like this is a valid question, and I don’t really know the answer. Anyone?

Model Independence Day

Filed under: — gavin @ 4 July 2018

We hold these truths to be self-evident, that all models are created equal, that they are endowed by their Creators with certain unalienable Rights, that among these are a DOI, Runability and Inclusion in the CMIP ensemble mean.

Well, not quite. But it is Independence Day in the US, and coincidentally there is a new discussion paper (Abramowitz et al) (direct link) posted on model independence just posted at Earth System Dynamics.

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  1. G. Abramowitz, N. Herger, E. Gutmann, D. Hammerling, R. Knutti, M. Leduc, R. Lorenz, R. Pincus, and G.A. Schmidt, "Model dependence in multi-model climate ensembles: weighting, sub-selection and out-of-sample testing", Earth System Dynamics Discussions, pp. 1-20, 2018.

30 years after Hansen’s testimony

Filed under: — gavin @ 21 June 2018

“The greenhouse effect is here.”
– Jim Hansen, 23rd June 1988, Senate Testimony

The first transient climate projections using GCMs are 30 years old this year, and they have stood up remarkably well.

We’ve looked at the skill in the Hansen et al (1988) (pdf) simulations before (back in 2008), and we said at the time that the simulations were skillful and that differences from observations would be clearer with a decade or two’s more data. Well, another decade has passed!

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  1. J. Hansen, I. Fung, A. Lacis, D. Rind, S. Lebedeff, R. Ruedy, G. Russell, and P. Stone, "Global climate changes as forecast by Goddard Institute for Space Studies three-dimensional model", Journal of Geophysical Research, vol. 93, pp. 9341, 1988.

If you doubt that the AMOC has weakened, read this

A few weeks ago, we’ve argued in a paper in Nature that the Atlantic overturning circulation (sometimes popularly dubbed the Gulf Stream System) has weakened significantly since the late 19th Century, with most of the decline happening since the mid-20th Century. We have since received much praise for our study from colleagues around the world (thanks for that). But there were also some questions and criticisms in the media, so I’d like to present a forum here for discussing these questions and hope that others (particularly those with a different view) will weigh in in the comments section below. More »

Transparency in climate science

Good thing? Of course.*

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The Alsup Aftermath

The presentations from the Climate Science tutorial last month have all been posted (links below), and Myles Allen (the first presenter for the plaintiffs) gives his impression of the events.
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Alsup asks for answers

Some of you might have read about the lawsuit by a number of municipalities (including San Francisco and Oakland) against the major oil companies for damages (related primarily to sea level rise) caused by anthropogenic climate change. The legal details on standing, jurisdiction, etc. are all very interesting (follow @ColumbiaClimate for those details), but somewhat uniquely, the judge (William Alsup) has asked for a tutorial on climate science (2 hours of evidence from the plaintiffs and the defendents). Furthermore, he has posted a list of eight questions that he’d like the teams to answer.

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