Climate Etc.

Atlantic vs Pacific vs AGW

by Judith Curry

I hope this will lead to a broader discussion about the contribution of natural variability to local climate trends and to the statistics of extreme events. – John Michael Wallace

The Chen and Tung paper is continuing to generate interesting discussion in the blogosphere, in particular the role of multidecadal oscillations in climate change attribution.

RealClimate

There is a new post at RealClimate IPCC attribution statements redux:  A response to Judith Curry, which responds to my post The 50-50 attribution argument.  I am ‘honored’ to receive such attention.

In the comments,  Bart Verheggen refers to this as a ‘take down.’

Here is how Gavin’s post is being billed on twitter:

Chris Colose:  @ClimateOfGavin on why @curryja‘s attribution statements for 5+ years now are demonstrably wrong/illogical/irrelevant

Climate 4 Revolution: I predict more @curryja drama: more cherry-picking, frustrated teeth-gnashing, & desperate name calling of @ClimateOfGavin.

Well, I’ve read Gavin’s piece twice (now thrice), I can’t find a single point that he has scored with respect to my main arguments.  I understand what the IPCC etc. have done – I think their conclusion is wrong and that circular reasoning is involved (Gavin doesn’t get my issue with detection). Gavin closes with:

If Judith is interested in why her arguments are not convincing to others, perhaps this can give her some clues. 

I appreciate all the effort Gavin put into this, but he misses my main points. Certainly illuminates his own thinking, tho.

Gavin and I seem to live on different planets:  I live on planet Earth observations, and Gavin lives on planet climate model.  I would appreciate some discussion that points out anything significant in Gavin’s post that refutes my arguments. This tweet sums it up for me:

Shub Niggurath: This article shows how you cannot ‘debunk’ someone if you have not understood their point. 

DotEarth

Pursuant to the Chen and Tung paper, Andy Revkin has a very good post A Closer Look at Turbulent Oceans and Greenhouse Heating.  Revkin interviews  Joshua Willis, Andrew Dessler, John Michael Wallace, and Carl Wunsch.   Interesting choices, particularly since all 4 have an observational perspective (focus on data). Excerpts (JC bold):

Josh Willis (NASA JPL)

If you are wondering whether [the ‘slowdown’] is meaningful in terms of the public discourse about climate change, I would say the answer is no. The basic story of human caused global warming and its coming impacts is still the same: humans are causing it and the future will bring higher sea levels and warmer temperatures, the only questions are: how much and how fast?

But it is not clear to me, actually, that an accelerated warming of some sub-surface layer of the ocean (at least in the globally-averaged sense) is robustly supported by the data itself.

Andrew Dessler (Texas A&M)

I think it’s important to put the hiatus in context. This is not an existential threat to the mainstream theory of climate. We are not going to find out that, lo and behold, carbon dioxide is not a greenhouse gas and is not causing warming.

I do think that ocean variability may have played a role in the lack of warming in the middle of the 20th century, as well as the rapid warming of the 1980s and 1990s.

Mike Wallace (U. Washington)

Back in 2001 I served as a member of the committee that drafted the National Research Council report, “Climate Change Science: An Analysis of Some Key Questions.” The prevailing view at that time, to which I subscribed, was that the signal of human-induced global warming first clearly emerged from the background noise of natural variability starting in the 1970s and that the observed rate of increase from 1975 onward could be expected to continue into the 21st century. The Fourth Assessment Report of the IPCC, released in 2007, offered a similar perspective, both in the text and in the figures in its Summary for Policymakers.

By that time, I was beginning to have misgivings about this interpretation. It seemed to me that the hiatus in the warming, which by then was approaching ten years in length, should not be dismissed as a statistical fluke. It was as legitimate a part of the record as the rapid rises in global-mean temperature in the 1980s and 1990s.

In 2009 Zhaohua Wu contacted me about a paper that he, Norden Huang, and other colleagues were in the process of writing in which they attributed the stair-step behavior in the rate of global warming, including the current hiatus, to Atlantic multidecadal variability.  The paper (Wu et al.) encountered some tough sledding in the review process, but we persisted and the article finally appeared in Climate Dynamics three years ago. [See Judith Curry’s helpful discussion.]

The new paper by Tung and Chen goes much farther than we did in making the case that Atlantic multidecadal variability needs to be considered in the attribution of climate change. I’m glad to see that it is attracting attention in the scientific community, along with recent papers of Kosaka et al. and Meehl et al. emphasizing the role of ENSO-like variability. I hope this will lead to a broader discussion about the contribution of natural variability to local climate trends and to the statistics of extreme events.

Carl Wunsch (MIT and Harvard):

The system is noisy. Even if there were no anthropogenic forcing, one expects to see fluctuations including upward and downward trends, plateaus, spikes, etc. If the science is done right, the calculated uncertainty takes account of this background variation. But none of these papers, Tung, or Trenberth, does that. Overlain on top of this natural behavior is the small, and often shaky, observing systems, both atmosphere and ocean where the shifting places and times and technologies must also produce a change even if none actually occurred. 

The central problem of climate science is to ask what you do and say when your data are, by almost any standard, inadequate? If I spend three years analyzing my data, and the only defensible inference is that “the data are inadequate to answer the question,” how do you publish? How do you get your grant renewed? A common answer is to distort the calculation of the uncertainty, or ignore it all together, and proclaim an exciting story that the New York Times will pick up.

JC reflections

This discussion generated by the Chen and Tung paper represents the climate blogosphere at its best – my posts, the participation of Tung (at least via email), Andy Revkin’s post eliciting significant comments from 4 mainstream climate scientists, and Gavin’s response (there are other blogs discussing this as well).

Uncertain T. Monster is very pleased by the responses by Wallace, Wunsch, Dessler and Willis (but not so pleased with Gavin’s essay).

I take issue with the following statements by Dessler and Willis:

This is not an existential threat to the mainstream theory of climate. – Dessler

The basic story of human caused global warming and its coming impacts is still the same: humans are causing it and the future will bring higher sea levels and warmer temperatures, the only questions are: how much and how fast? – Willis

I do regard the emerging realization of the importance of natural variability to be an existential threat to the mainstream theory of climate variations on decadal to century time scales.  The mainstream theory views climate change as externally forced, e.g. the CO2 control knob theory.  My take is that external forcing explains general variations on very long time scales, and equilibrium differences in planetary climates of relevance to comparative planetology.  But it does not explain the dominant variations of climate on decadal to century timescales, which are the time scales of relevance to policy makers and governments that are paying all this money for climate research.

On decadal to century timescales, climate dynamics – the complex interplay of multiple external forcings (rapid and slow), the spectrum of atmospheric and ocean circulation oscillations, interactions with biosphere – determines variations in climate.  Until the climate community gets serious about paying attention to natural variability, then we aren’t going to make much progress in understanding or predicting climate variability/change on decadal to century timescales.