Update (Tues 15 October 1:15 am AEDST):
Bob Tisdale is sending a few people over here this morning after writing a second WUWT article on the same topic - archived here. (Is Anthony Watts running out of contributors?).
Hello all and welcome :) I wonder how many of you recognise the fallacies in Bob's circular thinking? After you've read this article and had a bit of a wander around HotWhopper, you might find what Wotts' has to say on this topic interesting too.
Perennially Puzzled Bob Tisdale is a denier of anthropogenic global warming. His denial is amply demonstrated in his latest article on WUWT (archived here, and update here) about a new paper.
The paper, by Li et al (2013) is about to be published in GRL. It's available as open access (pdf file is here).
The authors detrended the NH temperature record to remove the warming from human activities. Their key quote that underpins the paper is this one, I believe:
Observational analysis shows that the NAO leads both the detrended NHT and oceanic Atlantic Multidecadal Oscillation (AMO) by 15–20 years.As I read it, the authors are looking to see if they can use the North Atlantic Oscillation to predict changes in Northern Hemisphere surface temperature.
It looks to me that they've done a mathematical extrapolation to surmise that the NH temperature will flatten and decrease slightly over the next couple of decades, even allowing for a rise in temperature from rising greenhouse gases. I'm not sure what they used to model future NH temperatures.
What Bob Tisdale has done is ignore Fig 3b. In fact he didn't put up any charts at all, not even his own, which makes a change. Bob writes this:
It’s time for the IPCC to start thinking about cutting back on their predictions of future global warming by at least 50%. The public is catching on to the fact that if natural variability can stop global warming for 2 to 3 decades, then it also contributed to the warming from 1975 to the turn of the century—something the IPCC failed to account for in its projections.Bob is wrong in his interpretation. It looks as if he is once again acting as if a cyclic pattern (an oscillation) leads to an overall rise in temperature. But it doesn't. Fig 3a above shows it as an oscillation having no net effect over the full cycle. As well as that, Fig 3b above shows that the Northern Hemisphere temperatures rose by more than 1° Celsius over the past century when stripped of the NAO-related temperature cycle.
The NH temperature is shown below in Fig 4a from Li et al, with their hindcasting of their NAO model shown as dots and lines.
The results obtained from the Hasselmann climate model provide an explanation for the phase lead–lag between the NAO and DNHT. This lead–lag relationship offers a simple but useful way to predict NHT around a decade and half in advance. Namely, the NAOI being shifted by 16 years can serve to predict NHT. A NAO-based linear model for predicting decadal NHT is therefore established as follows:
where t is time in years and the coefficients a, b and c are determined empirically by linear regression based on the data over the historical period, so that the regression error of Equation (2) is minimized.Applying this equation to the NH temperature, Li et al came up with a short term prediction shown in their Figure 4b below:
It will be interesting to see if the Li et al prediction is any more robust than the IPCC projections. The CMIP5 models of global temperature (don't know about NH only) also hindcast very well with the 20th century record. However the CMIP5 models project forward based on the physics (under given scenarios) and I don't know the extent to which they reflect the NAO/AMO.
Back to Bob Tisdale. He nearly forgot to put in a plug for his latest science-denying book so he adds it as a comment, together with his standard pledge of science rejection. Bob Tisdale says (my bold italics):
October 12, 2013 at 4:19 pm
Sheesh. I’m slipping. I forgot to call attention to the final few words of the Li et al. (2013) abstract, “that temporarily offsets the anthropogenically induced warming,” and the fact that ocean heat content data and satellite-era sea surface temperature data both indicate the oceans warmed via natural processes, not from manmade greenhouse gases. See my illustrated essay, “The Manmade Global Warming Challenge” (42MB):
Bob's "natural processes" is his code for "magic". And this comment of his is priceless:
Because North Atlantic sea surface temperatures have warmed, outgoing longwave radiation increases. Didn’t that just change the Earth’s energy budget—without any extra heat input? October 12, 2013 at 7:01 pmWhat he's (wrongly) saying, torturing logic and physics, is that:
- the temperature went up without any extra heat input!
- sea surface temperature went up leading to more heat leaving the system as longwave radiation therefore the energy budget changed. At the same time as arguing that the energy budget didn't change.
A question was asked in the comments about the forcings over the past century. Here is a chart from Chapter 8 of the AR5 WG1 IPCC report, which can be downloaded here. Click the chart to enlarge it.
the Technical Summary (Box TS.5 Fig 1 on page TS-103) showing radiative forcings (volcanic, solar and well-mixed greenhouse gases) going back over the past 1200 years or so compared with reconstructed NH temperature, which I posted in another article.
|Source: Box TS.5, Fig 1 IPCC WG1 AR5 Technical Summary|
From the WUWT comments
October 12, 2013 at 7:14 pm
” temporarily offsets the anthropogenically induced warming”
That’s point blank admitting they were wrong. They’re trying to spin it, but it doesn’t work. If natural causes can offset it, then humans are no longer the primary cause of climate change (not that they ever were). It’s not catastrophic. Crisis averted.
dalyplanet has read the paper itself and says:
October 12, 2013 at 7:21 pm
An interesting paper, but I find the Wyatt paper much more in agreement with the understanding that you have presented to me Bob. This paper agrees with an internal variability that nets to zero over decadal time scales, rather than a natural variability that does not necessarily net to zero in decadal or even centennial time scale.
Bob Tisdale has a habit of making up stuff and telling fibs, like when he writes:
Leo, are you aware that the only support for the hypothesis of human-induced global warming are climate models? Without climate models, we only know that surface temperatures have warmed. October 12, 2013 at 7:33 pm
October 12, 2013 at 7:55 pm
Bob Tisdale: No, I’m not new here. I am well aware of your opinions. I am more concerned with the how the opinions expressed in published research are presented or misrepresented. You are free to use phrases like “stoppage” or “cessation”. The authors of the paper clearly did not, and they say things throughout the paper at odds with your beliefs. Do not bootstrap your opinions onto their work.
Jianping Li1, Cheng Sun, Fei-Fei Jin (2013) NAO implicated as a predictor of Northern Hemisphere mean temperature multidecadal variability, Geophysical Research Letters DOI: 10.1002/2013GL057877