What never occurred to Judith Curry (and does 50% equal half?)

Update: Judith continues to talk nonsense - see below.

I find this extremely odd, coming from a climate scientist. Judith Curry wrote about the IPCC's AR5 attribution of global warming:

Until this exchange, it never occurred to me that the IPCC’s attribution statement was attempting to convey AGW attribution that was possibly outside the range of 0 to 100%.

As most people who follow climate science would know, the IPCC attributes virtually all of the warming since 1950 to human causes. Judith quotes the following statement:

It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together. The best estimate of the human induced contribution to warming is similar to the observed warming over this period.

In other words, the best estimate is that we've caused all the warming.


What happens is that deniers latch on to the first sentence in the paragraph and ignore the second.  Given Judith's preference for denial, it looks as if she did the same. Fancy her not realising until now, after all these years working in climate science, that the science shows we've probably brought about more than 100% of global warming (mostly via CO2 emissions) plus some offsetting global cooling (via aerosols).

Does anyone else find this really, really odd?

Judith has got a really long article (archived here) which is mostly her wondering whether or not "more than half" and "more than 50%" mean much the same thing or not. And how much more than half predominately is.

No. I'm not exaggerating. Look for yourself. Is that weird or what! Do you think she is mounting a defence of her denial by means of failing cognitive function?

The IPCC report shows in various different places how the current warming is down to all the extra greenhouse gases we've added to the atmosphere.  Here's one example from Box TS.5, Figure 1 of the IPCC AR5 WG1 report. The bottom curve in  the top chart is the greenhouse forcing, which you can see has gone up hugely since industrialisation. The bottom chart is the northern hemisphere averaged surface temperature. Click to enlarge as always.

Here's another example, in which the chart shows the contribution of different things to radiative forcing, since 1750. CO2 is the biggest forcing, but there are others both positive and negative. Natural forcing is miniscule by comparison with total anthropogenic forcing:

Figure 8.15: Bar chart for RF (hatched) and ERF (solid) for the period 1750–2011, where the total ERF is derived from Figure 8.16. Uncertainties (5–95% confidence range) are given for RF (dotted lines) and ERF (solid lines).  Source: IPCC AR5 WG1

I find Judith's article quite silly. What is more incomprehensible to me is her claim that she didn't realise till now that the IPCC indicated it quite likely that human activity is responsible for more than 100% of the warming in recent decades. She is a Professor and former Chair of the School of Earth and Atmospheric Sciences. How could she hold those posts and not learn this most fundamental finding?

Look, I know that researchers tend to focus in on their own particular area of study. However I cannot believe that anyone whose work is related to climate science wouldn't at some point step back and learn the big picture stuff. One of the first things that anyone learns about climate is that humans are responsible for most of the warming, and probably more than all of the warming since 1950.

By the way, Judith's article was meant to be a response to a criticism by Gavin Schmidt at realclimate.org, about her nonsense about human caused warming. She wrote:

If the IPCC does really mean ‘more than half’, but limited not to exceed 100%, then it is appropriate to view anthropogenically forced climate change and natural climate change as two parts of a divisible whole.  Therefore there is absolutely nothing wrong or illogical about my statement:

Pick one:
a) Warming since 1950 is predominantly (more than 50%) caused by humans.
b) Warming since 1950 is predominantly caused by natural processes.

There is lots wrong with the above, coming from a climate scientist.  Not least of which is the suggestion that b is a reasonable possibility. It's not. As Gavin Schmidt wrote:

This is not a good start. The statements that ended up in the IPCC SPMs are descriptions of what was found in the main chapters and in the papers they were assessing, not questions that were independently thought about and then answered. Thus while this dichotomy might represent Judith’s problem right now, it has nothing to do with what IPCC concluded. In addition, in framing this as a binary choice, it gives implicit (but invalid) support to the idea that each choice is equally likely. That this is invalid reasoning should be obvious by simply replacing 50% with any other value and noting that the half/half argument could be made independent of any data.

Do you think that Judith is just pretending to be so ignorant about climate science or do you think she really and truly doesn't have a clue?  Given her academic posts and the fact she's been blogging about climate science for years, I don't think the latter choice is possible. Which leads one to the unpalatable conclusion that she deliberately sets out to spread doubt, confusion and disinformation about climate.

Update - about that "other piece"

Judith Curry still cannot see where she is going wrong. She thinks some of us are "confused" writing:

curryja | January 20, 2015 at 11:25 am
ATTP and Tobis and Sou are ‘confused’, they think of course 110% is more than half. They think it is even funnier and stupider of me to respond but what if the other piece is 220%? If % are unconstrained between 0-100, you don’t know.

I am thankful to Denizens who are able to see the problems with this. Twitter can be painful, but I would expect better from those with Ph.D.’s in science.

Judith is referring to the fact that it's probable that human emissions of CO2 have accounted for more than all the warming between 1950 and now, and that this warming has been offset by aerosols. Thus 100% of the warming is comprised of CO2 warming less aerosol cooling. The "piece" is the greenhouse warming. The "other piece" is what has counteracted the greenhouse warming.

In my view, Judith  really needs to sort out her pieces. Let's define the "piece" and the "other piece" as follows:

• Piece A: this is CO2 forcing - brought about by human activity (burning fossil fuel etc). It has caused possibly more than 100% of the warming, say 110%.
• Piece B: this is aerosol forcing. It causes cooling. It has counteracted the warming. Without it, the world would be warmer. As it is, the 100% of the warming was brought about by the combined effect of greenhouse warming and aerosol cooling. Piece B is also Judith's "other" piece, which she argues could offset 220% of the warming.

Hypothesis - including Judith's "other piece"

The warming is 100%. All or even more than all of it is from human activities. Let's say more than all of the warming was from human activities.

• Piece A has contributed, say, 110% of the warming via the extra CO2
• Piece B has negated 220% of the warming via, say, aerosols, though I cannot recall a nuclear war recently. This represents Judith's "other piece".
• Piece C - there must be another "other piece", as yet unidentified by Judith. Total warming is 100%. Piece A contributed 110%. Piece B reduced this by 220%. Therefore Piece C accounts for 210% of the warming. 

Piece A + Piece B + Piece C = 100% of the warming; or 110 - 220 + 210 = 100% of the warming. 

Questions for Judith Curry

1. What could all the scientists in the world have missed that not only negated all the CO2 warming, but negated more than double it. (Judith's "other piece" - Piece B)
2. What could all the scientists in the world have missed that warmed the earth by almost double the equivalent of greenhouse warming, negating the huge cooling forcing from Judith's "other piece". (The balancing Piece C, required to get back to 100% of warming.)

Now who is confused again?

Added by Sou 21 Jan 2015 8:18 pm AEDT