by Judith Curry

Climate Feedback has interviewed a number of scientists regarding the recent House Hearing on climate science.

The article: Scientists reactions to the US House Science Committee hearing on climate science.

The scientists that were interviewed: James Renwick, Gavin Schmidt, Tim Osborn, Retto Knutti, Victor Venema, Mark Zelinka, Matt King, Andrea Dutton, Lauren Simkins, Valerie Trouet, Kerry Emanuel, James Elsner.

I am familiar with about half of these scientists.

Let’s look at the statements they were asked to respond to:

“It is an empirical fact that the Earth’s climate has warmed overall for at least the past century. However, we do not know how much humans have contributed to this warming and there is disagreement among scientists as to whether human-caused emissions of greenhouse gases is the dominant cause of recent warming, relative to natural causes” – Judith Curry

The responses say that there are a lot of studies that use climate models and focus on the period since 1950 that say human causes dominate. Ok, but I don’t find those studies convincing, and the HOW MUCH question has still not been quantified in a precise way. There is DISAGREEMENT about HOW MUCH. How can they argue that there is NOT disagreement over this issue, when two reputable, widely published scientists that have received external recognition (e.g. myself and Christy) clearly disagree?

And even the IPCC says more than half. That’s from 51 percent to 99 percent. That is a big interval… I just don’t know how much is human vs. how much is natural and I think there is a great deal of uncertainty and it is very difficult to untangle it” -Judith Curry

Yawn. ‘But human causes are more than 100%’. Get a dictionary and see how ‘HALF’ is defined. And yes, lets criticize my statement using climate model results, which are tuned to the recent warming as per several published papers and a blog post from Isaac Held. Their methodology for detection-attribution analysis is flawed. I have a draft post on this, but no time to complete. Get back to me with your attribution studies once you understand multi-decadal variability in the oceans and your climate models get the linkages, amplitudes and phasing correct. Head over to SOD, including his latest post.

[…] I demonstrate that the consensus of the models fails the test to match the real-world observations by a significant margin.” -John Christy

The responders argue that climate models shouldn’t be expected to predict short term (e.g. 20 years) temperature variations correctly. Well, that is a good argument since they don’t get multidecadal ocean variability correct. But if you accept this argument, then why should we believe the attribution studies using these models for warming since 1976?

Indeed, I am a co-author of a report in which we used a statistical model to reproduce, to a large degree, the atmospheric temperature trends without the need for extra greenhouse gases. In other words, it seems that Mother Nature can cause such temperature trends on her own, which should be of no surprise.” -John Christy

Mother nature can indeed cause substantial temperature trends on its own. The ‘detection’ part of ‘detection and attribution’ seems to have gotten lost during the past 10 years.

“the models tend to be too sensitive to greenhouse gases, likely related to the fact the models tend to shrink clouds more than in reality, so that more sunlight gets in and heats up the Earth more. […] The Earth has a way to release the heat that greenhouse gases try to build up.” -John Christy

Well even the IPCC AR5 seemed to be heading in this direction with its conclusion about ECS. Zelinka cites recent papers that use arguments related to low level clouds to argue for higher climate sensitivity. Many posts at CE argue for lower sensitivity. But more significantly, leading cloud expert and IPCC author Bjorn Stevens has argued for lower sensitivity (upper limit at 3.5C)

Everyone seems to agree that climate models are running to hot for the past ~20 years. There are a lot of possible reasons. But ignoring the evidence of Nic Lewis sensitivity analysis (and related studies) is not helpful in this regard. This is clearly an unresolved issue, and arguments for lower ECS are at least as valid as arguments for higher ECS.

“Climate models have a large amplifying effect from clouds and water vapor. The magnitude of this amplifying effect, and even the sign, are in dispute. A lot about the oceans that we don’t understand, how the ocean transports heat and carbon in the vertical is not well represented in the climate models. We also have these very large-scale, long-term ocean oscillations, which play a huge role in determining our climate. These are not well simulated and we don’t have good documentation of the really long time period oscillations. The effects of the Sun on climate, particularly the indirect solar effects.” -Judith Curry

The only responses to this one were about water vapor: “The large amplifying effect of water vapor is real and is well simulated by climate models.” There is little empirical evidence for a large long-term trend in water vapor path. The climate models have sloppy thermodynamics. The odds of climate models doing this correctly are slim.

The other points that I made were not rebutted.

“It’s been warming for hundreds of years! And we can’t explain all of that due to human causes..” -Judith Curry

Valerie Trouet argues that it has only been warming since 1850. I will leave it to Steve McIntyre to critique PAGES2K. But the IPCC has no explanation for warming between 1850 and 1950 – only a minuscule amount of this warming can be attributed to humans. This warming is natural, and the processes producing warming from natural causes did not stop in 1950.

“I have demonstrated that we cannot predict the behavior of climate.” -John Christy

Osborn responds that we can predict the annual cycle and response to volcanoes. Christy is correct that there is no evidence that we can predict the behavior climate on decadal to century time scales.

There is little scientific basis in support of claims that extreme weather events – specifically, hurricanes, floods, drought, tornadoes – and their economic damage have increased in recent decades due to the emission of greenhouse gases. In fact, since 2013 the world and the United States have had a remarkable stretch of good fortune with respect to extreme weather, as compared to the past.” -Roger Pielke, Jr.

Elsner and Emanuel respond that there is some evidence of hurricane intensity increase since 1987. However, this increase is only in certain ocean basins, and there is no way to determine whether this increase is caused by AGW or natural variability. Emanuel states an AGW caused increase should not be detectable until mid 21st century.

The rest of Pielke’s statements were not contested.

JC reflections

Well, I think of this as sort of a red team exercise. The IPCC report is the original blue team. Think of Christy, Curry, Pielke as the Red Team. The scientists providing responses in the Climate Feedback article are defending the Blue Team against critiques by the Red Team. And then this blog post responds to defenders of the Blue Team.

I think this kind of back and forth is very useful. The Goliath Blue Team didn’t manage to score any meaningful points against the Red Team in the Climate Feedback article, as far as I can tell. Obviously the selection of the individuals by Climate Feedback and the limited topics each individual chose to respond to does not necessarily cover all the bases or present the best possible arguments.

The Blue Team has its work cut out for it in defending their assertions. Even the small Red Team of Christy, Curry, Pielke scored some major points in this Hearing.

This kind of exchange is very illuminating, and I am strongly supportive of a more formal Red Team/Blue Team exercise.