In his recent testimony, Andrew Dessler reviewed what he thinks “are the most important conclusions the climate scientific community has reached in over two centuries of work”. I think that’s a very good choice to focus on, as the basics of what we know is most important, “at least as to the thrust and direction of policy” (Herman Daly). This focus served as a good antidote to the other witness, Judith Curry, who emphasizes (and often exaggerates) uncertainty to the point of conflating it with ignorance.
Dessler mentioned the following “important points that we know with high confidence”:
1. The climate is warming.
Let’s take this opportunity to show the updated figure by Cowtan and Way, extending their infilling method to the entire instrumental period (pause? which pause?):
2. Most of the recent warming is extremely likely due to emissions of carbon dioxide and other greenhouse gases by human activities.
This conclusion is based on several lines of evidence:
– Anthropogenic increase in greenhouse gases
– Physics of greenhouse effect
– Observed warming roughly matches what is expected
– Important role of CO2 in paleoclimate
– No alternative explanation for recent warming
– Fingerprints of enhanced greenhouse effect (e.g. stratospheric
warming cooling, which was predicted before it was observed)
Thus, we have a standard model of climate science that is capable of explaining just about everything. Naturally, there are some things that aren’t necessarily explained by the model, just as there’re a few heavy smokers who don’t get lung cancer. But none of these are fundamental challenges to the standard model.
He goes on to explain that the so-called “hiatius” is not a fundamental challenge to our understanding of climate, though it is “an opportunity to refine and improve our understanding of [the interaction of ocean circulation, short-term climate variability, and long-term global warming].”
What about alternative theories? Any theory that wants to compete with the standard model has to explain all of the observations that the standard model can. Is there any model that can even come close to doing that?
And making successful predictions would help convince scientists that the alternative theory should be taken seriously. How many successful predictions have alternative theories made?
3. Future warming could be large
On this point I always emphasize that the amount of future warming depends both on a combination of factors:
– the climate forcing (i.e. our emissions and other changes to the earth’ radiation budget)
– the climate sensitivity (the climate system’s response to those forcings)
– the climate response time (how fast will the system equilibrates).
Internal (unforced) variability also plays a role, but this usually averages out over long enough timescales.
4. The impacts of this are profound.
In the climate debate, we can argue about what we know or what we don’t know. Arguing about what we don’t know can give the impression that we don’t know much, even though some impacts are virtually certain.
The virtually certain impacts include:
• increasing temperatures
• more frequent extreme heat events
• changes in the distribution of rainfall
• rising seas
• the oceans becoming more acidic
Time is not our friend in this problem.
Nor is uncertainty.
The scientific community has been working on understanding the climate system for nearly 200 years. In that time, a robust understanding of it has emerged. We know the climate is warming. We know that humans are now in the driver’s seat of the climate system. We know that, over the next century, if nothing is done to rein in emissions, temperatures will likely increase enough to profoundly change the planet. I wish this weren’t true, but it is what the science tells us.
Peter Sinclair posted a video of Andrew Dessler’s testimony. Eli Rabett posted Dessler’s testimony in full.
A key distinction in the two senate hearings was that Andrew Dessler focused on what we know, whereas Judith Curry focused on what we don’t know (though “AndThenTheresPhysics” made a good point that Curry goes far beyond that, by e.g. proclaiming confidence in certain benign outcomes (e.g. regarding sensitivity) while claiming ignorance in areas where we have a half-decent, if incomplete, understanding, e.g. regarding the hiatus). I have argued before that emphasizing (let alone exaggerating) uncertainties is not the road to increase people’s understanding of the issue, where what we do know is much more important to convey (if your goal is to increase the public understanding of scientific knowledge). Alongside that I argue that much more attention is needed to explain the nature of science, which is needed to e.g. place scientific uncertainties in a proper context.
Herman Daly said it as follows, in a quote I’ve used regularly over the past few years:
If you jump out of an airplane you need a crude parachute more than an accurate altimeter.
Arguing whether the altimeter might be off by a few inches is interesting from a scientific/technological perspective, but for the people in the plane it’s mostly a distraction.