Scientists Talking Dirty: On “climate mitigation” and the goal of limiting warming to 2ºC (3.6ºF)?

October 1, 2014 2:31 pm0 comments

Climate mitigation

Intro by Michael Quirke: In light of last week’s climate summit, I’ve asked for some thoughts from the scientists on “climate mitigation,” which entails reducing fossil fuel combustion or capturing and storing emissions. [1] In the context of climate change, “mitigation” can be a very dirty word for conservatives because it implies more government intervention in the economy. Not only that, to actually reduce future warming and *mitigate* the risk of future impacts, it apparently requires intervention on a BIG scale. So we’re talking a carbon “tax,” “cap-and-trade,” or a whole lot more “EPA regulation”—all of which are anathemas to many conservatives’ ears.  Furthermore, effective mitigation calls for a global treaty or at least collective agreement with international monitoring. It’s a hard pill to swallow for a libertarian. Nonetheless, based on what I’m hearing in the Forum, this is what’s required if we’re ever going to get a handle on emissions, much less have a snowball’s chance in hell of limiting warming to 3.6°F. There hasn’t been much dialogue as to why the world’s nations established 2°C (3.6°F) as the threshold that ought not be crossed, so I am leading with that question and then presenting some common refrains from conservatives regarding mitigation. I recognize this is going beyond science and into values, but I would like to hear some thoughts from the scientists anyway. Ok, let’s talk dirty!

Why the target of 2ºC / 3.6ºF?


Dr. Andrew DesslerDr. Andrew Dessler: There are basically two reasons for this. First, if you look at the Holocene, the period in which human society as we know it now has evolved, temperatures have varied about this much.  Second, given the trajectory our climate is on, this is about the best we can hope for.



Dr. Will HowardDr. Will Howard: Though setting any particular number seems somewhat arbitrary, 3.6 F (or 2 C) has been agreed upon as a threshold beyond which some long-term impacts may be difficult or impossible to reverse, at least on societally-relevant time scales. Some of these include changes in ice sheet mass balance which would “commit” us to long-term sea-level rise. But another set of impacts are effects associated not with the temperature rises themselves, but the carbon dioxide concentrations giving rise to the warming. Biogeochemical impacts like ocean acidification are difficult to reverse because of the long timescales associated with the buffering by ocean uptake, carbonate dissolution, and weathering.As a geoscientist my perspective is long-term. When I talk about “long-term” I mean thousands of years if not longer. The longer we wait to bend the emissions curve, the harder it gets to mitigate. Aside from economic and technological “lock-in” we have long time constants in many parts of the climate system: ice-sheet dynamics, the geochemical buffering mechanisms in the ocean, the processes that move heat within the interior of the ocean, continental weathering. My own research has focused on ocean acidification. From the perspective of my bit of science, anything we can do *now* to cut even the rate of growth of CO2 emissions would be a good step.

These long time scales are part of what distinguishes the problem of climate change from other environmental problems we have faced, and in many cases solved. The long-term nature of the challenge, the uncertainties, and the fact that many of the anticipated impacts remain in the future, make mitigation a “hard sell.” Convincing people to sacrifice economic benefits now to avert future risks is not easy. However, waiting until we have absolute  “certainty” (in my view we may never have that) to act may mean we have less chance to mitigate.

Dr. Bart VerheggenDr. Bart Verheggen: The 2 degree target (in degrees Celsius) as it’s commonly referred to is meant to avoid dangerous anthropogenic interference with the climate system. It is however not a black and white distinction between “no problem” at 1.9 degrees C and “the end of the world” at 2.1 degrees C, of course. The temperature target has been arrived at from a variety of considerations, e.g. scientific considerations (more warming becomes increasingly difficult to adapt to, and climate impacts become negative across the board) but also socio-economic, historical and political reasons (as e.g. laid out in Randalls, 2010 

I view the reasons for this target as a mixture between what is scientifically known, what is socially desirable and what is politically/economically feasible. It is thus not a purely scientific number in my honest opinion.


President Obama and world leaders negotiating in the Copenhagen Summit of 2009. Hillarly Clinton reportedly said, "[It] was the worst meeting I've been to since eighth-grade student council." One of the few agreements coming out of the conference that the 2 degrees Celsius threshold ought not be crossed. Source. Republished under fair use.

World leaders negotiating in the Copenhagen Summit of 2009. Hillarly Clinton reportedly said, “[It] was the worst meeting I’ve been to since eighth-grade student council.” One of the few agreements coming out of the conference was that the 2 degrees Celsius threshold ought not be crossed. Republished under fair use. Source

“Whatever, we’ll adapt”

Some folks are ideologically opposed to any government intervention period. So what happens if we do just this—just adapt to whatever comes?

Dr. Verheggen:  Both adaptation and mitigation (emission reduction) are important, but I would emphasize mitigation, since it dominates the long-term risk we expose future generations to (CO2 concentrations remain elevated for a very long time after emission). Adaptation is an important short-term strategy in coping with unavoidable regional consequences, but in the long term adaptation without mitigation is like mopping the floor while leaving the tap running. Moreover, there are limits to what societies can realistically adapt to (e.g. sea level rise).

Dr. Dessler: This is a policy statement, not a scientific one. We could agree completely on all the science and still disagree over whether we should rely only on adaptation. That said, speaking as a citizen, I do not support relying entirely on adaptation. Doing so raises a number of moral and practical issues, which is why most serious analyses conclude that mitigation must be part of our response.

Dr. Howard: I don’t think this is a binary choice. I think adaptation needs to be considered part of the policy mix for two reasons: 1) I think we are already “locking in” some climate change and concomitant impacts already and we will have to adapt to these; 2) adaptation policies are likely to have co-benefits in building resilience to weather extremes (cyclones, floods, fires) and other natural hazards whether these arise from anthropogenic climate or not. So reducing vulnerabilities to such impacts does not require “settling” arguments about climate change and its causes.


Recent Twitter exchange with Paul C. Knappenberger of the Cato Institute on hypothetical worse case scenario; mitigation still not worth it according to Mr. Knappenberger.

Recent Twitter exchange with Paul C. Knappenberger of the Cato Institute on a hypothetical worse case scenario; mitigation still not worth it according to Mr. Knappenberger.


“The science is not settled!”

According to the latest dialogue on CCNF, the range of climate sensitivity estimates are pretty wide. And then there’s that unpredicted hiatus in global surface warming temperature rise. Can we kick this can down the road until the science becomes more clear?


“I still stand by that the science is not settled on man-made global warming,” Gov. Perry said on the campaign trail.

“I still stand by that the science is not settled on man-made global warming,” Gov. Perry said on the campaign trail. Republished  under fair use. Source

Dr. Dessler: Scientists never say the science is settled. Some parts of the science are settled, other parts are not (I talked about this in my Senate testimony). The certain impacts include increasing temperatures, more frequent extreme heat events, changes in the distribution of rainfall, rising seas, the oceans becoming more acidic. Speaking as a citizen, I think these are serious enough to compel action now.

Dr. Howard: The science indeed is not settled. Some of those arguing against mitigation action now cite the uncertainties, and the flaws in the models used to construct future scenarios. The uncertainties and the models’ flaws do exist, but can we presume the errors all go in the direction of sensitivity and impacts at the lower end of the range? In my view the question should not be “are the model-constructed scenarios wrong?,” but rather “in what direction are they wrong?”

See my point above about “waiting.” By the time the science is clear we may not be in a position to mitigate. The uncertainties argue for at least adopting “no-regrets” policies now.

Dr. Verheggen:  Some parts of climate science are known with greater confidence than others, but the term “settled science” is often a canard in trying to make scientists appear somehow unscientific. Regarding climate sensitivity, the likely range of this quantity hasn’t changed in 35 years of research. So waiting until we can better constrain the climate sensitivity might be akin to waiting for Godot (during which time the CO2 will continue to accumulate in the atmosphere). Society is well used to and capable of making decisions under uncertainty.

“We are an innovative bunch when we need to be, I’m sure we’ll devise a way to suck CO2 out of the air or something if it gets bad.”

It took our rivers catching on fire to pass the Clean Water Act, so what happens if we put off mitigation until things get really bad?


Dr. HowardNo question we humans are innovative. Indeed, the challenge of climate change is one by-product of our beneficial harnessing of the earth’s fossil energy resources to raise human living standards. This living standard is a good thing, but we now know it comes with a risky side effect.

Dr. Verheggen: Never schedule breakthroughs.

Dr. Dessler: I think that assuming the invention of a new technology is pretty risky. What happens if it doesn’t materialize on time?

We now need to apply our innovative and inventive collective mind to developing and scaling-up cost-effective and reliable alternatives to fossil-fuel energy, and to exploring the feasibility of strategies like carbon capture and storage.


Environmental Engineering

Artistic rendering of a “CO2 scrubber.” Based on what I’ve read, sucking CO2 out of the air on a global scale is about as easy as putting the cats back in the bag. One reader swore this is technology was ready. “Who would pay for it?” I asked. Image republished under fair use. Source


Michael Quirke: For the next two items, we’re definitely going beyond the science and getting into the realm of values. Recognizing this, let’s continue.


“I don’t care”

I’ve talked with some folks about the science and risks being communicated by the scientists’ in the Forum thus far. They seem to grasp it, but really don’t give a sh$%. Your thoughts?


One man's solution to curbing global warming. From the "People's Climate March" ahead of last week's UN Climate Summit.

One man’s solution to curbing global warming. From the “People’s Climate March” ahead of last week’s UN Climate Summit. All-Nite Images via Flickr

Dr. Dessler: That’s sad, particularly since their kids and grandkids are going to care.

Dr. Verheggen: I’d appreciate the honesty of someone saying this and prefer it over someone with the same opinion, but who tries to hide it by attacking the science instead. Nevertheless, it is a rather cynical and egotistical take on the issue (since people at different places and times will probably be adversely affected).

Dr. Howard: This is certainly not a matter of science. Humans respond to risk in many ways that have nothing to do with science. I think if science were the main driver of human behavior then no one would ever smoke another cigarette. But many people still do smoke, including health professionals who are unlikely to be ignorant of the science (JAMA. 2014;311(2):197-199. doi:10.1001/jama.2013.284871).

I would also say we have to consider there may be issues seen as having more immediacy and priority than climate change. For example, in the developing world, smoke from biomass cooking fires kills millions each year (Subramanian, 2014). If we told people at risk from those respiratory diseases they could have clean(er) fossil fuel energy for cooking now, but would risk climate change impacts later, what would they choose?

Subramaniam, M. (2014), Deadly Dinners, Nature, 509(548–551), doi:10.1038/509548a.


“I’ll leave it in the hands of God” (aka God will save us before it gets real bad)

Not sure if y’all are comfortable getting into a theological discussion, but this is a recent quote from Dan Patrick, the Republican candidate for the Lieutenant Governor of Texas.


Dan Patrick and Pope Francesco I on climate change

(Top) Texas State Senator Dan Patrick. Republished  under fair use. Source; (Bottom) Pope Francis. Source: Jeffrey Bruno via Flickr

Dr. Dessler: Lots of religious people, such as the Pope, would disagree. I basically think this is a convenient excuse to rationalize doing nothing.

Dr. Howard: Of course we cannot absolutely rule out the possibility of divine intervention. However I will note that many faith communities have taken on the issue of climate change from their respective traditions’ theological viewpoints, arising in part from a spiritual view that humans have a duty to act as responsible stewards of the earth. Rightly or wrongly, these faith communities have taken view that humans need to address this ourselves. Example: Common Belief: Australia’s Faith Communities on Climate Change.

Dr. Verheggen: I’ll refer to the evangelical climate scientist Katherine Hayhoe on this one (e.g. “From a Christian perspective, we have free will to make decisions and must live with their consequences. This is, after all, a classic Christian solution to the theological problem of evil.”

Michael Quirke: Thank you Drs. Dessler, Howard, and Verheggen for sharing your thoughts. I understand this topic is values-laden and outside of your usual comfort zones. Nonetheless, really appreciate the thoughts and insights.


[1] The IPCC defines mitigation as “an anthropogenic intervention to reduce the sources or enhance the sinks of greenhouse gases.” IPCC, AR4, Chapter 18

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