Saturday, November 30, 2013

Reviewing the 2°C target

As the UNFCCC evaluates the feasibility of the 2°C target a new paper explores the prospects of four possible alternative options. The authors warn against a too narrowly drawn and science based exercise: 

At the time of this writing, the Subsidiary Body for Scientific and Technological Advice (SBSTA) and the Subsidiary Body for Implementation (SBI) have jointly established a contact group to assist the COP in conducting the review. A structured expert dialogue to support the work of the joint contact group has been set up to enable an exchange of views, information and ideas and to ensure scientific integrity. At the first workshop, held on 5 June 2013, some scientists presented their latest research. … The UNFCCC review does seem to be a rather tightly drawn exercise at the moment, but it is argued here that it could, and indeed should, lead to a much more open debate on the 2°C target and some of its potential alternatives. While the existing literature points to a number of alternative options, in this paper we select four of them and explore what they might entail in practice. 

Here are the four options which can be described as (1) mitigate for 2°C but adapt for 4°C, (2) adopt new metrics and targets, (3) be more pragmatic, (4) carry on with 2 degree target.

Option 1: ‘mitigate for 2°C but adapt for 4°C’. Even pursuing 2°C to the maximum does not reduce the risk of 4°Cto zero. Society should therefore ‘hedge its bets’ by taking steps to adapt to a much warmer world while maintaining a high level of ambition regarding mitigation. … such an approach… could have three elements: Aim to stay below 2°C; Build and budget assuming 3–4°C; Contingency plan for 5–7°C of warming. Although its advocates acknowledge the potential contradictions within the position, these are considered manageable. Given the continuing uncertainties over climate sensitivity, the eventual magnitude of climate change, and societal capacities to adapt, policy makers should step up their current efforts to mitigate. For their part, adaptation policy makers may not have to do too much differently, particularly given the difficulty of drawing a neat distinction between the actions they will need to take for a 2°C world in 2050 and what might be required for 4°C…

Option 2: ‘adopt new metrics and targets’. Because a long-term temperature-based target appears unable to stimulate short-term policy responses and in any case does not represent current understandings of global climate system sensitivities, more specific and near-term targets should be adopted. Here, Lenton’s (2011a) views are taken as representative of a much larger and emerging line of thought on planetary boundaries (Rockstrom et al., 2009). Lenton (2011a) suggests that a range of potential thresholds of danger exist, not necessarily linked to global mean temperature change, but instead to (1) magnitudes of change, (2) rates of change, and (3) spatial gradients of anthropogenic radiative forcing. For example, monsoons could potentially be disrupted by localized warming altering local temperature gradients, which in turn are influenced by the uneven distribution of anthropogenic aerosols such as black carbon in the atmosphere. Future policy efforts could therefore be tailored to respond to these thresholds, rather than the ‘meta’ target of 2°C of warming. Article 2 of the UNFCCC (noted above) could even be revised to make limiting anthropogenic radiative forcing the principal objective, with the stabilization of GHG concentrations as one of a number of sub-objectives. The scientific literature is already beginning to frame scenarios in terms of radiative forcing (Moss et al., 2010). The main aim would be to prevent the crossing of large scale thresholds in physical systems, but it could also help to address some of the other ‘reasons for concern’ highlighted by the IPCC (Smith et al., 2009). 

Option 3: ‘be politically more pragmatic’. Society should accept that adopting science-informed targets such as 2°C has failed to drive social change and governors should instead concentrate on delivering what is politically achievable in the short to medium term. This option emerges from a discourse that has, since the early 1990s, repeatedly expressed scepticism towards the ‘hyperbolic multilateralism’ of UN climate policy (Prins et al., 2010, p. 7). Proponents argue that not only has this failed to achieve significant emissions reductions, it may also have impeded potentially more effective attempts to promote investment in low-carbon technologies at more local levels (Rayner, 2010; Victor, 2011). They argue that political momentum towards a more global-scale approach is more likely to be generated by demonstrating clear economic and social benefits from mitigating in a specific number of problem areas. Therefore (and in common with advocates of Option 2), they favour rapid action on powerful short-lived forcers (Kopp & Mauzerall, 2010), the benefits of which will be more quickly apparent, as well as increased levels of investment in research and development, rather than waiting for a perfectly comprehensive global deal that may never appear. This view is associated with scepticism towards certain other kinds of universalistic thinking (Ostrom, 2010), including the UNFCCC’s concept of dangerous anthropogenic interference. Pielke (2011), for example, calls for a new international convention that does not refer to ‘dangerous interference’ at all, but instead to the achievement of decarbonization consistent with meeting long-term targets for the stabilization of atmospheric concentrations. 

Option 4: ‘recommit to staying within 2°C’. The growing probability of highly risky rates of warming makes it even more important to recommit to ‘low stabilisation targets’ (Knopf, Luderer, & Edenhofer, 2011, p. 617). While accepting that it is, to some extent, a crude translation of the principle of avoiding dangerous climate change, advocates of Option 4 generally argue that the 2°C target nonetheless provides a critical role in the international regime (Hare, Stockwell, Flachsland, & Oberthür, 2010; Jaeger & Jaeger, 2011). In view of the many uncertainties associated with climate change (and in the event that emissions are not reduced fast enough to remain within 2°C, or climate sensitivity turns out to be at the higher end of scientific estimates), advocates of this option argue that it is preferable to recommit to the 2°C target rather than abandon it. In which case, it may be sensible to actively remove CO2 from the atmosphere now, e.g. by producing biochar or deploying bioenergy equipped with carbon capture and storage (CCS), although the political and technical feasibility of such strategies remains highly uncertain, particularly at the scale and within the timeframe necessary. However, in order to maximize the probability of staying within 2°C, even more radical measures might be deemed necessary (Anderson & Bows, 2008, 2011; Swart & Marinova, 2010). To deliver drastic emission reductions of the order of 9–10% per year, some proponents are willing to contemplate limits to economic growth in the short term, particularly in the industrialized world (Jackson, 2009). Of course, much depends on precisely what probability of remaining within 2°C is sought. This is no idle matter: the higher the probability of staying within 2°C sought, the lower the ‘budget’ of cumulative emissions available for policy makers to consider and hence the more radical the policy options will have to be. Be that as it may, for advocates of this option an increasing probability that the 2°C target will be exceeded is no reason to abandon it entirely, just as a common tendency among some drivers to exceed a given speed limit is no argument against having and enforcing speed limits.  

In conclusion, the authors write (my emphasis):

More is being learnt about the probability and also the implications of ‘going beyond’ 2°C, although huge uncertainties remain with respect to both these issues. Both should form an important part of the 2013–2015 review, but whether or not they do remains to be seen. Formally, the review should consider the following (UNFCCC, 2010, para. 139(a)): 1. The best available scientific knowledge, including the assessment reports of the IPCC 2. The observed impacts of climate change 3. An assessment of the overall aggregated effect of the steps taken by Parties in order to achieve the ultimate objective of the Convention 4. Consideration of strengthening the long-term global goal, referencing various matters presented by the science, including those in relation to temperature rises of 1.5°C 

However, many countries will not want to open up the debate around the fourth point too much, and some will likely try to restrict it to no more than issue 3, i.e. a report on what pledges and emission reductions have been made thus far in relation to the existing target of 2°C.
We argue that narrowing the scope of the review too much would be an important opportunity missed. When confronted with such a deep policy dilemma, policymakers should be as aware as possible of all the implications of pursuing alternative courses of action. In situations of high uncertainty and strong and enduring value differences, scholars of policy appraisal recommend ‘opening’ up policy dilemmas to wider framings and sources of expertise, rather than ‘closing them down’ in a valiant attempt to arrive at a scientifically precise answer regardless of whether it has societal support (Stirling, 2008, p. 262). We suggest that the international climate regime itself faces such a high risk, posed by a growing realization that 2°C is very probably unattainable, at least with current policy responses and current understandings of climate sensitivity (the latter issue becoming the subject of increased debate in 2013 – see for example Otto et al., 2013). For this reason, we recommend that the 2013–2015 review examine a range of alternative options. By examining (and challenging) some of these alternatives to the status quo, a wider societal debate about the ultimate objectives of climate policy could be stimulated.
As noted above, the 2013–2015 review is specifically directed to consider ‘various matters presented by the science’. This paper has initiated an exploration of some of the policy and governance implications of adopting four very different approaches, drawing upon science and social science perspectives. Often, these implications have been only superficially considered in debates about 2°C, yet history suggests these policy and governance implications are precisely the issues on which agreement at the international level has foundered. Bringing the options together proved to be very illuminating. It was shown, for example, that similar opportunities and risks apply to more than one option. This is important, because it suggests that no single option – including Option 4 – is uniformly ‘better’ than the rest. Indeed, future research could usefully explore the scope for combining elements of different options, as part of amore systematic comparison than space allows here, but which this journal has a record of publishing (see, e.g. Aldy et al., 2003). It has been shown that Options 2 and 4 are to some extent compatible with one another, as are Options 1 and 3.
Our key point, however, is that, as uncomfortable and threatening as it may be to sketch out and explore the risks, opportunities and uncertainties associated with alternative options, it could offer a more productive and in the longer term more politically sustainable way to grapple with the deep dilemma at the heart of contemporary climate policy. In fact, and perhaps rather ironically, it may encourage some of the more doubtful decision makers to (re-) commit to the existing 2°C target, however demanding it may be, as the least unattractive course of action. Nonetheless, introducing and appraising different options will serve at best to clarify, not remove, the underlying policy dilemma. 
Andrew Jordan, Tim Rayner, Heike Schroeder, Neil Adger, Kevin Anderson, Alice
Bows, Corinne Le Quéré, Manoj Joshi, Sarah Mander, Nem Vaughan & Lorraine Whitmarsh (2013) Going beyond two degrees? The risks and opportunities of alternative options, Climate Policy, 13:6, 751-769, DOI: 10.1080/14693062.2013.835705


PLG said...

Here's a good view as well:

Roger said...

Hi Reiner- How long is it going to take to for that community to realize that a delta surface temperature target (e.g. +2C) is seriously flawed even with respect to global warming, much less other changes in the climate. With the claim that heat is being sequestered deeper in the ocean, where a surface temperature would not sample it, it is even more clear that it is a flawed climate metric.

I have discussed this a number of times; e.g. see

Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335.

Best Regards

Roger Sr.

Georg Hoffmann said...


"How long is it going to take to for that community to realize that a delta surface temperature target (e.g. +2C) is seriously flawed even with respect to global warming,"

Since it is a political objective with loose scientific motivation.

You can declare in the evening news that the world is trying hard to avoid a 2C warmer world and sadly fails.
However you cannt declare that you will do everything to limit the ocean heat budget changes to 10^27 J/yr (or whatever) and fail as well.

The result is the same but the second option sounds too ridiculous.

Roger said...

Hi Georg - However, the first metric is not robust scientifically and the second is. Moreover, the ocean heat budget changes provide an accurate metric of warming and cooling of the entire climate system since ~90% of the heat changes are in the ocean.

I agree 2C is a political statement. As scientists, I urge us to be more rigorous.

Best Regards

Roger Sr.

Georg Hoffmann said...

Again, so if everyone knows that a) the 2C is a political statement with loose and very complicate scientific background and b) that it is completely out of question to communicate to the public an emission/climate objective linked to the oceans heat content so what is the problem then?
Here at the Klimazwiebel most commenters tend to think that it is very bad to speak about any objectives. Ok, I dont belive that. But, yes, it is a possibility to speak just about: Lets reduce a bit CO2 emsissions. Might be this works and might be that is not in the way of economic development. Thats an alternative.

But as long as you are talking about objectives (as something you want to talk about with Saudi Arabia and Togo at one table) you need to talk about global temperatures and similar stuff. The rest is simply not possible to communicate. Global temperatures is not the best scientific metric but it is the only one that works politically.

Roger said...

Hi Georg

The global temperature metric is not working politically. It has only accomplished a polarization of the process.

By linking to that metric, if that temperature, even with its warm bias as we have published on, does not rise as quickly as the models predict, it is going to further discredit the climate community.

Yet, even if temperatures do not rise, the atmospheric concentration of CO2 from human activity does. This will still cause a biogeochemical effect with incompletely understood consequences.

Sooner or later, the policymakers are going to recognize the multi-faceted inadequacies of the 2C value for both global warming and, much more completely, changes in the climate system.

Best Regards

Roger Sr.

@ReinerGrundmann said...

Different metrics have proven to be stumbling blocks in negotiations (e.g. absolute vs per capita emissions; current emissions vs cumulative; etc). In this context negotiators sought a purely technical measure which seems acceptable and allows to come to an agreement. Hence the rhetoric 'the science tells us'. But even if such a technical measure would be accepted by all nations (no matter if it is expressed in air temperatures or ocean heat content) the practical meaning would be contested again (who should reduce by how much? Should there be different categories of countries?)

This has led to a deadlock in the UN process (*not* skeptical propaganda) which is not going to go away. For this reason (among others) option 3 in the cited paper has been advanced by several advocates of a pragmatic climate policy.

Georg Hoffmann said...


I'll try it again.
We agree probably that there are two options: You formulate an objective or you dont.
Here at Klimazwiebel nobody wants objectives. One possiblity.
But if you formulate one it has to be an objective, that both people and politicians somehow understand. The idea that there is a negotiation with politicians discussing the necessity to limit ocean heat budget to 500 megatrillionbazillion Joule is ridiculous. So it is T_glob, what else?
" if that temperature, even with its warm bias as we have published on, does not rise as quickly as the models predict, it is going to further discredit the climate community."
And if the ocean heat budget does not rise as forseen you have the same problem. Again, another metric, the same problem (besides of the problem that nobody knows what the ocean heat budget is and why to worry about).

"Different metrics have proven to be stumbling blocks in negotiations"

It has been proven that nobody wants binding agreements.
It has not been proven that this has anything to do with a 2C objective or any other objective or any other metric to reach whatever objective.

@ReinerGrundmann said...


"It has been proven that nobody wants binding agreements"

You are quite wrong about this. Where have you been in the past 25 years?

Georg Hoffmann said...

"Where have you been in the past 25 years? "
France, but I doubt that this is the explanation.

I specify: "nobody wants binding agreements on CO2 emission reductions"
As we know in case of the ozone/CFC problem there was an agreement. I still think that the detailed comparison is enlightening.

Of course CFCs are a smaller problem in many aspects but might be the differences matter.

1) Time scale: 1o years vs 50 years (to get rid of CFCs or to change our energy system.)
2) Time scale: 10 years vs 200-500 years for the consequences of failing
3) Consequences: skin cancer vs unclear disasters in the far future
4) Pressure groups: Bosch refrigerators vs 50 of the 100 biggest enterprises of the planet
5) Method: Forbidding CFCs compared to the market, cap and trade, future techonology hopefully reduce CO2 emissions.
6) The objective of the negociations of the Montreal protcol was from the beginning the total abdiction of CFCs. So that is an objective much more ambitious than is today an objective like 2C.
7) What is not different between the CFCs and the CO2 however is the scientific basis which is rock solid but decorated with some quantitative uncertainties in both cases.

@ReinerGrundmann said...


I specify: "nobody wants binding agreements on CO2 emission reductions"

Still wrong. There are countries which in fact are pushing in this direction. Did this escape your attention?

Your CFC/CO2 comparison is too superficial and it would drive is off topic if I were to engage with the points on your list (you probably know that I have published research about this).

It is unfortunate that climate policy has tried to follow the footsteps of ozone policy and to insist that we need to stick to targets and timetables even when no agreement is in sight. Doesn;t this look like trying to wish away some basic facts of reality?

Georg Hoffmann said...

"Still wrong. There are countries which in fact are pushing in this direction. Did this escape your attention?"

No, but I looked a bit deeper into the heart of the ones that are so much pushing as you said.

To give just one of many examples.

Also the CO2 balance of the last years of the "pushing" Germany is interesting.

We both agree that the negotiations fail and will fail in the future. Now you say the problem is that there is an objective (2C or others) and too much timetable. And I say that the principal actors simply dont (really) want an agreement since it is too expensive, there is no reward in the near future and any agreement is unfair within just a couple of years.

I think it has to do with some of the differences I listed above. The time horizon e.g. is simply too long for our or any society.

Georg Hoffmann said...

Or let me put it this way. Why actually everyone believes that the problem of CO2 emissions can be solved/successfully negotiated etc.?

Is there any law in social sciences saying that any problem will be solved in a satisfying way? Might be this one is simply too big, too expensive, too far away, too much interplay with international politics, too much interwooven with questions of justice and development.
At least it strikes me that everyone is so convinced that obstacle to make any progress are some allegedly important details as "better use ocean heat content instead of surface temperatures" or "better dont speak of objectives or timetables". One should consider the possibility that the problem itself is just not made for solutions. Sometimes people fail.

Hans von Storch said...

Georg, I not think that you and Reiner are that far from each other. You should just try to recognize that Reiner is from another community, using different language and concepts.

But, who made this claim "Why actually everyone believes that the problem of CO2 emissions can be solved/successfully negotiated etc.?"
I do not believe that, not because of stupidity, lack of knowledge or evilness on the side of negotiators, but because of conflicting legitimate interests, perceptions, different levels of optimism and pessimism, and the like, in short: culture.

@ReinerGrundmann said...


Hans is right, we seem to be agreement when you ask

Is there any law in social sciences saying that any problem will be solved in a satisfying way? Might be this one is simply too big, too expensive, too far away...

this is called a wicked problem in social science jargon and is the reason why the Hartwell approach says we cannot solve the problem of climate change, only manage it more or less well.

This is option 3 in the paper by Jordan et al above.

So if you and Roger reconsider the options presented in the paper, would you come to the conclusion that this the most convincing one? I don't see that you and Roger are necessarily that far apart either, as you both have reservations about the temp. target.

MikeR said...

I really think that the issue here is that most people don't think that an emergency reaction is called for. If astronomers agreed that an asteroid was going to hit earth in 2070, of sufficient size to exterminate life on earth, I think you would see a different reaction. We would all be arguing on the best course of action (which might include building up our economy and doing R&D on space-flight technology - that might have a better chance than bankrupting ourselves for a bunch of ineffective spaceships right now) - but liberals and conservatives would agree that the problem would have to be solved at any cost whatever.

Most of us just don't feel that way about this issue. Even if there will be major impacts, the question I really care about is - can you estimate the chances of really catastrophic impacts, "tipping points"? If you think they are unlikely (and the IPCC seems to be saying that, even if no one can be sure), my response if probably going to be the same for almost any solution you propose - wait and adapt if necessary.

Georg Hoffmann said...

I see disagreement on several points.
Let me explain.
1) There is the issue whether T_glob should be mentioned/used as a metric of global change in international negotations and on the political scene in general. This would even be a point if we (as you and Richard suggest) drop the entire idea of targets and dangerous thresholds. My opinion (in contrast to Richard Pielke sr) is yes. We have to do that since a) this is a unit people and politicians understand and which can be communicated. and b) uncertainties and physical problems might point rather to ocean heat content as a suitable metric. But when talking about for example 2C there are huge uncertainties what that means in terms of emission reductions anyway (climate sensitivity, 50% chance to meet the target). So compared to these uncertainties the problem of mixing more or less heat into the ocean seems to me second order.
I prefer therefore to use a metric which is objectively less suitable but which is comprehensible to most people.
>> 2)

Georg Hoffmann said...

PS Change Richard against Reiner where necessary.

Georg Hoffmann said...

Further disagreement

2) "this is called a wicked problem in social science jargon and is the reason why the Hartwell approach says we cannot solve the problem of climate change, only manage it more or less well."

A)this implies for me that we dont consider the full range of uncertainties of climate projections.It is managable only for the lower/better half of the estimates. The other half is not managable without major disruptions. There might be good arguments for this estimate (low climate sensitivity? probability of major future technology breakthroughs) but it is not in agreement with the full IPCC uncertainty range.

3) Everyone calls his/hers approach to the problem "practical, realistic and based on common sense". At least I havent heard that one single person defends eg the emission pathway to a 2C as driven by ideology and unrealistic. So your selling point of "‘be politically more pragmatic’." is not so convincing as it seems since it just calls the others as not pragmatic (which they say they are).

3)" I do not believe that, not because of stupidity, lack of knowledge or evilness on the side of negotiators" But still some stupidity and evilness here and there helps to explain the mess we are in. It is part of the klimazwiebel approach to consider Greenpeace as influential as the 50 richest enterprises of the planet. So not everything is exactly equally legitimate.

But beside of this the people who came up with things like cap and trade or the Waxman bill are not stupid either. At least (in contrast to your pragmatic approach) they can claim that this approach once worked for other environmental issues (air pollution etc).

So in summary, nothing works and its not clear why the "pragmatic approach" should somehow work at least a little better.

Anonymous said...

@ Georg,

Richard, Reiner - .... - or Roger? ;-)


Karl Kuhn said...

I have two problems with the 2C goal.

Overconfidence: The 2C limit assumes a) that we can handily engineer the earth's temp by emitting more or less CO2, and b) that science 'knows' that warming beyond 2C is the equivalent of Armageddon. Both points are becoming more and more dubious - the more we learn.

The logic of urgency: The 2C limit was agreed when the researchers and activists behind it were still confident that temps would continue to rise like in the 80s and 90s. In that context the 2C was a handy tool to create a sense of hollywoodesque urgency that could legitimize the withdrawal of climate policy from widespread, open and patient public debate and bargaining. However, such hopes to end the debate rarely materialize, as they do not simply erase all the other incentives and constraints to which negotiators and the public are exposed. In addition, the hiatus of global temperatures inconveniently reduces the sense of urgency that the 2C goal was supposed to create.

Global warming is not the issue. Rather, I believe that relentless mining and burning of fossil fuels should make us nervous. I have doubts about the warming narrative, but this is no justification for turning the earth upside down in search of the last bit of oil, coal or gas (see brown coal in Germany or tar sands in Canada).

Therefore, instead of touting the apocalypse, I would welcome targets for reducing the share of dirty fossil fuels with contestable alternatives, be it the 'ecologically correct' renewables or nuclear. Then climate scientists could return to their desks and labs.

Germany is trying this with the Energiewende, but is hastening things too much (waste money on first-generation renewables) and too narrow-minded (exclude the nuclear option).

@ReinerGrundmann said...


if you look at the rhetoric, the defenders of current top down, global climate policies (where the 2 degrees target is a must) call their approach 'ambitious'. There is no mentioning of pragmatic steps. It is about saving the planet, nothing less.

The question is what happens when this approach will finally fail in Paris 2015. Oliver Geden has a nice post here:

See also the recent Op-ed in the Washington Post

Roger said...

Georg - Let me try one more time. You write

"The idea that there is a negotiation with politicians discussing the necessity to limit ocean heat budget to 500 megatrillionbazillion Joule is ridiculous. So it is T_glob, what else?"

The problem is one needs to be soundly based in physics before involving the policymakers in using physics to define thresholds.

The surface temperature metric works well for a 5cm diamter solid sphere. It is grossly inadequate for a sphere such as the Earth with its three dimensional complexity.

And yes, if the ocean fails to heat (or if it is actually being sequestered far down in the oceans) policymakers will see climate scientists as being discredited. That is already occurring as the "pause" continues.

Roger Sr.