Time to give up on 2 degrees?

*This is the summary of a response to an article published in the journal Nature by David Victor and Charles Kennel (both of University of California) that international efforts to address climate change should ditch the target of limiting global warming to 2 degrees Celsius above pre-industrial levels. 

Victor and Kennel argue that the target of limiting global warming below 2 degrees Celsius relative to pre-industrial levels (the “2-degree goal,” or rather, “limit”), adopted by the international community, should be dropped.

They put forward two main reasons: that it is no longer feasible to meet the 2 degrees limit, in large part because there has been insufficient action to date, and that the 2 degrees limit is not measurable and cannot be translated into emission limits for countries and regions. 

They go on to argue that there should be a new process started to develop a a new set of global goals starting in Paris to replace the 2 degrees limit.

But both major reasons put forward to drop the 2 degrees limit are hopelessly flawed or just plain wrong:

While no one is in doubt about the difficulty of limiting warming below 2 degrees, it is incorrect to claim that achieving this goal is infeasible and cannot be done. The scientific community, in the form of the IPCC AR5 Working Group III report, has assessed that limiting warming below 2 degrees limit is technically and economically feasible, and at low to modest cost.  No one in the scientific community has any doubt about the difficulty of the political decisions that need to made to realise this. Each person is entitled to their own views of whether or not political leaders will take the steps needed, but for the authors to dress up their own judgements – that these decisions will not be made – as a scientific fact is wrong.

The argument that the 2 degrees limit cannot be translated into emission goals and budgets is, to put it mildly, unconvincing,  and demonstrates a deep ignorance of scientific developments over the last 10 years.  If this were so, then there would be no science-based policy debate about the size of the gap between where emissions are headed at present and where they need to be in 2020 and 2030 at global, regional, and national levels.  In fact, there have been annual scientific assessments of this since 2010.

No global goal on an issue as complex as climate change is going to be perfect, however it turns out that a temperature limit is actually a very good composite indicator of many serious impacts and risks. And it is understandable to the public and to political leaders, and it can be translated into quantifiable emission actions, which can be updated with new science regularly, accounting for the full range of scientific uncertainties. 

There has been an enormous amount of work by the scientific community on issues related to planetary boundaries and on the implications of different indicators for emission pathways beyond global mean temperature.  When put together,  this research has shown the 2-degree limit provides an upper bound on emissions if other key systems are to be maintained, within safe limits, a fact which, startlingly,  does not come through at all in this Comment, despite the space spent discussing alternative climate indicators. On this issue, the scientific literature contradicts the authors and shows clearly that including other metrics (objectives, such as reducing sea level rise, reducing ocean acidification) will increase the level of mitigation (emission reductions) needed.

And last but not least,  the 2-degree limit has triggered considerable political action at national, regional and global level – indeed the present process to negotiate a new global agreement with legal force and applicable to all stems very much from the scientific “pressure” generated by the existence of this limit.  If action has not  been sufficient it’s certainly not because of the limit.  

Many countries have indeed taken action – or are now planning more ambitious measures;  however, in overall terms, the collective effort has been fully inadequate. The world is confronted with rapidly rising emissions -  fastest from one of the most intensive source of CO2 emissions, coal – exactly at a time when CO2 emissions should be decreasing.  It is wrong, however, to conclude that this means the issue is lost, when the main battle lies ahead and just when the process of developing a new agreement is building momentum. 

It would be an act of grave irresponsibility for the 2-degree limit to be dropped. This would signal a clear deflation of pressure to reach an ambitious agreement, delegitimise the international negotiations, weaken efforts at a national level to build ambitious policies, and send a highly adverse signal to the private sector. 

Without the emission pressures of the 2-degree limit there would effectively be a green light for continued massive expansion of coal and other fossil fuel intensive infrastructure in the next decade.  As the International Energy Agency has warned, this infrastructure could lock-in warming levels of 4 degrees Celsius this century.

Dropping the 2-degree limit , and with it pressure for the needed level of emission reductions, while starting a debate about a multitude of other goals is akin to doctors dithering over  a critically ill patient.  As in medicine, there are several indicators addressing different aspects of the vitality of the planet, but each of them would call for action if it reached a critical state.

The planet’s rising temperature is a vital sign and the prognosis is clear for future warming without urgent action.  What doctor would refuse to provide treatment to a patient with a body temperature exceeding 40 degrees Celsius because their blood pressure cannot be measured?

Read the full rebuttal to Victor and Kennel here. 

Dr Bill Hare is the CEO of Climate Analytics. He is a physicist with 25 years experience in climate science, impacts and policy responses to climate change and stratospheric ozone depletion.

Dr Michiel Schaeffer is director and Senior Scientist at Climate Analytics, a biophysicist who received his PhD in Dynamic Meteorology at University of Utrecht, The Netherlands, specialising in the interactions between atmosphere, ocean, ecosystems and society. 

Dr Carl-Friedrich Schleussner is a scientific advisor at Climate Analytics and a guest scientist at the Potsdam Institute of Climate Impact Research working on research topics such as the stability of the North Atlantic Ocean Circulation, continental moisture recycling in South America and the relation between climate extremes and civil conflicts.