“I doubt that we will meet the two-degree target”

April 17, 2014

The IPCC’s third and last Working Group presented its Fifth Assessment Report on Sunday. In their reports, Working Group I deals with the scientific basis of climate change, Working Group II focuses on the consequences and risks of climate change. Working Group III’s report addresses the question as to how climate change can still be mitigated – and at what cost. Jochem Marotzke from the MPI for Meteorology in Hamburg made a major contribution to the report, among other things as Coordinating Lead Author of Working Group I. We spoke to him about the importance of the report, the new findings and his personal assessment of our climate-related future.

Jochem Marotzke

What are the most important new findings of the 5th IPCC Assessment Report compared to the 4th Assessment Report of 2007?

In the case of Working Group I, to which I contributed as Coordinating Lead Author, two key statements are particularly important in my opinion: first, we can once again confirm that anthropogenic climate change is real and is already taking place. We managed to halve the uncertainty in relation to this fact from ten percent in 2007 to just five percent.

But this uncertainty only relates to the global warming already observed over the past 60 years. It does not answer the question as to whether human activity will change the climate in the future.

Yes, and that is an important distinction! There is practically no longer any doubt as to the fact that the increased volume of greenhouse gases in the atmosphere is causing the absorption of heat in the climate system. This five percent uncertainty only relates to the question whether the warming of the earth’s surface already being observed could perhaps be explained by natural factors.

The second key statement in the report - and this is new: We can now specify the level of carbon-dioxide emissions that will only just be compatible with specific climate objectives in the future. The political goal of limiting the rise in temperature to two degrees is only attainable if we emit a maximum of 1000 billion tonnes of carbon – irrespective of when that point is reached. The exact figure is still uncertain, but the statement that it is possible to calculate a maximum total volume of emissions for each climate objective is clearly very important.

And what is new in the report of Working Group II?

In its current report, Working Group II strongly focuses on the question as to which specific risks for humanity are associated with which changes in the climate. I find this very helpful because, although this question was always at the back of our minds in the past, it was never explicitly addressed. Moreover, the consequences we face, if no additional measures are taken to adapt to climate change, are clearly identified – as well as what we may expect if we implement additional adaptation measures. This is very important in my opinion as people are not sitting around doing nothing, but our governments will also have to react to climate change. Also, in my view, another, third, area is also much better resolved than previously, as the methodology has been further developed in the meantime: in the new report, observed changes, for example the progressive extinction of species and increasing scarcity of drinking water in many regions of the world, are evaluated very precisely in terms of whether they are really due to climate change or are more likely to have other causes.

And Working Group III?

What impresses me about Working Group III is the clear statement it makes to the effect that scientific analysis cannot always be carried out without interference from the scientists’ personal values. For example, when we analyse the costs of climate change, what exactly do we count as costs? Does environmental damage belong to this category? With the help of philosophers, Working Group III is systematically examining the question as to why scientific analysis cannot be cleanly separated from our value systems. This factor is therefore clearly stated and not subliminally incorporated into the analysis. I find this to be a very important and forward-looking step.

What are the political recommendations contained in the report?

The IPCC itself does not make any political recommendations. That is not its mandate. This means that, even if the report of Working Group III deals with possible solutions, it does not make any concrete recommendations as to what the governments should do.

What the report does is point out various options, with the help of which certain objectives can be attained. For example, if we want to limit climate change to a certain level, the research shows that measures A, B and C could prove successful. But the IPCC does not get involved in specifying which of these measures should be implemented. The decisions about these options must be taken by the world’s governments and populations.

The IPCC does not carry out its own research. So why are the IPCC reports, which are published every six or seven years, so important?

The IPCC assesses the status of knowledge about climate change. It reviews the available literature and summarises it, and also evaluates it in the overall context. The teams that compile the individual chapters are highly qualified and they read a huge number of publications as part of the reporting process. Based on the very wide-ranging expert knowledge that is gathered in this way, adjacent areas and topics can be related to each other. This actually gives rise to new knowledge – even though no new research is carried out. The synthesis process provides new insights into the big picture that could not be obtained through the isolated consideration of a particular topic or area. In addition, the texts are reviewed several times by experts and government representatives. A lot of questions are asked as a result, and this often prompts a more thorough consideration of certain statements. I have never worked on a scientific text that was as thoroughly reviewed as the IPCC Assessment Report.

Outside of science, however, attention is only paid to the comparatively slim summaries for policy-makers. Is the approach to the reporting adopted up to now really effective?

I have major doubts about this. The report is undoubtedly effective and clearly does what it is supposed to without limitations; it provides comprehensive and reliable information – including in the summaries. However, I have very strong reservations as to whether the process is efficient in this form. I do not think that it can continue to be carried out in this way, as the amount of work involved is unbelievable. And, as you said, outside of research, only around one percent of the entire report is ultimately read; in my Working Group alone, there is a summary of around 20 pages for a 1,500-page report. In so far, I think that the IPCC must fundamentally rethink its approach in future, and we should focus much more on the topics that are actually relevant for the policy-makers. These topics should be given thorough consideration at the beginning as part of an iterative process involving the government representatives – and only then developed in detail by the scientists.

What is the situation with regard to the scientific independence of the report if representatives of all governments have a say in it? According to Der Spiegel, the reference to the apparent 15-year hiatus in the warming of the earth’s surface was not presented in detail in the summary – supposedly at the instigation of the German government.

That is not true, it is included – the term “hiatus” is not used, but the effect is discussed. The claim in Der Spiegel that the German government tried to have the reference to this pause in global warming suppressed is simply untrue! You can verify this by checking the German government’s comments on the last draft of the report. What is written there is that the term “hiatus” should not be used. However, the term was not even used in the draft. So what was involved here was an inconsequential comment on the choice of words. Irrespective of this, the German government actually suggested that the hiatus in the warming should be more clearly discussed in the summary. In my view, the global warming hiatus has been given exactly the amount of attention that it deserves. In any case, the scientists always have the final say, so nothing can be included in the summary that they do not stand for.

So how can this global warming hiatus be explained?

We are very sure that this hiatus or slowdown in the rate of the earth’s surface warming is largely due to spontaneous climate variability and does not have any particular cause. It is comparable with weather variations which do not have to have any specific cause and often simply arise because events in the atmosphere and oceans have a strongly chaotic component and hence fluctuate strongly. This changes nothing in relation to the long-term trend of global warming.

Apart from the rise in the temperature of the earth’s surface, what are the clearest indications that climate change is already under way?

Over 90 percent of the additional heat in the climate system goes into the ocean. The observed warming of the oceans corresponds very clearly to the expected effects – and this process has progressed unabated for the last 15 years. In my opinion, this is the truly fundamental proof that anthropogenic climate change is already a fact. In addition, we can observe a very clear reduction in the sea ice in the Arctic and a very clear reduction in the ice cap in Greenland and in Antarctica. The observed rise in sea levels, which has accelerated again in the last 20 years, is also very noticeable. This can be explained in roughly equal parts by the melting of the land ice masses and the expansion of the water due to the rising water temperatures. This fits with the overall picture, and all of the climate indicators, for which we see a clear trend, point to the existence of global warming.

What is your personal assessment: Will we be able to reduce climate change to a manageable level in this century? And are you more optimistic or pessimistic than you were on the publication of the last report?

In terms of my expectations of climate protection, I am far more pessimistic today – or let’s say more realistic – than I was in 2007. The 2007 report propelled the topic of climate into the political mainstream and there was huge resolve among governments to stem the process of climate change. But the reality check happened and the governments, including our own German government, noticed that, from a certain stage, it takes considerable efforts to protect the climate. Moreover, there has been no success in combining these efforts with political and economic acceptance. In 2007, nobody really knew that the enthusiasm with which many governments subscribed to climate protection would not last.

Nevertheless, I still believe that we will manage to halt climate change. However, I personally doubt that we will meet the two-degree target. Some societies, in particular the poorer countries, face considerable problems. It will also be necessary to make enormous efforts in the area of adaptation to climate change. But I do not believe that it will all end in an unmitigated climate disaster.

Thank you very much for the interview!

Interview by Aaron Lindner.


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