Wednesday, June 23, 2010

Guest comment: Knutti Reto on an opening comment in an article ...

A reader quoted the two following two sentences from our recent review article about climate sensitivity:”The Earth’s climate is changing rapidly as a result of anthropogenic carbon emissions, and damaging impacts are expected to increase with warming. To prevent these and limit long-term global surface warming to, for example, 2°C, a level of stabilization or of peak atmospheric CO2 concentrations needs to be set.” That statement could be misinterpreted as a political statement of the authors of what has to be done about climate change, or a political statement driving the study.


First, we were not referring to the UNFCCC article, nor were we talking about "dangerous interference" but "damaging", and that was intentional. We only say there will be damaging impacts (which does not exclude that there may also be positive impacts) with warming, and they will get stronger with more warming. Few people would disagree. Also, based on evidence from the past, from models and from basic physics, more CO2 means more warming. Therefore, if the damages should be prevented or reduced, some upper bound on warming and therefore CO2 concentrations would be needed. What should be prevented, and where such a CO2 level might be, is a different question. We also explicitly mention “peak” as an alternative to stabilization, meaning CO2 may vary, and a peaking/overshoot scenario is an option. But there has to be some upper bound on CO2, otherwise warming would continue forever.

The crucial point however lies somewhere else. The sentences quoted are the two very first sentences of the summary paragraph of a review article in Nature Geoscience. Nature allows about two sentences at the beginning of a paper to set the stage, explain and motivate the problem, provide the context and relevance, and summarize all existing knowledge before jumping into results. At the same time these two sentences should not be technical, avoid jargon, and should be attractive to read, they should "draw readers into the piece" (in the words of the editor of our review), much like in a newspaper article where the first sentences need to catch the attention of the reader. So the challenge is to explain the link between CO2 and temperature, the link between climate change and impacts, and motivate the search for climate stabilization levels and therefore climate sensitivity as the most important number linking feedbacks and physical processes to stabilization targets. Everything in about two sentences, not more. The result, written in fact with substantial input from the editor, was the statement above, in our view a simple, short, yet reasonably balanced and attractive way of saying all that.

Seen in that context, we argue that the two sentences may look a bit different. We did not attempt to make a political statement; we just needed to explain in a few simple words why climate sensitivity is probably the most important quantity and source of uncertainty when talking about the overall magnitude and therefore impacts of climate change. Obviously if one had more space, such a statement could be formulated more clearly. But in any case it's important to realize that the first few sentences of such an article are setting the stage and sketching the problem, they are not a political statement that emerges as the conclusion of our work. As is often the case, placing individual sentences out of context may distort their interpretation.

Knutti Reto and Gabi Hegerl

8 comments:

Anonymous said...
This comment has been removed by a blog administrator.
mcrok said...

Hi Hans,

it's Reto Knutti, not Knutti Reto (unless we are going to use Chinese name order :)

Marcel

Anonymous said...

This post surprises me. In case the external pressure by bloggers and so on didn't exist, these authors wouldn't have to explain why did they write such obvious sentences.

"The Earth’s climate is changing rapidly ..."

Seems so, unless we do not trust neither any of the existing instrumental/proxy records nor the best numerical models of climate that currently exist. Why apologize for having written this? No need to do so. This is plain true except for people rejecting it due to their presumptions on the issue.


" ... as a result of anthropogenic carbon emissions, ..."

Most (if not all) of the scientists I know support this hypothesis, and, in terms of detailed computations of radiative forcing, it is indisputable. Just in terms of complete perfection:

as a result MAINLY of anthropogenic carbon emissions

Do they have to explain why they didn't write mainly? Please ...

" ... and damaging impacts are expected to increase with warming. "

Of course, and literature is abundant on this topic. Authors do not state that effects will be negative worldwide, but I don't think nobody can seriously pretend that climate change impacts will be beneficial for the world as a whole. I know some pretend it, but I am talking about serious people-scientists.

"To prevent these and limit long-term global surface warming to, for example, 2°C, a level of stabilization or of peak atmospheric CO2 concentrations needs to be set"

If the "politically motivated" part of this sentence is the mention to an upper bound of temperature increase of 2°C, it has to be noted they say "for example". For example means ... for example. And the 2°C example is ubiquitous nowadays.


For me, serious scientists like Knutti writing posts explaining why did him and Hegerl write sentences like the ones above has a profound meaning in the current state of the climate debate. This shows to what extent the debate is almost completely corrupted now by the external pressure.

Why are we accepting that the pressure is being exerted just in one direction (evil AGW advocates onto pure and innocent AGW-skeptics?). This post clarifies this is not happening now.

Scientist must wonder to what extent are they willing continue to accept the current status quo. Perhaps it is better to migrate to operational meteorology/operational oceanography and so on.

Reno, you don't have to explain any of this. It is obvious.

jon saenz

Anonymous said...

Hello,

I think it is very important today to explain these sentences to the people outside who start to mistrust climate scientists.

I don't criticize sentences like those cited above (2° warming etc...).

I followed the debate in Germany about climate change, and the first more realistic estimates about the warming was 2 to 4° in 100 years when Co2 doubles. I think that it is a pretty objective and scientific statement.

But scientists started acting as climate activists, when they started to talk about 2° maximum to save the planet. This was meant to be a political statement and it still is.

But using it like in the paper cited above is not a political statement. I could explain this much better in German, but I hope you understand what I want to express.


But, as a lay man, there are still 2 questions I can't get out of my head :

1) If Co2 is the mean climate driver, why couldn't it prevent the cooling at the end of a warm period, like the Eem.

http://www.skepticalscience.com/co2-lags-temperature.htm

2) How can we say that todays climate is the best for our planet? Would cooler periods be even better? Would an ice age be much better?

Or could a warmer period be better for our planet?

These ideas are similar to that made above "But there has to be some upper bound on CO2, otherwise warming would continue forever."

Do those questions from many lay people mean that we are stupid bastards who should shut our mouth? I don't think so.

Lay people expressing their doubts sometimes leads to comments by climate scientists like this one: "unglaublichen Schwachsinn und Ignoranz". I know that I'm "unbelievebly stupid", but this "scientist" is an unbelievable asshole (mit Verlaub). If you don't believe it google it!

Werner Krauss said...

Liebe Frau Hegerl, dear Herr Knutti,
I guess I was the one who quoted this paragraph out of context in a previous post.I did so (in a discussion with Georg H.) in order to demonstrate that the 'big questions' of climate politics are not only addressed in keynote speeches by some famous few 'loudspeakers', but that these big questions are an integral part of climate science.

I did not intend to criticize your article and attitude. I also do not suggest that politics (necessarily)corrupt science in general or here your article. I just wanted to state that the 'political climate' frames and sometimes even directs the practise of climate science. As simply as that.

Thus, the question for me is not how to separate politics and science (because they are not really separated); instead, I want to argue that the connections between science and politics have to be carefully established, traced and made transparent.

In my opinion, your article demonstrates this in an exemplary way. You place your argument in the political framework (anthropogenic climate change and how to deal with it); you bring in new information and results (climate sensitivity); you make new suggestions, and you give new policy advice (concerning mitigation and adaptation).
Each step from your scientific effort to policy advice via the overall question of how to deal with anthropogenic climate change is made explicit and transparent. Furthermore, I guess your insights are of great value for people who indeed have to deal with the effects of climate change in specific places. Thus, you help to localize climate change, or, to put it differently, you indeed help to settle knowledge about climate change. This again hopefully will be reflected in global climate politics.

Anyway, thanks for your reflections and considerations in response to my quoting you out of context. They are a really valuable insights into the production process of scientific knowledge - which indeed can be prettxy messy (editors, pressure etc).

Werner Krauss said...

@anonymous #3
I hope my previous comment (#5) helps to clarify this. It was never my intention to put pressure on the authors, to make them 'confess' or apologize. Far from that.
I hope that their post does not 'show(s) to what extent the debate is almost completely corrupted now by the external pressure'. Instead, I hope they posted their contribution out of a shared interest in the production of climate knowledge. It is really important (and insightful) to reflect this process.

Anonymous said...

Dear Werner.

Perhaps my previous post was not very clear. I was not referring particularly to your comment. For me, this case reflects a general state of affairs. I was talking about the general situation, not about your post.

I feel that the debate is basically corrupted now (in fact it is corrupted some time ago). I don't say you corrupt it. But I feel it is corrupted. And in my opinion this post reflects that. I might be wrong trying to infer the intention of the author, but this is my interpretation.

Just my two cents.


jon saenz

HaroldW said...

The article begins, "The Earth’s climate is changing rapidly as a result of anthropogenic carbon emissions, and damaging impacts are expected to increase with warming. To prevent these and limit long-term global surface
warming to, for example, 2 °C, a level of stabilization or of peak atmospheric CO2 concentrations
needs to be set. Climate sensitivity, the global equilibrium surface warming after a doubling of atmospheric CO2 concentration, can help with the translation of atmospheric CO2 levels to warming."

As you say, the first couple of sentences are meant to establish context and interest the reader. Wouldn't the following also suffice for that purpose:
"The Earth’s climate is warming as a result of anthropogenic carbon emissions. In order to assess the consequences of such climate change, we need to translate the increase in atmospheric CO2 levels to temperature changes. To that end, we require an accurate estimate of the climate sensitivity, defined as the global equilibrium surface warming after a doubling of atmospheric CO2 concentration."

The above topic paragraph doesn't touch any sensitive spots -- e.g. "damage", policy goals. But to my ear it is as descriptive of the significance and centrality of the subject.

My 1.5 cents' worth.