Profile: John Cook

Dedicating his career to dispelling myths and misunderstanding of climate change is John Cook, through his website Skeptical Science. As the Climate Communication Fellow for the Global Change Institute at the University of Queensland, he is in the perfect position to address doubts of climate change by making the findings of research papers easily accessible and understandable by the lay person. This role could not be more important today, as opinions are increasingly polarised. Read more

Making Sense of Sensitivity … and Keeping It in Perspective

Posted on 28 March 2013 by dana1981

Yesterday The Economist published an article about climate sensitivity – how much the planet’s surface will warm in response to the increased greenhouse effect from a doubling of atmospheric CO2, including amplifying and dampening feedbacks.  For the most part the article was well-researched, with the exception of a few errors, like calling financier Nic Lewis “an independent climate scientist.”  The main shortcomings in the article lie in its interpretation of the research that it presented.

For example, the article focused heavily on the slowed global surface warming over the past decade, and a few studies which, based on that slowed surface warming, have concluded that climate sensitivity is relatively low.  However, as we have discussed on Skeptical Science, those estimates do not include the accelerated warming of the deeper oceans over the past decade, and they appear to be overly sensitive to short-term natural variability.  The Economist article touched only briefly on the accelerated deep ocean warming, and oddly seemed to dismiss this data as “obscure.”

The Economist article also referenced the circular Tung and Zhou (2013) paper we addressed here, and suggested that if equilibrium climate sensitivity is 2°C to a doubling of CO2, we might be better off adapting to rather than trying to mitigate climate change.  Unfortunately, as we discussed here, even a 2°C sensitivity would set us on a path for very dangerous climate change unless we take serious steps to reduce our greenhouse gas emissions.

Ultimately it was rather strange to see such a complex technical subject as climate sensitivity tackled in a business-related publication.  While The Economist made a good effort at the topic, their lack of expertise showed.

For a more expert take on climate sensitivity, we re-post here an article published by Zeke Hausfather at the Yale Forum on Climate Change & the Media.

Climate sensitivity is suddenly a hot topic.

Some commenters skeptical of the severity of projected climate change have recently seized on two sources to argue that the climate may be less sensitive than many scientists say and the impacts of climate change therefore less serious: A yet-to-be-published study from Norwegian researchers, and remarks by James Annan, a climate scientist with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).

While the points skeptics are making significantly overstate their case, a look at recent developments in estimates of climate sensitivity may help provide a better estimate of future warming. These estimates are critical, as climate sensitivity will be one of the main factors determining how much warming the world experiences during the 21st century.

Climate sensitivity is an important and often poorly understood concept. Put simply, it is usually defined as the amount of global surface warming that will occur when atmospheric CO2 concentrations double. These estimates have proven remarkably stable over time, generally falling in the range of 1.5 to 4.5 degrees C per doubling of CO2.* Using its established terminology, IPCC in its Fourth Assessment Report slightly narrowed this range, arguing that climate sensitivity was “likely” between 2 C to 4.5 C, and that it was “very likely” more than 1.5 C.

The wide range of estimates of climate sensitivity is attributable to uncertainties about the magnitude of climate feedbacks (e.g., water vapor, clouds, and albedo). Those estimates also reflect uncertainties involving changes in temperature and forcing in the distant past. But based on the radiative properties, there is broad agreement that, all things being equal, a doubling of CO2 will yield a temperature increase of a bit more than 1 C if feedbacks are ignored. However, it is known from estimates of past climate changes and from atmospheric physics-based models that Earth’s climate is more sensitive than that. A prime example: Small perturbations in orbital forcings resulting in vast ice ages could not have occurred without strong feedbacks.


About Skeptical Science

The goal of Skeptical Science is to explain what peer reviewed science has to say about global warming. When you peruse the many arguments of global warming skeptics, a pattern emerges. Skeptic arguments tend to focus on narrow pieces of the puzzle while neglecting the broader picture. For example, focus on Climategate emails neglects the full weight of scientific evidence for man-made global warming. Concentrating on a few growing glaciers ignores the world wide trend of accelerating glacier shrinkage. Claims of global cooling fail to realise the planet as a whole is still accumulating heat. This website presents the broader picture by explaining the peer reviewed scientific literature.

Often, the reason for disbelieving in man-made global warming seem to be political rather than scientific. Eg – “it’s all a liberal plot to spread socialism and destroy capitalism”. As one person put it, “the cheerleaders for doing something about global warming seem to be largely the cheerleaders for many causes of which I disapprove”. However, what is causing global warming is a purely scientific question. Skeptical Science removes the politics from the debate by concentrating solely on the science.


About the author

Skeptical Science is maintained by John Cook, the Climate Communication Fellow for the Global Change Institute at the University of Queensland. He studied physics at the University of Queensland, Australia. After graduating, he majored in solar physics in his post-grad honours year. He is not a climate scientist. Consequently, the science presented on Skeptical Science is not his own but taken directly from the peer reviewed scientific literature. To those seeking to refute the science presented, one needs to address the peer reviewed papers where the science comes from (links to the full papers are provided whenever possible).


There is no funding to maintain Skeptical Science other than Paypal donations – it’s run at personal expense. John Cook has no affiliations with any organisations or political groups. Skeptical Science is strictly a labour of love. The design was created by John’s talented web designer wife.


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