smartphone orten software here handy ortung russland mspy auf iphone 6s Plus installieren spy cam app iphone 6s Plus handy kindersicherung internet vergleich sms spy yahoo
Skip navigation.
... for greater sustainability and local resilience

Comment and Discussion

Here you can put forward your thought and ideas, ask questions and comment on any subject connected you like, but hopefully with some connection to Transition, Peak Oil or Climate Change.

To add a topic click on 'add new comment'
To reply to an item, click on 'reply' at the bottom of the item

PaulS's picture

Leaked IPCC report doesn't let us off the hook

Leaked IPCC report doesn't let us off the hook

18:07 26 July 2013 by Michael Le Page

Can we all stop worrying about global warming? According to a recent rash of stories in the media, the "climate sensitivity" – the extent to which temperatures respond to more carbon dioxide in the atmosphere – is lower than expected, and thus that the world won't get as hot as predicted. One story, in The Economist, based on leaked information from a draft of the next assessment by the Intergovernmental Panel on Climate Change, claims the IPCC will revise its sensitivity estimate downwards when they release their official report this September.

The sceptics have mounted a concerted campaign to persuade journalists and politicians that climate scientists now think that climate sensitivity is lower, says Bob Ward of the Grantham Research Institute on Climate Change and the Environment, London. But is there any truth to the claims?

Climate sensitivity refers to how much the world will warm if carbon dioxide levels double. But this apparently simple concept is slippier than a Turkish wrestler. As the planet warms in response to rising CO2 levels, a whole series of feedbacks kick in over the following decades, centuries or millennia. Depending on which feedbacks are included and what the timescale is, there are many competing ways of defining sensitivity. To add to the confusion, there are also dozens of ways of calculating it.


One way is to look at how much warming there has been in response to rising CO2 levels over the past century. But this approach has all kinds of problems. For starters, we have been pumping out all kinds of pollutants, some of which may be masking the effect of CO2.

What's more, in the last decade, CO2 levels have continued to rise but with little surface warming. Such lulls are expected and the latest is probably a blip, due to the oceans soaking up more heat than usual. Unsurprisingly, this means that any sensitivity estimate that includes the past decade will produce a lower value than any calculated without taking the last decade into account, says Reto Knutti of the Institute for Atmospheric and Climate Science in Zurich, Switzerland. He co-authored one such study published earlier this year, which concluded that "equilibrium sensitivity" – usually taken to mean the warming expected after several decades of doubled CO2 – is between 1° C and 5° C, most likely 2° C.

Another way to calculate sensitivity is to look at how global temperatures changed thousands or millions of years ago in response to changing CO2 levels. Such studies point to a higher value for equilibrium sensitivity, closer to 3° C, says Knutti, who reviewed the evidence last year. But there are all kinds of problems with this approach too, such as the uncertainties about what the world was like in the past.

A third way to calculate sensitivity is to use climate models, which point to even higher values for equilibrium sensitivity, between 2.2 and 4.7° C, says Knutti: "Above 3 °C at least." But there's a lot missing from the models. For one thing, most only include fast feedbacks such as the effect of water vapour. They don't include slower feedbacks such as increasing vegetation, or the risk of a sudden methane "belch" as the Arctic warms.

No new consensus

The bottom line is that there is no new consensus that climate sensitivity is lower than previously thought, says Knutti. The observed trend points to lower values because of the recent slowdown, but other evidence continues to support higher values.

The last IPCC report stated that equilibrium climate sensitivity was between 2 and 4.5 °C, mostly likely 3 °C. The Economist claims the IPCC's next report will give a figure between 1.5 and 4.5 °C, with no most likely value. The IPCC won't confirm or deny it, but it's not a huge change if it is true.

"What matters for avoiding dangerous climate change is the upper end, and that hasn't changed," says Knutti. Ward makes the same point. "We can't afford to gamble on sensitivity definitely being low," he says.

But will it all be a huge waste if sensitivity does turn out to be low? Far from it. If we don't cut emissions, Knutti points out, all low sensitivity means is that it will take a decade or two longer for the planet to warm as much as it would if sensitivity was high. "It doesn't get away from the fact that emissions have to be reduced," he says.