Keenlyside et al. on the next decade


in Politics, Science, The environment

As reported in the BBC, a Nature article is arguing that computer models suggest that little global warming will occur in the next decade:

[O]ver the next decade, the current Atlantic meridional overturning circulation will weaken to its long-term mean; moreover, North Atlantic SST and European and North American surface temperatures will cool slightly, whereas tropical Pacific SST will remain almost unchanged. Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.

Climate is a naturally variable thing and, as such, it is always undergoing upward and downward oscillations. Anthropogenic greenhouse gasses definitely have a growing warming effect, but that effect is overlaid on top of the existing variations and feedbacks. As such, a natural downward tendency might drown out the human impact for a certain span of time.

Having relatively accurate decade-to-decade forecasts on climate change impacts could be very useful for adaptation planning. By providing guidance on things like weather conditions and extreme events, they could allow for the more intelligent selection of crops, the concentration of effort in the most threatened areas, and the general development of anticipatory policy.

While such studies are clearly important for increasing our understanding of the climate system, there is a big danger of misunderstanding them – whether wilfully or not. Plenty of people would interpret a decade of flat or falling temperatures as strong evidence that the climate change consensus is wrong. It provides new fodder for those intentionally seeking to confuse the issue, as well as new grounds for confusion among those who are genuinely trying to understand the situation. Of course, we cannot ask for science to always emerge in ways that help people deal with it appropriately. It would be pretty tragic if a brief but poorly timed deviation from the warming trend helped to undermine the case for action at the very time when we must begin the long and difficult task of building a low-carbon world.

{ 3 comments… read them below or add one }

. May 5, 2008 at 10:08 am

Nature article on ‘cooling’ confuses media, deniers
Next decade may see rapid warming, not cooling
Posted by Joseph Romm (Guest Contributor) at 1:06 PM on 04 May 2008

. May 8, 2008 at 11:12 pm

Global Cooling-Wanna Bet?

By Stefan Rahmstorf, Michael Mann, Ray Bradley, William Connolley, David Archer, and Caspar Ammann

Global cooling appears to be the “flavour of the month”. First, a rather misguided media discussion erupted on whether global warming had stopped, based on the observed temperatures of the past 8 years or so (see our post). Now, an entirely new discussion is capturing the imagination, based on a group of scientists from Germany predicting a pause in global warming last week in the journal Nature (Keenlyside et al. 2008).

The bet we propose is very simple and concerns the specific global prediction in their Nature article. If the average temperature 2000-2010 (their first forecast) really turns out to be lower or equal to the average temperature 1994-2004 (*), we will pay them € 2500. If it turns out to be warmer, they pay us € 2500. This bet will be decided by the end of 2010. We offer the same for their second forecast: If 2005-2015 (*) turns out to be colder or equal compared to 1994-2004 (*), we will pay them € 2500 – if it turns out to be warmer, they pay us the same. The basis for the temperature comparison will be the HadCRUT3 global mean surface temperature data set used by the authors in their paper.

To be fair, the bet needs an escape clause in case a big volcano erupts or a big meteorite hits the Earth and causes cooling below the 1994-2004 level. In this eventuality, the forecast of Keenlyside et al. could not be verified any more, and the bet is off.

The bet would also need a neutral arbiter – we propose, for example, the director of the Hadley Centre, home of the data used by Keenlyside et al., or a committee of neutral colleagues. This neutral arbiter would also decide whether a volcano or meteorite impact event is large enough as to make the bet obsolete.

We will discuss the scientific reasons for our assessment here another time – first we want to hear from Keenlyside et al. whether they accept our bet. Our friendly challenge is out – we hope they will accept it in good sportsmanship.

. May 12, 2008 at 10:07 am

What the IPCC models really say

Over the last couple of months there has been much blog-viating about what the models used in the IPCC 4th Assessment Report (AR4) do and do not predict about natural variability in the presence of a long-term greenhouse gas related trend. Unfortunately, much of the discussion has been based on graphics, energy-balance models and descriptions of what the forced component is, rather than the full ensemble from the coupled models. That has lead to some rather excitable but ill-informed buzz about very short time scale tendencies. We have already discussed how short term analysis of the data can be misleading, and we have previously commented on the use of the uncertainty in the ensemble mean being confused with the envelope of possible trajectories (here). The actual model outputs have been available for a long time, and it is somewhat surprising that no-one has looked specifically at it given the attention the subject has garnered. So in this post we will examine directly what the individual model simulations actually show.

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