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A paper in this week’s Nature predicts that, rather than warming, North Atlantic sea surface temperatures may actually decrease slightly in the next decade. What’s more, the paper suggests global surface temperatures may not actually increase either.

Has global warming stopped? Is this a nail in Al Gore’s coffin?

Well, no.

Despite headlines such as ‘Doubt is cast over global warming’ and ‘Global warming could stop NATURALLY for ten years, say scientists’ that is not what this paper is about.

What this new paper by Noel Keenlyside, of the Leibniz Institute of Marine Sciences in Germany, sets out to do is incorporate data on short term variations in climate into our models of climate change. By doing this they push us into the arena of creating shorter term predictions, in this case of the next decade.

In a “News and Views” commentary on the piece in the same issue of Nature Richard Wood explains:

Keenlyside and colleagues’ model uses a very simple ocean initialization method in which they add heat to or remove it from the ocean surface until sea surface temperatures across the globe are close to observed values. They use their model to produce a set of retrospective ‘forecasts’ starting from earlier states, which they test against what actually happened. Their system produces refined temperature predictions a decade ahead for large parts of Europe and North America.

As Woods points out, colleagues of his at the Hadley Centre in the UK published a similar sort of prediction research of a similar sort, though rather different in approach and with significantly different predictions, in Science last year, as we reported at the time. Combining real world data and modelling this way has only recently become possible.

The new model predicts North Atlantic, European and North American sea surface temperatures will cool slightly; tropical Pacific temperatures will likely be almost unchanged and global temperatures will probably be offset by this variation.

This does not mean we don’t need to worry about global warming. “The natural variations change climate on this timescale and policymakers may either think mitigation is working or that there is no global warming at all,” says Keenlyside (Reuters).

As the NY Times’s Andrew Revkin notes on his blog:

Whether their prediction of a plateau for warming for a decade in North America and Europe is correct or not, their research may signal a shift that many climate researchers have been calling for for awhile now — toward service-oriented climate science ...

The NY Times wraps up its main piece with a useful quote from Kevin Trenberth, of the US National Center for Atmospheric Research: “Too many think global warming means monotonic relentless warming everywhere year after year. It does not happen that way.”

Not everyone is happy though. Here's the always-worth-listening-to Roger Pielke Jr on his Prometheus blog:

I am sure that this is an excellent paper by world class scientists. But when I look at the broader significance of the paper what I see is that there is in fact nothing that can be observed in the climate system that would be inconsistent with climate model predictions. If global cooling over the next few decades is consistent with model predictions, then so too is pretty much anything and everything under the sun.

Image: NASA Glenn Research Center (NASA-GRC)

Cross posted by Daniel Cressey on The Great Beyond

Posted by Olive Heffernan on May 01, 2008
Categories: Climate Science, Climate prediction, Climate variability, Daniel Cressey, In the News | Permalink | Comments (8) | TrackBacks (0)

Just when everyone was getting sick of explaining that climate models are producing projections not predictions per se, it seems that some of them are indeed producing predictions. There's a paper (pdf) in Science from a team at the Hadley Center that shows how using real initial conditions improves the accuracy of ten year climate forecasts. They do a bit for hindcasting first, looking at historical data and comparing model runs with real initial conditions with run-of-the-mill runs. Then they do some prediction. This prediction is being treated as saying that we're at the end of a little plateau, and that at the end of this decade things will warm up further, giving a run of years in the early 2010s where the chances for new global records are good. Quirin Schiermeier wrote a story on this for news@nature, reporting that the modelling community seems pretty impressed. Here's a bunch more coverage (88 pieces at the time of googling), and for those with a subscription to Science here's the estimable Dick Kerr, who had longer to write the story than the rest of us...

Posted by Oliver Morton on August 10, 2007
Categories: Climate Science, Climate variability, Oliver Morton | Permalink | Comments (8) | TrackBacks (0)

Posted by Olive Heffernan on behalf of Quirin Schiermeier

The sun, despite claims to the contrary, is not a factor in recent climate change.

Nature had a news article last week about a paper – and the reactions to it - by Mike Lockwood and Claus Froehlich. Their comprehensive (and conclusive) (re)-analysis of solar trends concludes that the sum of natural changes in solar activity since 1985 would have cooled our climate, were it not for the strong warming effect of increased greenhouse gas concentrations.

The findings, published in Proceedings of the Royal Society A, went online yesterday and have triggered a world-wide echo in the media and in the climate-crazy blogosphere.

That is surprising inasmuch the data are by not what you would call a scientific breakthrough. Indeed, most climate scientists will hardly consider the findings particularly new or surprising. Granted, bringing into line solar observations and measurements (and associated theories) collected during the 20th century is anything but trivial. But no matter how one looks at the issue, existing data were long supposed sufficient to disprove the only seemingly reasonable idea that global warming might be the natural result of increased solar activity.

Lockwood and Froehlich’s study does however go a step further. The two find that the correlation between solar activity and temperature trends post-1985 is actually negative. This means that changes to the sun (including cosmic ray intensity, for that matter) have contributed Less than Zero to the recent sharp rise in average global temperatures.

End of debate? Unfortunately no, I would guess. The inaptly so-named ‘climate sceptics’ who are keen to let mankind off the global warming hook, will not easily abandon this battle-tried warhorse. A natural sun-climate link, albeit invisible and unverifiable, is just the most persuasive among the set of quasi-plausible arguments with which upright eco-optimists attempt to dismiss as a (left-wing? anti-liberal?) conspiracy theory mankind’s responsibility for global warming. The ‘Great Global Warming Swindle’ documentary, to be aired tomorrow in Australia, is just the most-recent example of such attempts to argue that climate change is the effect of the sun.

To further confuse things and the public, solar changes do seem to have had an impact on past climates. Moreover, it is at least not impossible that cosmic ray intensity does influences clouds and climate. There’s nothing wrong with investigating these things - that’s how science goes. But blaming the sun for recent global warming is no science-backed position anymore – it is deliberate disinformation.

Quirin Schiermeier
German Correspondent
Nature

Posted by Olive Heffernan on July 11, 2007
Categories: Climate Science, Climate variability, In the News, Quirin Schiermeier | Permalink | Comments (29) | TrackBacks (0)

Posted by Oliver Morton on behalf of Kevin E. Trenberth

I have often seen references to predictions of future climate by the Intergovernmental Panel on Climate Change (IPCC), presumably through the IPCC assessments (the various chapters in the recently completedWorking Group I Fourth Assessment report ican be accessed through this listing). In fact, since the last report it is also often stated that the science is settled or done and now is the time for action.

In fact there are no predictions by IPCC at all. And there never have been. The IPCC instead proffers “what if” projections of future climate that correspond to certain emissions scenarios. There are a number of assumptions that go into these emissions scenarios. They are intended to cover a range of possible self consistent “story lines” that then provide decision makers with information about which paths might be more desirable. But they do not consider many things like the recovery of the ozone layer, for instance, or observed trends in forcing agents. There is no estimate, even probabilistically, as to the likelihood of any emissions scenario and no best guess.

Even if there were, the projections are based on model results that provide differences of the future climate relative to that today. None of the models used by IPCC are initialized to the observed state and none of the climate states in the models correspond even remotely to the current observed climate. In particular, the state of the oceans, sea ice, and soil moisture has no relationship to the observed state at any recent time in any of the IPCC models. There is neither an El Niño sequence nor any Pacific Decadal Oscillation that replicates the recent past; yet these are critical modes of variability that affect Pacific rim countries and beyond. The Atlantic Multidecadal Oscillation, that may depend on the thermohaline circulation and thus ocean currents in the Atlantic, is not set up to match today’s state, but it is a critical component of the Atlantic hurricanes and it undoubtedly affects forecasts for the next decade from Brazil to Europe. Moreover, the starting climate state in several of the models may depart significantly from the real climate owing to model errors. I postulate that regional climate change is impossible to deal with properly unless the models are initialized.

The current projection method works to the extent it does because it utilizes differences from one time to another and the main model bias and systematic errors are thereby subtracted out. This assumes linearity. It works for global forced variations, but it can not work for many aspects of climate, especially those related to the water cycle. For instance, if the current state is one of drought then it is unlikely to get drier, but unrealistic model states and model biases can easily violate such constraints and project drier conditions. Of course one can initialize a climate model, but a biased model will immediately drift back to the model climate and the predicted trends will then be wrong. Therefore the problem of overcoming this shortcoming, and facing up to initializing climate models means not only obtaining sufficient reliable observations of all aspects of the climate system, but also overcoming model biases. So this is a major challenge.

Continue reading "Predictions of climate" »

Posted by Oliver Morton on June 04, 2007
Categories: Climate Science, Climate variability, Communicating Climate Change, Kevin Trenberth | Permalink | Comments (12) | TrackBacks (0)