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The year 2008 was likely the coolest year of the current decade, but it was still the tenth warmest year on record since instrumental climate records began in 1850.

The average global sea-surface and land-surface air temperature from December 2007 to November 2008 was 14.3 °C, the World Meteorological Organization (WMO) has announced. This is slightly lower than for all previous years of the ‘naughties’, but still some 0.3 °C above the 1961-1990 annual average. The warmest year on record is 1998, with an average global temperature just above 14.5 °C.

Left: Global map of surface temperature anomalies in degrees Celsius for the 2008 meteorological year. Right: Annual-mean global-mean anomalies, except 2008, which is the 11-month (Jan-Nov) mean anomaly. Credit: NASA Goddard Institute for Space Studies.

When calculating global average temperatures, climatologists prefer the meteorological year, from December through November, as it is easier to split it into actual seasons than is the calendar year.

The WMO temperature analysis is based on land-based weather stations in 188 countries, complemented by measurements from ships, buoys and satellites. NASA’s Goddard Institute for Space Studies and the UK Met Office, which both contributed their own datasets to the WMO analysis, independently arrive at very similar values.

Continue reading "2008 cooling, but the heat is on" »

Posted by Quirin Schiermeier on December 17, 2008
Categories: Climate prediction, Climate variability, Extreme Events, Quirin Schiermeier | Permalink | Comments (3) | TrackBacks (0)

More elderly readers of these pages may remember having heard in their school days back (circa 1970s) that scientists then thought an ice age would be coming soon. I certainly do – even though the alleged ‘global cooling consensus’ in the scientific literature of the time has recently been disproved as a myth.

Now an interesting new paper in Nature [subscription] suggests that a rapid natural transition towards a stable glacial climate, with permanent ice sheets covering large parts of North America and Eurasia, could indeed be ahead.

Thomas Crowley and William Hyde ran a coupled energy-balance/ice-sheet model to test their hypothesis. When forced with long-term variations in daily solar radiation which result from small cyclical changes in the Earth’s orbit, the best-fit model run (that is the one which most accurately reproduced ice sheet variations during the last 3 million years) predicted a rapid transition towards a cold climate regime to occur merely some 10,000 to 100,000 years from now.

Models and theory do indeed suggest that at critical points (namely when climate variability is at a maximum) large ice sheets can rapidly develop from very small perturbations in solar forcing.

Continue reading "Glaciation ahead - on a geological time scale " »

Posted by Olive Heffernan on November 12, 2008
Categories: Climate prediction, Climate variability, Features, Journal Club, Quirin Schiermeier | Permalink | Comments (1) | TrackBacks (0)

Cross posted from The Great Beyond

The contentious ‘hockey stick’ climate change graph has again been upheld as broadly accurate, doubtless to the rage of climate denialists/sceptics/whatevers.

A team led by Michael Mann of Penn State University has looked at a whole range of proxies for surface temperatures over the last 2,000 years in an attempt to counter criticism of the graph, which showed a long ‘handle’ and a sharp upturn (the blade).

Their findings? As the Christian Science Monitor puts it: “It still looks a lot like the much-battered, but still rink-ready stick of 1998. Today the handle reaches further back and it’s a bit more gnarly. But the blade at the business end tells the same story.”

The previous hockey stick had been accused of relying too much on data from tree rings so this PNAS study may silence some of the critics when it appears later.

Continue reading "Jolly hockey sticks " »

Posted by Olive Heffernan on September 02, 2008
Categories: Climate Science, Climate variability, Daniel Cressey, Features, In the News, Palaeoclimate | Permalink | Comments (4) | TrackBacks (0)

Global warming has been expected to bring not only droughts, but also floods, because what rain you get comes hammering down harder. And the downpours of the future now look to be even more drenching than expected.

A new Nature Geoscience paper (subscription required) considers the intensity of precipitation measured hour by hour for a century in the Dutch town of De Bilt. Theoretically, it’s thought that the intensity of rainfall, including the biggest cloudbursts, should rise by 7% for each degree Celsius that the temperature goes up. That’s based on a thermodynamics equation called the Clausius-Clapeyron relation - and it’s what you see if you look at extreme rainfall on the scale of days.

But it's the rainiest hours, not the rainiest days, that interest the paper's authors, Geert Lenderink and Erik Van Meijgaard of the Royal Netherlands Meteorological Institute. That turns out to make a difference.

Continue reading "A precipitous rise in extreme rainfall " »

Posted by Anna Barnett on July 21, 2008
Categories: Anna Barnett, Climate variability, Extreme Events, Regional climate | Permalink | Comments (1) | TrackBacks (0)

Andrew Revkin of the New York Times has been wondering whether climatologists could help turn down the “rhetorical noise” on recent temperature trends:

Given how much yelling takes place on the Internet, talk radio, and elsewhere over short-term cool and hot spells in relation to global warming, I wanted to find out whether anyone had generated a decent decades-long graph of global temperature trends accounting for, and erasing, the short-term up-and-down flickers from the cyclical shift in the tropical Pacific Ocean known as the El Niño - Southern Oscillation, or ENSO, cycle.

He queried Gavin Schmidt at RealClimate, who’s pondered how to reduce the noise (and beat the rhetoric) on climate trends before. Schmidt thought of the recent Nature paper in which David Thompson et al. removed ENSO fluctuations from the sea surface temperature record (and uncovered an abrupt 1945 temperature drop that they traced to buckets used to collect seawater after World War II).

Continue reading "The global warming signal minus the El Niño noise" »

Posted by Anna Barnett on July 10, 2008
Categories: Anna Barnett, Attribution, Climate Science, Climate variability, Uncertainty | Permalink | Comments (1) | TrackBacks (0)

The 20th century warming trend is not a linear affair. The iconic climate curve, a combination of observed land and ocean temperatures, has quite a few ups and downs, most of which climate scientists can easily associate with natural phenomena such as large volcanic eruptions or El Nino events.

But one such peak has confused them a hell of a lot. The sharp drop in 1945 by around 0.3 °C - no less than 40% of the century-long upward trend in global mean temperature - seemed inexplicable There was no major eruption at the time, nor is anything known of a massive El Nino that could have caused the abrupt drop in sea surface temperatures. The nuclear explosions over Hiroshima and Nagasaki are estimated to have had little effect on global mean temperature. Besides, the drop is only apparent in ocean data, but not in land measurements.

Now scientists have found – not without relief - that they have been fooled by a mirage.

The mysterious post-war ocean cooling is a glitch, a US-British team reports in a paper in this week’s Nature. What most climate researchers were convinced was real is in fact “the result of uncorrected instrumental biases in the sea surface temperature record,” they write. Here is an editor’s summary.

Continue reading "Post-World War II cooling a mirage" »

Posted by Quirin Schiermeier on May 29, 2008
Categories: Climate Science, Climate variability, Quirin Schiermeier | Permalink | Comments (7) | TrackBacks (2)

The Earth’s greenhouse history of the last 800,000 years is an open book now, thanks to years of detective work by two large international teams of climate scientists.

Nature has two papers this week, here and here, about the levels of atmospheric concentration of the two main greenhouse gases – carbon dioxide and methane – as derived from air entrapped in the EPICA Dome C ice core from Antarctica. Here is an editor's summary.

The first and foremost results: The present day concentration of both gases is higher than has ever been the case in the past 800,000 years. Also, the ups and downs in carbon dioxide and methane curves follows the succession of cold glacial climates and relatively warm periods (such as ours) in between. An 800,000 year temperature record had been reconstructed previously from Antarctic ice cores.

Together, the results provide powerful evidence for a strong link between greenhouse gases and climate. During most of the Earth’s history greenhouse gas concentrations have fluctuated in the absence of humans burning coal and other fossil fuels. But the unprecedented rise of greenhouse gases in the modern atmosphere, to concentrations which threaten to unhinge vital components of the Earth’s climate system, is clearly the result of human activity.

In the past, greenhouse gas concentrations have varied owing to subtle feedbacks between orbital changes and oceanic and terrestrial carbon cylcles. Carbon dioxide concentrations depend on oceanic uptake, whereas methane is linked with the size and distribution of wetlands releasing the gas.

Like all good science, the new data will raise many new questions. One is why the amplitude of the 100,000-year oscillation in methane and carbon dioxide concentrations (which correlates with the 100,000 year temperature cycle) has changes so markedly around 450,000 years ago. Warm periods in the more recent history of the Earth seem to have been warmer than the interglacials prior to 450,000 years ago. Carbon dioxide and methane concentrations mirror this trend, which might hint to the existence of a longer-term cycle not visible in the existing record.

Another question is how greenhouse gas concentrations measured in Antarctic ice cores relate to episodes of rapid warming and cooling in Greenland and the northern hemisphere. It seems that more that 70 such temperature jumps, perhaps as a result of changes in ocean circulation, have occured over the last 800,000 years.

“These new benchmark data for greenhouse-gas variability pose questions as to what a much longer record might show,” writes Ed Brook in a news and views article. The search for the best drilling site which could produce such a record is beginning.

Quirin Schiermeier

Posted by Quirin Schiermeier on May 15, 2008
Categories: Climate Science, Climate variability, Features, Journal Club, Palaeoclimate, Quirin Schiermeier | Permalink | Comments (0) | TrackBacks (0)

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)