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The North Atlantic Ocean may still be an active storehouse for atmospheric carbon dioxide, said scientists at the European Geosciences Union here in Vienna yesterday.

Following evidence published last year showing that both the Southern Ocean and North Atlantic Ocean have weakened as carbon sinks in the past two decades, the new results suggest that the trend has recently reversed in the North Atlantic.

Scientists have feared that the weakening trend could be a long-term impact of global warming and that it could be typical of the ocean as a whole, which absorbs an estimated 25 per cent of anthropogenic carbon dioxide emissions yearly. If the ocean switches from a storehouse to a source of the greenhouse gas, this would jeopardise efforts to stabilise atmospheric greenhouse gas levels.

Speaking at a press conference at the EGU assembly yesterday, Ute Schuster from the University of East Anglia in Norwich, UK and Christoph Heinze at the University of Bergen, Norway, presented the results of a yearly analysis of carbon dioxide fluxes across the North Atlantic Ocean.

Previously, Schuster and colleagues showed that carbon uptake by the North Atlantic had halved between the mid-1990s and the early 21st century. But further analysis of the data on a year-by-year basis has shown that the uptake of carbon dioxide in the region has been increasing since 2002 and showed an even greater increase, relative to the early 2000s, in 2005.

The researchers caution that the results are preliminary and are not yet published. The coverage was poor in 2006 and they have not yet finished the analyses for 2007, but they say that the results so far indicate that the trend in weakening of the North Atlantic carbon sink is not linear.

The reasons for this variation are unclear. “I personally think we can’t say with confidence that the trend [in weakening sinks] is attributable to [anthropogenic] climate change”, says Schuster. Surface circulation in the North Atlantic has changed in recent years, she says, but these changes could be due to natural climate variability. Specifically, the North Atlantic Oscillation, a large-scale atmospheric pattern that has important impacts on European climate, could be influencing the rate of carbon dioxide uptake.

Continue reading "EGU: North Atlantic Ocean may regain status as carbon sink" »

Posted by Olive Heffernan on April 17, 2008
Categories: Biosphere feedbacks, Climate Science, Conferences and Meetings, EGU 2008, Ocean science, Olive Heffernan | Permalink | Comments (0) | TrackBacks (0)

It’s been quite a while since the Gulf Stream was last on the Nature cover. This week the old highlight is back.

Now that’s a topic which has caused an awful lot of confusion before. “How global warming will cause the next ice age”, stuff like that. So just to be clear: the Gulf Stream is the mostly wind-driven upper limb of the Atlantic meridional overturning circulation, which ceaselessly transports warm surface water from the Caribbean to middle and high latitudes on the other side of the Atlantic. Yes, ceaselessly. As long as the Earth keeps rotating there’s really nothing in the world (not even global warming) that could bring it to a halt.

It is common knowledge - and true - that the British Isles and Scandinavia enjoy a much warmer climate than Newfoundland or Labrador thanks to the Gulf Stream. But its climatic influence goes far beyond that, a US-Japanese team report in a paper in Nature this week.

They detected the Gulf Stream’s signature in the entire lower atmosphere - namely in air and cloud temperatures, rain bands, pressure fields and wind convergence - above its meandering cross-Atlantic course, and far inland in Europe.

That the influence of the Gulf Stream might penetrate deeply into the atmosphere has been previously assumed. Firm evidence that this is indeed the case, and vehemently so, comes from the combination of satellite observations, operational weather analysis and atmospheric circulation models which the team utilised for their study.

Very likely the Gulf Stream’s direct local effects on the atmosphere are tele-connected, via planetary atmospheric waves, with weather conditions in far-away regions. How frequent and pronounced these remote responses might be is not at all clear. But it seems at least as if Gulf Stream-driven atmospheric dynamics over the North Atlantic have a marked influence on hemisphere-wide climatology.

This, you’ve guessed it, adds another piece to the climate change puzzle. Come what may, the Gulf Stream will not ‘run dry’. But its strength does vary, and a possible weakening of the Atlantic overturning circulation, to which it belongs, is unlikely to leave the Gulf Stream unaffected.

A new ice age will not come over Europe because of that, but storm tracks and rainfall patterns could be affected in rather unpredictable ways.

Quirin Schiermeier

You can vote or comment on the importance of the new Gulf Stream paper in the Journal Club of Nature Reports Climate Change.

Posted by Olive Heffernan on March 12, 2008
Categories: Extreme Events, Features, Journal Club, Ocean science, Quirin Schiermeier | Permalink | Comments (5) | TrackBacks (0)

If you like coral reefs you should enjoy them while you can, they won’t be around for long. Global warming and the ocean acidification that comes with it will decimate reefs by the end of this century, according to a new review article in Science.

“The impact of climate change on coral reefs is much closer than we appreciated. It's just around the corner,” says study author Ove Hoegh-Guldberg, of the University of Queensland. “... The warmer and more acidic oceans caused by the rise of carbon dioxide from the burning of fossil fuels threaten to destroy coral reef ecosystems, exposing people to flooding, coastal erosion and the loss of food and income from reef-based fisheries and tourism. And this is happening just when many nations are hoping that these industries would allow them to alleviate their impoverished state.” (Reuters ... Telegraph)

Although there is no new original research here, when all the numbers are brought together they are pretty frightening. Atmospheric carbon dioxide will exceed 500 parts per million sometime between 2050 and 2100. This will drive global temperatures up at least 2°C, “values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved” says the paper.

It adds ominously, “Under these conditions, reefs will become rapidly eroding rubble banks such as those seen in some inshore regions of the Great Barrier Reef, where dense populations of corals have vanished over the past 50 to 100 years.”

The appearance of a massive swarm of jellyfish, and their subsequent decimation of an Irish salmon farm, are this week being blamed on global warming.

Stock worth £1million were suffocated in their cages by the swarm, which is estimated to have covered 25 square kilometres of sea and been up to 10 metres thick. The fish farm's director said “It was unprecedented, absolutely amazing. The sea was red with these jelly fish and there was nothing we could do about, it, absolutely nothing.” says Northern Salmon Company managing director, John Russell (Telegraph). The full story is on The Great Beyond.

This isn't the first time climate change has been linked to jellyfish outbreaks. Last summer, the same jellyfish (Pelagia notiluca) was spotted in unusually high concentrations in the Mediterranean, again prompting speculation about impacts of sea temperature rise (New Scientist). Reuters reported that a volunteer campaign had removed eight tons of jellyfish from the Spanish coastline. Both reports mention temperature and decline in predators as causes.

A recent study linked increasing populations of jellyfish in the North Sea to climate change and predicted that more jellyfish would appear over the next 100 years.

If the two events are truly linked the UK's salmon industry may have to be added to the list of climate change victims.

Image via Wikipedia

Daniel Cressey and Anna Barnett

Posted by Anna Barnett on November 23, 2007
Categories: Anna Barnett, Daniel Cressey, In the News, Ocean science | Permalink | Comments (1) | TrackBacks (0)

An interesting contribution from the comments thread on Lovelock and Rapley propose cure for global warming by Peter Williams which I thought I'd hoist up here for wider circulation. -- Oliver

Lovelock and Rapley (Nature, 449,403, 2007) put forward the idea that by pumping up nutrient rich deep oceanic water, the subsequent stimulation of planktonic photosynthetic production would give rise to a very significant drawdown atmospheric CO2. The concept is flawed scientifically on two accounts. Planktonic photosynthesis results in the assimilation of inorganic nitrogen and CO2 in a ratio which has a modal value in the region of 6.6 – the so-called Redfield ratio. A fraction of the organic particles that arise as a consequence of photosynthetic production, sink into the deeper parts of the ocean. The C/N ratio of these particles is somewhat higher than the Redfield ratio, as there is some fast decomposition of the nitrogen (and phosphorus) rich organic components before the particles reach deep water. The particles are eventually decomposed in the deeps, with the production in inorganic nutrients, along with CO2. If this water, now enriched in inorganic nitrogen (and phosphorus), were brought to the surface, it would indeed stimulate planktonic photosynthesis and result in the assimilation of CO2. However, the upwelled water is not only enriched in inorganic nitrogen but also CO2 produced at the same time, the latter being slightly in excess of the Redfield requirement due to the elevated C/N ratio of the settling particles. Thus, rather than drawing down atmospheric CO2 from the atmosphere, there would be export of CO2. The situation in fact would be worse, as the upwelled water would need to warm up (otherwise it would simply sink back again) this would reduce the solubility of CO2, resulting in further export of oceanic CO2 into the atmosphere.

Further, from the engineering point of view the concept is infeasible – to lift up a 10m diameter column of dense (cold) to the surface would require a net lift of a number of tonnes and would almost certainly collapse a flexible tube or would cause a ribbed tube to concertina.

Even if the engineering problems could be solved, and the system made cost effective, both of which seem very doubtful, the proposal would have the reverse effect of that claimed.

Posted by Oliver Morton on October 08, 2007
Categories: Biosphere feedbacks, Ocean science | Permalink | Comments (4) | TrackBacks (0)

Posted by Olive Heffernan on behalf of Kevin Trenberth

The 2007 hurricane season is about to get officially underway. Never mind that nature has already provided the first named storm in the North Atlantic: Andrea. Several forecasts suggest that the 2007 season in the North Atlantic will be well above average. Sea surface temperatures (SSTs) are above normal and atmospheric conditions look likely to be favorable for tropical storm activity.

In 2005, the record breaking year in the North Atlantic, record high SSTs in the critical region from 10 to 20 degrees N in the North Atlantic provided ample fuel for the 28 named storms (normal about 15, previous record 21 in 1933) and 15 hurricanes (normal about 6, previous record 12). Atmospheric conditions were favorable with weak wind shear (that otherwise tends to tear a vortex apart) and the absence of stable layers that prevent convection from developing. In contrast in 2006, SSTs were much lower and closer to the long term normal, and the atmospheric conditions were not favorable, as a developing El Niño in the Pacific created an atmospheric circulation that increased the wind shear in the Atlantic. This year, in 2007, there is no El Niño in the Pacific, and SSTs and the upper ocean heat content are more favorable for Atlantic storms.

There seems to be general agreement on these points, yet the whole issue of Atlantic hurricanes is mired in controversy over the role of global warming. It is not a disagreement that SSTs are higher but rather whether the warming is due to natural processes such as the Atlantic Multi-decadal Oscillation or global warming. To the public, the result is the same for now. To me this is obvious: global warming is “unequivocal” to quote the recent IPCC Working Group I report and global SSTs have increased about 0.6 degrees C. In the last half century this warming is associated with increased greenhouse gases in the atmosphere. It is not possible that the Atlantic has escaped from this warming.

The latest shot fired on this issue was by Chris Landsea in Eos on the long term Atlantic hurricane record. The Atlantic has the best record of tropical storms owing in part to aircraft surveillance since 1944. It is widely recognized that the older records are less reliable as the reports depend on shipping or landfall of the storms. Landsea makes this case quite well, but he goes further. He assumes that the percentage of landfalling storms should be constant over time and this provides a basis for adjusting the older records and increasing the numbers of storms by 2.2 per year from 1900 to 1965, when the satellite era began. The critical assumption is that this fraction should remain the same, yet it is abundantly clear that SSTs have increased and so other things have not remained the same. Given the dependence of hurricanes on high SSTs above about 26 degrees C, shouldn’t increased SSTs increase the scope for storms to develop farther to the east over what were colder waters and for the tracks to become longer? An example may be Vince in October 2005, which was the first tropical storm to make landfall in Spain and Portugal. Indeed shouldn’t one expect a decreasing fraction of landfalling storms in a warming climate?

Continue reading "Global climate change and hurricanes" »

Posted by Olive Heffernan on May 16, 2007
Categories: Climate Science, Kevin Trenberth, Ocean science | Permalink | Comments (3) | TrackBacks (0)