viernes, 29 de enero de 2010

CO2: ¿etroalimentación positiva o negativa?

¿Una buena noticia al fin?

¿Habrá o no un efecto de retroalimentación en la subida de la termpratura o está el clima de la Tierra en un equilibrio estable, a pesar de nuestra intervención?

Temperature and CO2 feedback loop 'weaker than thought'

By Roger Harrabin
BBC environment analyst

Ice core
The new study used data from tree rings and ice cores

The most alarming forecasts of natural systems amplifying the human-induced greenhouse effect may be too high, according to a new report.

The study in Nature confirms that as the planet warms, oceans and forests will absorb proportionally less CO2.

It says this will increase the effects of man-made warming - but much less than recent research has suggested.

The authors warn, though, that their research will not reduce projections of future temperature rises.

Further, they say their concern about man-made climate change remains high.

The research, from a team of scientists in Switzerland and Germany, attempts to settle one of the great debates in climate science about exactly how the Earth's natural carbon cycle will exacerbate any man-made warming.

Positive, negative

Some climate sceptics have argued that a warmer world will increase the land available for vegetation, which will in turn absorb CO2 and temper further warming. This is known as a negative feedback loop - the Earth acting to keep itself in balance.

But the Nature research concludes that any negative feedback will be swamped by positive feedback in which extra CO2 is released from the oceans and from already-forested areas.

The oceans are the world's great store of CO2, but the warmer they become, the less CO2 they can absorb. And forests dried out by increased temperatures tend to decay and release CO2 from their trees and soils.

Commenting in Nature on the new research, Hugues Goosse from the Université Catholique de Louvain in Belgium said: "In a warmer climate, we should not expect pleasant surprises in the form of more efficient uptake of carbon by oceans and land… that would limit the amplitude of future climate change".

I don't think they can rule out that the positive feedback from the carbon cycle could become stronger in a significantly warmer climate
Tim Lenton
University of East Anglia

The IPCC's fourth assessment report had a broad range of estimates as to how far natural systems would contribute to a spiral of warming. The Nature paper narrows that range to the lower end of previous estimates.

The report's lead author, David Frank from the Swiss Federal Institute for Forest, Snow and Landscape Research, told BBC News that many of the calculations for the IPCC assessment report did not include an integrated carbon cycle.

He said that if the results his paper were widely accepted, the overall effect on climate projections would be neutral.

"It might lead to a downward mean revision of those (climate) models which already include the carbon cycle, but an upward revision in those which do not include the carbon cycle.

"That'll probably even itself out to signify no real change in the temperature projections overall," he said.


The team's calculations are based on a probabilistic analysis of climate variation between the years 1050 and 1800 - that is, before the Industrial Revolution introduced fossil carbon into the atmosphere.

Using 200,000 data points, the study - believed by Nature to be the most comprehensive of its kind so far - compared the Antarctic ice core record of trapped CO2 bubbles with so-called proxy data like tree rings, which are used to estimate temperature changes.

The most likely value among their estimates suggests that for every degree Celsius of warming, natural ecosystems tend to release an extra 7.7 parts per million of CO2 to the atmosphere (the full range of their estimate was between 1.7 and 21.4 parts per million).

Satellite composite view of South Pole (SPL)
The oceans' ability to absorb CO2 figures strongly into the debate

This stands in sharp contrast to the recent estimates of positive feedback models, which suggest a release of 40 parts per million per degree; the team say with 95% certainty that value is an overestimate.

"This is a valuable paper that helps to constrain certain feedback components for the past," said John Schellnhuber, director of the Potsdam Institute for Climate Impact Research.

"However, it is probably not suited for extrapolation into the future and it does not cover the really interesting processes like anthropogenic activation of permafrost carbon or methane clathrates."

The paper will surely not be the last word in this difficult area of research, with multiple uncertainties over data sources.

"I think that the magnitude of the warming amplification given by the carbon cycle is a live issue that will not suddenly be sorted by another paper trying to fit to palaeo-data," Professor Brian Hoskins, a climate expert from Imperial College London, told BBC News.

Another crucial issue is the degree to which past trends will line up with potentially very different future scenarios.

Professor Tim Lenton from the University of East Anglia said: "It looks intriguing and comforting if they are right. The immediate problem I can see is that past variations in CO2 and temperature over the last millennium were very small, and this group are assuming that the relationship they derive from these very small variations can be extrapolated to the much larger variations in temperature we expect this century.

"We have plenty of reason to believe that the shape of the relationship may change (be nonlinear) when we 'hit the system harder'. So, I don't think they can rule out that the positive feedback from the carbon cycle could become stronger in a significantly warmer climate."

jueves, 7 de enero de 2010

Calentamiento y el metano oceánico

Y para equilibrar el anterior comentario....

Me habían comentado hace años que podría ser posible, un escape súbito del metano atrapado en los océanos hacia la atmósfera, que podría causar una restroalimentación rapídisima del efecto invernadero. Pues podría estar ya aquí.

Methane release 'looks stronger'

By Michael Fitzpatrick
Science reporter, BBC News

Bubbles of methane ice (SPL)
Frozen depositories are giving up methane to the sea

Scientists have uncovered what appears to be a further dramatic increase in the leakage of methane gas that is seeping from the Arctic seabed.

Methane is about 20 times more potent than CO2 in trapping solar heat.

The findings come from measurements of carbon fluxes around the north of Russia, led by Igor Semiletov from the University of Alaska at Fairbanks.

"Methane release from the East Siberian Shelf is underway and it looks stronger than it was supposed [to be]," he said.

Professor Semiletov has been studying methane seepage in the region for the last few decades, and leads the International Siberian Shelf Study (ISSS), which has launched multiple expeditions to the Arctic Ocean.

The preliminary findings of ISSS 2009 are now being prepared for publication, he told BBC News.

Methane seepage recorded last summer was already the highest ever measured in the Arctic Ocean.

High seepage

Acting as a giant frozen depository of carbon such as CO2 and methane (often stored as compacted solid gas hydrates), Siberia's shallow shelf areas are increasingly subjected to warming and are now giving up greater amounts of methane to the sea and to the atmosphere than recorded in the past.

Methane gas is trapped inside a crystal structure of water-ice
The gas is released when the ice melts, normally at 0C
At higher pressure, ie under the ocean, hydrates are stable at higher temperatures

This undersea permafrost was until recently considered to be stable.

But now scientists think the release of such a powerful greenhouse gas may accelerate global warming.

Higher concentrations of atmospheric methane are contributing to global temperature rise; this in turn is projected to cause further permafrost melting and the release of yet more methane in a feedback loop.

A worst-case scenario is one where the feedback passes a tipping point and billions of tonnes of methane are released suddenly, as has occurred at least once in the Earth's past.

Such sudden releases have been linked to rapid increases in global temperatures and could have been a factor in the mass extinction of species.

According to a report by the US National Oceanic and Atmospheric Administration (Noaa), the springtime air temperature across the region in the period 2000-2007 was an average of 4C higher than during 1970-1999.

That is the fastest temperature rise on the planet, claims the university.

The recent thaw over the last decade means that some of the large reserve of carbon from organic material such as dead animals and plants in sediments is now being released into the sea and into our atmosphere.

Trapped below that is the methane hydrate now warming and leaking through holes in the defrosting sediments.

Infographic (BBC)
1. Methane hydrate is stable at high pressure and low temperature
2. Nearer the surface, where water pressure is lower, hydrates break down earlier than at greater depth as temperatures rise
3. Gas rises from the sea-bed in plumes of bubbles - some of it dissolves before it reaches the surface
4. The ISSS team says it has detected methane breaking the ocean surface

Previously it was thought much of this gas was absorbed into the sea.

But according to a recent report that Professor Semiletov and his team compiled for the environmental group WWF, the shallow depth of arctic shelves means that methane is reaching the atmosphere without reacting to become CO2 dissolved in the ocean.

Professor Semiletov's fellow researcher aboard the Russian icebreaker that carries the ISSS team each year is Professor Orjan Gustafsson from Stockholm University in Sweden.

He said that methane measured in the atmosphere around the region is 100 times higher than normal background levels, and in some cases 1,000 times higher.

'No alarm'

Despite the high readings, Professor Gustafsson said that so far there was no cause for alarm, and stressed that further studies were still necessary to determine the exact cause of the methane seepage.

"It is important now to understand how fast it is being released and how much is being released," he said.

However, there is a real fear that global warming may cause Siberia's subsea permafrost to thaw.

Some estimates put the amount of carbon trapped in shelf permafrost at 1,600 billion tonnes - roughly twice as much carbon as in the atmosphere now.

The release of this once captive carbon from destabilised ocean sediments and permafrost would have catastrophic effect on our climate and life on Earth, warn the scientists.

Limitando la población

Envidio a los países con tradiciones protestantes. A veces los miembros de sus iglesias son bastante responsables, como es el caso de los anglicanos pidiendo limitaciones sobre el número de personas que pueden vivir en el Reino Unido.

Immigrants should understand Christian heritage - Carey

Former Archbishop of Canterbury Lord Carey has said immigrants to the UK should have an understanding the country's Christian heritage.

He is among a group of MPs and peers warning that the population should not be allowed to go beyond 70 million.

Lord Carey said immigration angered many people and could lead to violence, and that the system had to focus more on maintaining "values".

Labour says the system works, but the Tories want caps on incoming workers.

All the main parties are sceptical about setting population targets which they believe is unrealistic and counter-productive.

Last year the Office for National Statistics said, if current trends continued, the UK population would rise by 10 million to more than 71.6 million by 2033 - the fastest rise in a century.


Two-thirds of that increase would be caused, directly or indirectly, by migration to the UK, it suggested.

The Balanced Migration Group - made up of 20 parliamentarians, including Lord Carey, former Commons Speaker Baroness Boothroyd, five Labour MPs and 10 Conservative MPs - is backing a campaign calling for curbs on immigration.

We've got to be more outspoken. What I'm calling for is a debate, a debate without any rancour
Lord Carey

Lord Carey told BBC Radio 4's Today programme: "We are not calling for a ban or anything like that because we value people from abroad."

"What I think I'm concerned about is not saying we must put a limit on people who are non-Christian populations. That's not the point. We welcome everybody and that's always been the generous spirit of the United Kingdom."

But, he said, immigrants must "understand" the UK's culture, including parliamentary democracy "which is built upon Christian heritage", "our commitment to the English language" and an understanding of the country's history.

The system should not "give preference to any particular group", he said, but added that points-based immigration could take these cultural aspects into consideration.

'Competing groups'

Lord Carey added: "If there's going to be an implementation of that points system, it must focus much more on values rather than religions...

"If there are competing groups wanting to come in, some groups which may have a greater understanding, an espousal to that, may be given preference under a points system, but that's not what I'm arguing and certainly not what the cross-party group is arguing."

Lord Carey told BBC Radio 5 live: "We've got to be more outspoken. What I'm calling for is a debate, a debate without any rancour."

He added that immigration was an issue that mattered to "ordinary working-class people" and that it was important to tackle "that kind of resentment which could build and is building up already".

Lord Carey said too much population growth in the UK could foster "dangerous social conditions", with some minority ethnic groups, such as young Muslim men, suffering "disproportionate" unemployment.

Labour MP Field and Tory MP Nicholas Soames, the co-chairmen of the migration group, said: "Poll after poll shows the public to be deeply concerned about immigration and its impact on our population.

"It is time parties turned their rhetoric into reality by making manifesto commitments to prevent our population reaching 70 million by 2029."

70 million 'unlikely'

The government must "restore control" over the UK's borders and "break the present almost automatic link between coming to Britain and later gaining citizenship", the group said.

Cabinet ministers have tried to do more to address public concerns about immigration, saying the issue must not become the preserve of the BNP.

Last November, Gordon Brown promised to "tighten" the UK's immigration rules by reducing the number of professions which can recruit from outside Europe while making it harder for illegal workers to enter the UK by obtaining student visas.

He said new restrictions were having an effect, adding the 70 million projection was unlikely to materialise.

The Conservatives have said they would keep the government's points-based system but place an overall annual limit on numbers and try to attract more highly qualified migrants.

The Lib Dems say they would ensure migrants were directed to parts of the country where they are most needed, where they will be welcomed and there are the resources to accommodate them.

Net migration - the number of people who come to live in Britain minus those who leave - fell by more than a third in 2008 but critics say this was driven by eastern Europeans returning home and immigration levels must fall to levels of the early 1990s.