Feedbacks And Global Warming

Posted on Friday, January 05 at 14:23 by bracewell
THE YEAR OF FEEDBACKS
......During the past year, scientific findings emerged that made even the most doom-laden predictions about climate change seem a little on the optimistic side. It was the year in which the potential scale of global warming came into focus.
......And at the heart of the issue is the idea of climate feedbacks - when the effects of global warming begin to feed into the causes of global warming. The trouble is, everywhere scientists looked in 2006, they encountered feedbacks that will make things worse - a lot worse.
......The last Intergovernmental Panel on Climate Change (IPCC) report in 2001, had little to say on the subject of climate feedbacks. This year they didn't like what they learned.
......The IPCC had regarded the Earth's climate as something that will change gradually and smoothly. Now they fear that feedback reactions may begin to kick in and suddenly tip the climate beyond a critical threshold from which it cannot easily recover.
......Climate feedbacks could turn the Earth into a very different planet over a dramatically short period of time. It has happened in the past, and it could easily happen in the future given the unprecedented scale of the environmental changes caused by man.

FEEDBACKS
......There are two types of feedback that can play a role in the future direction of the Earth's climate . The first is a "negative" feedback - it works against things getting worse. A "positive" feedback makes things worse by adding to the existing problem - it brings about a vicious circle.
......"The main concern is that the more we look, the more positive feedbacks we find," says Olivier Boucher, a climate scientist at the Met Office. "That's not the case when it comes to negative feedbacks. There seems to be far fewer of them."
......The sentiment is echoed by Chris Rapley, the director of the British Antarctic Survey in Cambridge: "When we look at the list of all the feedbacks in the climate, the list of positive feedbacks is worryingly long - a lot longer than the negative feedbacks. To be honest, it's a wonder that the climate has remained so stable."

ARCTIC ICE TIPPING POINT
......In regards to Arctic sea ice - in March, Nasa satellites monitored a 28-year record low for winter sea ice. Normally sea ice recovers during the long Arctic winter, but this was the second consecutive year that the ice failed to re-form fully to its previous winter extent. This meant there was less ice at the start of the northern summer, with the result that last September saw the second monthly minimum for summer sea ice - almost hitting the record minimum set in September 2005. "Our hypothesis is that we've reached the tipping point," says Ron Lindsay of the University of Washington in Seattle.

PERMAFROST FEEDBACK
......Take a look at another positive feedback - the frozen permafrost of Siberia and northern Canada, which locked up vast stores of carbon in the form of methane for more than 12,000 years. But now the permafrost is melting and the gas is bubbling free into the atmosphere.
......Sergei Kirpotin, a botanist at Tomsk State University in Russia, has been studying the extent of the melting permafrost of Western Siberian lakes getting bigger and bigger as the solid permafrost underneath liquifies. He said: "As we predicted in the early 1990s, there's a critical barrier. Once global warming pushes the melting process past that line, it begins to perpetuate itself."
......Exactly how much is being released into the atmosphere is unknown, although some estimates put it as high as 100,000 tons a day - which means a warming effect greater than America's man-made emissions of carbon dioxide. But Katey Walter of the University of Alaska believes even this could be seriously underestimated, and could be anywhere between 10 per cent and 63 per cent higher than suspected.
......So the message is clear: frozen peat bogs that turn into heat-absorbing lakes release methane, which means a stronger greenhouse effect and higher temperatures, leading to more permafrost melting. The cycle was clearly documented in 2006 but just how strong this positive feedback turns out to be has yet to be fully determined.

“CARBON SINK” DISABLED
......Another study in 2006 looked at perhaps the most important climate feedback there is. Yet it went unreported - so listen up. What if something were to interfere with our very useful carbon "sinks"?
......A huge international team of climatologists asked these questions in a little-known study published in the July issue of the Journal of Climate. The conclusion makes depressing reading. All the models agreed that as the world heated up, the ability of the land and the oceans to keep on absorbing carbon as efficiently as they have in the past 200 years gets appreciably worse.

“CARBON SINK” BECOMES “SOURCE”
......These carbon sinks can also turn into carbon sources. Many models suggest that the terrestrial biosphere could become a net carbon producer by the mid 21st century. Signs are that it is already happening in some parts of the world.
......Guy Kirk of the National Soil Resources Institute at Cranfield University found that the soil of Britain is releasing more carbon dioxide into the atmosphere than a quarter of a century ago because increasing temperatures are speeding up the rate of organic decay.

OCEANS & CO2
......The important carbon sinks of the ocean are also suffering from feedback. As more carbon dioxide dissolves in seawater to form carbonic acid, the acidity of the ocean increases - the rate is 100 times faster than at any time for millions of years.
......There is a physical feedback - it is just harder for more carbon dioxide to dissolve in acid water - as well as a biological feedback. Tiny organisms called coccolithophores use dissolved carbon to make their shells, but acidic seas make this more difficult. This blocks an important biological pump that pushes carbon to a long-term store on the seabed.
......Yet another ocean feedback was monitored in 2006. Nasa satellites showed earlier this month that phytoplankton are finding it harder to live in the more stratified layers of the warmer ocean, which restrict the mixing of vital nutrients. Since 2000, the photosynthetic productivity of phytoplankton have decreased in some ocean regions by 30 per cent.
......"As climate warms, phytoplankton production goes down, but this also means that carbon dioxide uptake by ocean plants will decrease," says Michael Behrenfeld of Oregon State University. "That would allow carbon dioxide to accumulate more rapidly in the atmosphere, making the problem worse."

“ABRUPT CHANGE” AS HISTORY AND PRELUDE
......Some climate scientists believe that the risk of dangerous feedbacks tipping the Earth's climate system beyond a threshold is so great that there should be wider recognition of what they term "abrupt changes". It has happened repeatedly in the past.
......It happened 55 million years ago when a trillion tons of methane were suddenly and mysteriously released from frozen stores on the seabed, causing global temperatures to soar 10C, and a mass extinction of species.
......It happened 14,500 years ago when ice sheets catastrophically collapsed into the ocean causing sea levels to rise by 20 metres in just 400 years.
......And it happened 6,500 years ago when the Sahara was suddenly turned from lush vegetation to dry desert.
......Scientists say that what is happening now to the planet in terms of carbon dioxide levels and global temperatures is just as abrupt as anything that has occurred in the past. "What we are doing now to the Earth is unprecedented," says Professor Rapley of the British Antarctic Survey, "so we cannot rule out the possibility that we are doing something that will create a strong positive feedback, which will push the Earth into a domain where things will happen that have never happened before."

POPULATION MIGRATION - OUR FUTURE
......The single most momentous environmental image of 2006 was a holiday snap, on August 3 on Tejita beach in Granadilla. It had been a day of utter normality for tourists, then came a boat. Out of it fell pitiful figures - exhausted, terrified, dehydrated, starving. They were African migrants who, out of desperation, had risked the long voyage from the African coast to the Canaries; for the Canaries are part of Europe, a place of hope and opportunity.
......The tourists rushed to the aid of fellow men and women. But will they offer such a welcome when whole countries or regions need to move? For that is coming.
......As climate change takes hold this century, agriculture may fail in some of the poorest and most densely populated parts of the world.
......Sir Crispin Tickell, Britain's former Ambassador to the UN, who is one of the most far-sighted of environmental commentators, pointed out as long ago as 1990 that global warming is likely to create environmental refugees in the hundreds of millions. We have paid little attention to his warning.
......But if you look at the picture taken on Tejita beach, you can see something even more dramatic than the fact that the ordinary European holidaymaker has a lifestyle most Africans can only dream of. You can see the future, starting to happen. [Proofreader's note: this article was edited for spelling and typos on January 8, 2007]

Note: 2004: Pentagon says ... Review of the year: Gl...

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