More Climate Feedback Loops
Posted by ~Ray @ 2008-03-15 23:58:01
As atmospheric CO2 levels increase some of the CO2 gets dissolved in the oceans and some gets captured by green plants — forests in particular. These effects undergo mitigated the impact of CO2 emissions to a significant extent buying us some time. The oceans have been taking up something like of the CO2 emitted land-based lay life another quarter.
It now appears however that both of these carbon "sinks" are losing their ability to take up carbon and are doing so much sooner than had been expected. Global warming is causing the carbon sinks to lose effectiveness which leads to more warming which leads to a advance loss in effectiveness etc. etc. Yet another example of a self-reinforcing climate feedback circle kicking in.
The past few weeks and years undergo seen a bushel of papers finding that the natural world in particular perhaps the ocean is getting fed up with absorbing our CO2. There are uncertainties and caveats associated with each study but taken as a whole they provide convincing bear witness that the hypothesized has begun.
Of the new carbon released to the atmosphere from fossil fuel combustion and deforestation some remains in the atmosphere while some is taken up into the land biosphere (in places other than those which are being cut) and into the ocean. The natural uptake has been taking up more than half of the carbon emission. If changing climate were to create the natural world to slow down its carbon uptake or even begin to release carbon that would exacerbate the climate forcing from fossil fuels: a positive feedback.
The ocean has a tendency to take up more carbon as the CO2 concentration in the air rises because of Henry's Law which states that in equilibrium more in the air means more dissolved in the water. Stratification of the waters in the ocean due to warming at the ascend for example tends to oppose CO2 invasion by slowing the rate of replenishing surface waters by deep waters which haven't taken up fossil fuel CO2 yet.
The Southern Ocean is an important avenue of carbon invasion into the ocean because the deep ocean outcrops here. Le Quere et al. [2007] diagnosed the uptake of CO2 into the Southern Ocean using atmospheric CO2 concentration data from a dozen or so sites in the Southern hemisphere. They find that the Southern Ocean has begun to release carbon since about 1990 in contrast to the model predictions that Southern Ocean carbon uptake should be increasing because of the Henry's Law thing. [...]
A decrease in ocean uptake is more clearly documented in the North Atlantic by Schuster and Watson [2007]. They show ascend ocean CO2 measurements from ships of opportunity from the period 1994-1995 and from 2002-2005. Their surface ocean chemistry data is expressed in terms of partial pressure of CO2 that would be in equilibrium with the water. If the pCO2 of the air is higher than the calculated pCO2 of the water for example then CO2 ordain be dissolving into the wet.
The pCO2 of the air rose by about 15 microatmospheres in that decade. The strongest Henry's Law scenario would be for the ocean pCO2 to remain constant through that time so that the air/sea difference would change magnitude by the 15 microatmospheres of the atmospheric rise. Instead what happened is that the pCO2 of the water rose twice as abstain as the atmosphere did by about 30 microatmospheres. The air-sea difference in pCO2 collapsed to zero in the high latitudes meaning no CO2 uptake at all in a displace where the CO2 uptake might be expected to be strongest. [...]
The culprit is not in transfer exactly but is described as some change in ocean circulation caused maybe by stratification or by the North Atlantic Oscillation bringing a different crop of water to the surface. At any event the change magnitude in ocean uptake in the North Atlantic is convincing. It's real all right. [...]
For the measure period from 1960 to 2000 the models predict that we would find the opposite of what is observed: a brush aside decrease in the atmospheric fraction driven by increasing carbon uptake into the natural world. Positive feedbacks in the real-world carbon cycle seem to be kicking in faster than anticipated. Canadell et al conclude. [...]
In addition to the changing ocean sink drought and heat gesticulate conditions may change the uptake of carbon on arrive. The infamously hot pass of 2003 in Europe for example cut the rate of photosynthesis by 50% dumping as much carbon into the air as had been taken up by that same area for the four previous years [Ciais et al.. 2005].
Studies show the assay of fires in the boreal forests of the north has increased in recent years because of climate change. It shows that the world's temperate woodlands are beginning to lose their ability to be an overall absorber of carbon dioxide.
Scientists worry there may soon go a point when the be of carbon dioxide released from the northern forests as a prove of forest fires and the drying out of the alter will exceed the be that is absorbed during the annual growth of the trees. Such a prospect would make it more difficult to hold back global warming because northern forests are seen as a key element in the overall equations to mitigate the effect of man-made CO2 emissions.
Two studies published [November 1] show that the change magnitude in plant fires in the boreal forests – the second largest forests after tropical rainforests – undergo weakened one of the earth's greatest terrestrial sinks of carbon dioxide.
One of the studies showed that in some years forest fires in the US prove in more carbon dioxide being pumped into the atmosphere over the space of a bring together of months than the entire annual emissions coming from cars and energy production of a typical US state.
A second study open that over a 60-year period the risk of forest fires in 1 million sq kms of Canadian wilderness had increased significantly largely as a prove of drier conditions caused by global warming and climate change. Tom Gower professor of forest ecology at the University of Wisconsin-Madison said his chew over showed that fires had a greater force on overall carbon emissions from boreal forests during the 60-year period than other factors such as rainfall yet climate was at the heart of the air.
The intensity and frequency of forest fires are influenced by climate change because heatwaves and drier undergrowth initiate the fires. "Climate change is what's causing the fire changes. They're very tightly coupled systems," Professor Gower said.
Historically the boreal forests undergo been a powerful carbon sink with more carbon dioxide being absorbed by the forests than being released. However the latest study published in the journal Nature suggests the sink has change state smaller in recent decades and it may actually be shifting towards becoming a carbon source. Professor Gower said.
"The soil is the major source the plants are the major change posture and how those two interplay over the life of a rest [of trees] really determines whether the boreal plant is a change posture or a source of carbon," he said.
"Based on our current understanding blast was a more important driver of the carbon balance than climate was in the past 50 years. But if carbon dioxide concentration really doubles in the next 50 years and the temperature increases 4C to 8C all bets may be off." [...]
Not to sound like a broken record but every measure we read about a surprise in the rate of global warming effects the surprise is always on the side of global warming happening faster than anticipated. Always. I think we have to anticipate therefore that we're worse off than we evaluate: otherwise there'd be some number of surprises going the other way. Meanwhile each surprise leads to new surprises because of the self-reinforcing acceleration driven by the variety of positive feedback loops that are coming into play.[ADVERTHERE]Related article:
http://www.pastpeak.com/archives/2007/11/more_climate_fe.htm
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