Forests absorb one third our fossil fuel emissions

Jul 15, 2011

The world's established forests remove 2.4 billion tonnes of carbon per year from the atmosphere – equivalent to one third of current annual fossil fuel emissions – according to new research published in the journal Science.

"This is really a timely breakthrough with which we can now clearly demonstrate how forests and changes in landscape such as wildfire or forest regrowth impact the removal or release of atmospheric carbon dioxide (CO2)," says CSIRO co-author of the paper: A Large and Persistent Carbon Sink in the World's Forests, Dr Pep Canadell.

"What this research tells us is that forests play a much larger role as carbon sinks as a result of tree growth and forest expansion."

Dr Canadell, who is also the Executive Director of the Global Carbon Project, said the international research team combined data from forest inventories, models and satellites to construct a profile of forests as major regulators of atmospheric CO2.

In addition to the large carbon sink, he said scientists now know that deforestation is responsible for emitting 2.9 billion tonnes of carbon per year – an exchange that had not been known in the past because of a lack of data. For comparison, total from fossil fuels are currently above eight billion tonnes of carbon per year.

Dr Canadell said emissions from deforestation are much larger than previously thought, suggesting that the potential benefits of avoiding deforestation through the United Nations-backed Reduced Emissions from Deforestation and Degradation (REDD) scheme, are much larger than previously appreciated.

The REDD scheme aims to formulate a financial value for the carbon stored in forests.

Dr Canadell said a surprising finding was the large capacity of tropical forest re-growth to remove atmospheric CO2. Regrowth takes place following the end of logging and slash-and-burn land clearing projects. and, to a lesser extent, when new forest plantations are planted.

"We estimate that tropical forest regrowth is removing an average of 1.6 billion tonnes of carbon per year. Unfortunately, some countries have not looked on forest regrowth as a component of REDD, and so are missing a very important opportunity to gain even further climate benefits from the conservation of forests.

"Combining the uptake by established and re-growth plus emissions from deforestation, the world’s forests have a net effect on atmospheric CO2 equivalent to the removal of 1.1 billion tonnes of carbon every year.

" exchanges from tropical forests have the highest uncertainties in this analysis and this research has required a concerted effort to refine them to our best knowledge," Dr Canadell said.

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User comments : 11

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Bob_Kob
3.7 / 5 (3) Jul 15, 2011
Who would've guessed vegetation regulated co2 and o2 levels on the planet!
lengould100
5 / 5 (1) Jul 15, 2011
Hmmmm.. Uptake, 2.4 GT carbon/yr, release 2.9 GT carbon/yr. So how are forests doing anything to mitigate atmospheric CO2 from fossil fuel burning? We'd need to inprove forest uptake by 0.5 GT carbon / yr just for the forests themselves to stay at net zero effect on atmospheric CO2.

Also, once a particular forest area reaches maturity, it normally operates at net zero effect on atmospheric CO2, releasing as much CO2 from rotting material as it takes up.

The VERY BEST we can hope to accomplish by improving existing forests is to have them have no worse effect on atmospheric CO2 levels. They can do nothing to help regarding fossil CO2 releases from burning oil and coal. Perhaps we should get smart and start harvesting forests and sequestering the wood in a way that it cannot rot.
SteveL
5 / 5 (1) Jul 15, 2011
This is how I read their data:

Established forests absorb 2.4 billion tonnes per year. Reforestation absorbs 1.6 billion tonnes per year. (The part it seems you missed)
Slash and burn deforestation creates 2.9 billion tonnes per year.

Established forests plus new growth forests are absorbing 4 billion tonnes of CO2 per year. Minus the 2.9 billion tonnes released from slash and burn there is a net effect of 1.1 billion tonnes of CO2 absorbed each year by forests. I'm supposing the point is that if we (humans in general) were not practicing slash and burn and were instead reforesting at least half of our CO2 emissions could be absorbed by forests.

Human use carbon emmissions are at given as 8 billion tonnes per year.
SteveL
not rated yet Jul 15, 2011
It would likely take hundreds of years for a forest to reach maturity and the rotting plant matter likely releases more methane than CO2. (Apparently a significantly more serious global warming gas than CO2) By the time a forest reaches maturity significant amount of CO2 would be absorbed.
emsquared
not rated yet Jul 15, 2011
The oceans (70% of global surface area) absorb 1/3 of AG carbon. This capacity is shrinking as the globe warms.

According to the FAO, about 30% of earth's land area is covered by forest. So let's just call it 1/3 of our land area (9% of global surface area) absorbing 1/3 of AG carbon. Is this capacity shrinking or growing? Given the expansion of temperate climates, this is certainly growing. Faster than we're deforesting though? Probably not.

So ~80% of the earth's surface is absorbing ~66% of AG carbon.

Given that ~70% of the earths land is covered by vegetation, what is the rest of that vegegation's (40% of land area) CO2 absorption capabilities? Crops, plains, swamps, etc.

According to http://en.wikiped...ology%29 , forest biomass productivity is slightly less than 50% of total global terrestrial biomass productivity. So what can we reason there?

That the rest of terrestrial vegetation should take up a similar amount of CO2 as forests, no? What's that? 1/3
Dichotomy
not rated yet Jul 15, 2011
OK I think I've got it. We harvest the rotting stuff to keep the CO2 from spreading (use it to make ethanol or something since its already rotting) Also if we cut down the old trees to make things out of wood, we can plant new trees there and keep the cycle going. Why can't the politicians figure all this out?
emsquared
not rated yet Jul 15, 2011
It would likely take hundreds of years for a forest to reach maturity and the rotting plant matter likely releases more methane than CO2.

Looking at anaerobic decomposition it depends on what basis we're talking (%vol, % weight, ppm), decomposition releases roughly equal parts CO2 to CH4, 3 molecules to 3 molecules. Which by volume and weight is significantly bent toward CO2, but on a carbon balance basis is equal.

Of course with bio-degradation factored in, even more biomass (carbon) is taken into microbes and sequestered in them and or beneath the soil via their deaths and excretions.
Vendicar_Decarian
3 / 5 (2) Jul 15, 2011
This research is defunded on Aug 2, 2011.
GSwift7
1 / 5 (1) Jul 19, 2011
Also, once a particular forest area reaches maturity, it normally operates at net zero effect on atmospheric CO2, releasing as much CO2 from rotting material as it takes up


That is almost correct, but not quite. The forest takes in CO2 and efficiently converts a large portion to methane, mainly through the action of insects and decay, which is an even worse greenhouse gas than CO2.

There are two ways that a forest can actually sequester carbon for long term storage. The first is when forest refuse gets flushed into bodies of water and then accumulates as sediment. The other is when there is a forest fire and some portion of the forest biomass is turned into char, which is much more stable and long-lived in the soil than non-char biomass. The stronger the fire, the more char you'll get deeper down in the soil. Ideally, you want it to form polycarbonate minerals, but the process is very slow. I would say slow as dirt, but that would be too much. Doh!
GSwift7
1 / 5 (1) Jul 19, 2011
Of course with bio-degradation factored in, even more biomass (carbon) is taken into microbes and sequestered in them and or beneath the soil via their deaths and excretions


That reaches an equilibrium point relatively quickly. There's a maximum amount the soil will hold, based on local conditions. The carbon budget of a forest, both above and below the ground, is in a state of dynamic equilibrium. The equilibrium point changes constantly, from time of day, wind, seasons, etc. but there's an overall balance that stays pretty much constant from year to year for a mature forest.

That is a good question, in regard to which is produced in greater quantity, CO2 or CH4, overall. Living things make both CH4 and CO2 too. Plant respiration stops when there's no air motion to stir around the CO2, because they consume all of it near them very quickly. Lucky for us, that we have lungs to stir our own oxygen around.
GSwift7
2.3 / 5 (3) Jul 19, 2011
This research is defunded on Aug 2, 2011


If you're talking about the US budget negotiations, then get a clue. The main thing that will get put on hold if there's no debt ceiling adjustment is payment of Federal bonds. People who have maturing Federal Treasury Bonds will have to wait to cash them in, most likely. If they put a hold on bond payments, then they won't need to shut anything else down.

That wouldn't be the end of the world either. Companies such as insurance companies who are counting on bond payments to bridge into thier next investment cycle can still borrow from traditional lenders using the value of the bonds as collateral. The bonds will still collect interest, even when they are on hold, so the bearers will eventually get their money.