Tropical forest carbon sinks

2009-02-23

in Science, The environment

Shadows in downtown Ottawa

A recent Nature article discusses the status of forest-based carbon sinks in general, with special emphasis on an African sink that is estimated to be absorbing 1.2 billion tonnes of carbon dioxide per year: nearly twice the level of Canada’s 2006 emissions.

Today’s launch of the Orbital Carbon Observatory should help scientists to gain a better sense of how carbon dioxide is moving through and between the atmosphere, hydrosphere, and biosphere.

All told, the article estimates that 18% of human carbon dioxide emissions are being absorbed by tropical forests. The article highlights the uncertainties involved in the future trajectory of absorption by this sink. It may be that additional atmospheric CO2 causes it to maintain or even increase its absorption in the medium term. Conversely, it may be that the trees will reach a maximum size and cease to absorb further carbon, or that temperature and precipitation changes caused by global warming will restrict growth.

In any event, humanity will be in a better position to plan for the future once we have a deeper understanding of the nature of existing carbon sinks, and better projections for how they will respond to future conditions. In the mean time, working to avert further tropical deforestation is an important precautionary step.

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{ 6 comments… read them below or add one }

Tristan February 23, 2009 at 11:26 am

Paradoxically, I think the best way to preserve carbon in a forest is to burn it – whereas dead trees rot, burnt trees stay in place for hundreds or thousands of years.

What I mean, of course, is not burning forests, but perhaps selective logging – and when that logging is not needed for production, it could be seared on the outside to prevent it rotting, and simply buried.

Perhaps that’s a bit crass. However, one surely relevant fact is that time after time, selective logging gives higher total yield numbers over time, in board feet. This is important because a “board foot” is not only a building material but a unit of carbon – so, to extract the most carbon, you need to extract the most “board feet”, which means we need to stop with this horrific practice of clearcutting which is easy on the machines but detrimental to the forests. Otherwise, we’ll end up with English mountainsides.

. February 23, 2009 at 12:14 pm

IPCC Special Report on Land Use, Land-Use Change And Forestry

The Intergovernmental Panel on Climate Change (IPCC) Special Report on Land Use, Land-Use Change, and Forestry (SR-LULUCF) has been prepared in response to a request from the United Nations Framework Convention on Climate Change (UNFCCC) Subsidiary Body for Scientific and Technological Advice (SBSTA). At its eighth session in Bonn, Germany, 2-12 June 1998, the SBSTA requested a report examining the scientific and technical implications of carbon sequestration strategies related to land use, land-use change, and forestry activities. The scope, structure, and outline of this Special Report was approved by the IPCC in plenary meetings during its Fourteenth Session.

This Special Report examines several key questions relating to the exchange of carbon between the atmosphere and the terrestrial pool of aboveground biomass, below-ground biomass, and soils. Vegetation exchanges carbon dioxide between the atmosphere and the terrestrial biosphere through photosynthesis and plant and soil respiration. This natural exchange has been occurring for hundreds of millions of years. Humans are changing the natural rate of exchange of carbon between the atmosphere and the terrestrial biosphere through land use, land-use change, and forestry activities. Consequently, it is important to examine how carbon flows between different pools and how carbon stocks change in response to afforestation, reforestation, and deforestation (ARD) and other land-use activities.

Milan February 23, 2009 at 12:19 pm

If you look at the Summary for Policymakers from the IPCC report above, you can see that the estimated carbon content of soils significantly exceeds that of trees:

For tropical forests: vegetation (212 gigatonnes carbon) soil (215 Gt C)
Temperate: vegetation (59) soil (100)
Boreal: vegetation (88) soil (471)

Forest total: vegetation (359) soil (786)

I don’t know what happens to the carbon in soil when forest is burned.

. February 23, 2009 at 8:37 pm

Amazon dieback could be prevented

17 February 2009

Parts of the Amazon rainforest may face less serious droughts this century than previously feared, according to new research.

Scientists compared 19 global climate models with actual rainfall measurements for the region.

The team found that the models tended to underestimate current rainfall levels because the models don’t quite capture some of the peculiar features of the geography of South America. The models also ‘vary greatly in their projections of future climate change in Amazonia,’ according to the paper.

Some climate models have predicted that parts of the eastern Amazon will turn from rainforest to savannah this century. The new findings, with corrected rainfall patterns, suggest the region may move from year-long wet seasons to wet and dry seasons. This will result in a seasonal forest – not quite a rainforest, but, crucially, not savannah.

. October 22, 2010 at 2:56 pm

SIR – In your recent coverage of the REDD programme you neglected to mention the disincentive of donor countries to monitor compliance. Many donor countries support REDD because of the cheap carbon credits that they will receive. When this is the case they will not want to look too carefully at results for fear of losing their credits. Impartial third-party monitoring from an initial baseline level of forests is essential for the real success of the programme, along with a willingness to withhold payments to countries who do not comply.

Lee J. Alston
Krister Andersson
Institute of Behavioural Science
University of Colorado
Boulder, Colorado

. June 23, 2014 at 4:04 pm

Cutting down on cutting down

How Brazil became the world leader in reducing environmental degradation

But how did it break the vicious cycle in which—it was widely expected—farmers and cattle ranchers (the main culprits in the Amazon) would make so much money from clearing the forest that they would go on cutting down trees until there were none left? After all, most other rainforest countries, such as Indonesia and the Democratic Republic of the Congo, have failed to stop the chainsaws. The answer, according to a paper just published in Science by Dan Nepstad of the Earth Innovation Institute in San Francisco, is that there was no silver bullet but instead a three-stage process in which bans, better governance in frontier areas and consumer pressure on companies worked, if fitfully and only after several false starts.

The first stage ran from the mid-1990s to 2004. This was when the government put its efforts into bans and restrictions. The Brazilian Forest Code said that, on every farm in the Amazon, 80% of the land had to be set aside as a forest reserve. As the study observes, this share was so high that the code could not be complied with—or enforced. This was the period of the worst deforestation. Soyabean prices were high and there was a vast expansion of soyabean farming and cattle ranching on the south-eastern fringe of the rainforest.

During the second stage, which ran from 2005 to 2009, the government tried to boost its ability to police the Amazon. Brazil’s president, Luis Inácio Lula da Silva, made stopping deforestation a priority, which resulted in better co-operation between different bits of the government, especially the police and public prosecutors. The area in which farming was banned was increased from a sixth to nearly half of the forest.

The third stage, which began in 2009, was a test of whether a regime of restrictions could survive as soyabean expansion resumed. The government shifted its focus from farms to counties (each state has scores of these). Farmers in the 36 counties with the worst deforestation rates were banned from getting cheap credit until those rates fell. The government also set up a proper land registry, requiring landowners to report their properties’ boundaries to environmental regulators. There was a cattle boycott modelled on the soya one. And for the first time, there were rewards as well as punishments: an amnesty for illegal clearances before 2008 and money from a special $1 billion Amazon Fund financed by foreign aid.

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