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Deep Green: Forests: Carbon Sink or Carbon Bomb?

Background - 29 May, 2009
Deforestation contributes to global warming. A rising Earth temperature kills trees and damages forests. Dying trees release more carbon. Atmospheric carbon increases planet temperatures. This cycle of forest collapse represents a critical feedback loop that will likely drive warming for centuries, change life cycles on Earth in general, and usher in a sweeping transformation of human civilisation.

Rex Weyler

Worldwide forest destruction - due to logging, human habitat sprawl, and clearing for crops such as soybeans and palm oil - continues at a net loss of about 13 million hectares each year. Many cleared forests are burned on the site. Meanwhile, trees die or grow slower due to global warming. Declining forests absorb less CO2 and release more carbon.

Drought, heat, and fires

Drought and heat are making forests more susceptible to insects and fire. David Gilbert, with the Commonwealth Scientific and Industrial Research Organisation in Australia, will publish a study this year that shows forests have less biomass and increased mortality in warmer earth conditions.

Due to warmer temperatures, bark beetles have attacked boreal forests in the US, Canada and Russia. In western Canada, where I live, over nine million hectares of pine forest have been devastated by beetles, due to warmer conditions. Stands of simply dryer trees make forests more vulnerable to fire. Carbon, sequestered by forests over centuries, can be released in just a few days by wildfires, as experienced in southern Australia in recent years. Fires are increasing worldwide and now contribute about a third as much atmospheric carbon as burning fossil fuels.

Previous climate projection models expected forests and oceans to absorb much of humanity's carbon pollution. The data now shows, however, that oceans and forests are less effective than the models predicted. The oceans' ability to absorb carbon dioxide has weakened since 1981, due to increased warmth and carbonic acid buildup. Research published this year shows that forests absorb less carbon due to industrial deforestation and forest death caused by the warming.

Deforestation is already responsible for 20 per cent of global warming, and some boreal forests are now transforming from carbon sinks to carbon sources. Dr. J. Michael Waddington at McMaster University in Canada says, "Forests we once hoped would sequester carbon now appear to be a ticking carbon bomb."

Biofuels and soybeans

Climate scientists emphasise the importance of preserving tropical forests, the world's most efficient storehouses of carbon. Unfortunately, tropical forests are being cleared daily to grow biofuels, palm oil, and soybeans. Peter Frumhoff, head of the Union of Concerned Scientists' climate programme equates replacing tropical forests with biofuel plantations to "weatherising your house while keeping your windows open."

In Brazil, soybean cropland has been doubling every five years. In Argentina, I have witnessed bulldozers operating like Panzer divisions, levelling and burning forests at the rate of about 200,000 hectares each year. In Indonesia, palm oil production tripled during the 1990s and has tripled again in the last decade. In all cases, forests are destroyed, species go extinct, and indigenous forest communities are displaced into urban slums, all to supply cattle feed, food, and biofuels to rich consumers in industrialised countries.

Holly Gibbs, at Stanford University's Woods Institute for the Environment, has analysed satellite images to track deforestation and climate change. Gibbs' data show that between 1980 and 2000, over 80 per cent of new cropland came from rainforests, most from intact forests, "contrary to what some biofuel proponents have suggested."

"This is a major concern," says Gibbs. "If we run our cars on biofuels produced in the tropics, we are effectively burning rainforests in our gas tanks." She believes that environmental disaster looms "just around the corner without more thoughtful energy policies that consider the ripple effects on tropical forests." Tropical forests and their soils harbour over 340 billion tons of carbon, equivalent to more than 40 years' worth of global carbon dioxide emissions from burning fossil fuels.

Tipping points

The world's leading climatologists met in Copenhagen in March and urged governments to act decisively next December, when they attempt to replace the Kyoto climate treaty. Scientists have observed that global warming and ice melting are proceeding faster than the most extreme scenarios had predicted. The scientists expressed concern that deforestation and shrinking forests could aggravate this trend and lead to runaway global warming.

Climatologists, who once warned that humanity must limit global warming to 2°C to avoid risk of runaway feedback cycles, now believe that such hope is a lost cause. The average Earth climate has warmed by 0.75°C already, and climatologists expect we will reach the 2°C threshold by 2050. According to Chris Jones, of the Hadley Centre in Exeter, UK, such an increase could result in a loss of 20 to 40 per cent of the Amazon rainforest.

"This meeting in Copenhagen may be humanity's last chance to take climate change seriously. Human civilisation is teetering on the brink of the greatest natural disaster in our history: runaway global warming."

Furthermore, research shows that the impact of climate change is non-linear. After the 2°C threshold, we will experience not a steady decline, but a dramatic shift in ecosystem damage, forest dieback, species loss, and permafrost melt, releasing CO2 and methane. A 5°C warming would likely trigger ecosystem collapse and bring about uninhabitable conditions for present human civilisation.

A recent scientific paper shows that this non-linear response is due to the perilous interaction between tipping point elements. The climatologists predict that when one element tips - forest die-off or methane release, for example - other critical factors can be pushed beyond their tipping points. Scientists in Copenhagen also revealed that drying peat bogs add to the problem by increasing respiration, oxidising the peat, producing heat, and releasing CO2, another dangerous tipping point and feedback loop.

© Greenpeace / Daniel Beltra


Janet Cotter, with the Greenpeace Science Unit at Exeter University, attended the meetings and reported that climate models still do not adequately link human deforestation with forests dying from fires, heat, and drought. Researchers are attempting to put these factors into their models now, and to make educated predictions. Keep in mind, past predictions have been too conservative, underestimating the rates of climate change.

Some forestry scientists expressed the opinion that there may be no point in conserving forests destined to disappear with climate change. This view suggests we might be better off concentrating on protecting forests that are climate resilient.

"The forest science community is still dominated by foresters rather than ecologists," says Cotter, "and the opinion of not protecting forests may be biased in favour of logging these regions." On the other hand, forest ecosystem science shows that fragmentation by logging makes forests more vulnerable to drought. "Preserving healthy forest ecosystems, regardless of their decline due to warming, makes these forests less vulnerable. The analysis of abandoning certain forests was challenged."

A scientific paper from the Proceedings of the US National Academy of Sciences (Malhi, et. al. 2009) examines the likelihood of an Amazon forest dieback and conversion to grassland, a scenario that may be averted by preventing deforestation and associated fire.

"The dieback of the forests of E. Amazonia in the 21st century is far from inevitable but remains a distinct possibility," the authors report. They suggest that reducing global greenhouse gas emissions represents the first priority to minimise this risk, but add, "Just as human activity and the spread of fire may be critical in triggering a breakdown of forest resilience and consequent dieback, direct intervention to maintain forest area and limit the spread of fire offers the potential to maintain forest resilience and avoid any such tipping point. … Such intervention may be enough to navigate E. Amazonia away from a possible tipping point, beyond which extensive rainforest would become unsustainable."

The report concludes, "Maintaining forest cover would not only be a strategy for climate-change mitigation, regional development, and biodiversity conservation but also a potential strategy for adaptation," as the Amazon climate inevitably changes.

This is it

Forests represent vast stores of carbon. Forest destruction releases that carbon, increases global warming, and leads to forest dieback, a vicious cycle. Deforestation magnifies climate change impacts by fragmenting forests, making them drier and more vulnerable to drought-induced fire. The ultimate risk is runaway climate change, leading to loss of biodiversity and vital ecosystem services.

Last fall, Deutsche Bank economist Pavan Sukhdev, in a European study on ecosystems, reported that deforestation reduces the value of Earth's natural capital - carbon sequestration, biodiversity, water filtration, and so forth - by up to USD 5 trillion every year. That's five thousand billion dollars of value lost every year, compared to the recent global financial crash that eroded about USD 1.5 trillion in paper wealth.

Intact primary forests require priority protection at the UN Climate Summit in December. This meeting in Copenhagen may be humanity's last chance to take climate change seriously. Human civilisation is teetering on the brink of the greatest natural disaster in our history: runaway global warming. Seventeen years of Kyoto drafts, conferences, dithering, and handshakes has produced zero net decrease in human carbon emissions. Even with some notable successes in Europe, humanity as a whole has not yet even reduced the growth rate of emissions or forest destruction. We can't afford another dud or more climate change denial.

It is already too late to avoid some chaos caused by our reckless consumption of Earth's biophysical systems. We may avoid absolute disaster, but only if we are absolutely serious. Our decisions now must be wise and courageous. We must drastically reduce carbon emissions immediately, and we must preserve every square centimetre of our planet's forests.

- RexWeyler

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