Brazilian scientists are playing a leading role in contesting the controversial claims made in a strongly “climate change skeptic” article published by Nature, which alleges that 150 years of human-induced land changes including deforestation and an increase of arable land area, has actually helped to cool the planet, rather than warm it up. The author’s claims were repeated in the New York Times.
The study by Nadine Unger of Yale University’s School of Forestry and Environmental Studies where she is an assistant professor of atmospheric chemistry, was published in Nature Climate Change on the eve of the 2014 United Nations special session on climate change, which resulted in the New York Declaration on forest protection.
The US scientist backed up her scholarly article with a more inflammatory commentary in the New York Times Sept 19th in which she claimed that when it comes to the accepting effect of forests on mitigating global warming, “conventional wisdom is all wrong.” Rubbing salt into the ecologists’ wounds, Unger continued: “President Ronald Reagan was widely ridiculed in 1981 when he said, “Trees cause more pollution than automobiles do.” He was wrong on the science — but less wrong than many assumed.”
A rebuttal article published on 21st September and signed by 31 leading scientists led by Daniel Nepstad of the Earth Innovation Institute says they “strongly disagree with Prof Unger’s core message.” The letter was widely republished – but not (yet) by the New York Times.
The letter was signed by Brazil’s best-known climate change scientist and IPCC lead author Paulo Artaxo of the University of São Paulo; by Prof. Reynaldo Victoria of the same university, who heads up Climate Change programs at the São Paulo Research Foundation, and by leading US academics from Stanford, Columbia, Berkeley and the National Academy of Sciences.
Unger’s article focuses not on traditional concerns about carbon emissions increased by burning forest etc, but on the action of biogenic volatile organic compounds (BVOCs) released by untouched forest cover into the atmosphere, including tropospheric ozone (O3), methane (CH4) and aerosols.
Her conclusion is that these BVOCs can cause global warming and substituting the forests that create these chemicals for additional cropland, actually cools the planet. She writes that the “effects of the global cropland expansion between the 1850s and 2000s on BVOC emissions and atmospheric chemistry have imposed an additional net global radiative impact of −0.11 ± 0.17 W m−2 (cooling).
While the Nature article acknowledges the global warming effect of the release of stored carbon to the atmosphere as CO2 when deforestation takes place, its focus on the cooling effects achieved by removing large amounts of dark, heat-absorbing forest, has proved to be a red rag to the climate change establishment. This “albedo effect” means that more lightly-covered land may reflect the sun’s heat better, just as snow or rock would.
In their rebuttal, the scientists say that although Unger’s science is sound, her conclusions are totally wrong. They say she has neglected that fact that tropical rainforests form clouds that are highly effective as solar reflectors. In the heavily-contested world of climate change science, angry spats between scientists are not uncommon – especially when one side produces controversial new data that appears to refute the growing consensus around the causes for man-made global warming.
Any such data may be seized upon by industry, or by politicians who are climate change skeptics. For that reason the scientists state that the UN initiative is a “critically important effort to slow the clearing and degradation of tropical forests as a cost-effective contribution to climate change mitigation.”
But both the content and the timing of Unger’s article – coming just as the United Nations gathered in New York to address the problem of deforestation at the Climate Simmut 2014 – is noteworthy. Her NYT column warned “More funding for forestry might seem like a tempting easy win for the world leaders at the United Nations, but it’s a bad bet.” Unsurprisingly, this provoked the shrill response to Unger, not least from the Washington Post, which carried a forest-friendly opinion piece.
September’s New York Declaration pledges to halve the rate of deforestation by the end of this decade and to restore hundreds of millions of acres of degraded land. Backers of the New York Declaration on forests claim their efforts could save between 4.5bn and 8.8bn tonnes of carbon emissions per year by 2030 – the equivalent of taking all the world’s cars off the road. You can read a copy of the declaration by clicking here.
The scientists’ letter charges Nature’s conclusions are flawed because the US scientist neglects to take into consideration special conditions in the tropics, where forest cover is most critical. Prof Unger, says the letter, “ignores the effect of forests on increasing thealbedoof the skyabove the land, which is the stronger effect in the tropics.”
One of the biggest near-term opportunities to mitigate climate change is to slow down deforestation and forest degradation in the tropics, where the lion’s share of the world’s forest loss is taking place. Brazil has reduced deforestation rates in the Amazon region by 70%, for example, keeping 3.2 billion tons of carbon dioxide out of the atmosphere since 2005 and elevating this nation to global leadership in climate change solutions
In recent months a critical spotlight has been shone upon the shortcomings of a number of articles on the links between tropical forests and global warming, that were historically published by Nature. One recent study found that flawed analysis of satellite data over the Brazilian Amazon forest had led to wholly erroneous conclusions about the forest’s ability to withstand drought because the satellites — and the scientists — had been victims of a “trick of the light.” You can read more about an extraordinary volte face by Nature which in early 2014 published articles that refuted early studies in the same publication, by clicking here and also by clicking here.