A war of words has broken out between Brazil’s highest court and the nation’s scientific community over the role that tropical deforestation plays in exacerbating global warming, just as a group of international experts have produced a definitive climate model pinpointing how less tropical forest means more climate change – and warning that global temperature rises could have been underestimated.
The acrimonious stand-off over deforestation in the Brazilian Amazon and its effect on global climate change was triggered by a Supreme Court ruling that relaxes controls on farmers and ranchers who hitherto had been obliged to retain large portions of their land as forest reserves.
In February 2018 the court issued a landmark ruling that not only approved a controversial new forestry law, but also effectively exonerated large landowners from fines relating to all pre-2008 infringements of legal limits to clear-cutting. Scientists had extensively criticised the proposed changes, which they believe propitiate the powerful agribusiness lobby by rolling back environmental safeguards in defiance of scientific facts.
On the judiciary’s side, the tone of the debate was highly dismissive of the science. Supreme court judge Gilmar Mendes — already a controversial and publicly divisive figure for his outspoken interventions in Brazil’s corruption-induced political turbulence — was reported as dismissing scientists’ concerns about deforestation as “mero achismo” – uninformed or opinionated shooting from the hip. After the Supreme Court session members of the Brazilian Academy of Sciences formally repudiated Mendes’ position and accused him of denigrating the reputation of science.
The ruling brings to an end six years of uncertainty and rival lobbying over proposed changes to the Forestry Code (Law 12.651 / 2012). A majority on the Supreme Court bench approved the changes because of provisions in the Environmental Regularization Program (ERP). This obliges the owners of severely degraded land to undertake a restoration programme over a 20-year timeframe – in exchange for forgiveness for having caused the damage in the first place.
Passionate arguments on either side continue to rage, just as a new report published by Nature Communications provides the clearest and most unequivocal evidence of the links between deforestation and greenhouse gas emissions on a global scale and scope.
The study – one of whose authors is Brazil’s best–known climate change scientist Paulo Artaxo – is global in nature. It shows how biogenic volatile organic compounds (BVOCs) emitted by vegetation in both tropical and temperate forests drive the effects of so-called short-lived climate forcers (SLCFs), which include the greenhouse gases and aerosols plus ozone and methane. The report also shows how changes to surface vegetation drive the albedo effect — the earth’s ability to reflect the sun’s heat backwards into space.
Less forest cover means less albedo effect reflecting heat away from the earth, and fewer BVOCs able to mitigate the effects of the SLCFs. Result: global warming predictions (including those of the IPCC) that did not factor in deforestation effects may have been too optimistic.
In fact, the study finds, the global warming process may turn out to be even more intense than originally forecast unless deforestation can be halted, especially in the tropical regions. So seemingly-obscure legal squabbles in Brazil – home to the largest tracts of tropical rainforest – could have a direct bearing on the pace of global warming for every nation.
The Nature Communications report profiles the work of an international group of scientists and uses sophisticated computer modelling. Authors of the text include Brazilians Paulo Artaxo, a professor at the University of São Paulo’s Physics Institute (IF-USP), and Luciana Varanda Rizzo, a professor at the Federal University of São Paulo’s Environmental, Chemical & Pharmaceutical Science Institute (ICAQF-UNIFESP).
“If we go on destroying forests at the current pace – some 7,000 km² per year in the case of Amazonia – in three to four decades, we’ll have a massive accumulated loss. This will intensify global warming regardless of all efforts to reduce greenhouse gas emissions,” Artaxo told a Brazilian reporter.
The researchers used a numerical model of the atmosphere developed by the Met Office, the UK’s national meteorological service.
The report’s “what if” comparative scenario dating back to 1850 compared global warming as it is today, with the outcome the world would have experienced if all forests had already been removed. The result, according to Artaxo, was “a significant rise of 0.8 °C in mean temperature. In other words, today the planet would be almost 1°C warmer on average if there were no more forests.”
Having spent years collecting data on the functioning of tropical and temperate forests, the gases emitted by vegetation, and their impact on climate regulation, the group succeeded in mathematically reproducing the planet’s current atmospheric conditions, including levels of aerosols, anthropogenic and biogenic volatile organic compounds (VOCs), ozone, carbon dioxide, methane, and all the other factors that influence global temperature, such as surface albedo.
The study also showed that the difference observed in the simulations was due mainly to emissions of biogenic VOCs from tropical forests. “When biogenic VOCs are oxidized, they give rise to aerosol particles that cool the climate by reflecting part of the Sun’s radiation back into space,” Artaxo said. “Deforestation means no biogenic VOCs, no cooling, and hence future warming. This effect was not taken into account in previous modelling exercises.”
Brazil made a significant contribution to the research through collection of data from the Amazon. This began in 2009 as part of two Thematic Projects supported by FAPESP and with Artaxo as principal investigator: “GoAmazon: interactions of the urban plume of Manaus with biogenic forest emissions in Amazonia”, and “AEROCLIMA: direct and indirect effects of aerosols on climate in Amazonia and Pantanal”.
The conclusion is that while clear-cutting tropical forest does indeed produce atmospheric carbon through burning, the long-term effects of low-level forest degradation that compromise both the albedo effect and the production of benign VOCs, are just as dangerous for our future.
“The urgent need to keep the world’s forests standing is even clearer in light of this study. It’s urgent not only to stop their destruction but also to develop large-scale reforestation policies, especially for tropical regions. Otherwise, the effort to reduce greenhouse gas emissions from fossil fuels won’t make much difference,” Artaxo told the Brazilian journalist.
You can read the Nature Communications article here: nature.com/articles/s41467-017-02412-4.
You can read an article by Brazilian journalist Karina Toledo by clicking here.