Das mit den Palmölplantagen im Tropischen Regenwald war vielleicht doch nicht eine so gute Klimaschutz-Idee. Pressemitteilung der Fundação de Amparo à Pesquisa do Estado de São Paulo vom 7. März 2018 (auch auf Science Daily):
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Deforestation may intensify global warming even more than previously predicted
The global warming process may be even more intense than originally forecast unless deforestation can be halted, especially in the tropical regions. This warning has been published in Nature Communications by an international group of scientists. The 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 Agência FAPESP.
The findings of the study are based on computer modeling and forest measurements coordinated by Catherine Scott, a researcher at the University of Leeds in the United Kingdom.
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.
Albedo is a measure of the reflectivity of a surface. The albedo effect when applied to Earth is a measure of how much of the Sun’s energy is reflected back into space. The fraction absorbed changes according to the type of surface.
The researchers used a numerical model of the atmosphere developed by the Met Office, the UK’s national meteorological service.
“After adjusting the model to reproduce the current conditions of Earth’s atmosphere and the rise in surface temperatures that has occurred since 1850, we ran a simulation in which the same scenario was maintained but all forests were eliminated,” Artaxo said. “The result 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.”
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 modeling exercises.”
Temperate forests produce different VOCs with less capacity to give rise to these cooling particles, he added.
Data collection
The article notes that forests cover almost a third of the planet’s land area, far less than before human intervention began. Huge swathes of forest in Europe, Asia, Africa and the Americas have been cleared.
Collection of data on the functioning of the Amazon rainforest 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 data on temperate forests was obtained in Sweden, Finland and Russia. Collection was coordinated by Erik Swietlicki, a professor at Lund University in Sweden.
“It’s important to note that the article doesn’t address the direct and immediate impact of forest burning, such as emissions of black carbon [considered a major driver of global warming owing to its high capacity for absorbing solar radiation]. This impact exists, but it lasts only a few weeks. The article focuses on the long-term impact on temperature variation,” Artaxo said.
Deforestation, he stressed, affects the amount of aerosols and ozone in the atmosphere definitively, changing the atmosphere’s entire radiative balance.
“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 said.
The article “Impact on short-lived climate forcers increases projected warming due to deforestation” (doi:10.1038/s41467-017-02412-4) by C. E. Scott, S. A. Monks, D. V. Spracklen, S. R. Arnold, P. M. Forster, A. Rap, M. Äijälä, P. Artaxo, K. S. Carslaw, M. P. Chipperfield, M. Ehn, S. Gilardoni, L. Heikkinen, M. Kulmala, T. Petäjä, C. L. S. Reddington, L. V. Rizzo, E. Swietlicki, E. Vignati and C. Wilson can be read at: nature.com/articles/s41467-017-02412-4.
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Passend dazu eine Pressemitteilung des European Commission Joint Research Centre vom 20. Februar 2018:
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Land use change has warmed the Earth’s surface
Recent changes to vegetation cover are causing the Earth’s surface to heat up. Activities like cutting down evergreen forests for agricultural expansion in the tropics create energy imbalances that lead to higher local surface temperatures and contribute to global warming.
Natural ecosystems play a crucial role in helping combat climate change, air pollution and soil erosion. A new study by a team of JRC researchers sheds light on another, less well-known aspect of how these ecosystems, and forests in particular, can protect our planet against global warming. The research team used satellite data to analyse changes in global vegetation cover from 2000 to 2015 and link these to changes in the surface energy balance. Modifying the vegetation cover alters the surface properties – such as the amount of heat dissipated by water evaporation and the level of radiation reflected back into space – which has a knock-on effect on local surface temperature. Their analysis reveals how recent land cover changes have ultimately made the planet warmer.
„We knew that forests have a role in regulating surface temperatures and that deforestation affects the climate, but this is the first global data-driven assessment that has enabled us to systematically map the biophysical mechanisms behind these processes“, explains Gregory Duveiller, lead author of the study. The study also looked beyond deforestation, analysing changes between different types of vegetation, from evergreen forests to savannas, shrublands, grasslands, croplands and wetlands. However, they found that the removal of tropical evergreen forest for agricultural expansion is the vegetation cover transition most responsible for local increases in surface temperature. From a greenhouse gas perspective, the cutting of forests might only affect the global climate in the mid-to-long term. However, the scientists point out that local communities living in areas where the trees are cut will immediately be exposed to rising temperatures.
The study was published in Nature Communications today and the datasets behind are fully described in Scientific Data.