We often think — wrongly — of ecological systems as linear. Adding a certain amount of CO2 to the atmosphere means a certain amount of warming. Twice that amount, twice the warming. Losing 10 percent of a forest means 10 percent less forest. Twice that amount of deforestation means twenty percent less forest. Stuff like that.
But that's not how ecological systems operate. They're integrated. Their components rely on one another to function properly.
If you were to lose 20 percent of your heart function, you'd have a good chance of dying. If you lose a leg, you don't go from running a mile in 9 minutes to running it in 18. Massive blows to holistic systems can be crippling, especially when they can't be replaceable by intricate and expensive artificial substitutes as is sometimes possible for human organs. We don't know how to "substitute" for the water cycle short of expensive desalinization plants on a coast, and we can't replace the pollination that bees perform.
For that reason, among others, the precautionary principle applies. When you don't know the effects of damaging a highly complex, invaluably important ecological system, make sure not to damage it.
This is the lesson from a recent World Bank-sponsored preliminary assessment analyzing the combined effects of deforestation and climate change. Among the study's authors are researchers from Japan and Brazil, the University of Exeter, and the Potsdam Institute for Climate Impact Research.
The study notes that the Amazon contains about 10 percent of the world's land-based carbon and recycles perhaps half the rain that falls upon it, in effect determining rainfall patterns across a huge swath of Latin America, and indeed far-flung locales like Europe and Central Asia. But when forests become more arid, there is less transpiration. In turn, there is less surface cooling from rainforests, and regional air temperatures increase, exacerbating evaporation and water stress.
Furthermore, as a team of researchers comments in the Proceedings of the National Academy of Sciences,
"Land-use change and fire also affect the rainfall regime by greatly increasing the aerosol content of the atmosphere through smoke and dust. High aerosol content favors less frequent but more intensive convective rain and possible suppression of rain in the dry season."
A serious enough blow to the Amazon's vitality could induce decarbonization, "eventually forcing the Amazon through a gradual process of savannization," now a real and pressing concern.
Many of these risks and processes are at best poorly understood. However, preliminary assessments are dire. Thomas Lovejoy, the chair of biodiversity at the Heinz Center for Science, Economics and the Environment, in Washington D.C., and the chief adviser for biodiversity to the World Bank, characterizing the layered, destructively synergistic results of climate change, deforestation and fire, told Tierramérica,
"The tipping point for the Amazon is 20 percent deforestation," and that is "a scary result."
Earlier studies of the Mato Grosso, the southern portion of the Amazon, found similar danger thresholds. When soil quality deterioration and deforestation were modeled together, they found that 20 percent deforestation turned the northern part of the Mato Grosso into dry savannah. Their modeling suggested that even after 50 years there would be no recovery.
But such earlier studies didn't properly analyze what would happen when deforestation and soil destruction occurred in concert with global warming.
Since forests produce their own rain, as deforestation occurs, there is less rainfall. Decreased rainfall means increased dryness. Increased dryness leads to increased frequency of forest fires, incinerating the forest and drying out stands of trees that aren't directly affected. The process is destructively cyclical, eventually turning great chunks of the forest to cerrado, Brazilian savanna.
These findings are in line with previous studies, which had taken the worst-case 2007 IPCC scenarios as their own worst-case scenarios. But climate-change has advanced well beyond even the worst possible scenarios envisioned by the modelers whose work was used in 2007 IPCC report, and in turn, the outcomes for the Amazon and other ecologically sensitive regions will likely be worse than the 2007 models have predicted.
Other studies have suggested that substantial forest loss has already pushed eastern Amazonia to the edge of its ecological limits. And in the event of a forest-fire, "it could be considered that E. Amazonia had passed a tipping point in ecosystem structure and function," the PNAS researchers note.
The World Bank report, presented at the Biodiversity Science Policy Conference in Paris, concluded:
"Major impacts are projected in Eastern Amazonia. The combined effects of climate and deforestation result in a severe decrease of the rainforest biome, in relation to its original extension for forest area. The remaining forest biome, by 2075, accounting for 50 percent deforestation and/or the effects of fires, is about 5 percent."
Overall, the study found that "climate change alone" would reduce the size of the Amazon by one-third by the end of the century. The report recommends monetizing the benefits that the Amazon provides to humanity — perhaps questionable, since putting a dollar value on a world with an intact Amazon vs. a world without one doesn't seem like something most people would want to do.
The tipping points that will push along this process are 2 degrees Celsius and 20 percent deforestation. Seventeen to 18 percent of the Amazon has already been lost, according to Lovejoy, while the beef and soy production that accelerates deforestation continues apace.