The fires in the Brazilian Amazon have been in the news a lot lately. Some of that is due to the controversial nature of Brazil’s President Jair Bolsonaro. Both his policies and his tendency for sacking or criticizing the bearers of bad scientific news have grabbed attention.
While the fire season has been referred to as record-setting, it’s only clearly the most active in eight years. Plus, September is usually the most active month for fires in Brazil, and public attention may have temporarily reversed any policy-driven incentive for land clearing and burning.
So, the politics are interesting, but what about the climate implications? Should we care about the Amazon rainforest any more than, say, the Indonesian rainforest or the Siberian steppes?
From a global perspective, we might care about a particular place if large changes can easily happen there and those changes can substantially affect global climate.
By that standard, the Arctic is an obvious focal point. Geologic records, instrumental data, and computer models all agree that climate change, whatever the cause, is larger in the Arctic than in the rest of the globe. Arctic climate change, in turn, amplifies global climate change in multiple ways.
The super size of Arctic climate change has a ready explanation. Snow and ice are rather white, meaning they reflect sunlight rather than absorbing it. Warmer temperatures mean less snow and ice, so sunlight that would have been reflected now gets absorbed by the newly exposed land and ocean. This upsets Earth’s energy balance sheet: extra sunlight absorbed means a buildup of energy and rising temperatures.
It turns out that other factors are at least as important at making the Arctic warm rapidly, but this feedback caused by melting snow and ice is already happening and is one reason for climate-minded folks to care about the Arctic. After all, a slow change in the rate of snow melt in the Arctic is generally accepted to be the trigger of the Ice Ages, so we know the Arctic can have an outsized climate effect.
Another concern in the Arctic is the possibility of release of methane from the Arctic tundra if temperatures warm enough, which would further enhance the greenhouse effect. Unlike the snow and ice thing, it’s not clear what it would take to get big methane releases. But if they did happen, they would cause further warming, which in turn would produce further methane releases. This sort of thing may already have happened, most recently millions of years ago.
Ice ages and runaway Arctic methane releases are examples of “multiple equilibria” — when two vastly different things can happen under the same conditions. The Arctic stores lots of methane, but it could just as easily store very little. North America doesn’t have a big ice sheet, but for most of the past 100,000 years it did. While you may not have heard of the term “multiple equilibria,” you’ve probably heard of the term for when the transition suddenly takes place: a “tipping point”.
This brings us back to the Amazon. When scientists first started trying to simulate global vegetation in computer models, a strange thing happened. According to many of the early models, there shouldn’t be a rainforest there. Well, hmm.
After a while, as scientists gathered more data and improved the models, the reason for the discrepancy became clear: The Amazon makes its own weather. Most of the rain that falls in the Amazon evaporates from the jungle itself. Take the jungle away, and the climate transitions to one that supports a tropical savanna, not a jungle. So, in place of the Amazon imagine the Serengeti.
Where’s the tipping point for the Amazon? Nobody knows really. Current thinking is that the combination of global warming and about 20 percent to 25 percent additional clearcutting of rain forest would prevent the jungle from making enough weather to sustain itself, and the central and eastern Amazon would inevitably become savanna. Out west, the Andes would still trigger enough rainfall to keep a remnant of the Amazon rain forest alive.
Okay, so large changes can easily happen there. How would that affect global climate?
In the Arctic, the fear is the release of methane. In the Amazon, the fear is the release of carbon dioxide.
Forests are made (mostly) of carbon. A forest fire releases lots of carbon dioxide into the atmosphere — but only temporarily. As the forest grows back, the carbon is sucked back out of the atmosphere.
If the forest doesn’t grow back, as happens when Amazon rainforest is converted to cropland, or worse, if the rainforest can’t sustain itself, the atmospheric carbon dioxide increase is just as long-lasting as when we burn fossil fuels. The enhanced greenhouse effect, in turn, leads to more global warming.
Back in 1997, there were massive fires in and near the rainforests of Indonesia. People burning land for agricultural purposes, with fires enhanced by weather conditions. Big health impacts for those living downwind, but not as big a climate concern because Indonesian rainforests can grow back if the farming stops before all the nutrients are gone. In the Amazon, if you burn enough of it, it’s not going to grow back anymore.
John Nielsen-Gammon is Regents professor of Atmospheric Sciences at Texas A&M University and serves as the Texas state climatologist. He is a fellow of the American Meteorological Society. Follow him on Twitter at @ClimaTexas.