Back in 2005, and again in 2010, the vast Amazon rainforest, which has been aptly described as the world’s lungs, briefly lost its ability to take in atmospheric carbon dioxide. Its drought-stressed trees were not growing and respiring enough to, on balance, draw carbon out of the air. Fires roared through the forest, transforming trees into kindling and releasing the carbon stored in their wood back into the air.
These episodes were the first times that the Amazon was documented to have lost its ability to take in atmospheric carbon on a net basis. The rainforest had become what’s called carbon-neutral. In other words, it released as much carbon as it took in. Scientists saw this as kind of a big deal.
This summer, a similar switch-off appears to be happening again in the Amazon. A severe drought is again stressing trees even as it is fanning wildfires to greater intensity than during 2005 and 2010. Early satellite measures seem to indicate that something even worse may be happening — the rainforest and the lands it inhabits are now being hit so hard by a combination of drought and fire that the forest is starting to bleed carbon back. This gigantic and ancient repository of atmospheric carbon appears to have, at least over the past two months, turned into a carbon source.
(High levels of carbon dioxide, in the range of 410 to 412 parts per million, and methane in the atmosphere over the Amazon rainforest during July and August of 2016 is a preliminary indicator that the great forest may be, for this period, acting as a carbon source. Image source: The Copernicus Observatory.)
Carbon Sinks Can’t Keep Up
Though the story of human-forced climate change starts with fossil-fuel burning, which belches heat-trapping carbon dioxide into the atmosphere, sadly, it doesn’t end there. As that burning causes the Earth to heat up, it puts stress on the places that would, under normal circumstances, draw carbon out of the atmosphere. The carbon-absorbing oceans, boreal forests, and great equatorial rainforests all feel the sting of that heat. This warming causes the oceans to be able to hold less carbon in their near-surface waters and sets off droughts and fires that can reduce a forest’s ability to take in that carbon.
In the context of the global cycle of carbon entering and being removed from the Earth’s atmosphere, oceans and large, healthy forests serve to take in greenhouse gasses. We call these carbon sinks, and throughout the past 10,000 years of our current epoch, the Holocene, they’ve helped to keep these gasses, and by extension, Earth’s temperatures, relatively stable.
(Without the ability of forests, soils and oceans to take in carbon — to act as carbon sinks — global atmospheric CO2 would have already risen well above 500 parts per million by 2009 due to fossil-fuel burning. These sinks are a helpful mitigating factor to the insult of human carbon emissions, but if they become too stressed, they can become sources of carbon instead. Image source: IPCC/CEF.)
However, for a long time now human fossil-fuel emissions have far exceeded the ability of the world’s carbon sinks to draw in excess carbon and keep greenhouse gas levels stable. Though these sinks have taken in more than half of the great volume of carbon emitted from fossil-fuel burning, the total portion of heat-trapping CO2 has risen from 280 ppm to more than 400 ppm. The oceans acidified as they strained beneath the new carbon overburden. And the forests took in this carbon even as they fought off expanding deforestation. As a result of all the excess carbon now in the atmosphere, the Earth has warmed by more than 1 degree Celsius above 1880s levels. And combined with the already strong stress imposed by clear-cutting and slash and burn agriculture, the added heat is a great strain on an essential global resource.
Global Warming Causes Carbon Sinks to Switch Off, or Worse, Turn into Sources
In this tragic context of heat, drought, ocean acidification and deforestation, it appears that the grace period that the Earth’s carbon sinks have given us to get our act together on global warming is coming to an end. Heating the Earth as significantly as we have is causing these sinks to start to break down — to be able to draw in less carbon, as was the case with the Amazon rainforest in 2005 and 2010. At these points in time, the sink was carbon-neutral. It was no longer providing us with the helpful service of drawing carbon out of the atmosphere and storing it in trees or soil. But, more ominously, in 2016, it appears that the Amazon may also to be starting to contribute carbon back to the atmosphere.
(High surface methane readings over the Amazon in excess of 2,000 parts per billion is a drought and wildfire signature. It is also a signal that the rainforest during this period was emitting more carbon than it was taking in. Image source: The Copernicus Observatory.)
After each of these brief periods of failing to draw down carbon in 2005 and 2010, the Amazon carbon sink switched back on and began to function again for a time. But by 2015 and 2016, record global temperatures had again sparked a terrible drought in the Amazon region. According to NASA officials, the new drought was the worst seen since at least 2002 and was sparking worse fire conditions than during 2005 and 2010 — the last times the Amazon’s carbon sink switched off. In July of 2016, the Guardian reported:
“Severe drought conditions at the start of the dry season have set the stage for extreme fire risk in 2016 across the southern Amazon,” Morton said in a statement. The Brazilian states of Amazonas, Mato Grosso, and Pará are reportedly at the highest risk.
Per NASA’s Amazon fire forecast, the wildfire risk for July to October now exceeds the risk in 2005 and 2010 — the last time the region experienced severe drought and wildfires raged across large swaths of the rainforest. So far, the Amazon has seen more fires through June 2016 than in previous years, which NASA scientists said was another indicator of a potentially rough wildfire season.
(Extensive wildfires over the southern Amazon and Brazil coincide with apparent atmospheric methane and CO2 spikes. Indicator that the Amazon carbon sink is experiencing another period of failure. Image source: LANCE MODIS.)
At the same time that drought and related wildfires were starting to tear through the Amazon, atmospheric carbon monitors like the The Copernicus Observatory were picking up the signal of a carbon spike above the Amazon with methane levels higher than 2,000 ppb (which is often a drought and wildfire signature) and carbon dioxide levels in the range of 41o to 412 ppm. It was a spike comparable to those over industrial regions of the world like eastern China, the U.S. and Europe.
In context, these Amazon carbon spikes are occurring at a time of record atmospheric CO2 increases. For the first seven months of 2016, the average increase in CO2 versus 2015 was 3.52 ppm. 2015’s overall rate of CO2 increase in the range of 3.1 ppm year-on-year was the fastest annual increase ever recorded by NOAA and the Mauna Loa Observatory. So far this year, the rate of atmospheric gain in this key greenhouse gas is continuing to rise — this in the context of carbon spikes over a region that should be drawing in CO2, not spewing it out.
Hat tip to Colorado Bob
Hat tip to DT Lange