The Australia bushfires, which are still burning and claimed an additional three lives this week, have released enough greenhouse gases to double the country's annual greenhouse gas emissions from burning fossil fuels, new scientific estimates show.
Guido van der Werf, who helps maintain the Global Fire Emissions Database, says the fires in New South Wales and Victoria in particular have emitted around 400 million tons of carbon dioxide so far, “pushing country-level estimates for all of 2019 to a new record in the satellite era” of about 900 million tons of carbon dioxide.
According to the Global Carbon Project, in 2018, Australia emitted 421 million tons of carbon dioxide, making it the 16th-largest emitter worldwide, ranking just above the UK. Typically, fire-related emissions are not included in annual estimates of a country's emissions, since such pollutants tend to be reabsorbed over time.
In a typical fire year in Australia, large amounts of grasslands burn in sparsely populated areas. The carbon emitted by these fires tends to be reabsorbed during the following wet season.
However, this year, vast forest ecosystems that serve as long-term carbon savings accounts, having taken in carbon and stored it in biomass, went up in flames, such as in the Blue Mountains of New South Wales. This carbon was released into the atmosphere during the fires, and it could take decades for the forests to recover to the point where they are net absorbers of such quantities of carbon dioxide once again.
In fact, full recovery may never happen, particularly if more fires burn in these forests in rapid succession, Mr van der Werf noted.
In another indication of the climate change implications of the bush fires, the UK Met Office said on Friday that the Australian fires could account for 1 to 2 percent of the acceleration in the growth of the global concentration of carbon dioxide in the planet's atmosphere in 2020.
Mr Van der Werf cautioned that the Australia fire emissions estimate comes with “substantial” uncertainties traced mainly to the unprecedented nature of these fires.
Niels Andela, a research scientist at NASA who also works on the fire emissions database, says two independent examinations of greenhouse gas emissions from the 2019-2020 bush fires both reached relatively similar conclusions, bolstering his confidence in the numbers.
In an interview, Mr Andela said the emissions estimates are generated using instruments carried by different satellites that detect the heat signatures of wildfires. The emissions database utilises historical data to locate hot spots as well as the energy released by wildfires, both of which spiked to unprecedented heights in southeastern Australia in recent months.
The historical data and observations is fed into a computer model to determine the likely emissions.
However, more accurate measurements will require information about the ecosystems burnt as well as the precise burnt area, which takes time to generate.
Mr Andela said the uncertainty involved in near-real-time estimates could be as high as 50% due to questions about historic estimates of fire emissions. In the case of the Australia bush fires, he says, the uncertainty is high because no one has ever seen fires burn like this in these ecosystems under such historically hot and dry conditions.
This could throw off assumptions in the model about how much of the forests burned.
Last year was the hottest and driest year on record in Australia, and December saw the country shatter its record for the hottest-ever day nationally.
With climate extremes becoming more severe and common worldwide as the global temperatures increase, real-time wildfire emissions estimates are likely to take on added importance. In 2019, for example, there was a spate of fires throughout the boreal forest in the Arctic, and 2018 was the most damaging and deadly fire year in California's history.
Mr Andela says the carbon cycle implications of the Australian forest loss are hugely important, since it will take decades for these forests to become efficient absorbers of greenhouse gases again. And that will only happen if more bush fires do not disturb these regions during their recovery period and logging does not expand.
In Australia, a debate is taking place over whether to thin out forests to make them less fire-prone, although scientific evidence shows the biggest drivers of fire risk is heat and drought, not forest density. Climate change heightens both of these risk factors.
Rob Jackson, a professor of Earth system science at Stanford University, said it's possible that by the time the bushfires are finally extinguished, the emissions from this fire season will be close to a billion tons of carbon dioxide. This would be below the fires that burned in Indonesian peatlands in 1997-1998, but roughly on par with the peat fires there of 2015-2016.
Jackson said even a half billion tons of carbon emissions is important, since, “It's the extra [carbon] that keeps adding up in the atmosphere.”
“If fire emissions increase in Australia and Western North America, they will make our job harder,” Jackson said, referring to efforts to cut greenhouse gas emissions. “More importantly,” he said, “They'll change lives. We'll have to rethink firefighting, controlled burns, where we live, that's happening in California too.”
“Is this a transformation of Australia's ecosystems?” he said.
Noting that many national parks saw the most severe fires, Jackson said such fires have been “devastating” from a carbon storage perspective as well as species conservation.
“They're having catastrophic fires in the parks. And the parks have in many places the biggest biomass, the richest systems,” he said. “It's more than just acreage. It's what acres are being burned.”
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