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Carbon emissions from Amazon wildfires could ‘counteract’ deforestation decline

The loss of carbon from wildfires fuelled by drought could “counteract” efforts to cut deforestation in the Amazon rainforest, research suggests.

A new study finds that, while rates of deforestation have sharply fallen in the Amazon over the past decade, the number of wildfires affecting the region has remained stubbornly high – particularly in drought years.

Emissions from wildfires totalled more than 1bn tonnes of CO2 from 2003-2015, the lead author tells Carbon Brief, and climate change, along with forest fragmentation, could cause a further increase in the number of forest fires in the coming decades.

The author adds that, if current efforts to curb deforestation are reversed, the combination of forest fires and deforestation could cause carbon loss from the Amazon to “escalate to proportions never experienced before”.

Three billion trees

The Amazon rainforest is the largest rainforest in the world, spanning an area that is 25 times the size of the UK.

The forest’s three billion trees absorb CO2 from the atmosphere during photosynthesis and then use it to build new leaves, shoots and roots. As they grow, these trees account for a quarter of the CO2 absorbed by the land each year.

The new study, published in Nature Communications, explores how this enormous carbon store is being affected by both deforestation and drought-driven wildfires.

The clearing of trees during deforestation causes previously locked-up carbon to be released back into the atmosphere.

The study finds that, despite remaining a major driver of forest carbon loss, rates of deforestation in the Amazon have fallen by 76% between 2003 and 2015. This reflects efforts by the Brazilian government to curb both legal and illegal deforestation, the study notes.

However, the amount of carbon loss from drought-driven wildfires has remained high, says lead author Dr Luiz Aragão, leader of the tropical ecosystems and environmental sciences group (TREES) at the National Institute for Space Research in Brazil. He tells Carbon Brief:

“This is the first time that we could clearly demonstrate how much widely-spread forest fires during recent droughts influence Amazonian carbon emissions. During these droughts, forest fires can overtake emissions from deforestation.”

Fanning the flames

Glossary

El Niño: Every five years or so, a change in the winds causes a shift to warmer than normal sea surface temperatures in the equatorial Pacific Ocean – known as El Niño. Together with its cooler counterpart, La Niña, this is known as the El Niño Southern Oscillation (ENSO) and is responsible for most of the fluctuations in temperature and rainfall patterns we see from one year to the next.

El Niño: Every five years or so, a change in the winds causes a shift to warmer than normal sea surface temperatures in the equatorial Pacific Ocean – known as El Niño. Together with… Read More

Although wildfires occur regularly in the Amazon, fire incidence is at its highest in drought years.

“Drought years” happen on average every five years in the Amazon and are typically a result of changes to wind and weather patterns brought about by warming in the Atlantic Ocean during events of the climate phenomenon El Niño.

Although droughts have been a natural part of the year-to-year variations in the Amazon’s climate, both the frequency and severity of droughts in the rainforest have been increasing over the last decade because of climate change, Aragão says:

“These natural swings can be intensified by global warming. Another catalyst of this Atlantic oceanic warming is the declining Northern Hemisphere aerosol production, which is also influenced by climate change.”

Previous research (pdf) shows that aerosols influence cloud formation in the rainforest and, therefore, the amount of regional rainfall.

Wildfires are usually sparked by humans clearing land, either for small-scale farming or major deforestation, Aragão says. During drought years, these small fires can quickly spread to large areas of the rainforest.

A lack of rainfall during drought years causes large sections of the lush canopy to dry out and die. These dry, dead leaves can then act as tinder, allowing small fires to spread, says Aragão:

“These forests would not burn naturally. Most of the fires that happen during droughts are human-driven. When the climate is drier, fires that are set for land management are more likely to leak into surrounding forests.”

As large areas of forest burn, huge stores of previously stored carbon are released into the atmosphere. The amount of carbon loss is greatest when fires “leak into” previously pristine forest, which may have been storing carbon for decades or even centuries, Aragão adds.

Assessing the damage

The researchers used satellite data to record the number and regional spread wildfires in the Amazon from 2003-15. The figure below shows the annual fire counts of each year of the study (red bars and numbers), with bold text signifying drought years (2005, 2010 and 2015). The numbers on the x-axis correspond to the fire season months from June (month 6) to December (month 12).

The length of the grey bars corresponds to the sum of all months with more than 10,000 fires. The colour within the grey bar shows the number of fire counts during the year’s “peak month”, with dark red showing a count of more than 40,000 and green showing a count of 10,000 to 15,000.

The chart also displays annual deforestation rates in the Amazon (khaki bars), which were derived from the Brazilian government.

The chart shows how the number of forest fires tends to spike in drought years. For example, during the 2015 drought, fire incidence was 36% higher compared to the average for the previous 12 years, the study finds.

Annual absolute fire counts (red bars) and deforestation rates (khaki bars) in the Amazon from 2003-15. Number of fires during drought years (2005, 2010, 2015) are shown in bold. The length of the grey bars corresponds to the sum of all months with more than 10,000 fires. The colour within the grey bar shows the number of fire counts during the year’s “peak month”, with dark red showing a count of more than 40,000 and green showing a count of 10,000 to 15,000. Source: Aragão (2018)

The results show that, while deforestation rates are decreasing, forest fire counts have not seen a similar decline.

This suggests that the role that deforestation plays in sparking forest fires is diminishing over time, says Aragão:

“Before we used to observe that fires in Amazonia were strongly related to deforestation. Now this relationship is weak. We think that there are few explanations, but a strong one is that because the Amazon is more fragmented, there are more edges between the deforested land and forests. This increases the chances of fires from open lands to propagate into forests.”

The effect of fragmentation could be magnified by future climate change, which is expected to bring more extreme droughts to the Amazon, he says:

“We expect that drought intensity and frequency will increase towards the end of the century. So, with more droughts it is very likely that fire incidence will also increase if no policy actions are taken to curb ignition sources.”

The researchers also used satellite data to record the total amount of CO2 released as a result of deforestation and wildfires over the study period.

The results are shown on the chart below, which shows annual CO2 emissions in teragrams (one teragram is equal to 1m tonnes of CO2) for forest fires (dark green) and deforestation (light green).

Over the course of the study period, emissions from wildfires in drought years alone totalled more than 1bn tonnes, Aragão says. The release of CO2 during forest fires could increase further as the climate warms, he adds.

Annual CO2 emissions in teragrams (1m tonnes) of forest fires (dark green) and deforestation (light green) in the Amazon from 2003 to 2015. Source: Aragão (2018)

‘Compelling’ results

The “comprehensive” study raises concerns over the growing threat of wildfires in the Amazon, says Prof Guido van der Werf from Vrije University in the Netherlands, who was not involved in the study. Van der Werf was part of a team that developed the Global Fire Emissions Database. He tells Carbon Brief:

“What is particularly compelling to me is the observed decoupling of fire and deforestation; they used to go hand in hand as fire was the cheapest tool in the deforestation process, but in recent years fires are observed more outside the deforestation regions, especially during drought years.

“Controlling these forest fires may be more difficult than controlling deforestation as it only takes one simple ignition to burn down a large area and many fires occur in secondary forests which may be less well monitored.”

The research uses a “sound methodology” but relies on statistics from the Brazilian government, which research suggests could be overstating recent deforestation reductions, says Dr Richard Birdsey, a senior scientist specialising in quantifying forest carbon budgets from the Woods Hole Research Centre, who also wasn’t involved in the research. He tells Carbon Brief:

“Some studies question the official statistics of deforestation in Brazil, suggesting that the reduction over previous decades may be overestimated. If deforestation is higher than the estimate used in this paper, then the relative effect of drought-induced fire would not be as large as stated here, and the decoupling of fire incidence from deforestation rates would not be as significant.”

Another factor not considered in the study is that forests tend to recover more quickly from wildfires than deforestation, he adds:

“Fires create young forests that will rather quickly recover significant amounts of lost biomass and usually have higher productivity compared with old-growth for several decades. Thus, considering the effects of fires over decades is an important consideration not addressed in this paper.”

Further carbon loss as a result of drought-driven wildfires could “counteract” efforts to curb deforestation in the Amazon, says Aragão. And, if efforts to stop deforestation are unsuccessful, the scale of carbon loss from the Amazon could reach “unprecedented” levels, he says:

“The main worry is that if deforestation increases, in combination with the increase fragmentation, increase in drought probability [caused by climate change] and the use of fires by humans, carbon emissions could escalate to proportions never experienced before.”

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Negative emissions have ‘limited potential’ to help meet climate goals

The potential for using negative emissions technologies to help meet the goals of the Paris Agreement could be more “limited” than previously thought, concludes a new report by European science advisors.

Negative emissions technologies (NETs) describe a variety of methods – many of which are yet to be developed – that aim to limit climate change by removing CO2 from the air.

Some of these techniques are already included by scientists in modelled “pathways” showing how global warming can be limited to between 1.5C and 2C above pre-industrial levels, which is the goal of the Paris Agreement.

However, the new report says there is no “silver bullet technology” that can be used to solve the problem of climate change, scientists said at a press briefing held in London.

Instead, “the primary focus must be on mitigation on reducing emissions of greenhouse gases,” they added.

Zero emissions

The 37-page report was produced by the European Academies Science Advisory Council (EASAC), an independent group made up of staff from the national science academies of EU member states, Norway and Switzerland, which offers scientific advice to EU policymakers.

Drawing on the results of recently published research papers, the report assesses the feasibility and possible impacts of NETs.

The report splits these “technologies” into six categories:

  • Afforestation and reforestation
  • Land management to increase soil carbon
  • Bioenergy with carbon capture and storage (BECCS)
  • Enhanced weathering
  • Direct capture of CO2
  • Ocean fertilisation.

A Carbon Brief article published in 2016 explained how these proposed technologies might work.

Though differing in approach, all of the proposed NETs aim to slow climate change by removing CO2 from the atmosphere and storing it underground or in the sea.

Some scientists argue that such technologies could be used to soak up some of the CO2 that is released by human activity, which could, in turn, help the world to achieve “net-zero” greenhouse gas emissions.

Net-zero emissions is a term used to describe a scenario where the amount of greenhouse gases released by humans is balanced by the amount absorbed from the atmosphere.

Achieving net-zero emissions within this century will be key to limiting global warming to between 1.5C and 2C above pre-industrial levels, says Prof Michael Norton, EASAC environment programme director and member of the expert group behind the report. At a press briefing, he said:

“Indeed, without assuming that technologies can remove CO2 on a large, that’s gigatonne [billion tonne] scale, IPCC scenarios have great difficulty in envisaging an emission reduction pathway consistent with the Paris targets.”

However, the new report suggests that there is currently no “silver bullet” technology that can absolve the world of its greenhouse gas emissions, scientists said at a press briefing. The report concludes:

“We conclude that these technologies offer only limited realistic potential to remove carbon from the atmosphere and not at the scale envisaged in some climate scenarios.”

The report also shows that many of the NETs could have large environmental impacts, says Prof John Shepherd FRS, emeritus professor of ocean and Earth sciences at the University of Southampton and member of the expert group behind the report. He told the press briefing:

“Some of these techniques would have adverse environmental impacts, including some of the ones that appear to be natural. There is an emotional response in most people to prefer natural appearing solutions, but, in many cases, the environmental are as great as the more engineering-type applications.”

The “pros and cons” of each proposed technology are summed up on the table below. The top half of the table includes: the technical status of each technology; the amount of carbon that could be removed if the technology were to be implemented on a wide scale; the potential cost of implementing the technology (low/medium/high); and the likely efficacy of each method.

The bottom half of the table assesses: the relative security of the carbon storage of each technology; the possibility that the technology may actually contribute to climate change; and the possibility that the technology could have environmental impacts.

A summary of the strengths, weaknesses and uncertainties of negative emissions technologies (NETs). Technologies include afforestation and reforestation (AR), land management (LM), bioenergy with carbon capture and storage (BECCS), enhanced weathering (EW), direct air capture and storage (DACCS), ocean fertilisation (OIF) and carbon capture and storage (CCS). Source: EASAC (2018)

Blow for BECCS?

One of the techniques under scrutiny in the new report is BECCS. Put simply, BECCS involves burning biomass – such as trees and crops – to generate energy and then capturing the resulting CO2 emissions before they are released into the air.

BECCS has been labelled one of the “most promising” NETs and is already included by scientists in many of the modelled “pathways” showing how global warming can be limited to 2C above pre-industrial levels.

However, BECCS has yet to be demonstrated on a commercial basis, the report finds, and its ability to effectively store large amounts of carbon is still “uncertain”.

Recent research has revealed a number of “drawbacks” to using BECCS on a wide scale, Norton said:

“These include the reality that even if all the carbon emitted when the biomass is burnt were to be captured, extensive emissions across the supply chain will not be captured, thus severely limiting its effectiveness as a negative carbon technology.”

In other words, the emissions resulting from the different stages of BECCS, including on transportation and on applying nitrogen fertilisers, may significantly reduce the technology’s overall ability to reduce the amount of CO2 in the atmosphere. In some cases, biomass energy might have higher emissions than fossil fuels.

On top of this, implementing BECCS on a large scale would require large amounts of land to be converted to biomass plantations, which could have considerable environmental impacts, the report notes. Carbon Brief recently covered new research investigating how using BECCS could affect different aspects of the natural world.

Forest fall out

The report also assesses the potential of afforestation, creating new forests on land that

was not previously forest, and reforestation, planting new trees on land that was once forest, to remove carbon from the atmosphere.

Trees absorb carbon from the atmosphere during photosynthesis and then use it to build new leaves, shoots and roots. By doing this, trees are able to store carbon for long periods.

However, implementing afforestation on a large scale could have “significant” environmental impacts, the new report finds. This is because growing new forests would require a large amount of land-use change and the application of nitrogen fertilisers. The production of nitrogen fertilisers releases a group of potent greenhouse gases known as nitrous oxides, along with CO2.

On top of this, new trees take many years to grow and so will not be able to immediately absorb large amounts of carbon from the atmosphere, Norton said:

“We can also see many scenarios in which the land-use change involved in extending forestry would be counterproductive for decades or even centuries.”

Norton said that curbing the rate of deforestation, which is causing the release of large stores of carbon from the world’s tropical regions, should be a priority for policymakers. He added:

“Forestation and reforestation offer simple ways of increasing carbon stocks, but it would be a mistake to be distracted from the reality of the current situation which is that…carbon is being lost by continuing deforestation.”

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Cutting to the chase

Despite potential drawbacks, there may be some scenarios where the use of NETs will be “necessary” to balance the release of greenhouse gases, said Shepherd:

“They are especially likely to be necessary to deal with intractable sources of greenhouse gases, in particular aviation and agriculture.”

In other words, NETs may be needed to compensate for industries that are unable to radically cut their rate of greenhouse gas emissions.

Such industries could include cattle ranching and rice production, says Dr Phil Williamson, associate fellow at the University of East Anglia, who was not an author of the new report. At the sidelines of the press briefing, he told Carbon Brief:

“There’s a whole lot of things that are going to be very difficult to control, including methane from cattle and methane from rice. We’re not going to stop growing rice, so we’re still going to have methane emissions. In order to have that balance, we’re still going to need some negative emissions technologies.”

However, the “primary focus” of policymakers should be on rapidly cutting greenhouse gas emissions, said Prof Gideon Henderson FRS, professor of Earth sciences at the University of Oxford and reviewer of the report. He told the press briefing:

“The primary focus must be on mitigation, on reducing emissions of greenhouse gases. That’s not going to be easy, but it’s undoubtedly going to be easier than doing NETs at a substantial scale.”

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