Tag Archives: negative emissions

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.”

The post Negative emissions have ‘limited potential’ to help meet climate goals appeared first on Carbon Brief.

Geoengineering carries ‘large risks’ for the natural world, studies show

Reducing the impacts of human-caused climate change through the use of bioenergy with carbon capture and storage – better known as BECCS – could have major consequences for wildlife, forests and water resources, a new study shows.

The large-scale conversion of existing land to BECCS plantations could cause global forest cover to fall by as much as 10% and biodiversity “intactness” to decline by up to 7%, the lead author tells Carbon Brief.

And the introduction of solar geoengineering could also threaten wildlife, a second study shows. The new research finds that implementing – and then not sustaining – such a technology could cause global temperatures to rebound rapidly, leaving many species unable to cope with the sharp change in conditions.

The two studies reiterate the need to fully consider the possible consequences of implementing geoengineering technologies if they are used to lessen the effects of global warming, the authors of both studies tell Carbon Brief.

The findings also highlight “the solution to global warming is mitigation”, one author concludes. “In order to achieve climate goals, it is now essential to immediately reduce CO2 emissions, instead of using harmful technologies to compensate for a more leisurely pace,” another author says.

Bargaining with BECCS

The first study, published in Nature Climate Change, assesses how using BECCS could affect different aspects of the natural world, including forest cover, biodiversity and freshwater resources.

BECCS has been labelled by many as a promising “negative emissions technology”, meaning it could be used to reduce the amount of CO2 in the atmosphere. 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.

Though yet to be demonstrated on a commercial basis, large-scale BECCS is already included by scientists in many of the modelled “pathways” showing how global warming can be limited to 2C above pre-industrial levels.

Some scientists hope that BECCS 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” emissions.

The new study explores whether this could be achieved without causing too much damage to many aspects of the natural world.

BECCS could cause problems for the natural world by taking up a large amount of land, water and other resources, explains lead author Dr Vera Heck, from the Potsdam Institute for Climate Impacts Research (PIK).

Her research finds that using BECCS on a wide scale could come with “large risks” for the natural world. She tells Carbon Brief:

“Using large-scale biomass plantations to extract CO2 from the atmosphere might contribute to climate protection, but can lead to transgressing many other environmental limits, implying large risks for biodiversity, nutrient and water cycles and land use. Therefore, biomass as a means of CO2 removal can only be a limited contribution to sustainable climate mitigation pathways.”

Pushed to the limit

For the study, the researchers estimated how BECCS could impact the nine “planetary boundaries”.

The idea of planetary boundaries is to identify how much humans can develop and use the Earth’s resources while staying safely within limits of what the planet can take. Four out of the nine planetary boundaries, including climate change, have already been breached as a result of human activity.

You can see the nine boundaries in the graphic below, which also shows the status of each one, according to a 2015 Science study.

Graphic by Rosamund Pearce

To understand how BECCS may affect the planetary boundaries, the researchers ran a series of models that considered both future climate change and how agricultural land use patterns may differ in the future.

For each scenario, the researchers worked out how many BECCS plantations could be created while staying within the “safe” zone of the planetary boundaries. The researchers considered “safe” to mean the implementation of BECCS with no additional damage to the planetary boundaries.

They find that implementing BECCS within safe boundaries could allow for negative emissions of up to 60m tonnes of carbon a year. This corresponds to less than 1% of current global CO2 emissions, Heck says.

Taking risks

The researchers also estimated how much carbon could be captured if BECCS was implemented within “risky” boundaries. This definition allowed further damage to the planetary boundaries, while still preventing a move into the “high risk” zone (see earlier graphic).

This would allow for negative emissions of around 1.2bn to 6.3bn tonnes of carbon, depending on the type of bioenergy that is used, the researchers found.

Achieving the highest amount of negative emissions would require the use of the conversion of biomass to hydrogen with carbon capture and storage. But the technology needed to facilitate the conversion of biomass to hydrogen is still far from being viable, Heck says.

However, implementing BECCS within risky boundaries could have major consequences for the environment, she adds:

“The risky scenarios imply substantial risk of triggering negative Earth system feedback and might undermine the stability and resilience of the Earth system.”

Among impacts, the introduction of BECCS within risky limits could cause global forest cover to fall by 10% and biodiversity “intactness” to fall by 7%. This is because a large amount of land would need to be converted to biofuel plantations, Heck says.

On top of this, the additional water demand derived from all of the newly created BECCS plantations could be more than double that required by global agriculture, Hecks adds.

The new research confirms earlier findings that BECCS may have a “significant adverse impact on land and freshwater”, says Prof Pete Smith, chair in plant and soil science at the University of Aberdeen, who was not involved in the research. He tells Carbon Brief:

“The authors find that relying on widespread BECCS is risky, but there are regions where the risk is low. This study is robust and helps to move the currently debate away from the currently polarised positions of ‘BECCS is always bad’ or ‘BECCS is always good’. More integrated assessments such as these are required to bolster the evidence base upon which decisions on negative emissions will be taken.”

Simulating solar geoengineering

The second study, published in Nature Ecology & Evolution, explores how the introduction of solar geoengineering could affect biodiversity.

Solar geoengineering, or “solar radiation management” (SRM), describes an array of methods – all of which remain hypothetical – for artificially reducing sunlight at the Earth’s surface in order to dampen global warming.

The new study focuses on the impacts of one type of SRM, which involves injecting aerosols into the stratosphere. Once in the atmosphere, it has been suggested that the aerosols could form a protective veil around the Earth that is able to reflect sunlight and, therefore, cool the planet.

Aerosols have a limited lifetime in the stratosphere and would need to be released at regular time intervals in order to be effective. If the release of aerosols were suddenly stopped, global temperatures could rapidly rise again.

The new study finds that this sudden termination of SRM would leave many species unable to cope with the rapid change in environmental conditions, says study author Prof Alan Robock of Rutgers University. He tells Carbon Brief:

“The main findings are that any implementation of stratospheric geoengineering could end catastrophically for many species. Although if geoengineering were ever done, it would not make sense to abruptly end it, there are credible scenarios where this might happen. Should society ever take that risk?”

Modelling a global shift

To understand how the rapid termination of solar generation could affect wildlife, the researchers used models to compare changes in temperature and rainfall under a scenario in which SRM runs from 2020 until 2070 to a scenario with no geoengineering and an intermediate level of greenhouse gas emissions (RCP4.5).

Glossary

RCP4.5: The RCPs (Representative Concentration Pathways) are scenarios of future concentrations of greenhouse gases and other forcings. RCP4.5 is a “stabilisation scenario” where policies are put in place so atmospheric CO2 concentration levels off around the middle of the century, though temperatures do not stabilise before 2100. These policies include a shift to low-carbon energy technologies and the deployment of carbon capture and storage. In RCP4.5, atmospheric CO2 sits at 540ppm by 2100 – roughly 140ppm higher than now – equivalent to 630ppm once other forcings are included (in CO2e). By 2100, global temperatures are likely to rise by 2-3C above pre-industrial levels.

RCP4.5: The RCPs (Representative Concentration Pathways) are scenarios of future concentrations of greenhouse gases and other forcings. RCP4.5 is a “stabilisation scenario” where policies are put in place so atmospheric CO2 concentration levels… Read More

The researchers then calculated the “climate velocities” of each scenario, which quantifies the speed and direction of shifting climates.

The results are shown on the charts below, which show the change in temperature velocity for (a) a modelled scenario showing the introduction of SRM, (b) the termination of SRM, (c) the current climate between 1960 and 2014 and (d) an unengineered world with moderate emissions.

In the chart, deep red signifies a rapid increase in the rate of temperature rise, while blue shows rapidly decreasing temperature.

The change in temperature velocity under (a) a modelled scenario including the introduction of solar geoengineering, (b) the termination of solar geoengineering, (c ) the current climate between 1960 and 2014 and (d) a world without solar geoengineering with moderate emissions (RCP4.5). Red shading shows increasing temperatures, while blue shows decreases; the darker the shading, the faster the rate of change. Source: Trisos et al. (2018)

The results show that while the implementation of solar geoengineering could cause temperatures to fall fairly quickly, sudden termination could cause rapid increases as temperatures rebound.

The rate of change in temperature under the termination of SRM could be two to four times larger than those caused by climate change itself, the researchers conclude. The study also finds similar – though not as drastic – changes on rainfall.

This large change in environmental conditions could leave many species unable to adapt and at a high risk of extinction, the researchers say.

Animals that do not find it easy to adapt to new environments, such as species found in tropical rainforests and small island habitats, will be the least able to adapt to these changes, they add. The risk could be highest for slow-moving amphibians, the researchers note in their paper:

“While differences in climate velocity between terrestrial hotspots for some taxa [animal groups] are small, that amphibian biodiversity hotspots have the highest temperature velocities from sudden termination suggests that increased extinction risks would be especially severe for this group.”

In other words, a large number of amphibians are found in areas that are expected to be most affected by a sudden SRM termination.

The new research makes an important contribution to the “broader conversation” surrounding the risks of solar geoengineering, says Dr Ben Kravitz, a climate scientist from the Pacific Northwest National Laboratory, who was not involved in the new research. He tells Carbon Brief:

“Although there are many issues that arise when one talks about ecosystems, to the best of my knowledge, this study the first quantitative look at what might happen to biodiversity under different scenarios of geoengineering. And, importantly, the study was done using multiple climate models, meaning we have estimates of how robust the model responses are.”

The research highlights the need for developing a governing framework for geoengineering, says Janos Pasztor, executive director of  the Carnegie Climate Geoengineering Governance Initiative (C2G2).

“This paper is precisely the kind of research we need to help us better understand the risks and potential benefits of stratospheric aerosol injection [SAI]. For this reason, part of the initial governance frameworks addressing SAI has to cover research, including encouraging more research that results in clarifying the risks and potential benefits of SAI.”

Finding ‘the solution’

The findings show that dampening global warming through the use of solar engineering could come with “many possible risks”, says Robock. This suggests that cutting global emissions would be the best way of limiting future climate change, he says:

“The solution to global warming is mitigation. It is not too late to rapidly switch to wind and solar power and rapidly reduce our emissions of CO2 to the atmosphere.”

Mitigating climate change through the use of BECCS also comes with “substantial” risks, says Heck:

“It would be risky to rely on BECCS as a strategy to achieve the Paris Agreement. Notable negative emissions from biomass plantations come at the expense of enormous pressures on the global environment as a whole.

“In order to achieve climate goals, it is now essential to immediately reduce CO2 emissions, instead of using harmful technologies to compensate for a more leisurely pace.”

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