Seven Years On

The last seven year have seen too little progress on solving the climate change problem, despite some welcome developments.  Much more rapid progress is now needed.

It is now seven years since I started this blog – my first post was on 3^rd March 2013.  It seems a good time to take a look at what has gone well and what has gone badly over that period in efforts to reduce climate change.  So here are seven ways in which things have gone badly, and seven ways in which they have gone well.

Things that have gone badly over the last seven years

1. Annual CO₂ emissions from energy and industry have increased over the last seven years, continuing the long-term trend, when they need to be decreasing rapidly.

Chart 1: Emissions of CO₂ from energy and industry (excluding land use)

Source: EDGAR  https://edgar.jrc.ec.europa.eu/booklet2019/Fossil_CO2andGHG_emissions_of_all_world_countries_booklet_2019report.pdf

2. Deforestation has not fallen – if anything it’s increased.

This not only bad for the climate, it’s bad for biodiversity and the wider stability of ecosystems.

Chart 2: Tropical primary forest loss (million hectares)

See:  https://www.bbc.co.uk/news/science-environment-48104037

3. Over 15% of the remaining carbon budget has been used since 2013, even on the most optimistic view[i].

In 2013 the remaining carbon budget (that is, total cumulative CO₂ emissions that remain possible while limiting global mean surface temperature rises to 2 degrees) was around 1900Gt CO₂.  It is now around 1600Gt CO₂.The remainder is getting used up ever more quickly as emissions continue to rise.

4. Large amounts of high carbon infrastructure are still being built.

This includes large amounts of new coal-fuelled power generation. This risks lock-in of emissions for decades.

5. There is a lack of progress with developing and implementing low carbon technologies in many sectors

Most emissions intensive industries, notably steel, have made little progress in changing their processes to reduce emissions.  One of the main technologies likely to be needed for decarbonising industrial emissions, CCS, has seen very little deployment, with only about an additional 10 mtpa[ii] stored from projects coming on line since 2013.  The largest contributor to the increase has been the Gorgan project, which is natural gas production, so not likely to be part of a net zero emissions world.  10 mtpa is only about 0.02% of global emissions.  CCS is also likely to be essential for achieving negative emissions from Bioenergy with CCS (BECCS), among other things.  There has also been only very limited progress to date on deploying low carbon hydrogen.

6. China appears to be making emissions reduction less of a priority.

Among other factors, recently slowing economic growth seems to have focussed attention in China towards economic stability and energy security rather than the threats from climate change.

7. Most countries have targets that are far too weak

Existing pledges under the Paris Agreement imply a continuing increase in global emissions rather than the rapid decrease that is needed[iii].

This is a daunting list of problems.  However, there is also some good news, although in all cases it would be even better if positive trends were happening faster.

Good news from the last seven years

1. Costs of low carbon technologies have fallen rapidly, and continue to fall.

Wind and solar electricity are in many cases now competitive with, and often cheaper than, electricity from new fossil fuel generation.  Falling battery costs will enable to the electrification of surface transport and help balance the grid.

This seems to me to be by far the greatest cause for optimism.  Low carbon options will simply become the default choice for new investment in many cases, and policies to reduce emissions will increasingly be working to support a trend that is driven by economic as well as environment imperatives.

2. Some countries have put binding targets in place for net zero emissions.

The UK already has such a target for 2050, seeking to end the UK’s contribution to climate change.  The EU seems likely to formalise a similar target very soon.

3. Some countries have cut emissions significantly, showing what can be done.

The UK has cut its annual emissions by nearly 20% since 2013[iv], with the largest component of this being a reduction in coal use in the power sector, a change readily replicable elsewhere.

4. Public concern about climate change has risen while scepticism about the science has largely disappeared, at least outside the USA and a few other countries.

85% of UK voters are now concerned about climate change[v] with over a quarter ranking it among their top three issues[vi].  This was reflected during the recent general election campaign[vii] in all parties offering policies to reduce emissions to net zero .  Over time this should create the political space for some of the more challenging policies that will be needed to reduce emissions to close to zero.

5. Additional policies are being put in place, and carbon pricing is increasingly widespread.

For example, almost all major economies now have renewables targets, and there are over 50 carbon pricing systems in place around the world.

6. Governments increasingly see economic opportunities in decarbonisation rather than costs.

The opportunities created by new industries are increasingly recognised as part of wider industrial policy.

7. The Paris Agreement has been signed.

Almost all countries have now committed to limit temperature rises to below 2 degrees and to make a contribution to reaching that target, recognising different national circumstances.  Some may consider this is the main piece of good news over the past seven years.  However its effectiveness remains to be proven, and its success looks likely to depend on some of the other trends I’ve highlighted, notably falling costs for low carbon technologies.

Looking at these trends together, I am both less optimistic and more optimistic than I was in 2013.  I am less optimistic because seven years of rising emissions and continuing investment in high carbon infrastructure have made the challenge of limiting climate change even greater than it was.  But I am more optimistic because there is greater recognition and acceptance of the problem, more is now being done (though still nowhere near enough) and, above all, because low carbon energy is rapidly becoming cheaper than high carbon energy.  As a result it looks likely that emissions from the energy sector will eventually be greatly reduced and even halted entirely.  This may make it easier to focus on reducing other emissions as well, especially those from deforestation.

But eventually will be too late.  Much damage is already being done to our world.  More will inevitably follow. This will include the loss of irreplaceable parts of the natural world.  Given rising emissions, and how much of the carbon budget has been used up, it now looks practically impossible to keep temperature rises to 1.5 degrees, and difficult, though still possible, even to limit them to 2 degrees.

However it could still get much worse.  The task now is to avoid the worst of the risks by keeping emissions and accompanying temperature rises as low as possible, including keeping global temperature rises to below 2 degrees.  With a lot of effort and a little luck there is still time (just) to achieve this.  But the task has never been greater or more urgent.

Adam Whitmore – 9^th March 2020

[i] For a 50% chance of remaining below 2 degrees, based on cumulative CO₂ emissions.  See https://onclimatechangepolicydotorg.wordpress.com/2018/10/

[ii] https://www.globalccsinstitute.com/resources/global-status-report/

[iii] https://climateactiontracker.org/global/cat-emissions-gaps/

[iv] https://www.theccc.org.uk/publication/reducing-uk-emissions-2019-progress-report-to-parliament/

[v] https://www.ipsos.com/ipsos-mori/en-uk/concern-about-climate-change-reaches-record-levels-half-now-very-concerned

[vi] https://www.bbc.co.uk/news/science-environment-50307304

[vii] https://onclimatechangepolicydotorg.wordpress.com/2019/11/25/the-uks-political-consensus-on-climate-change/

 

Hydrogen and heat pumps may both play a role in UK building heating

Low carbon hydrogen and electricity via heat pumps may both play a large role in decarbonising building heating in the UK.  Ways forward are needed that maintain optionality around solutions while more is learnt about the right mix.

Decarbonising building heating in the UK poses a range of challenges.  First, the required transition is very large scale.  There are around 27 million households in the UK, with many more commercial buildings, small and large.  This implies around a million or more premises a year on average need to be converted to low carbon heat between now and 2050.

Along with scale, there is cost.  Replacing the UK’s heating system is expensive both in total and by household, even if the existing natural gas network can be used for hydrogen.   This challenge is made more difficult by the high seasonality of heating demand (Chart 1).  Building natural gas supply chains, reformers to produce hydrogen from natural gas, CCS, low carbon electricity and heat pumps all involve major capital investment.  Running this for only part of the year – the colder months – increases unit costs substantially. The chart below shows daily gas and electricity demand from non-daily metered (i.e. small) customers.  Demand for energy from gas, the major source of building heating at present, is about two or three times electricity demand during winter, and is much more seasonal.

Chart 1: Heating demand is highly seasonal …

Source: BEIS (2018) ‘Clean Growth – Transforming Heating’ https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/766109/decarbonising-heating.pdf

Furthermore, the transition to low carbon heat needs to be made largely with the UK’s existing building stock, which is mainly old and often badly insulated.  Improved insulation is a priority in any programme, but there are practical and cost constraints on what can be done with existing buildings.  (Buildings also need to be able to cope with the increased prevalence of heat waves as the climate warms, but that is a separate topic.)

Finally, building heating directly affects people’s day to day lives, so consumers’ acceptance is critical.  On the whole the present system, based mainly on natural gas boilers, works quite well except for its emissions.  Any new system should preferably work as well or better.

The leading candidates for low carbon heating in buildings are electricity, almost certainly using heat pumps to increase efficiency, and low carbon hydrogen.  Biomass seems unlikely to be available either at the scale or cost that would be needed for it to be a major contributor to low carbon heating, though it may find a niche.  District heating networks require low carbon heat and this must draw on the same ultimate set of sources of heat.  Waste heat from nuclear, once discussed as a possibility, no longer seems likely to be either practical or cost effective.

Recently the Committee on Climate Change (CCC) analysed the costs of decarbonising heat in 2050 using different approaches.  They looked at electricity, hydrogen, and combinations of the two.  The analysis concluded that a 50% increase over current costs was likely (Chart 2).  The remarkable thing about the analysis is that this cost was similar for all of the options considered.  Any differences were well within the uncertainty of the estimates.

Chart 2: Costs of different modes for decarbonising building heating …

Source:  Committee on Climate Change

With no large cost difference leading to one or the other option being preferred there is a need to test each option out to see which works better in practice.  Mixed solutions may be appropriate in many cases.  For example, hydrogen may be useful in providing top-up heat even if heat pumps are providing the baseload, or may be the only solution for some poorly insulated properties for which heat pumps don’t run at high enough temperatures.

The CCC’s analysis includes expected cost savings.  The transition to low carbon heat will clearly be more acceptable if this cost can be reduced further.  In particular there seem likely to be both technical advances and large economies of scale in heat pump manufacture and installation, and the costs of low carbon power may fall by more than assumed by the CCC.  As the analysis stands, a 50% increase is clearly politically difficult, especially when there do not seem to be advantages for the customer, and potentially some drawbacks.  However, this is less than a 2% p.a. compound increase in real terms over a 30 year period, which might be politically feasible if introduced gradually and spread across all consumers.

With such large changes in demand between summer and winter, seasonal storage is a major issue for reasons of both cost and practicality.  This is an under-researched area, and needs further work.  There are various possibilities – storage of hydrogen itself in salt caverns, storage of hydrogen as ammonia or storage of heat in ground sinks, but each has its problems and the scale involved is very large.

A final uncertainty is the form which hydrogen production will take.  At the moment methane in reformers predominates and, with the addition of CCS, may continue to do so.  However both the costs of low carbon electricity and of the electrolysis are decreasing rapidly.  Over the long term this may become a more significant pathway for hydrogen production.

These uncertainties imply that building heating poses a particularly difficult set of choices for policy.  It is not clear what route, or mix of routes, is the right one.  The transition needs to be quite rapid relative to the lifetimes and scale of existing infrastructure, and it involves the need for consumer acceptance.  There are also potentially strong network and lock in issues.

The best approach is likely to be to develop several types of solution in parallel, maintaining optionality while learning, and being prepared for some approaches to be dead ends.  The implications of this include the need for roll out of low carbon heat sources in some districts now to get an idea of how they will work at scale.

Some of this is happening, much more is needed.

Adam Whitmore -29^th October 2019.

 

Comparison of cost estimates with previous analysis by this blog.

Around four and a half years ago I looked at the costs of decarbonising domestic heating in the UK in winter using low carbon electricity.  I concluded that switching to low carbon heat would add 75% or more to domestic heating bills, with some drawbacks for consumers (I also looked at higher cost case, but this case no longer seems likely due to the fall in the costs of low carbon electricity, especially offshore wind, since the analysis was done.)  I suggested that this meant that the transition would be difficult and that reductions in capital costs were necessary.

This analysis is broadly consistent with the CCC analysis quoted here, which suggests a 50% increase on current costs.  The estimates are roughly similar given the large uncertainties involved , the inevitable differences is assumptions, and different basis of the estimates.  In particular the CCC analysis factors in reductions in costs of low carbon heating likely by 2050, whereas my previous analysis was based on current costs to make the point that cost reductions are necessary,  Consequently it would be expected that the CCC analysis would show a smaller cost increase relative to current costs.  Also, the CCC’s analysis may exclude some costs – estimates such as these have a tendency to go up when you look at them more closely.  Equally it may understate the cost reductions possible over decades.

 

 

How well is the UK on track for zero emissions by 2050?

By 2020 the UK will have very nearly halved its emissions over 30 years.  Reducing emissions by the same amount over the next 30 years will get the UK very close to zero.  However this will be very much more difficult.

A robust net zero target has been recommended for the UK …

A recent report by the UK’s Committee on Climate Change (CCC), the Government’s official advisory body, recommends that the UK adopts a legally binding target of net zero emissions of greenhouse gases by 2050[i], that is remaining emissions must be balanced by removal from the atmosphere.  If the Government agrees, this will be implemented by amending the reduction mandated by the Climate Change Act, from an 80% reduction from 1990 to a 100% reduction.

The target has several features that make it particularly ambitious.  It:

• sets a target of net zero emissions covering all greenhouse gases;
• includes international aviation and shipping;
• allows no use of international offsets; and
• is legally binding.

This is intended to end the UK’s contribution global warming.  It has no precedents elsewhere, although in France a bill with comparable provisions is under consideration[ii].

Progress to date has been good …

The UK has made good progress so far in reducing emissions since 1990.  Emissions in 2018 were around 45% below 1990 levels, having reduced at an average rate of about 12.5 million tonnes p.a. over the period.  On current trends, over the thirty years from 1990 to 2020 emissions will be reduced to about 420 million tonnes p.a., 47% below their 1990 levels.  Emissions will thus have nearly halved over the 30 years 1990 to 2020, half the period from 1990 to the target date of 2050.

Chart 1 shows how the UK’s progress compares with a linear track to the current target of an 80% reduction, to a 95% reduction and to a 100% reduction.  (For simplicity I’m ignoring international aviation and shipping).  The UK is currently on a linear track towards a 95% reduction by 2050.

Chart 1: Actual UK emissions compared with straight line progress towards different 2050 targets

 

Source: My analysis based on data from the Committee on Climate Change and UK Government.  Data for 2018 is provisional[iii]

The largest contributor to the total reduction so far has been the power sector.  Analysis by Carbon Brief[iv] showed that the fall in power sector emissions has been due to a combination deploying renewables, which made up about of third of generation in 2018, reducing coal use by switching to natural gas, and limiting electricity demand growth.

Industrial emissions have also fallen significantly.  However some of this likely represents heavy industry now being concentrated elsewhere in the world, so likely does not represent a fall in global emissions.  Emissions from waste have also fallen, due to better management.

Reducing emissions will be relatively easy in some sectors …

There are also reasons for optimism about continuing emissions reductions.  Many technologies are now there at scale and at competitive prices, which they were not in previous decades.  For example, falling renewables costs and better grid management, including cheaper storage, will help further decarbonisation of the power sector.  Electrification of surface transport now appears not only feasible, but likely to be strongly driven (at least for cars and vans) by economic factors alone as the cost of batteries continues to fall.

But huge challenges remain …

Nevertheless important difficulties remain for complete decarbonisation.

CCS is identified by the report as an essential technology.  However, as I have noted previously, it has made very little progress in recent years in the UK or elsewhere[v].  CCS is especially important for decarbonising industry.  This includes a major role for low carbon hydrogen, which is assumed to be produced from natural gas using CCS – although another possibility is that it comes from electrolysis using very cheap renewables power, e.g. at times of surplus.  CCS also looks to be necessary because of its use with bioenergy (BECCS), to give some negative emissions, though the lifecycle emissions from this will require careful attention

Decarbonising building heating, especially in the residential sector, continues to be a challenge.  The report envisages a mix of heat pumps and hydrogen, perhaps in the form of hybrid designs, with heat pumps providing the baseload being topped-up up by burning of hydrogen in winter.  I have previously written about the difficulties of widespread use of heat pumps[vi], and low carbon hydrogen from natural gas with CCS is also capital intensive to produce and therefore expensive to run for the winter only.  The scale of any programme and consumer acceptance remain major challenges, and the difficulties encountered by the UK’s smart meter installation programme – by comparison a very simple change – are not an encouraging precedent.

Emissions from agriculture are difficult to eliminate completely, and no technologies are likely to be available by 2050 that enable aviation emissions to be completely eliminated.  This will require some negative emissions to balance remaining emissions from these sectors.

Policy needs to be greatly strengthened …

Crucially several of the necessary transformations are very large scale, and need long lead times, and investment over decades.  There is an urgent need to make progress on these, and policy needs to recognise this.  This includes plans for significant absorption from reforestation, as trees need to be planted early enough that they can grow to be absorbing substantial amounts by 2050.

The UK’s progress on emissions reduction so far has been good, having made greater reductions than any other major economy[vii].  And technological advances in some areas are likely to enable substantial further progress.  However much more is needed.  In particular policy needs to look now at some of the difficult areas where substantial long-term investment will be needed

Adam Whitmore – 22^nd May 2019

 

 

[i] https://www.theccc.org.uk/2019/05/02/phase-out-greenhouse-gas-emissions-by-2050-to-end-uk-contribution-to-global-warming/

 

[ii] The CCC report notes that Norway, Sweden and Denmark have net zero targets, but they allow use of international offsets (up to 15% in the case of Sweden).  France has published a target similar to the UK’s in a bill.  The European Commission has proposed something similar for the EU as a whole, but this is a long way from being adopted. California has non-legally binding targets to achieve net zero by 2045.  Two smaller jurisdictions (Costa Rica, Bhutan) have established net zero targets but these are expected to be achieved mainly by land use changes.  New Zealand has a draft bill to establish a target, but eliminating all GHGs will be difficult because of the role of agriculture in the New Zealand economy.

 

[iii] https://www.gov.uk/government/statistics/provisional-uk-greenhouse-gas-emissions-national-statistics-2018  The change from 2017 to 2018 is applied to the data series from 1990 produced by the CCC (the two data series differ very slightly in their absolute levels).

 

[iv] https://www.carbonbrief.org/analysis-uk-electricity-generation-2018-falls-to-lowest-since-1994

 

[v] https://onclimatechangepolicydotorg.wordpress.com/2018/04/25/a-limited-but-important-medium-term-future-for-ccs/

 

[vi] https://onclimatechangepolicydotorg.wordpress.com/2015/05/18/reducing-the-costs-of-decarbonising-winter-heating-needs-to-be-a-priority/

 

[vii] https://onclimatechangepolicydotorg.wordpress.com/2017/05/09/uk-emissions-reductions-offer-lessons-for-others/

 

The constrained role of biomass

The role of biomass in the world energy system looks likely to be constrained, so there will be a need to focus on high value applications where there are few low-carbon alternatives.

This is the second of two posts looking at the role of biomass.  Here I focus on potential resource constraints.

A wide range of possibilities

The amount of biomass available to provide energy depends a lot on the amount of land available to grow energy crops, and how much that land can yield.   Different assumptions on these variables produce quite different estimates of the total resource, and numerous studies over the years have produced a wide range of results.    The amount of waste biomass available also matters, but potential availability from this source is smaller.

A comprehensive review of estimates of the biomass resource was carried out two years ago by researchers at Imperial College[i] (see chart).  It showed a variation in estimates of a factor of around 40, from of the order of 30 EJ to over 1000 EJ (1EJ =10¹⁸ J, or a billion GJ, or 278 TWh).  This compares with total world primary energy demand of just under 600 EJ, transport demand of around 100 EJ, and at least 250 EJ to produce present levels of electricity, assuming biomass combustion to remain relatively inefficient[ii].

Estimates of available biomass resource

Source: Slade et. al. (2014)

The authors examine reasons for differences in estimates, which I’ve summarised in the table below.  The differences are largely assumption driven, because the small scale of commercial bioenergy at present provides little empirical evidence about the potential for very large scale bioenergy, and future developments in food demand and other factors are inevitably uncertain.

Reasons for variation in estimates of total biomass supply

Range	Typical assumptions
Up to 100EJ	Limited land available for energy crops, high demand for food, limited productivity gains in food production, and existing trends for meat consumption.  Some degraded or abandoned land is available.
100-300 EJ	Increasing crop yields keep pace with population growth and food demand, some good quality agricultural land is made available for energy crop production, along with 100-500Mha of grassland, marginal, degraded and deforested land
300-600EJ	Optimistic assumptions on energy crop availability, agricultural productivity outpaces demand, and vegetarian diet
600 EJ +	Regarded as extreme scenarios to test limits of theoretical availability

 

Reasons for caution

In practice there seem to me to be grounds for caution about the scale of the available resource, although all of these propositions require testing, including through implementation of early projects.

Land Availability

• There will rightly be emphasis on protection of primary forest on both carbon management and biodiversity grounds, with some reforestation and rewilding.
• There is little evidence of a shift away from meat consumption. With the exception of India, less than 10% of people in  most countries are vegetarian despite many years of campaigning on various grounds[iii].   In China meat consumption is associated with rising living standards.
• Demand for land for solar PV will be significant, although a good deal of this will be on rooftops and in deserts

Yield

• The nitrogen cycle is already beyond its limit, constraining the role of fertiliser, and water stress is a serious issue in many places (agriculture accounts for 70% of current fresh water use). The UN Food and Agriculture Organisation has projected fairly modest increases in future yields.

Policy support

• Difficulties in limiting lifecycle emissions from biofuels are likely to lead to caution about widespread deployment.
• Concerns about food security may limit growth of biofuels.

Small scale to date, despite many years of interest

• There has been little progress to date compared with other low carbon technologies. Though traditional biofuels remain widely used, modern biofuels account for a very small proportion of demand at present.  World biofuels consumption currently accounts for only 0.2% of world oil consumption[iv] .  Many biofuels programmes have had subsidies cut and there is still limited private sector investment.

In this context some estimates of the potential for biomass to contribute to energy supply seem optimistic.  For example, Shell’s long-term scenarios (Oceans and Mountains) show biomass of 74 EJ and 87 EJ respectively for commercial biomass, 97-133 EJ including traditional biomass by 2060[v].  These totals are towards or above the more cautious estimates for the resource that might ultimately be available (see table above).  A recent review article[vi]  suggested that by 2100 up to 3.3 GtCp.a. (around 12 billion tonnes of CO₂) could be being removed, and producing around 170EJ of energy.  However the land requirements for this are very large at about 10% of current agricultural land.  The authors suggest instead a mean value for biomass potential of about a third of that, or 60EJ.

On balance it seems that biomass is likely to account for at most less than 10% of commercial global energy (likely to be around 800-900EJ by mid-century), and potentially much less if land availability and difficulties with lifecycle emissions prove intractable.

It thus seems likely that biomass energy will be relatively scarce, and so potentially of high value.  This in turn suggests it is likely to be mainly used in applications where other low carbon alternatives are unavailable.  These are not likely to be the same everywhere, but they are likely often to include transport applications, especially aviation and likely heavy trucking, and perhaps to meet seasonal heat demand in northern latitudes.  For example, according to Shell’s scenarios aviation (passengers + freight) is expected to account for perhaps 20-25EJ by 2050, and biomass could likely make a useful contribution to decarbonisation in this sector.

None of this implies that biomass is unimportant, or has no role to play.  It does imply that policies focussing on deploying other renewable energy sources at large scale, including production of low carbon electricity for transport, will be essential to meeting decarbonisation targets.  And the optimum use of biomass will require careful monitoring and management.

Adam Whitmore  – 11^th April 2016

 

[i] Slade et.al., Global Bioenergy Resources, Nature Climate Change February 2014

[ii] Data on final consumption and electricity production from Shell and IEA data.  35% efficiency for biomass in electricity is assumed, which is likely to be somewhat optimistic, especially if CCS is employed.

[iii] https://en.wikipedia.org/wiki/Vegetarianism_by_country

[iv] BP Statistical Review of World Energy

[v] http://www.shell.com/energy-and-innovation/the-energy-future/shell-scenarios.html  These totals include biofuels, gasified biomass and biomass waste solids, and traditional biomass.

[vi] Smith et. al., Biophysical and economic limits to negative CO₂ emissions, Nature Climate Change, January 2016.  The paper estimates land requirement for 170 EJ of 380-700 Mha, around 10% of total agricultural land area in 2000 of 4960Mha.

Deploying CCS on fossil fuel plant is more of a priority than implementing negative emissions technologies

The potential for biomass with CCS and direct air capture of CO₂ should not distract from deployment of CCS on fossil fuel plants over the next few decades.  Among other things, learning from CCS on fossil fuels will help make eventual deployment of CCS on biomass cheaper and more effective.

There appears to be increasing likelihood that atmospheric concentrations of greenhouse gases will grow to exceed levels consistent with the target specified in the recent UNFCCC Paris agreement of limiting temperature rises to “well below” two degrees.  Such an outcome would require CO₂ to be removed from the atmosphere faster than natural sinks allow, in order to restore concentrations to safe levels.  Near zero net emissions in the latter part of this century will also be needed to stabilise concentrations.

Many models of future emissions pathways now show negative emissions technologies (technologies that result in a net decrease in CO₂ in the atmosphere) needing to play a major role for in meeting climate goals. They have the potential to remove carbon dioxide from the atmosphere in the event of “overshoot” of target atmospheric concentrations, and to balance remaining emissions from sectors where abatement is difficult with a view to achieving net total emissions of close to zero.  But the application of such technologies should not be considered in isolation.

Bio Energy with CCS (BECCS)

Bio energy with CCS (BECCS ) is the most widely discussed approach to negative emissions.  BECCS is not a single technology but a combination of two major types of CO₂ removal.  Bioenergy from burning biomass to generate electricity or heat emits a substantial amount of CO₂  on combustion – around as much as a coal plant.  However much of this can be captured using CCS.  More carbon dioxide is reabsorbed over time by the regrowth of the plants, trees – or perhaps algae – that have been harvested to produce the bioenergy.  Together, the capture of the CO₂ from the flue gas and the subsequent absorption of CO₂ from the atmosphere by regrowth of biomass can lead to net removal of CO₂ from the atmosphere, although this takes time.  (The net amount of CO₂, that is emitted on a lifecycle basis from burning biomass without CCS depends on the type of biomass and is subject to considerable variation and uncertainty – a controversial topic that would need another post to review.)

However at an energy system level, where the CO₂ is captured – biomass plant or fossil fuel plant – is less relevant than the total amount that’s captured.  Broadly speaking, if there is a biomass plant and fossil fuel plant both running unabated the same benefit can be achieved by capturing a tonne of CO₂ from either.

Indeed there may be advantages to putting CCS on a conventional plant rather than biomass plant.  It may be technically more tractable.  Furthermore, CCS require a lot of energy to capture the CO₂ and then to compress and pump it for permanent storage.  Biomass is likely to be supply constrained (again, this is an issue that requires a post in itself), so using biomass rather than fossil fuels to provide this energy may limit other applications.  Only when there are no fossil fuel plants from which to capture CO₂ does biomass plant become unambiguously a priority for CCS.  This is clearly some way off.

Furthermore biomass with CCS for electricity generation may not be the best use of bioenergy.  Converting sunlight to bioenergy then turning that into electricity is a very inefficient process.  Typically only 1-2% of the sunlight falling on an area of cropland ends up as useful chemical energy in the form of biofuels.  There are various reasons for this, not least of which is that photosynthesis is a highly inefficient process.  Burning biomass to make electricity adds a further layer of inefficiency, with only perhaps a third or less of the energy in the biomass turned into electricity.  Sunlight therefore gets converted to electricity with an efficiency of perhaps 0.5%.  This compares with around 15- 20% for solar cells, implying that scarce land is often likely to be best used for solar PV.  (The calculation is closer if solar PV is used to create storable energy e.g. in the form of hydrogen).   For similar reasons the use of biofuels rather than electricity in transport is inefficient, in part because internal combustion engines are less efficient than electric motors.

Limited available biomass may be better used for those applications where it is the only available lower carbon energy source, notably in aviation and (likely) heavy trucks, or for other applications such as district heating with CCS, where the ability to store energy seasonally is especially valuable.

At the very least, detailed system modelling will be required to determine the optimal use of biomass.  Suggesting that BECCS should have a major role to play simply because in isolation it has negative emissions may lead to suboptimal choices.

Direct Air Capture (DAC)

Direct Air Capture (DAC), where carbon dioxide is chemically absorbed from the atmosphere and permanently sequestered, can also reduce the stock of CO₂ in the atmosphere.  However the typical concentration of CO₂ in a flue gas of a power plant or industrial plant is several percent, about a hundred times as great as the concentration of 0.04% (400 ppm) found in the atmosphere.  This makes the capture much easier.  Furthermore, millions of tonnes can be captured and piped from a single compact site using CCS, generating economies of scale on transport and storage.  In contrast DAC technology tends to be more diffuse.  These considerations imply that CCS from power plants and industrial facilities is always likely to be preferable to direct air capture until almost all the opportunities for CCS have been implemented, which again is a very long way off.

Uncertainties and optionality

There are many uncertainties around negative emissions technologies, including the availability of biomass, cost, and the feasibility of reducing emissions in other sectors.  For these reasons developing optionality remains valuable, and research to continue to develop these options, including early trial deployment, is needed, as others have argued[i].

One of the best ways of developing optionality is to deploy CCS at scale on fossil fuel plants.  This will reduce the costs and enable the development of improved technologies through learning on projects.  It will also help build infrastructure which can in turn benefit  BECCS.  This needs to run in parallel with ensuring that the lifecycle emissions from the bioenergy production chain are reduced and biodiversity is safeguarded.

Negative emissions technologies may well have a role to play in the latter part of the century.  But they seem likely to make more sense when the economy is already largely decarbonised.  In the meantime deployment of CCS, whether on industrial facilities or power plants, needs to be a much greater priority.

Adam Whitmore – 21^st March 2016

[i] Investing in negative emissions, Guy Lomax,  Timothy M. Lenton,  Adepeju Adeosun and Mark Workman, Nature Climate Change 5, 498–500 (2015)  http://www.nature.com/nclimate/journal/v5/n6/full/nclimate2627.html?WT.ec_id=NCLIMATE-201506