Written Evidence Submitted by Dr Jennifer L Castle and Professor Sir David F Hendry
Climate Econometrics, Nuffield College, Oxford University
A strategy for achieving net-zero emissions by 2050
To achieve greenhouse gas emissions targets of net zero requires an integrated symbiotic strategy across all fossil fuel uses and all other emitters, less natural absorption and carbon capture and storage, possibly combined with atmospheric CO2 extraction. Clean electricity generation is achievable with known technologies, but faces a major storage problem when renewables do not generate power. Small modular nuclear reactors (SMRs) could help with background supply, but storage can be facilitated by decarbonizing the transport sector & using electric vehicles as storage units plugged into an intelligent network connected to the grid to facilitate balancing electricity flow. Batteries alone seem inadequate for this, so we propose supplying electric vehicles via supercapacitors using graphene-based nanotubes (GNTs) which can charge and discharge rapidly and store sufficient power for distance driving. This overcomes an impediment to the uptake of electric vehicles and helps reduce toxic mining. GNTs could supply trains in place of diesel-electric, and are very light so advance developments in electric aircraft. By ensuring continuity of electricity supply, renewables capacity can be greatly expanded, so could sustain methane pyrolosis production of hydrogen when other electricity demands are low. Hydrogen gas could replace methane use by households, and liquid hydrogen would supply a high heat source for industry. A by-product of methane pyrolosis is black carbon, which could add to the material available for making graphene, though waste plastic could also be used. New buildings must be constructed to be net zero.
Turning to agriculture, methane, nitrous oxide and carbon dioxide emissions are all by-products of modern food production. Ruminant emissions can be markedly reduced by dietary changes, and nitrous oxide by reducing nitrogen fertiliser use, replacing some by basalt dust that also absorbs carbon dioxide. Crop production efficiency can be greatly improved, benefitting the environment and reducing cropland, along with vertical and underground farms. Aquaculture (including seaweed production) could be greatly improved: off-shore wind farms also act as marine reserves. Human dietary changes to eating less mammal meat are feasible.
Renewables electricity is fully competitive economically, more so if the storage comes free from GNT vehicles; graphene prices are falling; there may be `Moore’s laws’ for nanotube manufacture, and even bulk SMRs; and while hydrogen made from methane (or electrolysis) will be a more expensive fuel, by sustaining 100% capacity renewables’ generation at `off-peak’, its production could be cost saving. Eliminating catalytic convertors would be a large cost saving in vehicle manufacture. The above developments interact and would maintain employment and real per-capita growth in new industries with steady and coordinated expansion, as well as in retrofitting of vehicles and housing. Many skills are in place, from off-shoring, manufacturing and supply through making electric engines. Animal dietary changes could be cost saving with lower feed input, as methane production wastes energy; and waste basalt dust is far cheaper than artificial fertilisers. Taxing non-recyclable and high-carbon content products (following the success with plastic bags) would incentivise alternatives. Carbon pricing, cap & trade, and research support tools remain available.
The analysis is illustrated by the UK as it created the Industrial Revolution leading to the greenhouse gas problem; its Climate Change Act of 2008 has markedly reduced its emissions at little aggregate cost; and we have modelled its performance in economic and climate terms. References to the evidence behind our strategy are embedded in the text as direct links.
Climate change will continue until the target of net zero greenhouse gas (GHG) emissions is achieved. The benefits of starting now seem likely to far exceed the costs of tackling the problem. Recent research increasingly supports the aim of the Paris Accord at CoP21 to limit temperature increases to less than 2°C, and `to pursue efforts to limit it to 1.5°C'. The Special Report by the Intergovernmental Panel on Climate Change (IPCC) emphasises that the latter is still just achievable, but rapid action is required if it is to be achieved. Among the major likely adverse consequences of ever increasing levels of atmospheric CO2 are extreme weather conditions that can be dangerous to life, including high `wet bulb' heat, wild fires as seen recently in the USA west coast, Amazon, Siberia and Australia, increasingly powerful cyclones, increased coastal flooding as well as inland flooding from `rivers in the sky’, yet more intense and longer droughts. Moreover, there is the potential for climate tipping points, such as when an ice-free Arctic Ocean in the past led to large-scale methane release from permafrost melting in the tundra, causing further rapid climate warming. The added danger of species extinctions, as happened in earlier climate changes, doubly threatens food security, and hence increased flows of refugees and migrants. More positively, sensitive intervention points (SIPs) in the post-carbon transition could induce leverage in both policy actions and technology developments, which will be our focus on here.
Some countries have moved towards decarbonizing their economies by increased use of both renewable (solar and wind) and non-greenhouse gas methods (nuclear, geo-thermal, hydro and biomass) for generating electricity, using that supply to reduce other GHG emitters based on fossil fuels. However, to date doing so has not greatly reduced global GHG emissions as economic activity has also expanded. Despite legislation mandating zero net emissions, we know of no comprehensive strategy for achieving such a target, and public support for a purely green economy will wane if the economic or social costs are too high. Net zero is an excellent target, but incredibly difficult to achieve, especially when maintaining employment and real per-capita growth. While dealing with the costs of the Covid-19 pandemic seems to add to the difficulties, it may be an opportune time to begin rapidly decarbonizing economies. To do so requires an integrated approach of the form we propose here, albeit one still requiring significant, but not science-fiction, technological advances that we document.
The structure of the analysis is as follows. Section 2 notes the background precedent that an all-electric-based, rather than fossil-fuel-based, economy began to emerge at the end of the 19th century before being out-competed by cheap oil. Section 3 discusses moving towards a net-zero GHG emissions economy. Section 4 considers achieving zero GHG electricity generation as the first key ingredient. Then section 5 turns to decarbonizing ground transportation and the symbiotic role that could also play as a storage system for renewable electricity. Section 6 discusses how to decarbonize households and reduce GHG emissions in construction, then section 7 turns to agriculture. Section 8 notes the issues needing tackled for the chemical industry, manufacturing and waste management, and `imported CO2’ is considered in section 9. Section 10 concludes. Throughout we use the United Kingdom as our illustrative example, partly because we have analysed it in detail, but also given its major historical role in the Industrial Revolution and its recent legislation mandating net-zero GHG emissions by 2050.
Although much of the modern world is powered by fossil fuels, that was not an inevitable outcome of technology and relative costs. The first electricity generator in the UK in 1868 was hydro driven, the first commercial photovoltaic solar panel was developed by Charles Fritts in 1881, building on the creation by Edmond Becquerel in 1839 of the first photovoltaic cell, the first wind turbine to generate electricity was built by James Blyth in 1887, and by the 1930s wind-generated electricity was relatively common on US farms. Moreover, electric cars date back to the 1880s after Thomas Parker built a vehicle with a high capacity and rechargeable battery: the 1897 Bersey Electrical Cab can be seen at the British Motor Museum.
Thus, an all-electric powered society is just going back to a future where we might have been 125 years ago. However, gasoline and diesel powered vehicles proved more attractive to early buyers and soon outcompeted electric cars in both running cost and distances that could be travelled.
In 2019, the UK Government amended its original 2008 Climate Change Act (CCA) target to zero net GHG emissions by 2050. To meet such a net zero target, all fossil fuel use must be reduced to near zero, including coal, oil and natural gas. Then all other sources of GHG emissions must go to a level such that carbon capture and storage (CCS), possibly combined with atmospheric CO2 extraction methods, must remove the rest. Indeed, facing an irreducible non-zero minimum demand for oil and gas (e.g., for chemicals), to achieve zero net emissions by 2050 probably requires major technological developments into removing CO2 or reusing existing CO2 as a fuel, as natural absorption cannot increase indefinitely.
UK total energy use in 2018 was approximately 2250 terawatt hours (TWh = billion kWh) equivalent to using nearly 200 million tonnes of oil equivalent (Mtoe). That comprised roughly 70Mtoe petroleum, 70Mtoe natural gas (which is mainly methane) and 60Mtoe non-CO2, with almost negligible coal use. To replace all fossil fuel use to have an all-renewable electricity generation system with appropriate storage, supplying an all-electric transport system, replace natural gas use either directly by electricity or indirectly via hydrogen (which in turn requires electricity), and eliminate most other uses of oil, will necessitate a 20-fold increase in non-CO2 electricity over the next 30 years, which is a compound annual growth rate of 10.5% p.a. Then one must eliminate GHG emissions in construction, agricultural and from waste.
Coal use has fallen to near zero in the UK since the CCA, without obvious aggregate costs in terms of per capita GDP: we comment on local costs below. Thus oil and natural gas use must be removed next. Section 4 describes how both oil and natural gas can be removed from electricity production by increased renewable sources, and we assume they will be replaced in that role by 2050. Section 5 considers the removal of oil from transportation leading to possible solutions to both the electricity storage and grid balancing problems resulting from renewables only generation. Section 6 considers the replacement of methane by hydrogen for household indoor and water heating and in manufacturing and services. Although household natural gas (and some oil) usage could be reduced by increased taxes encouraging the adoption of solar panels for water heating and (e.g.) air heat pumps, without massive retrofitting of the housing stock for greatly improved insulation, that is insufficient to get to net zero use. Thus, more radically, the UK could switch back from a national gas household distribution system using natural gas to one based on hydrogen. Indeed, the UK had a hydrogen-based gas distribution system prior to 1969, and the switch to natural gas required conversion of all household equipment that burned coal gas (often called town gas, composed of about 50% hydrogen), to natural gas, so this too is back to the future.
Total electricity production in 2018 was 350TWh where 120TWh came from renewables (34%, plus 16% from nuclear), up nearly 10-fold over the previous decade, with 64TWh from wind (from 24GigaWatts installed). The recent UK announcement of installing another 40GW of wind-power electricity by 2030 (which would generate around 110TWh pa) roughly doubles renewables output, so could replace much of natural gas generated electricity.
The rapidly falling costs of renewable-energy sources like onshore wind turbines combined with improved storage methods should substantially reduce oil and gas use in electricity production. Offshore wind turbines have also fallen greatly in cost per Btu (British thermal unit) and increased in efficiency over the past two decades, so that for the UK at least they offer a low cost alternative (with the incidental benefit of creating marine reserves and fish sanctuaries), cheaper than combined-cycle natural gas turbines even before adding the costs of CCS that would be needed for zero net emissions. The benefits would be considerably greater if the UK developed a much larger manufacturing capacity for wind turbines.
Solar photovoltaics come next in cost per Btu (for the UK!) if CCS is enforced. Renewables’ share of overall UK electricity generation reached a peak of 60.5 per cent at one stage in April 2020, according to National Grid data. However, relying only on both wind and sun sources of electricity requires both large backup storage systems for (e.g.) windless nights, and potentially long cloudy and still winter weather, and plugged into an intelligent network connected to the grid which is managed by its controller to facilitate balancing electricity flow, issues addressed in the next section.
Natural gas (methane, CH4) usage has increased 3.5 fold since the mid-1980s, and contributes about 40% of electricity output, with 140 megatons (Mt) p.a. CO2 emissions—despite producing less than half those of coal per Btu. Steady replacement of natural gas in electricity generation by non-CO2 emitting methods seems feasible by 2050, but adding the electrification of transportation and the production of hydrogen by either electrolysis or methane pyrolysis will require at least a doubling of electricity output. Nevertheless, over the next 30 years with ever improved technologies and continued cost reductions in renewable electricity generation, a near zero target for its use of natural gas does not seem impossible without reducing GDP growth, perhaps even increasing it with new opportunities.
However, no future technology is certain, so as an option, more research effort should be devoted to developing safe small modular nuclear reactors (SMRs) based on the well-developed nuclear-powered engines in submarines. Standardisation and learning-by-doing when constructing larger numbers of SMRs could make them cost effective. Variants of SMRs such as molten-salt waste-burners might be able to use non-fissionable thorium or the ‘spent’ uranium fuel rods from older reactors, helping reduce the serious problem of transuranic-waste disposal. Part of those disposal-cost savings should be subtracted from the costs of building SMRs.
Even over our horizon of 30 years, nuclear fusion seems unlikely to be a key energy contributor despite many ongoing important developments, among others those increasing output efficiency, and reducing internal damage to tokamak materials from helium (which might then be collected, offsetting a potential shortage). Nevertheless, recent calculations including important advances with superconducting magnets offer the prospect of a shorter time frame.
Reducing oil use in transport will take longer following current strategies, even with more efficient engines (diesel being phased out completely given its toxic pollutants), and much higher taxes on gasoline. Improved electricity-based public transport would help, but without a major improvement in lithium-ion battery powered electric cars or a radical advance in solid-state batteries, their relatively short journey capacity, yet taking a non-negligible time to recharge, discourages the replacement of internal combustion engines. However, recent advances have occurred in understanding the properties of graphene, with potentially large falls in its cost of production from ‘graphene in a flash’ using plastic and food waste, with carbon black as a potential by-product of methane pyrolysis in section 6. Graphene-based nanotubes (GNTs) (obtained by `rolling up’ sheets of graphene) can act as electrode super-capacitors as an electricity storage system. Consider sandwiching an array of GNTs between two Faraday cages in a prefabricated modular unit fitted to a vehicle’s roof (perhaps even retrofitted on existing car roofs) to supply the battery driving the electric motor, so the vehicle becomes the storage unit. GNTs seem capable of rapid charging, and should be able to sustain viable distances on a single charge. There may be something like a variant of Moore’s law (based on processing power of computers doubling every two years) for cost reductions in graphene from a large increase in their production (about $70,000 per ton currently).
Moreover, if such electric vehicles became ubiquitous, having them plugged in when not in use, a vast electric storage system would be available for no additional investment, with cars acting as the national grid’s storage. An intelligent grid would be needed to measure flows of electricity to and from every vehicle identified by a code like a credit card. To encourage the adoption of vehicle-to-grid technology, a 10%─25% additional fee could be added for electrically recharging a vehicle that had not been registered as plugged in as a storage unit over the previous 24 hours. Moreover, plugging such electric vehicles into an intelligent network connected to the grid and managed by its controller would facilitate balancing second by second electricity flows in an otherwise increasingly non-resilient system dependent on highly variables renewable supplies. Thus, renewable sources of electricity could be widely adopted without worrying about security of supply.
There are undoubtedly many technical issues needing solved as to how such a system would work in practice, but there is much ongoing research, such as developing 2-dimensional tri-layers of graphene as an insulator, superconductor and magnet. There are also recent proposals for plant-based super-capacitors which could play a similar role. The potential benefits of such a power source could be huge as a SIP. By not demonising road transport for its CO2 footprint and dangerous pollution, cars with internal combustion engines could be replaced at a rate matching obsolescence and the increased need for storage from the extension of renewables. The basics of electric engines are established, so employment can be maintained in vehicle manufacture and many of its ancillary industries rebased on GNTs. Two side benefits are a potential reduction in both mining for lithium and cobalt, and later disposal of, or recycling, the resulting toxic battery waste; and eliminating the need for expensive catalytic converters, cutting production costs, eliminating a target for theft (which then exacerbates air pollution and GHGs, especially nitrous oxide), and reducing palladium mining and its import.
Indirectly, GNTs could solve the UK’s rail system problem of a lack of electrification across much of the network by replacing diesel-electric trains by GNT-supplied electric ones, although some progress is occurring with hydrogen driven trains in Germany and the UK. As GNTs are so light, they might even stimulate a large increase in economical electric-powered aircraft. But as noted above, a large increase in non-CO2 electricity generation would be needed to sustain an electricity-only powered transportation system.
Housing accounted for around 30% of all the UK's CO2 emissions (40 million tonnes of carbon or roughly 150 million tonnes of CO2, as a tonne of carbon equals 3.67 tonnes of CO2). Much of this was by burning natural gas, mainly methane (CH4). Currently the UK consumes around 80 billion cubic meters of natural gas, roughly 30b m³ for households, and 25b m³ each for generating electricity and for other uses, including industrial (10b m³) and various services (15b m³). However, about half of the UK natural gas is imported.
Section 4 discussed replacing natural gas in electricity production, possibly other than as a back-up instead of coal-fired plants. Section 8 considers its replacement in manufacturing. Here we consider the household sector, which might also cover some services.
Natural gas usage in household boilers and gas hobs replaced coal gas (mainly hydrogen) from 1969 onwards, so above we noted the possible solution of reversing that change and use hydrogen. To be non-GHG emitting, this would need to be obtained either by electrolysis or by methane pyrolysis: we consider these in turn.
To get the Btu equivalent of 80b m³ of methane p.a. would need about 240b m³ of hydrogen. It takes 18kg (nearly 4 gallons) of water to produce 1 kg of H2 by electrolysis, which is roughly 11.1 m³, using 40kWh of electricity to do so. So 1 gallon of water weighing 4.55 kg produces 2.8 m³ using 10kWh of electricity. To get 240b m³ of hydrogen pa would require 85b gallons of water using 850TWh of electricity, almost 80 times the UK’s use of fresh water (1.3b gallons pa) and seven times current UK renewable supply of electricity. One could store both hydrogen and oxygen as liquids since both are valuable. Efficiency improvements in electricity used in production may be achieved by catalyst-based electrolysis, and could be done when there is `spare' renewables electricity which might be at a negative price as currently National Grid pays suppliers to switch off. Even replacing all electricity currently generated by methane with renewables, and heating household water by electricity only roughly halves these to need 120b m³ of hydrogen. This approach does not seem feasible.
Methane pyrolysis converts CH4 to C (black carbon) and 2H2 using about 76 kJ (roughly 0.021 kWh) per mole of CH4 (roughly 0.03 m³), so about 0.7 kWh per m³. Burning 1 m³ of methane would deliver about 890kJ whereas burning the resulting 2 m³ of hydrogen yields about 572kJ less the 76kJ used in production so approximately 500 kJ net, although we assume `spare’ renewable electricity will be available at various times of the day. Then, converting the 80b m³ of methane currently used would make 160b m³ of hydrogen to provide 80b m³ for each of households and non-electric generation, delivering somewhat more Btus than now to each. Current estimates of the world's methane hydrates are over 6 trillion tonnes which is roughly twice the carbon content of all fossil fuels. Whether electricity was free or not, the electricity required would be around 56TWh. This seems feasible, although there may be GHG leaks in the supply chain, and the new gas piping likely to be required will probably be plastic based, so will need CCS during its manufacture.
Most recently, microwave deconstruction of commercial plastic using cheap catalysts has been shown to produce hydrogen and multi-walled carbon nanotubes, again potentially turning a burgeoning problem, here of plastic waste, into part of the solution to climate change.
Gradual replacement of natural gas by hydrogen for domestic use over 30 years would require continuously increasing output by around 5 billion m³ of hydrogen annually, assuming none will be needed for electricity generation except possibly as a back-up. Employment in pipe manufacture and laying would result.
Prefabrication of new highly-insulated dwellings must be a priority to reduce emissions, focusing on using less greenhouse-gas-intensive building materials. Graphene added to cement could strengthen it and lower the volumes needed in construction. Cutting electricity costs would make hydrogen cheaper and so lower the costs of making glass: cheaper triple glazing will help ensure high insulation. Further proposals for new dwellings include installing solar photovoltaics (PVs) and evacuated tube solar collectors on roofs; air heat pumps; more use of rain water; and better designed settings and landscapes facing a hotter and probably windier world as hurricanes intensify, whereas the use of natural gas from the grid should be banned.
Looking further ahead, but less certain, some new technologies seem promising: halide perovskite-based solar windows that look like tinted glass could generate electricity, noting that even bricks can be supercapacitors.
Retrofitting existing dwellings
Better house insulation is essential to reduce CO2 emissions from heating and cooling and could include installing double or even triple glazing, better loft insulation, foil between radiators and walls, etc. As with new dwellings, installing solar panels and air heat pumps would reduce demands on GHG emitting energy sources, as would LED lighting.
Refrigerant gasses can be bad for climate change if released into the atmosphere: chlorofluorocarbons (CFCs) were destroying the ozone layer before the Montreal Protocol in 1987, but replacements by halons and halocarbons including hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs) are dangerous greenhouse gases. Again research is needed for better alternatives, perhaps funded by prizes to avoid patent restrictions. Raising fridge and freezer insulation standards to minimize cold loss should also reduce the compressor size needed (which could lower prices) as well as electricity consumption.
Coal gas containing hydrogen, methane, ethylene and volatile hydrocarbons was replaced from 1969 in the UK when switching to natural gas (mainly methane) by fitting different-sized burner jets for the correct gas/air mixture. Coal (or town) gas had a Btu of 540 per cubic foot as against 1015 for methane. The total cost of the conversion was £100m at the time, so approximately £3b in current prices or £1000 per house. If the switch from natural gas to hydrogen occurs, an investment in new burners of about twice that may be required, given the increase in the number of households.
At present, greatly lowering agriculture’s carbon `foodprint’ looks problematic, although there is progress in efficiency improvements in some areas. Best-practice high-yield farming could reduce demands on global cropland. Inner-city underground and vertical farms economize on land water, fertilizer and energy (partly from transport reductions) and are increasingly viable given the falls in costs and their electricity consumption of LED lighting. Transport costs, food waste and potential emissions are reduced, and multiple crops can be grown per year. Fish of various kinds can be bred in the water used for hydroponic systems. When grown in a vertical farm, a commonly low yielding crop such as wheat has a yield increase of 600 times compared to that grown in the field. Saving virgin forest and other previously unused land from farming is becoming imperative to avoid mass extinctions of species from loss of habitat. Meanwhile, the COVID-19 pandemic has seen a surge in home working, which if it persists would see many vacant multi-storey buildings, and potentially large falls in their prices.
There is considerable research on altering farm-mammal diets to reduce methane emissions, including adding dietary fumaric acid (from plants like lichen and Iceland moss), where lambs showed a reduction by up to 70%. On the island of North Ronaldsay in the Orkneys, the local breed of sheep are forced to live off seaweed by a dry stone dyke surrounding the island to keep them on the beach areas because a high grass diet can be dangerous for them from copper intake. Eating the seaweed controls the usual methanogenic bacterial activity in ruminants, so the sheep belch far less methane than grass-fed relatives elsewhere. Feeding lactating dairy cows on a diet including just 1% of the seaweed Asparagopsis taxiformis reduces their methane output by up to 3/2rds as well as economises on their feed intake (reducing unused methane saves energy). Similar improvements in emission reductions and weight gain have been found for other ruminants at even lower levels of dietary additions with `the potential to revolutionize management of greenhouse gas emissions across the ruminant livestock sector with complementary benefits to the environment, and economy of the wider agriculture sector’. On a global scale, adoption would require substantial aquafarming if adequate supplies of Asparagopsis are to be available, and attempts to do so are ongoing.
An increasing problem from agriculture is the release of nitrous oxide (N2O) from excess use of nitrogen fertilisers: N2O emissions have doubled in the last 50 years. Noting that areas round volcanoes are very fertile, ground-up basalt and even basalt dust waste may be an excellent fertilizer alternative. Moreover, basalt is a major source of atmospheric CO2 removal as shown by an experiment in Iceland. Experiments pumping carbon-rich fluids into ophiolite rock formations show that carbonate minerals can form very rapidly. Absorption of atmospheric CO2 by basalt post Permian-Triassic was slow but very extensive and could be greatly accelerated by policy.
Aquaculture may be essential to continue the supply of seafood and Asparagopsis seaweed but needs serious productivity improvements in many areas and faces health concerns in others. To enhance the supply of `wild seafood’, more and larger marine reserves and saltwater fish sanctuaries with strong legal protection must be mandated. Other than policing against illegitimate fishing, these are relatively costless, and above we noted this incidental benefit of off-shore wind farms.
Changes to human diets also need encouraging, eating less mammal meat and more avian and plant nutrition. Simple steps can facilitate that shift, such as just reordering items on a menu, and preparing more enticing vegetarian and vegan meals while improving dietary health.
Decarbonizing heavy industries’ direct emissions is essential because even if all their indirect power sources came from renewables, they would still comprise at least 20% of GHG emissions globally. Heavy industry is particularly carbon intensive when making products like iron and steel, using facilities with long lifetimes and high capital intensity. Investment in mitigating these large direct emissions of CO2 is therefore required now. Low-carbon high-heat solutions for manufacturing include liquid hydrogen, highlighting the key role this gas would play in a zero-net emissions world.
Chemicals and plastics are more problematic, so are a key area for research on reducing or removing their carbon emissions. Recycling more, using more waste for fuel, and landfilling less to reduce methane leakage are all essential as is increased research on catalysts. The 5 pence charge on plastic bags in the UK led to a 90% fall in their use (almost 500 million fewer per annum): similar charges for other non-recyclable items could be equally effective. The purchasing clout of large retail chains could pressure suppliers to improve, as (e.g.) Walmart is doing.
The UK’s total ‘consumption induced CO2’ equivalent emissions are higher than the domestic level through CO2 embodied in net imports, although the large reductions achieved to date have a major domestic component. ‘Consumption induced’ CO2 will fall as the CO2 intensity of imports falls with reductions in GHG emissions by exporting countries. However, targeting consumption rather than production emissions has the unwanted consequence of reducing incentives for emitting industries or exporting countries to improve their performance, as these would not be counted against them (e.g., if nationally decided contributions−NDCs−used a consumption basis). Border carbon taxes have a role to play in improving both exporters’ and importers’ performance. Similarly, allocating emissions from transport and packaging to (say) the food sector would again alleviate those intermediate sectors of the responsibility to invest to reduce what are in fact their emissions by attributing them to retail outlets or consumers. Finally, deforestation is now recorded worldwide by satellites and a general high tariff on all imports from countries guilty of large-scale deforestation would put pressure on reducing destruction from many companies in that country, adding to international pressure.
A joined up approach to decarbonizing is needed as virtuous circles seem to be missed when there is isolated thinking rather than seeing the interacting policies needed for reductions in CO2 as a whole. The problems need to be tackled jointly as the solution to each can facilitate solving others.
The UK data provide little evidence of high aggregate costs to its reductions in CO2 emissions, which have dropped by 186Mt from 554Mt to 368Mt annually (34%) so far this century, during which period real GDP per capita has risen by more than 25%, despite the ‘Great Recession’ (not including the recent pandemic-induced falls). Carbon prices could be used to facilitate further reductions, though evidence of public opposition in a number of countries suggests possible limitations even when the revenue raised is rebated. Cap and trade could also help, and legislation in Europe has also forced change. There are many studies of these approaches, so here we have focused on potential SIPs in the decarbonisation process.
Historically, those in an industry that was being replaced (usually by machines) lost out and bore what should be the social costs of change, from cottage spinners, weavers and artisans in the late 18th–early 19th centuries (inducing ‘Luddites’), to recent times (from a million coal miners in 1900 to almost none today). Greater attention needs to be focused on the local costs of lost jobs as new technologies are implemented: mitigating the inequality impacts of policies introduced to avoid climate change must matter in such decisions. Given the important role of the capital stock in production, ‘stranded assets’ in carbon producing industries are potentially problematic as future legislation imposes ever lower CO2 emissions targets to achieve zero net emissions, but jobs in those industries are equally at risk. An excellent ‘role model’ that offers hope for major reductions in energy use is the dramatic increases in lumen-hours per capita consumed since 1300CE of approximately 100,000 fold yet at one twenty-thousandth the price per lumen-hour. While some of the above proposals are speculative and require substantial further research, they suggest possible strategies for moving towards at least a very low-carbon future by 2050: let’s not waste the recovery from the pandemic by ignoring the chance to tackle burgeoning climate issues.
 That paper cites the UK’s Climate Change Act of 2008 as a timely intervention with a large effect.
 Tax increases, such as to VAT on household fuel, are to change behaviour, not to raise revenue, so should be redistributed to families facing fuel poverty.
 Sulfur hexafluoride (SF6) protecting electric sub-stations from explosions is an excellent electrical insulator being inorganic, colorless, odorless, non-flammable, and non-toxic, but is an extremely potent greenhouse gas like HCFCs.