Climate lock-in wedges

Nearly a decade ago the then CEO of BP, Lord John Browne, gave a landmark presentation on climate change mitigation in the City of London. He introduced to the broader interest group (the work had already circulated in the academic sector) the idea of stabilization wedges, which had been developed by Stephen Pacala and Robert Socolow at Princeton within a research program supported by BP. Each wedge represented one of a number of quantifiable actions that together were necessary to move from a business as usual (BAU) global emissions trajectory to a given atmospheric stabilization of CO2. In the initial study that stabilization was 500 ppm.


Wedges were on a very large scale (up to 1 GtC/annum) and consisted of actions such as:

  • Increase fuel economy for 2 billion cars from 30 to 60 mpg
  • Replace 1400 GW 50%-efficient coal plants with gas plants (four times the current production of gas-based power)
  • Introduce CCS at 800 GW coal or 1600 GW natural gas (compared with 1060 GW coal in 1999) power plants.
  • Add 700 GW (twice the current capacity) of nuclear fission capacity

This was the first real attempt to quantify the physical changes required in the energy system and turn that into an overriding story which people could actually understand. Many variations on the approach followed in subsequent years. More recently, researchers from universities in the USA and China looked again at the wedges and concluded that the scale of the issue had grown and that an even more ambitious set of wedges would be required to address the climate issue. The team behind this analysis introduced the concept of “phase-out” wedges, or wedges that represent the complete transition from energy infrastructure and land-use practices that emit CO2 (on a net basis) to the atmosphere to infrastructure and practices which do not. But this raises the major issue of stranded assets, or assets that have to be abandoned before their useful life has ended, typically because of economic impairment.

An alternative way of looking at this issue is to consider “lock-in” wedges. Each represents a chunk of infrastructure in use today that is very likely to continue operating until the end of its normal life, emitting CO2 while doing so and therefore adding to the growing accumulation of CO2 in the atmosphere. According to the Oxford University Department of Physics, cumulative carbon emissions today stand at some 567 billion tonnes (since 1750). Limiting the global temperature rise to 2°C requires limiting cumulative carbon emissions to one trillion tonnes. Each wedge adds towards a total committed block of emissions, which in turn would lock us into a 2°C or greater outcome should that commitment block be greater than 433 billion tonnes (1 trillion less 567 billion). Major wedges are described below:

  1. The largest existing commitment is coal fired power stations. While the next generation of facilities may well be fitted with Carbon Capture and Storage (CCS) or at least be “CCS ready”, existing power stations may never be retrofitted. Today there is some 2000 GW of coal fired capacity, with each GW emitting about 6 million tonnes of CO2 per annum. More than half of this has been built in this century, so we might assume an average age of 16 years for the existing facilities. That leaves about 30 more years of operation. Even assuming that no more are built, that means cumulative CO2 emissions of 300 billion tonnes, or 80 billion tonnes of carbon. But we could well build another 1000 GW without CCS, so that alone adds another 225 billion tonnes of CO2, or 60 billion tonnes of carbon.
  2. There are about 1 billion passenger cars in the world today and production is now over 60 million per annum. Assuming the average age of a current world car is 7-8 years and the average lifetime of a car is 15 years, this population could emit a further 10 billion tonnes of carbon. We will almost certainly build another billion internal combustion engine cars, which in turn will add a further 16 billion tonnes of carbon to the atmosphere.
  3. Natural gas use in power generation is growing rapidly, with some 1600 GW in use today, growing to 2000 GW over this decade. By the early 2020s, only a tiny fraction  of this capacity will have CCS. Given that a gas fired power station emits less than half the amount  CO2 compared to a similar sized coal plant, this fleet could see a further 140-150 billion tones of CO2, or about 40 billion tonnes of carbon emitted prior to retirement.
  4. According to the IEA, residential use of gas results in 1 billion tonnes of CO2 emissions per annum. This is somewhat hard wired into cities, so difficult to dislodge any time soon (although having replaced our gas boiler at home with an electric one because of new UK flue regulations, it’s clearly not that difficult). Nevertheless, this could well continue for 30-40 years, so perhaps another 10 billion tonnes of carbon.
  5. Aviation and shipping have both an existing fleet and show almost no sign of finding viable large scale routes to zero emissions (but biofuels may be the solution for both). Expect another thirty years of emissions at a minimum, which is another 10 billion tonnes of carbon.
  6. Finally, there is manufacturing industry which emits 6 billion tonnes of CO2 per annum globally. This includes refineries, ferrous and nonferrous metal producers, cement plants, chemical plants, the pulp and paper industry and various other sectors. Capacity is renewing rapidly both because of growth and development but also because of the gradual decline of developed country capacity in favour of much larger and more efficient production in regions such as the Middle East. New capacity will operate for thirty years at least, so this sector could be responsible for another 120 billion tonnes or more of CO2 or about 32 billion tonnes of carbon.

The sum of these “climate lock-in wedges” now looks something like this:

Climate lock-in wedges (II)

This picture includes the major sources of emissions (e.g. oil fired power stations not included) and probably represents the best case in terms of retirement of existing assets. Staying within the trillion tonne limit therefore leaves little room for complacency with regards the next generation of assets and particularly the use of CCS in power generation. An alternate view of this would be to just look at the current proven reserves of oil, gas and coal which amount to about 1.3 trillion tonnes (BP Statistical review of World Energy). If totally consumed without the application of CCS, they would result in over 1 trillion tonnes of carbon emissions, bringing the total accumulation since 1750 to 1.7 trillion tonnes.