Further information

What will it take to achieve 2ºC?

This infographic draws on analysis conducted as part of the DECC/DEFRA/NERC-funded AVOID 2 Rates of decarbonisation work package. This analysis is contained principally in report WPC2a [1].


The analysis uses three energy systems models:

  • the Imperial College London Grantham Institute’s TIMES Integrated Assessment Model (TIAM-Grantham),
  • the International Institute for Applied Systems Analysis (IIASA)’s MESSAGE-GLOBIOM model,
  • the Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC)’s WITCH model.

Each of these models simulates the evolution of the global energy system over the 21st century, under a variety of scenarios, imposing limits on global CO2 emissions in order to achieve specified long-term global temperature goals. Each model uses the same set of population and economic output growth assumptions, Shared Socio-economic Pathways 2 (SSP2)), which represent a “middle-of-the-road” scenario in which no significant deviations from current and historical socio-economic trends occurs, thereby representing a reasonably central estimate of future global population and development


The infographic considers the consequences of mitigation action towards achieving a less than 2OC global average temperature increase in 2100 (with 50% probability), comparing 2 scenarios: 1) global coordinated action beginning in 2020; 2) action beginning in 2030.

Model constraints

These models are used to simulate CO2 emissions from fossil fuel combustion in the energy system (i.e. the electricity, transport, buildings and industry sectors) and from industrial processes only, since for AVOID 2 they are used to understand how energy systems could transform in different mitigation scenarios, and therefore do not contain land-use emission totals. The models are constrained by a 2OC-consistent cumulative level of CO2 emissions from these sources over the 21st century. As explained in AVOID 2 report WPC2a, this figure (1,340 GtCO2 from fossil fuel combustion and industrial processes) has been arrived at through analysis by the Met Office. This assigns a “budget” to cumulative CO2 emissions from these sources, considering the likely magnitude of other GHG emissions sources in the same socio-economic (SSP2) scenario as drives CO2 emissions. This analysis draws primarily from other established emissions scenarios called the Representative Concentration Pathways(RCPs) used in the IPCC’s Fifth Assessment Report.

Costs of mitigation

The costs of mitigation shown in the infographic are the additional costs compared to a business-as-usual reference scenario which has no CO2 constraints, over the whole of the 21st century, as reported by the TIAM-Grantham model.

Rates of decarbonisation

The rates of decarbonisation shown are the average annual global rates in the first decade following the start of global coordinated mitigation action (i.e. 2020-2030 in the scenario with action starting in 2020, and 2030-2040 in the scenario with action starting in 2030). The range reflects the range across the three energy systems models. In energy systems models in general, the rates of decarbonisation are highest in these early decades following the start of mitigation action, as carbon-intensive energy technologies are replaced by low-carbon energy technologies.

Deployment rates

The annual deployment level (in Gigawatts) of each power generation technology is the highest value shown across the three models when looking at the average annual deployment in the decade following the start of mitigation action. Both the economy-wide rate of decarbonisation and the deployment rate of individual technologies are arrived at through a least-cost optimisation method for each model, so as to meet a given global emissions constraint at the lowest overall global economic cost.

Energy mix in 2100

The second infographic shows the energy system mix of primary energy sources in the year 2100 in the 2ºC scenario where global coordinated mitigation action begins in 2020. This mix is arrived at through each model’s simulation of the least-cost transition from a carbon-intensive energy system to a low-carbon system which meets future energy needs and any imposed CO2 constraint. Diferent model results arise from different assumptions around future technology and energy resource costs and availability. Hence, these scenarios are purely illustrative rather than prescriptive. There are a variety of possible energy mixes which will deliver a low-carbon future, depending on technology parameters, but also on factors not represented in these models, such as political and social factors. The table below shows the total primary energy demand for each major source in 2100, as used in the figures shown in the infographic.

EJ (1018 J) of energy TIAM-Grantham MESSAGE-GLOBIOM WITCH
Oil            124                0              38
Coal              60            134              47
Gas              96              84              77
Nuclear              37            117              57
Biomass            329            222            254
Hydro              59              34              19
Solar            157            127              11
Wind            375            157              27
Other              35              11                2
Energy demand reduction            196            561            617

Behaviour change cost reductions

The second infographic also states that reducing energy demand through behaviour change can save 25% in mitigation costs. This result comes from AVOID 2 report C4 and is based on analysing the cost of achieving the 2ºC goal with and without an imposed 10% reduction in road transport and residential heating demand (levels which illustrate modest but feasible – based on recent policy evidence – levels of demand reduction), using the TIAM-Grantham model.