Setting a target for emission reduction
Given the evidence that continued emissions of greenhouse gases will cause increasingly serious climate effects, it is necessary to consider how, and at what level, to constrain emissions.
The CCC has considered this issue (see our 2008 and Fourth Carbon Budget reports) and assessed the level of global average temperature increase considered “dangerous” and therefore ideally avoided.
Analysis does not point to one specific danger point as temperatures rise, but it does suggest a range of increasingly harmful effects and increased probabilities of irreversible losses. Read more on how a changing climate affects us
Two other factors need to be considered: first, global emissions continue to grow, even though current levels in the atmosphere may already be enough to warm us beyond 2°C. Second, there are uncertainties in our understanding of the climate system which mean that, for any given path of future emissions, a spread of temperature increases are possible.
Looking at this evidence, the CCC’s judgement was that: Central estimates of global temperature increase by 2100 should be limited to as little above 2°C over pre-industrial levels as possible, and the likelihood of a 4°C increase should be kept to very low levels (e.g. less than 1%).
A similar, if not more stringent, target has been agreed by the international community through the United Nations Framework Convention on Climate Change . Global temperature should not exceed 2°C above pre-industrial levels, with the possibility of further tightening this to 1.5°C.
Global emissions reductions
To achieve these climate targets requires a global reduction in emissions. And in deciding how much reduction is necessary it is important to understand that the temperature increase by 2100 is primarily a function of the total emissions over time, rather than the level of emissions in 2050 alone.
The Committee gave consideration to a range of potential emissions scenarios. These varied according to the period in which it is assumed that global emissions peak; the pace of emissions reduction which follows that; and the ultimate emissions floor. The CCC’s conclusion was that to meet the climate objective, global emissions should peak by 2020 and be halved (or more) by 2050. This means that following the peak, global CO2 emissions will need to fall by a rate of 3-4% a year.
Achieving the required global reduction in emissions would imply a global level of emissions in 2050 of around 20-24 gigatonnes on a CO2-equivalent basis (GtCO2e). This would be around a 50% reduction in emissions as against recent levels.
Given a projected global population in 2050 of around 9 billion, such a level of emissions implies per capita emissions averaging around 2 tonnes CO2e.
It is hard to see how the UK’s emission allowance for 2050 could be higher than that average. Allowing for expected population growth, emissions of 2 tCO2e/capita in the UK translates to an emissions reduction target of 80% in 2050 relative to 1990.