There is a wide range of future greenhouse-gas emissions pathways that meet any given climate target. Whilst the AVOID programme has produced a large number of emissions scenarios and pathways to date, AVOID has not produced a systematic assessment of the different mitigated emissions pathways that are consistent with different climate targets. Such an assessment is desirable to inform decisions about the characteristics of emissions pathways that span a range of climate outcomes and approaches to mitigation of climate change such as doing “less sooner” or “more later”.
This study develops over 150,000 plausible mitigation pathways and assesses their climate outcomes to examine the potential flexibility of emissions pathways leading to climate targets from 1.5 to 3°C above preindustrial levels. As well as a much fuller coverage and analysis of possible emission pathways than was available previously, the report’s analysis includes the possibility of large scale negative emissions technology later in the century, in line with the estimates of the land available for bio-energy from Committee on Climate Change’s 2011 report on Bio-energy and DECC’s estimates of potential efficiency of bio-energy carbon capture and storage (BECCS).
Probabilistic impacts projections for 2050 and 2100 are also presented from a new modelling framework developed under AVOID, to aid interpretation of the relative climate impacts at different levels of climate change.
The main findings of the report are;
- The lowest median 2100 temperature target found to be possible in this study was 1.6°C. This was only found possible with a peak in global emissions in 2014, and emissions reductions rates and long-term negative emissions at the very limit of what is currently understood to be feasible.
- Without negative emissions in the longer term, a 2°C target by 2100 was the lowest found to be possible in the current framework. This requires the highest emissions reduction rates currently considered feasible (3.5% /yr) and a peak in global emissions before 2016.
- Less than 1% of the scenarios that lead to 2°C of warming by 2100 and which do not include net-negative emissions have reached their maximum global average temperature and started to cool by 2100. Of those scenarios meeting 2°C in 2100 which do include negative emissions, over 90% have reached their peak warming and started to cool by 2100.
- Temperature targets a few tenths of a degree above 2°C in 2100 introduce significant flexibility in the range of emissions pathways that are consistent with a given target, allowing lower reductions rates of emissions, later peaks in global emissions and a larger long-term minimum of global emissions.
- Including the possibility of long-term negative emissions technology, such as BECCS (bio-energy with carbon capture and storage), significantly increases the feasibility of mitigation strategies for every climate outcome. The introduction of BECCS at the scale of the “Further Land-use Change“ scenario of the Committee on Climate Change, where agricultural land may be converted to growing fuel for bio-energy, allows the peak in global emission to be delayed from 2016 to 2026 while still meeting a 2°C global target, but with significant implications for land use change.
- The use of large-scale negative emissions allows climate targets to be met with global emissions peaking later. However, this may increase pressure on land available for agriculture in the future.
- If global mitigation strategy plans for a strong emphasis on BECCS later in the century to allow a delay in peaking of global emissions until later in the century, this will increase the risk of missing targets if BECCS is not able to be made an effective negative emissions source. If BECC is made effective and not used to it’s full extent, though other demand and supply side change, then BECC could be used to supply possible flexibility to meet climate targets at a later stage.
- Increasing the required probability of meeting a given temperature target for a given emissions scenario (c.f. imposing a stronger climate target) can be interpreted as shifting the projected temperature distribution to lower temperatures in the target year. In this study’s modelling framework, specifying a 66% chance of meeting a particular target is equivalent to a 50% chance of meeting a temperature rise that is 10% lower. For example, a 66% chance of meeting a 2°C target in 2100 is akin to setting a 50% target at 1.8°C.
- In 2100, at levels of warming beyond 3°C, many impacts in many countries start to increase more rapidly with temperature than between 2°C and 3°C.