If fast and substantial reduction of greenhouse gas emissions is postponed further, there are fewer options available to stay below a 2 OC warming at the end of the century. Delayed action is likely to lead to measures that remove CO2 directly from the atmosphere by planting forests and using bioenergy in combination with carbon capture and storage. The latter technique still involves considerable challenges. Climate policy decisions over the next ten years will determine the level of global dependency on such carbon-negative solutions.
This is the main conclusion of a study by PBL Netherlands Environmental Assessment Agency, ‘Implications of long-term scenarios for medium-term targets (2050)’, that was published today. At the request of Norwegian Environment Agency PBL assessed how cuts in emissions before 2050 will affect what policy measures will be necessary in the second half of the century to limit global warming to 2 degrees above pre-industrial times.
"Implications of long-term scenarios for medium-term targets (2050)"
Written by Van Vuuren, D.P., van Sluisveld, M. and Hof, A.F. (2015), PBL Netherlands Environmental Assessment Agency. The work was funded by the Norwegian Environment Agency. A draft was presented during a seminar organised by the Norwegian Environment Agency on 20 November 2015.
Several policy proposals have indicated that the world must reduce greenhouse gas emissions by 40 to 70 per cent compared with 2010 levels by 2050 for it to be likely (66 per cent chance) to stay below a 2 degree warming, quoting the recent IPCC report. However, the wide range from 40 to 70 per cent is, to a considerable extent, a reflection of policy choice. Policy strategies that do not want to rely on removing CO2 from the atmosphere should be at the lower end of the range. This is illustrated by the observation that scenarios reflecting such strategies show emission reductions of more than 60 per cent in 2050.
The Intergovernmental Panel on Climate Change (IPCC) stated in its Fifth Assessment Report that the world must reduce greenhouse gas emissions by 40 to 70 per cent compared to 2010 levels by 2050 for it to be likely (66 per cent chance) to stay below a 2 degree warming. In the scenario database assessed by IPCC, just over 100 scenarios result in a global mean temperature increase of less than 2 degrees at the end of the century, and that are thus in line with the so-called low-emission pathway from the Fifth Assessment Report (RCP 2.6). The assessment of these scenarios showed that the ones that had reduction levels of 40-60% by 2050, relied on negative emissions in the period after 2050 in order to reach the emission levels required to stay below 2 OC by the end of the century. The scenarios that reduced emissions by more than 60% by 2050, did not have negative emissions. In other words: fewer reductions before 2050 require more substantial reductions and negative emissions in the last half of the century.
With continuing high emissions over the next few years, the world will become more dependent on the large-scale implementation of negative-emission measures to limit warming to two degrees in the longer term. This can be attractive to allow for a smooth transition in the short-term, but would also imply a faster and more demanding readjustment in the middle and latter part of the century. Fast and substantial emission reductions will give greater flexibility for the preparation of policy choices and strategies, and a more gradual readjustment as we approach 2050.
Bioenergy with carbon capture and storage (BECCS) is an important element in a future energy system, but there are considerable challenges relating to the effects of land use. One example is that lack of suitable storage capacity for CO2 and social acceptance may limit the use of BECCS in some countries. Identifying the full potential for BECCS and the relationship with reduction targets in the short- and medium-term (for example 2050) would require further assessment.
According to the IPCC, cumulative future emissions of CO2 must be limited to a ’carbon budget’ of approximately 1,000 billion tonnes to keep global warming below 2 degrees. If the world’s emissions continue to increase rapidly and follow the highest emission pathway of the IPCC, the PBL analysis suggests the world will have spent 70 per cent of the 2-degree ’carbon budget’ by 2030 – i.e. within the next 15 years.
Simplified presentation of how the world can stay within the carbon budget of 1,000 billion tonnes of CO2, which makes it likely (66 per cent chance) that warming will be limited to 2 degrees. Left panel: A future with fast and substantial emissions reductions, with less dependence on negative emissions after 2050. Right panel: A future with delayed reductions in greenhouse gas emissions and heavier reliance on removing CO2 form the atmosphere in the second half of the century. Source: Netherlands Environmental Assessment Agency/State of the Environment Norway
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