A new EU report highlights the urgency of reducing emissions of greenhouse gases if a 2°C target is to be met.
Global emissions of greenhouse gases must peak in three to five years and be reduced by three per cent annually thereafter, according to a report1 recently published by the European Union Presidency, which looks at scientific perspectives on climate one year after the Copenhagen Climate Conference.
The report argues that a peak in emissions by 2015 is required if we are to have a reasonable chance of limiting average global surface warming to 2°C, the ultimate objective of the United Nations Framework Convention on Climate Change. The later the peak, the higher the subsequently required reduction rates become. Peaking after 2015 would likely require more than a three per cent reduction in emissions each year.
The Copenhagen Accord sets a goal of 2°C and calls for parties to the Convention to submit their 2020 emission reduction pledges in order to begin the work towards achieving this goal. Additionally, it allows for a review of a 1.5°C limit in 2015. The EU report does not analyse in detail the reductions needed to reach 1.5°C, a target advocated by more than 100 countries and NGOs. Instead, the report examines the chances of reaching the 2°C target with present climate commitments.
According to the report, the current emission reduction pledges associated with the Copenhagen Accord fall short of the 2020 goals required to provide a reasonable chance of limiting warming to 2°C, without requiring potentially infeasible post-2020 reduction rates. Even the most optimistic interpretation of the current pledges leaves a gap of between two and six gigatonnes of CO2 equivalent emissions by 2020. Excluding the conditional pledges and other optimistic hypotheses, the gap in 2020 is approximately ten gigatonnes of CO2 equivalents.
The main conclusions of the report are based on what would be required to provide at least a 66 per cent probability that the temperature increase would be limited to 2°C, and would require global emission reductions of 50 to 70 per cent relative to 1990 levels by 2050.This assumes further emission reductions after 2050. If a higher probability of staying below 2°C is required, then greater emission reductions would be needed. If a lower probability is considered acceptable (for instance, a 50 per cent chance) then emission reductions could also be lower.
However, the analysis of the current Copenhagen Accord pledges shows that, GHG emissions must peak by 2015 even allowing for a lower 50 per cent chance of limiting warming to below 2°C, current commitments would require post-2020 emission reduction rates that may not be feasible.
To ensure at least a 66 per cent chance of limiting global warming to less that 2°C, the EU report suggests:
- Reductions of long-lived GHGs, such as carbon dioxide
- Complementary measures for shorter lived warming agents
- In the longer-term (post 2030), possible deployment of technologies that achieve negative CO2 emissions.
Cumulative emissions of GHGs are most important. Given the short atmospheric lifetime of some warming agents, temperatures in the longer term will be little affected by mitigation action of these agents in this decade, although mitigation could slow the current rate of warming.
The achievement of the large reductions in anthropogenic GHGs required to meet the 2°C limit is highly dependent upon the implementation of effective policy instruments.
Recent scientific literature reinforces the evidence provided by the IPCC Fourth Assessment Report that limiting warming to less than 2°C considerably reduces the risk of triggering accelerated or irreversible changes in the climate system, as well as large-scale adverse impacts. Nevertheless, significant risks do still remain. Impacts of climate change will, in addition, not be the same everywhere and some regions or sectors might experience a disproportionate amount of adverse impacts.
As mentioned, the EU report also notes that the Copenhagen Accord calls for a review, in 2015, of a potential 1.5°C limit. It concludes that research in relation to this is expected to be synthesised in the upcoming IPCC Fifth Assessment Report. The few limited assessments currently available give preliminary evidence that such a goal might only be possible by allowing temperatures to initially exceed 1.5°C, followed by temperature reductions towards the end of the century or later.
Reinhold Pape
1. Scientific perspectives after Copenhagen. Information reference document, October 2010.