Instructors seeking a good analysis for students of the current landscape of emissions commitments post-Copenhagen should consider a new piece in Environmental Research Letters, Joeri Rogelj, et al., Analysis of the Copenhagen Accord Pledges and its Global Climatic Impacts – A Snapshot of Dissonant Ambitions, 5 Environmental Research Letters 1-9 (2010).
The key take-aways of the piece:
- 138 Parties have now expressed their intention to be associated with the Copenhagen Accord, which is framing the ongoing negotiations toward a global successor agreement to Kyoto;
- If nations agreed to 50% reduction by 2050 from 1990 levels, global emissions would need to decline by 3-3.55 annually from 2000 levels, requiring “unprecedented political will” by contrast, global emissions rose by 21% between 1990 and 2005;
- The study looked at a low ambition “Case 1” scenario, without a post-2020 target, and a “Case 2” scenario in which emissions are halved by 2050 from 1990 levels and emissions continue to decrease after 2050 with an exponential decrease at a rate equal to the average reduction rate in the last decade before 2050
- The Case 1 scenario yields emissions of 53.2 GtCO2eq in 2020, and Case 2, 47.4 GtCO2eq
- Under the Case 1 scenario, temperatures are projected to rise between 2.5-4.2C above pre-industrial levels by 2100, and still increasing afterwards. Under the Case 2 scenario, temperatures rise between 1.5-2.6C, with a 49% chance to stay below 2C
- In the Case 1 scenario and without a 2050 target, media estimates would exceed 450ppm CO2 threshold in approximately 2030; this is concentration threshold where coral reefs would face “rapid and terminal decline;” and aragonite undersaturation, a critical manifestation of ocean acidification, would also occur at this concentration. Even under a Case 2 scenario, the globe would see rapid declines of coral reefs and arctic argonite undersaturation during the 21st Century;
4. Higher ambitions for emissions reductions for 2020 are necessary to keep options for holding temperature increases to 1.5C or 2C without relying on potentially infeasible reduction rates after 2020;
5. The absence of a mid-century emission goal is a critical deficit in the Copenhagen Accord.