After a year of extreme weather events and recent studies outlining climate change’s impacts, it’s become increasingly clear that we must understand what emissions reduction pathways are necessary to avoid these risks. The Intergovernmental Panel on Climate Change’s (IPCC) last Assessment Report, for example, outlined the emissions reductions needed from developed countries to stabilize concentrations of greenhouse gases (GHG) consistent with limiting warming to 2°C. Further research has continued to examine the global GHG emissions reductions necessary to avert dangerous climate change. And as countries implement existing policies and consider new ones, the scale of required emissions cuts is a fundamental question. In fact, it’s one of the most pressing questions facing the international climate change community.
One new study shows that we have to reduce emissions even more than scientists initially thought in order to avoid climate change’s worst impacts. A paper published in Energy Policy on February 20th by Michel den Elzen and colleagues examines new information on likely future emissions trajectories in developing countries. This includes recent clarification of assumptions and conditions related to developing country pledges. In addition, countries have also come forward with further information on their emissions projections. As a result, the report finds that developed countries must reduce their emissions by 50 percent below 1990 levels by 2020 if we are to have a medium chance of limiting warming to 2°C, thus preventing some of climate change’s worst impacts.
This level of reductions is considerably higher than what the scientific community thought was necessary to meet the 2°C goal. The most recent IPCC Fourth Assessment Report laid out a recipe for a medium chance[^1] of limiting warming to 2°C. This report—compiled by the world’s leading climate scientists—stated that developed countries would have to reduce their emissions by 25-40 percent below 1990 levels by 2020, and developing country emissions would have to be reduced substantially from their business-as-usual emissions trajectories.