Results of a recent modeling exercise by the Columbia Climate Center in a collaborative project with Deutsche Bank Climate Change Advisors indicate that the combined impact of more than 350 energy and emissions policies in place across the world fails to reach, by 2020, an emission trajectory consistent with stabilizing atmospheric levels of CO2 at 450 ppm in 2050.
Other analyses have produced similar results when evaluating the impacts of emission pledges under the Copenhagen Accord. We modelled the impacts of a comprehensive set of emissions targets and mandates from state, regional and national levels. In our classification, emissions targets establish economy-wide reductions in absolute emissions or carbon intensity to be achieved in a given time-frame; policies designed to reduce emissions from energy use, either across the economy or in specified sectors are classified as mandates.
In the set of policies we modeled, mandates have a greater impact than emissions targets, resulting in emissions of 51 GtCO2e in 2020, versus business-as-usual emissions (BAU) of 60Gt in 2020. Emissions targets reduce 2020 emissions to 53 Gt.
We also estimated a maximum potential abatement by selecting the category of targets (emissions or mandates) that delivers the greatest abatement for each country. This produces emissions of 49Gt in 2020, 11Gt below BAU. According to most estimates, in order to have a 60% chance of stabilization at 450 ppm in 2050, 2020 emissions must not exceed 44Gt.
Thus, even if countries achieve the maximum reductions available under current policy, an abatement gap of at least 4 Gt in 2020 remains.
Our results suggest that it would be beneficial to shift the focus of the international climate discussion away from targets and timetables (emission targets) and on to concrete actions (mandates).
Though pleasingly elegant, and theoretically economically efficient, economy-wide emissions targets fail to address the critical question of how emissions will be reduced.They are also politically fraught. Mandates may achieve higher levels of ambition because they appear less sweeping and can be tailored to the technical and economic considerations of the sectors involved.
Emissions targets without complementary mandates are purely symbolic, meaningless in terms of actual reductions. For instance, the United States has an ambitious federal emissions target, 17% below 2005 emissions in 2020, a reduction of 1.1 Gt below BAU. Federal mandates, however, provide only 400Mt of abatement in 2020. This mismatch indicates a lack of strategic coordination in the US approach to emission reduction. South Africa and Mexico demonstrate a similar dynamic, while in the EU-27, mandates greatly exceed emission targets in their level of ambition. Germany and Japan both exhibit particularly strong coherence of emission targets and mandates, suggesting strong political commitment and good coordination.
Implications for the atmosphere
Greenhouse gas emissions cause climate change because they trap heat. The high rate at which carbon dioxide is added to the atmosphere is not balanced by absorption by the oceans and other natural sinks: it accumulates in the atmosphere where it remains for centuries. The higher atmospheric carbon dioxide levels go, the longer it takes to decline, regardless of how radically emissions are reduced.
In our maximum potential reduction scenario, emissions in 2020 are almost 11 GtCO2e (or 3 GtC) lower than BAU (emissions continue to grow annually in absolute terms, .3% on average).
After accounting for absorption by the ocean and the biosphere, this reduction amounts to 3 ppm less CO2 in the atmosphere. For reference, the United States emitted about 6 GtCO2e in 2007, while China emitted ~8 GtCO2e. Thus, in 2007, to achieve a reduction of 11GtCO2e would have required a moratorium on US emissions plus a more than 50% reduction in China’s emissions. This gives a hint of the scale of effort and investment these reductions will require, and reflects the slow response of the carbon stock to changes in emissions.
If we assume (quite optimistically) that after 2020 emissions decline 2.4% per year, CO2 reaches 471 ppm in 2050, a substantial improvement over the BAU scenario of 540 ppm, but still above the 450 ppm target.
Implications for the climate
Even if we stopped emitting CO2 altogether today, global average temperature will continue to rise. The warming is dictated by physics and chemistry, and is now locked in by economic and political decisions. The response of the climate and natural systems remains complicated and uncertain, but we do know that change is coming. We must reduce emissions because that is the only way to limit future climate change. It is equally imperative to build adaptability to climate change into every aspect of our societies, beginning yesterday.