To assess the climatic impact of the targets put forward by countries, we first construct a global emissions pathway to 2100. This global pathway is then used as input to a climate model (MAGICC), which is run multiple times in order to obtain a probability distribution of outcomes such as global mean temperature, CO2 concentration, and total greenhouse gas concentration. The detailed methodology is outlined in Meinshausen et al. 2009.
Annex I aggregation
The pathways calculated for developed countries shown on the Climate Action Tracker, including LULUCF accounting for 2008-2020, provide unilateral/low-ambition target pathways up to 2050, which were used in this calculation.
We assume that surplus credits from countries with target pathways above their business-as-usual (BAU) are banked. This leads to the result that emissions for the aggregate of developed countries are held at BAU levels up to 2020, because the amount of banked surplus credits is high enough to allow for this.
Emission levels from 2050 are held constant to 2100.
Non Annex I aggregation
For the remaining countries the unilateral/low-ambition target pathways were used up to 2020.
The following post-2020 rules were applied:
- Costa Rica and the Maldives pledge carbon neutrality by 2021 and 2020 respectively; subsequent emissions were held constant to 2100.
- Mexico and South Korea have 2050 targets (50% below 2002 for Mexico, 50% below 2005 for South Korea), which were held constant to 2100 (or until BAU drops below, after which emissions follow BAU until 2100).
- The rest follow a constant percent below BAU to 2100, with the percentage defined as the percent below BAU in 2020 defined by the individual pledges. India has a further limit of not surpassing Annex I per capita emissions. The BAU for these countries was constructed by extending the BAU pathways provided in this analysis with the growth rates of the PRIMAP2 baseline constructed from National Communications, POLES, and MATCH data, described in greater detail on the www.primap.org website.
- Two additional countries have policies that were applied to the PRIMAP2 baselines. Madagascar is 25% below 2000 in 2050, with the 2050 value is held constant to 2100 (until BAU drops below). The Philippines is 5% below 1990 in 2010, and then held constant to 2100 (until BAU drops below). Time constraints have not allowed for creating individual country pages for these yet.
- All other countries not already specified follow their individual BAU pathways.
For information on bunkers, i.e. maritime and aviation emissions, we use IMO data from Buhaug et al. (2009), and data from Owen et al. (2010) respectively. Global reductions were applied to IMO data, while aviation follows BAU.
A business-as-usual pathway for global deforestation emissions is provided by the RCP8.5 scenario (Riahi et al. 2007), the high side of the range of new emission scenarios (see http://www.iiasa.ac.at/web-apps/tnt/RcpDb) developed for assessment in IPCC's Fifth Assessment Report (AR5).
This global pathway is consistent with global carbon budget modeling and is subsequently split into contributions by individual countries (Houghton 2008; Houghton 2009; van der Werf et al. 2009).
Proposed reductions by individual countries are then applied to the business-as-usual pathways for these countries that are thus consistent with the historical global carbon budget.