Global Warming Potentials
Previous assessments of the Climate Action Tracker used the global warming potentials (GWPs) from the IPCC’s Second Assessment Report (SAR). For this assessment we have updated all figures and time series to GWPs from the Fourth Assessment Report (AR4).
Historical data is taken from Mexico’s National Inventory of Greenhouse Gases and Compounds (INEGyCEI in Spanish) (INECC, 2018). It was developed using the IPCC’s 2006 inventory guidelines and uses GWPs from the IPCC’s Fifth Assessment Report (AR5). Since the inventory provides granular information specifying all gases and sectors per year, we were able to convert to AR4 GWPs.
While the LULUCF sector is not considered in CAT analysis, we do display emissions from this sector on the graph, these emissions do not include sinks stemming from land use (e.g. forests remaining forests).
Pledge for 2020
The reference level projections for the 2020 pledge are from the technical annex to Mexico’s National Climate Change Strategy from 2013 (Federal Government of Mexico, 2013). We used this baseline because it is included in Mexico’s national law as a reference for the pledge. We first calculated the pledge including LULUCF emissions. We then deducted the LULUCF emissions, as presented on the same document.
To quantify the absolute emissions level resulting from the NDC, we used the baseline provided in the NDC document. The document specifically states that emissions were calculated using Global Warming Potentials from the IPCC’s 5th Assessment Report. The CAT uses GWPs from the Fourth Assessment Report as a common reference. We were not able to convert the emission levels because the distribution of gases in the given baseline levels are unknown. Instead, we applied the growth rates from the NDC baseline scenario to the historical data (in AR4) starting after 2013. We then calculated the NDC contribution including LULUCF based on this harmonised baseline scenario. To exclude emissions from the LULUCF sector, we deducted the projected LULUCF emissions from the NDC baseline scenario.
Current policy projections
In previous analyses, we have quantified the impact of the PECC 2014-2018. The PECC was expected to achieve emissions reductions of about 83 MtCO2e in 2018 from a baseline of 1009 MtCO2e (in 2020, incl. LULUCF). The baseline scenario from the NDC, once harmonized to historical data, projects emissions of 808 MtCO2e in 2020, incl. LULUCF. The difference between the PECC and NDC baselines is nearly 150 MtCO2e, and so we assume that the reductions from the PECC are achieved in the NDC baseline and do not quantify the impact of the PECC further.
As a starting point for the current policy projections, we took the business as usual (BAU) scenario as reported in the documentation accompanying the NDC (Government of Mexico, 2015). From that scenario, we estimated a GDP compound average growth rate (CAGR) between 3.5–3.9%/yr. We consider this CAGR to be too high—in comparison, other GDP projections for Mexico estimate GPD growth between 2.6%/yr and 3.2%/yr (SENER, 2017b; OECD, 2018). We therefore, adapted the BAU from the NDC document by estimating the GHG emissions elasticity of GDP. For this, we took GHG emissions from the energy and industrial processes sectors (given lack of energy-related CO2 projections) as reported in the NDC BAU. We also estimated GDP values from the calculated CAGR. We only considered these two sectors as waste and agriculture emissions are often not directly linked to GDP growth. Then, we applied two different GDP forecasts from the Mexican government (SENER, 2017b). To this range, we added emissions from the waste and agriculture sector as reported in the NDC BAU scenario. This resulted in a range for the adapted BAU.
We took the adapted BAU and assessed three scenarios for the implementation of the clean energy targets and electricity generation through 2030. The scenarios assumed different electricity mixes based on the first three long-term energy auctions, and electricity generation projections from the Mexican government (SENER, 2017b). A first scenario assumes that the clean energy targets will be reached according to the fuel mix provided in the Energy Outlook by SENER (2017b). This includes a 7% share of nuclear in 2030 (which suggest a 250% increase in nuclear power generation compared to current values). In a second scenario, we assumed that generation from nuclear would remain constant to 2030 (as it is projected through 2027), and that the additional electricity would be generated using efficient cogeneration—which according to a Mexican regulation can emit up to 100 gCO2/kWh (Cámara de Diputados del H. Congreso de la Unión. Diario Oficial de la Federación, 2015). Mexico includes efficient cogeneration in its definition of clean energy, and has projected higher shares of cogeneration in the past (SENER, 2015b). In a third scenario, we have estimated the impact of long-term electricity auctions. We have assumed that long-term auctions will continue to happen at similar levels and frequency as the first three, that all awarded projects will be built and that these projects will operate at least four years after being awarded.
We estimate that the net effect of black carbon emission reductions additional to those resulting as a co-benefit from reductions in CO2 to be negligible. There is no established scientific method to compare the climate benefits of black-carbon reductions to those of CO2 and other greenhouse gases. The IPCC has not provided such estimates even in its most recent Fifth Assessment Report. Although the NDC does specify a metric to compare with CO2 (GWP of 900), this value is unsuitable to use in this policy context and the single literature source (Bond et al., 2013) to which the NDC refers to states:
- "… the summed climate forcing of all species for a source category emitting in a particular region (or season) may have a different magnitude than the global average, or even a different sign.”
- “The 100-year global-warming-potential (GWP) value for black carbon is 900 (120 to 1800 range) with all forcing mechanisms included. The large range derives from the uncertainties in the climate forcing for black carbon effects.”
- “Co-emission effects … are not captured by BC metrics presented here…”
- “These and other differences raise questions about the appropriateness of using a single metric to compare black carbon and greenhouse gases.”
The paper to which the NDC refers to (Bond et al. 2013) estimates that the combined global warming effect of black carbon and its co-emitted species is slightly negative and notes that the “reduction of aerosol concentrations by mitigating BC-rich source categories would be accompanied by small to no changes in short-term climate forcing.”
Note: this is not generally the case for certain other air pollutants (e.g. reductions in sulphate aerosols would lead to warming), so that while measures to reduce black carbon do not generally help to combat climate change, these are highly welcomed as a climate-neutral measure to improve local air quality, thereby reducing health impacts.