Historical data is taken from Mexico’s National Inventory of Greenhouse Gases and Compounds (INEGyCEI in Spanish) (INECC, 2018). The inventory includes a complete series of national emissions from 1990 until 2015 and has additionally reported emissions for 2017 (excluding LULUCF). We interpolated emissions for 2016 assuming a continuation of the trend between 2015 and 2017. LULUCF emissions and captures have remain constant since 2011, so we assumed this will also be the case for 2016-2017.
Mexico’s emissions inventory was developed using the IPCC’s 2006 inventory guidelines and takes Global Warming Potentials (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 these to AR4 (Fourth Assessment Report) GWPs.
NDC and other targets
The NDC baseline is taken directly from the NDC submission, which reported emissions using AR5 GWPs (Gobierno de Mexico, 2020). We converted these numbers to AR4 GWPs using an average conversion factor from AR5 to AR4 based on the inventory’s granular information on all gases and sectors per year. We did not harmonise the NDC baseline scenario to the historical emissions pathway as the NDC target depends directly on the reference scenario included in the NDC (it provides absolute numbers linked to the targeted reduction).
We calculated the unconditional NDC target as the 22% reduction below the baseline scenario (including LULUCF emissions), as indicated in the NDC (Mexico reports LULUCF removals separately) (Gobierno de Mexico, 2020). Mexico did not provide information on the extent to which reducing LULUCF emissions will contribute to achieving its NDC target. To exclude LULUCF emissions, we assumed Mexico will achieve the same sink, as reported in the 2016 NDC, and have deducted that amount from the 22% emission limit. For the conditional target (36% below baseline), we assumed the same contribution for the LULUCF sector as for the unconditional target. A higher baseline and a constant contribution of the LULUCF sector lead to higher emissions level under the mitigation targets.
By contrast, if Mexico anticipates that the LULUCF sector will contribute the same percentage (rather than absolute amount) as provided for in the original NDC, Mexico’s unconditional target would remain the same as in its first NDC. This uncertainty only serves to highlight the need for countries to be transparent in the extent to which they intend to reply on the land sector to achieve their NDC targets.
The updated NDC submission also included an adaptation component as well as a target to reduce black carbon (BC) between 51%-70% below BAU. Given that reductions in BC are generally not additional to those in CO2 emissions, we do not quantify the additionality of the BC target (see box below on BC for more details).
Black Carbon and Mexico’s NDC
Mexico’s NDC includes a target to reduce black carbon (BC) emissions, which has substantial co-benefits for human health. However, reductions in black carbon are generally not additional to reductions in CO2 emissions, because large fractions of black-carbon emissions stem from the same emission sources as CO2. Emission reduction policies therefore often reduce CO2 and black carbon simultaneously, and this is already included in calculations of the emissions reductions in greenhouse gases required to hold warming well below 2°C globally, such as the “emissions gap” and “fair share” reductions.
From the climate perspective, however, there is no established scientific method to compare the climate benefits of black-carbon reductions to those of CO2 and other greenhouse gases. In the AR5, the IPCC does not provide calculations of GWP for BC comparable to those provided for greenhouse gases, merely noting the inherent difficulties in doing so and limiting itself to just displaying estimates from the pre-AR5 literature. While Mexico’s NDC specify a metric to compare BC with CO2 (GWP of 900), this is based on a single literature source (pre-dating IPCC AR5), which itself notes very large uncertainties of around 100%.
The long-term target is directly taken from the Mid-century Strategy (MCS) which provides absolute numbers for expected emissions in 2050. As the MCS does not provide further details on the LULUCF share to the target, we assumed 2050 LULUCF emissions will range between the emissions levels in 2030 for "baseline" and "unconditional target" scenarios from the NDC.
We converted the reported numbers from AR5 to AR4 GWPs using an average conversion based on the inventory’s granular information on all gases and sectors per year.
The reference level for the 2020 pledge is taken from the technical annex to Mexico’s National Climate Change Strategy from 2013 (Federal Government of Mexico, 2013). The numbers in this document were reported using GWPs from the IPCC’s Second Assessment Report (SAR). To convert these into AR4 GWPs, we estimated an average conversion factor from SAR to AR4 based on the inventory’s granular information on all gases and sectors per year.
Mexico’s 30% reduction below BAU includes LULUCF emissions. After calculating the absolute emission level with LULUCF, we deduct LULUCF emission (share based on numbers reported in the same document). Finally, we applied the conversion factor to go from SAR to AR4 GWPs.
Current policy projections
As a starting point for the current policy projections, we took the baseline scenario as reported in the NDC document and the 6th National Communication to the UNFCCC (Government of Mexico, 2015; SEMARNAT, 2019a). Although projected emissions under this baseline are quite high, we decided to use this time series based on the alarming fact that as of 2013, historical emissions as reported in Mexico’s inventory are higher than those under the NDC baseline. We converted these numbers to AR4 GWPs using an average conversion factor from AR5 to AR4 based on the inventory’s granular information on all gases and sectors per year. For the purpose of our calculations, we harmonised the NDC baseline scenario to the historical emissions pathway to obtain a continuous line until 2030.
The 6th National Communication provides a disaggregation of the reference scenario at the sectoral level, as well as the expected mitigation impact of major current policies for electricity, transport and buildings:
- Policies included for electricity sector: electricity policy “Prospectiva del Sector Eléctrico 2017-2031”
- Policies included for transport sector: actions included in the Clean Transport Program (namely Training in driving, fuel efficient technologies, fleet renovation)
- Policies included for building sector: policies aiming to reduce fuel and energy use in both commercial and residential buildings
Once again, we converted the expected mitigation impact to AR4 GWPs using the average conversion factor from AR5 to AR4. We then deducted this expected mitigation impacts from the respective sectoral reference scenarios for these three sectors and assumed no change compared to the baseline for waste, agriculture, industry and oil & gas sectors.
Based on current developments and the government’s roll back of policies that were put in place to support the clean energy targets (e.g. administration’s decision to modernize fossil fuel electricity generation, cancellation of the renewable energy auctions), we estimated a range based on the likelihood of implementation of the electricity policy (Prospectiva del Sector Eléctrico 2017-2031). The upper end assumes that Mexico will not achieve its clean electricity targets and the related mitigation potential; while the lower end assumes that they will, the policy’s mitigation impact is taken as reported in the 6th National Communication (SEMARNAT, 2019a). In both cases, we assumed the mitigation potential of transport and buildings policies would be achieved.
We applied a novel method to estimate the COVID-19 related dip in greenhouse gas emissions in 2020 and its impact until 2030. The uncertainty surrounding the severity and length of the pandemic creates a new level of uncertainty for current and emissions. We first update the current policy projections based on the most recent developments, before the pandemic. We then distil the emission intensity (GHG emissions/GDP) from this pre-pandemic scenario and applied it to the most recent GDP projections that take into account the effect of the pandemic.
The projections from the government of Mexico (Secretaría de Hacienda y Crédito Público), which projects a GDP decrease of -7.4% in 2020, were used to create the upper bound of our current policy projections, while the most recent GDP projections from the IMF expecting a decrease of -10.5% in 2020 and an increase of 3.3% in 2021, were used create the lower bound of our current policy projections (Forbes, 2020; IMF, 2020). We also considered the most recent GDP projections from the World Bank, but these fell within this range estimated as described above.
Global Warming Potentials values
The CAT uses Global Warming Potential (GWP) values from the IPCC's Fourth Assessment Report (AR4) for all its figures and time series. Assessments completed prior to December 2018 (COP24) used GWP values from the Second Assessment Report (SAR).
We estimate that the net effect of black carbon (BC) 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 BC 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 Mexico’s NDC does specify a metric to compare with CO2 (GWP of 900), we consider this value to be unsuitable for use in the policy context and the single literature source (Bond et al., 2013) to which the NDC refers, 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 in reference 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 the case for certain other air pollutants (e.g. reductions in sulphate aerosols would lead to warming), so while measures to reduce BC 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.