Here, we provide the methodological summary of our NDC quantifications. If you use this work, please use the citation below for now (we are working on a paper, so stay tuned).
Meinshausen, M, J. Lewis, J. Guetschow, Z. Nicholls, R, Burdon (2021), NDC factsheets, available at https://www.climate-resource.com/tools/ndcs
Our quantification of the NDCs starts from what countries submit to the official NDC portal at the United Nations Framework Convention on Climate Change. We then use officially reported inventory data. However, many of the officially reported datasets are rather sparse, so we complement it by using one of probably the world’s best compilation of third-party data, namely the PRIMAP database, specifically the dataset PRIMAP-hist TP, available at the page of our partners at the Potsdam Institute for Climate Impact Research. All of this underlying data is publicly available at the links above.
Conditional and unconditional, min-max
The Annex I countries - they tend to be the rich industrialised countries - are expected to state their targets unconditionally as nobody would really consider international support for those countries. They have sufficient historical responsibility and also the capability to reduce their emissions first and foremost. The same actually holds for a number of countries that have rich and industrialized economies, such as South Korea, Mexico or China. However, for many so-called developing countries, especially the least developed countries, the international community is expected to provide both technological and financial support. Thus, many of those developing countries will specify an unconditional target, which they implement purely with domestic resources. On top of that, conditional targets are specified. As a short-hand description, the targets that are labelled “conditional” are comprising both the unconditional and the conditional elements of the NDCs. A few countries also state ranges for their targets. For example, the (quite insufficient) targets that Australia put forward in Paris, a 26%-28% reduction below 2005 levels by 2030 are stated as a range. At other times, the quantification of targets is a bit uncertain, and alternative assumptions of some key underlying assumptions can lead to higher or lower 2030 emission level projections.
In these factsheets, we provide three different compilations. The first is the unconditional setting, ranging from the minimal to maximal unconditional NDC target. Often that unconditional NDC target is just a single emission level, not a range. The second is the conditional setting, ranging from the minimal to maximal emission level that would be in line with the full implementation of NDCs (full implementation of both conditional and unconditional elements). If the country does only have an unconditional NDC, then only that one is shown. The third setting is the min-max setting, ranging from the highest emission level of the unconditional target to the lowest emission level of the full implementation NDC (conditional and unconditional).
Inter- and extrapolations to 2030.
Our quantification of the NDCs goes through each submitted NDC document and attempts to decipher what the quantifiable future emissions for 2025, 2030, and 2050 are. In just a few cases, countries only submitted 2025 or even submitted only 2035 or even (in one case) 2040 targets. We then employ linear interpolations and extrapolations to derive the 2030 emission level.
Covered and non-covered emissions, and LULUCF
More and more countries present their NDCs as whole-economy targets, that comprise emissions from the energy sector (usually including transport etc), the industrial and process emissions, waste, and agriculture. On forestry, i.e. the so-called land-use, land-use change and forestry (LULUCF) emissions, the countries vary in their coverage. Anyway, if a country does not include, for example, the agricultural sector, then we assume reference level emissions for those non-covered emissions, as they are not subject to the NDC target. We source these reference level emission changes from the SSP5 reference, downscaled to a country-by-country emission level (Guetschow et al., 2021). Sometimes, when countries include LULUCF into their NDC target, and we have a “with measures” LULUCF projection (many countries in fact provide those), then we infer the implicit target for total emissions without LULUCF. For example, in the case of the US, you can see in the factsheets that there is a small thin line below the bold fat one. The bold fat one indicates total emissions without LULUCF and the thin line is the net emission line, i.e. total GHG emissions including the net uptakes that the USA reports for its LULUCF sector. The NDC targets in fact relate, in the case of the USA, to the net total emissions including LULUCF. However, given that countries report natural carbon cycle fluxes as part of their LULUCF emissions (Grassi et al. 2021), this reported LULUCF emission is inconsistent with indicators such as the remaining global carbon budget. Thus, our primary reference point in these NDC factsheets are total emissions without LULUCF.
The term 'hot air' was coined when Russia and other countries set themselves so unambitious targets that future emission levels would never overshoot them, even if not a single climate policy would be put in place. That hot air was then sold on the international market, leading to a substantial erosion of trust in international emission trading systems at the time of the Kyoto Protocol. Times have moved on and it is not standard practice any more to simply trade hot air. Nevertheless, a few countries, such as Turkey or a few developing countries, put forward targets that seem way out of tune with a normal increase of emissions, even if no climate policies were undertaken. That means that their NDC targets are almost certainly achieved, and overachieved by a large margin. Not because of emission reductions and climate policies but because of insufficiently ambitious NDC targets. Similar things can be said for Australia and its Kyoto Protocol targets by the way, but that is another story.
Anyway, in these factsheets, we provide you an option to approximate this 'hot air' effect. You can choose to exclude hot air, in which case we show the future emission levels that are the lower of the two: The NDC targets as the countries states them, or the SSP5-reference emission projections, as downscaled by our collaborator Johannes Guetschow (see Guetschow et al., 2021).
Per-capita emissions are calculated using the [median UN population projection] (https://population.un.org/wpp/). For international aviation, an approximation has been undertaken by dividing international aviation emissions by the number of people that approximately (before COVID) use international travel. While the total percentage of the world's population being in a plane is roughly estimated at 10-15% in any given year (and probably 80% of humanity have never flown), the fraction of people using international flights is more like 4% or 5%. Hence, per-capita emission levels for international aviation is shown relative to 5% of the world's population.