A recent study by Bjorn Lomborg found that the combined Intended Nationally Determined Contributions (INDCs) Governments have submitted to the UNFCCC are only sufficient to reduce warming by 0.017 to 0.02°C by 2100.
The study massively underestimates the impact of INDCs on global emissions, and therefore warming, because it assumes emissions begin rising rapidly post-2030.
To estimate the impact of the Paris Agreement, an emission scenario including the INDCs must be compared with an emission scenario excluding the INDCs. INDCs are only defined until 2025/2030, so to estimate the temperature impact one needs to make assumptions on emissions after 2030. These emissions have a significant impact on temperatures in 2100.
The approach taken in the study by Bjorn Lomborg is incorrect because:
- The paper assumes a fast increase in emissions in the US, China and the EU after 2025/2030, catching up with business-as-usual levels. This assumption is not consistent with the near-term action indicated by INDCs: the effect of any policies and action put in place are assumed stop and reverse after 2030. Whilst the direct impact of the INDCs is in the near-term, the policies required to achieve the INDCs set the stage for longer-term transformation for the rest of the century. In not following this logic, Lomborg,ignores the current knowledge of energy systems and low-carbon transformation, and instead implies a rapid reversal of the changes required to implement the INDCs.
- After 2030, emissions are assumed to return to a business-as-usual scenario, rising more rapidly than ever in the US, China and the EU. This assumption results in higher emissions than is projected from current action at present. This means that not only is Lomborg completely ignoring the longer-term effect of INDCs, but is also discounting current policy action, assuming in effect that this reverses.
- A 2°C compatible scenario could never be reached with the Lomborg method: as it is assumed that the impact of INDCs is reversed after 2030, the method ensures that the impact on temperature in 2100 is minimal - even if the INDC levels were consistent with a 2°C compatible pathway in 2025 and 2030.
- An example of one of the many flaws in this paper is the calculation around China. An important element of China’s INDC is to peak CO2 emissions. Lomborg’s paper assumes that China’s GHG emissions will continue increasing until the end of the century. It therefore either assumes that all emissions other than CO2 will increase by up to roughly 10 GtCO2e by 2050—which is absurd—or incorrectly assumes that China will not achieve its INDC, thereby missing a significant impact on the global temperature.
To put the analysis of Lomborg in an analogy: Say, we want to travel from Beijing to Paris and want to arrive in three weeks, in time for the COP. We have planned the route until Moscow and agree to plan the last part of the route further down the road. According to Lomborg, we will not arrive in Paris, because he assumes we do not only stop travelling in Moscow, but he also assumes we return and travel back east.
What CAT is doing is looking at whether we can be in time in Moscow (GHG emissions in 2030) to allow a timely arrival in Paris (keeping global temperature rise below 2°C by 2100).
The above issues are just some of the problems with the approach and method taken, but are the most fundamental.
Some of our colleagues from around the world have also taken a look at the study and come to similar conclusions:
- Bob Ward at LSE blog post: “A recent climate change publication is ideology masquerading as scholarship”
- Malte Meinshausen at the university of Melbourne’s Facts4Paris
- Joe Romm of Climate Progress article “Bjorn Lomborg’s New Paper ‘Appears To Have No Basis In Fact’“