The chapter on mitigation measures (WG3) of Assessment Report 6 presents 8 new emissive scenarios. Those that meet the target of 1.5 at C all foresee an overrun, even if temporary. And the peak of carbon to 2025, more drastic reductions in fossil use
Only 2 virtuous scenarios according to the IPCC climate report
(Sustainabilityenvironment.com) – There is now almost absolute certainty that we will overcome 1.5 degrees of global warming. Even if temporarily and remaining below 2°C. This was reiterated in the IPCC climate report published yesterday, in the third and last chapter dedicated to climate change mitigation measures that we have available. In the more than 3000 pages of the section of Assessment Report 6 prepared by Working Group 3, the authors summarize the most up-to-date climate science and present the possible emissive scenarios.
C1: the most optimistic emissive scenario
In scenario C1, the Intergovernmental Panel on Climate Change inserts some emissive paths that are defined as the most optimistic. All predict that they will reach 1.6 degrees of global warming with a probability of 50%, and then arrive at 1,2-1,4°C in 2100. There is, therefore, overshooting, although very limited.
To follow these paths, the planet must reach the peak of emissions between 2020 and 2025 and limit annual greenhouse gas emissions to 29-33 billion t of CO2 equivalent (GtCO2e) to 2030, 16-18 GtCO2e to 2040, and 8-9 GtCO2e to 2050. To better understand, just think that, in 2019 we issued about 55 GtCO2e. In this way, we would have virtually the certainty of remaining below 3°C of global warming, and a very high probability (85-98%) of staying lower than 2°C. While the probability of staying really below 1.5 degrees would vary between 33 and 58%.
This is the category with the most drastic cuts and with less possibility of relying on technologies to remove CO2 from the air. “Modelled global pathways that limit heating to 1.5% C (>50%) without or with limited overshoot result in faster and deeper short-term greenhouse gas emission reductions until 2030, and are expected to have less net negative emissions of CO2 and less carbon dioxide (CDR) removal in the long term, compared to routes that bring heating back to 1.5°C (>50%) after a high overshoot (category C2)“, reads the report.
C2: below 1.5°C, but in extremis
The scenario called C2 foresees that the overshoot of the threshold of 1.5 degrees is consistent and prolonged, even if in the long run the global temperature returns below this threshold always with a probability of 50%. In this case the overshoot reaches 1.8 degrees and in 2100 the temperature of the Planet is 1.2-1.5 degrees.
To get back on this path, we have to go down from 55 GtCO2e in 2019 to 42 in 2030, 25 in 2040 and 14 in 2050. The carbon peak here is given on average around 2025 but with some margin to exceed towards 2030, while in 2025 it must take place that of other greenhouse gases (such as methane).
In this scenario, as in C1, “the global use of coal, oil and gas in 2050 should decrease with median values of about 95%, 60% and 45% compared to 2019”, writes the authors of the IPCC climate report.
C3 and C4: global warming below 2 degrees
In this group of emissive routes, global warming is kept below the highest threshold established by the Paris agreement The C3 does it with a percentage of 67% and requires cutting emissions to 44 GtCO2e (2030), 29 (2040) and 20 (2050) reaching the peaks of CO2 and other greenhouse gases as in C2. Carbon neutrality is only really achieved in 2070-2075.
All scenarios described so far “involve rapid and deep reductions and in most cases immediate greenhouse gas emissions in all sectors“, the IPCC climate report reiterates. Mitigation strategies to follow these paths include “the transition from fossil fuels without CCS to very low or zero-carbon energy sources, such as renewable energy or fossil fuels with CCS, demand-side measures and efficiency improvement, the reduction of non-CO2 emissions and the use of carbon dioxide (CDR) removal methods to counteract residual greenhouse gas emissions“.
As for the fate of fossils, in these scenarios, they must drop considerably by 2050: by 85% coal, by 30% oil, by 15% gas. These are roughly the scenarios we would be moving on if the promises made at COP26 were to be respected and put into practice.
Worst-case scenarios in the IPCC climate report
Scenarios from C5 to C8 predict global warming of 2.5°C, 3°C, 4°C and again 4°C but with a further increase beyond 2100. The first 3 describe in a rather adherent way the trajectory on which we find ourselves today. It is the result of the implementation of policies decided until 2020, but without any strengthening in the current decade. In practice, looking at Europe, is like fulfilling our climate commitments to the letter before the Green Deal.
In scenarios from C6 to C8, during this century no goal of carbon neutrality and not even a temperature peak is achieved. If in the 2 worst routes (C7 and C8), the emission peak arrives only in 2080-2095, for the path C6 that limits the heating to 3 system C the peak must however arrive by 2035.
