2021 remaining carbon budgets

 And 2020 is almost gone by…, with the smoke of the COVID-19 pandemic and its aftermath unable to completely shade the escalating impacts of climate change.

CO₂ emissions in 2020 have been high. Despite an estimated 7% reduction of energy-related emissions  because of the pandemic, LULUCF (Land Use, Land Use Change and Forestry) emissions have likely maintained its increasing trend with forests around the world burning as a consequence of global warming, poor management and irresponsible extractive policies. If we assume last year’s trend in LULUCF emissions is maintained, global CO₂ emissions in 2020 will be around 41 GtCO2/y, a barely 4% reduction from 2019.

Hence, the clock keeps ticking and the available carbon budget for any transition roadmap starting in 2021 will be reduced from the one that was available in 2020.

Figure-1 presents the 2021 carbon budget as function of global warming and the likelihood to limit global warming at these values. These carbon budgets have been derived from the IPCC 1.5SR  (which provides 2018 carbon budgets), updated with the 2018, 2019 and 2020 CO₂ remissions (from the Global Carbon Project, except for 2020 emissions that have been estimated assuming a 7% reduction in energy-related emissions and a trending evolution of LULUCF emissions), including the conservative estimate for earth system feedbacks reported in the IPCC 1.5SR and the estimate of the impact from the 2019 updated UK’s Met Office sea surface temperature (SST) database (HadSST4). In order to estimate the impact from the SST database update, we used the transient climate response to cumulative carbon emissions (TRCE) for each likelihood derived from the IPCC SR1.5.

Figure-1: Remaining carbon budgets for 2021, as function of global warming for different likelihoods (33%, 50% and 67%)

 

As Figure-1 shows, the remaining carbon budget for keeping global warming below 1.5^oC is quickly shrinking.

The 2021 carbon budget is the yardstick against which the cumulative emissions from any transition roadmap should be compared in order to check its climate consistency. As Figure-2 shows, this means that in order to have a 50% likelihood (the flip of a coin) to limit global warming to 1.5^oC, cumulative emissions from 2021 to 2100 should be below 250 GtCO₂. If the likelihood of success is increased to 67% (which should be a minimum policy goal in the face of the increased climate damages if warming goes beyond 1.5^oC), cumulative emissions should be below 109 GtCO₂. 

Figure-2: The carbon budget is the measuring stick to check the climate consistency of transition roadmaps. As of 2021, consistency with 1.5^oC global warming requires limiting cumulative emissions to 250 GtCO2 if a 50% likelihood of success is the policy goal, but to 109 GtCO2 if likelihood of success is increased to 67%.

In 2021 we’ll just go beyond the red line where just one hand’s fingers suffice to count the remaining years at current emissions level to exhaust the 1.5^oC carbon budget.