Monitoring global carbon emissions!

These 2021 emissions consumed 8.7% of the remaining carbon budget for limiting anthropogenic warming to 1.5 °C, which if current trajectories continue, might be used up in 9.5 years at 67% likelihood.

Global CO₂ emissions have exhibited a rapid increase (Fig. 1). However, embedded within this long-term trend are inter annual fluctuations arising from global energy, finance and health crises. For example, during 2020, global lockdowns owing to the COVID-19 pandemic temporarily reduced CO₂ emissions. The Carbon Monitor program — which provides near-real-time daily global CO₂ emissions from power generation (29 countries), industry (73 countries), road transportation (406 cities), aviation and maritime transportation, and commercial and residential sectors (206 countries) — offers an opportunity to track the evolution of these CO₂ emissions, and in doing so, assess remaining carbon budgets and progress in reaching the Paris Agreement. Here, we document the status of CO₂ and fossil CH₄ emissions for 2021, revealing a rebound from COVID-related 2020 reductions and a corresponding decrease in the remaining CO₂ budget.

Temporal evolution of historical CO₂ emissions⁵ (navy; including emissions from fossil fuel combustion and the process of cement production), near-real-time CO₂ emissions (red), projected CO₂ emission mitigation pathways (dark blue and aqua), and historical fossil CH₄ emissions^4] (light blue; 1970–2018 data from EDGARv6.0, scaled to 2021 with IEA data). Solid/dashed lines and shading represent the median and range, respectively. The inset depicts daily near-real-time CO₂ data over 2019 to 2021, and the corresponding year-on-year changes in annual CO₂ emissions. Current emission trends will use up the allowed future emissions for limiting anthropogenic warming to 1.5 °C (the remaining carbon budgets) within 10 years.

One of the key features of 2021 global CO₂ emissions is the rebound from 2020 levels (which exhibited a reduction from 2019 associated with COVID-19-related lockdowns. In particular, global annual emissions increased from 33.3 GtCO₂ in 2020 (with a range of 33.0–33.6 GtCO₂; including the leap day of February 29, 2020) to 34.9 GtCO₂ (with a range of 34.6–35.2 GtCO₂) in 2021, representing a 4.8% increase (3.8–5.7% range). Despite rising case numbers and new variants, the impact of the COVID-19 pandemic on CO₂ emissions therefore appears to be less in 2021 compared to 2020 owing to a reduction in restrictive policies.

These rebounds are apparent in most sectors and big emitting nations. For instance, 2021 emissions from power, industry and ground transport (the largest emitters) rebounded by 5.0% (657 MtCO₂), 2.6% (256 MtCO₂) and 8.9% (513 MtCO₂) from 2020 levels, respectively; collectively, these sectors contribute 89% (1.4 GtCO₂) of the total global rebound. However, the largest rebounds occurred in the aviation sector, including 25.8% (65 MtCO₂) and 18.1% (50 MtCO₂) increases from domestic and international aviation. At the country level, 2021 emissions in China, the USA, the 27 European Union countries (EU27) and the UK, India, and Russia, also rebounded by 5.7% (597 MtCO₂), 6.5% (296 MtCO₂), 6.7% (193 MtCO₂), 9.4% (212 MtCO₂), and 6% (91 MtCO₂) from 2020 levels, respectively. Among the top emitters, Japan was the only country not to exhibit a substantial rebound; here, emissions dropped 4.7% (51 MtCO₂) from 2019 levels in 2020, and 5% (54 MtCO₂) from 2019 levels in 2021.

Methane (CH₄) emissions, a short-lived climate forcer with larger comparative impact than CO₂, also exhibited substantial changes (Fig. 1). Similar to CO₂, fossil-related methane emissions dropped by 5.7% from 2019 to 2020, but then rebounded by 3.7% in 2021 owing to increased demand of natural gas and other fossil fuels⁴.

Although the amplitude of CO₂ and CH₄ changes (the initial drop and subsequent rebound) are unprecedented, such crises and rebounds are not unique. Indeed, since the 1970s there have been global events in every decade that caused temporary negative growth in global CO₂ emissions⁵: the energy (oil) crises of 1974, 1980–1982 and 1992, and the financial crisis of 2008. In all cases, emissions rebounded substantially after the event, shifting the downward trend such that average decadal growth rates were 3%, 1%, 1%, 3% and 2% for each decade since the 1970s. Thus, while there was a record CO₂ decline in 2020, the rebound in 2021 could signal that history is being repeated, reducing confidence in global climate mitigation actions.

Guest Editorial