When COVID-19 disrupted the world’s economies last year, global carbon dioxide (CO2) emissions from fossil fuel use fell by two billion metric tons. As some of the lead scientists of the Global Carbon Project (an international group that tracks greenhouse gas emissions), we wrote about how to keep this emissions drop going, including how COVID presented opportunities to rethink transportation and why stimulus funds should be used to promote green rather than brown (fossil) energy use.

We also wrote: “Such emissions declines are enormous and unprecedented—but won’t last.” A car or airplane (or steel plant, for that matter) parked for a year will pollute just as much when it finally returns to service, and it takes years to replace fossil infrastructure with cleaner technologies.

We expected fossil carbon emissions to approach pre-COVID levels when global economic activity returned closer to normal. And now, as we present in papers available online in Earth System Science Data and arXiv.org, they have.

Our new reports suggest that by the end of 2021, global fossil carbon emissions will reach 36.4 billion metric tons of CO2, a rise of approximately 4.9 percent compared to 2020. This rebound not only cancels out the COVID-19-associated decrease of 5.4 percent we reported in 2020, but almost returns us to 2019 levels, when the world emitted 36.7 billion tons of CO2.

The rebound is troubling for several reasons. Some people hoped that the record drop in emissions last year would mark the beginning of the sustained decline in carbon emissions needed to keep global average temperature increases below 1.5 or 2 degrees Celsius. That doesn’t appear to be the case, at least yet, and won’t happen until more fossil fuel infrastructure is replaced by low-carbon technologies.

Because CO2 stays in the atmosphere for centuries, we need to lower fossil fuel–based carbon emissions to zero—or even remove carbon from the atmosphere—to keep temperatures from rising further. Another 36 billion tons of fossil carbon pollution this year (and any future year) is incompatible with a safe, stable climate. Climate scientists often say, “We’re running out of time,” but it’s true. If the goal is to limit global warming to 1.5 degrees C, we now have at most a decade’s worth of CO2 we can release into the atmosphere, based on current emissions. If we don’t meet that goal, we have perhaps 30 years’ worth of current emissions before the planet warms 2 degrees C.

Of all fossil fuels, coal and natural gas use contributed the most to this year’s emissions rebound, mainly in the industrial and power sectors. Coal use in 2021 is expected to rise above 2019 levels to 15 billion tons of CO2. Emissions from coal are now only slightly (less than 1 percent) below their 2013 peak. CO2 emissions from natural gas use in 2021 should also rebound above 2019 levels. Only CO2 emissions from oil will remain well below 2019 levels this year at about 11.5 billion tons of CO2.

The resurgence in emissions is global in scope but varies by country and economic sector. Based on data year-to-date, we expect fossil carbon emissions in Europe (EU27) and the United States to rebound by 8 percent in 2021 after declining more than 10 percent in 2020. Transport- and power-based emissions in the United States are still below 2019 levels, but industrial emissions have grown slightly. Europe’s transport and industrial emissions have also fully recovered, but its power sector remains well below 2019 levels. India’s fossil carbon emissions will jump almost 13 percent this year, just above 2019 levels, attributable to increases in its power sector that outweigh combined decreases that linger in its industrial and transport sectors.

China saw an even larger rebound in its emissions this year. Its estimated fossil emissions in 2021 are 11.2 billion tons of CO2, an increase of about 4 percent compared with 2020 emissions and 6 percent higher than in 2019. China’s post-COVID-19 economic recovery started earlier than in most other countries, and its emissions rebound began earlier, too. Its power and industrial sectors have rebounded the fastest. Coal use has jumped substantially this year in China; its COVID-19 recovery efforts appear to have stimulated activity in industries dependent on coal-fired power.

Some sectors will continue to see suppressed emissions globally, although those declines are largely offset by increased use in other parts of the global economy.

One sector of the global economy that remains strongly affected by COVID-19 is aviation. The International Civil Aviation Organization’s latest report released in October predicts that the number of airline passengers will remain 50 percent below 2019 levels this year. Aviation comprises only a few percent of global fossil carbon emissions, though, so even a decline by half this year is relatively modest in terms of absolute emissions (“only” half a billion tons of avoided carbon emissions).

There was at least some good news in the emissions data of 2020 and 2021. Renewables saw strong growth of 10 percent globally in 2020, despite declines in both global energy use and the use of all three fossil fuels (2 percent, 4 percent and 10 percent declines in 2020 for gas, coal, and petroleum, respectively). Moreover, almost two dozen countries that contribute about a quarter of global fossil carbon emissions saw their emissions decline significantly in the decade of 2010–2019 prior to COVID-19. This list of countries includes the United States, Mexico and Japan, as well as various nations in Europe, including the United Kingdom, France, Germany and Sweden. In general, we expect fossil carbon emissions to continue declining in these countries in the future.

What will happen in 2022? We can’t rule out a further rise in emissions, particularly if transportation returns to prepandemic levels and coal use remains near 2021 levels or, worse, rises further. The ultimate effect of COVID-19 on fossil carbon emissions remains uncertain and will depend on short-term economic incentives and climate policies. Fully one third of the $15–20 trillion in global economic stimulus packages already passed globally is going to fossil fuels and carbon-intensive heavy industries. Here in the U.S., unless the Build Back Better bill passes, very little of our stimulus spending will go to green energy and clean tech. As a result of stimulating fossil-based industries, carbon emissions are likely to continue rising.

COVID-19 demonstrated the scale of emissions reductions that are required, year after year, for climate stabilization. It also showed how much cleaner our air could be in a fossil-free world. Policy makers need to redouble efforts to shape emissions reductions more equitably in the future, without the economic disruption felt mostly by the global poor.

Like millions of people around the world, we’re watching the Glasgow climate change conference carefully. Pledges to end deforestation could reduce five or more billion tons of carbon dioxide pollution a year, while preserving global biodiversity. Additionally, at Glasgow, more than 40 countries have pledged to phase out coal use. Notable countries missing from the list include China, India, Australia and the United States.  

All authors are members of the Global Carbon Project, an international group of scientists tracking emissions of CO2 and other greenhouse gases from land, oceans, industry and agriculture.