Humans have seemed unable to get a handle on climate change, with global emissions of greenhouse gases continuing to grow every year. But a microscopic pathogen, so structurally simple that it does not even have a single cell and is arguably not even alive, may be capable of accomplishing what our political leaders thus far cannot.

Experts say greenhouse gas emissions in China, the world’s largest current contributor to climate change, are down 25 per cent in recent weeks as the country conducted a massive societal intervention to stop the spread of the virus. Air pollution is also down, due to decreased driving and less coal burning.

Meanwhile, as the virus enters a second phase, spreading beyond China to other countries, it is dampening global demand for oil and air travel, and threatening overall global economic growth. All of these are strongly linked to greenhouse gas emissions.

While it’s too early to say for sure, if these trends continue, the coronavirus could join rare company.

Since the year 1900, greenhouse gas emissions have risen dramatically. During that period, the escalation of emissions has been nearly constant, with 2019 projected to set yet another record high. And when significant declines have happened, it’s usually been because of sweeping economic contractions or large-scale geopolitical events such as the fall of the Soviet Union.

When it comes to an emissions decline, “whatever the driver, it will have to be big, and global,” says Glen Peters, an expert on carbon emissions at Norway’s Centre for International Climate Research and a contributor to the Global Carbon Project.

The last time global emissions fell noticeably was in the wake of the Great Recession, from 2008 to 2009 – when US GDP fell 4.3 per cent, unemployment doubled from 5 to 10 per cent, housing prices crashed and the stock market lost, at the nadir, more than half of its value. But even in that moment of economic and societal trauma, the global emissions decline was fleeting. Emissions started to rise again almost immediately.

Still, if the current emissions contraction that happened first in China spreads around the world, and is sustained, then it might cause a similar impact.

Elizabeth Economy, a China expert at the Council on Foreign Relations, says the nation’s emissions have increased every year for the past three until coronavirus paralysed entire regions. “If there is a bright side to the coronavirus,” she says, “it is that the drop in industrial production, manufacturing, and automobile use will produce a noticeable drop in CO2 emissions for at least the first two months of the year.”

Granted, the bounce back could be rapid if China tries to juice its economy through some type of stimulus once the situation stabilises. South Korea has already enacted roughly $10bn (£7.6bn) in stimulus in the wake of the virus’s spread, and Italy is planning an infusion of $8.4bn.

“The reductions are substantial, but they are most certainly only temporary, and there will likely be a rebound effect,” says Joanna Lewis, an expert on China’s energy sector at Georgetown University. “Once people go back to work and factories restart, they may try to make up for lost time. This could result in a surge in emissions.”

Still, the change since the start of the year in the world’s most greenhouse-gas-intensive economy has been striking to behold.

Lauri Myllyvirta, lead analyst at the Centre for Research on Energy and Clean Air, found that carbon emissions in China are down at least a quarter over the month of February. He estimates it amounts to a reduction of 200 million tons of carbon dioxide compared with emissions levels in 2019.

Concentrations of nitrogen dioxide, or NO2 – which are produced by cars, trucks and energy-intensive industries – are down about 40 per cent during the same stretch, he found. In addition, small-particle air pollution also has fallen across the country.

Airports empty as Coronavirus affects aviation industry Show all 11 1 /11 Airports empty as Coronavirus affects aviation industry Airports empty as Coronavirus affects aviation industry Ben Gurion International airport, Israel Empty El Al Israel Airlines check-in counters are seen at Ben Gurion International airport in Lod, near Tel Aviv, Israel February 27, 2020. REUTERS/Amir Cohen AMIR COHEN Reuters Airports empty as Coronavirus affects aviation industry Daxing International Airport, Beijing This picture taken on February 14, 2020 shows two men wearing face masks walking through a nearly empty terminal at Daxing international airport in Beijing, as travel has ground to a halt in the wake of the the COVID-19 coronavirus outbreak. (Photo by NICOLAS ASFOURI / AFP) (Photo by NICOLAS ASFOURI/AFP via Getty Images) NICOLAS ASFOURI AFP via Getty Airports empty as Coronavirus affects aviation industry Taoyuan International Airport, Taiwan epa08238057 The empty departure hall of the No 2 Terminal at the Taoyuan International Airport in Taoyuan City, northen Taiwan, 22 February 2020. The coronavirus causing COVID-19 disease which originated from Wuhan, China, has devastated Taiwan's tourism and aviation industries, forcing airlines to cancel flights and travel agencies to lay off workers or close. EPA/DAVID CHANG DAVID CHANG EPA Airports empty as Coronavirus affects aviation industry Noi Bai International Airport, Vietnam A woman walks in the nearly empty arrival hall of Noi Bai International Airport in Hanoi on February 27, 2020, as the number of air travellers has plummeted amid fears over the spread of the COVID-19 coronavirus. (Photo by Mladen ANTONOV / AFP) (Photo by MLADEN ANTONOV/AFP via Getty Images) MLADEN ANTONOV AFP via Getty Airports empty as Coronavirus affects aviation industry Haneda Airport, Tokyo A man wearing protective face mask, following the outbreak of the coronavirus, pushes his luggage past desks, closed for construction, at Haneda Airport in Tokyo, Japan, March 4, 2020. REUTERS/Stoyan Nenov STOYAN NENOV Reuters Airports empty as Coronavirus affects aviation industry Changsha Huanghua International Airport, China A woman wearing a face mask stands in the empty luggage collection hall at the airport in Changsha, Hunan Province, as the country is hit by an outbreak of a new coronavirus, China, January 27, 2020. REUTERS/Thomas Peter THOMAS PETER Reuters Airports empty as Coronavirus affects aviation industry Shanghai Pudong Airport in Shanghai, China epaselect epa08194188 A passenger wearing a protective mask stands in the empty hall of Shanghai Pudong Airport in Shanghai, China, 04 February 2020 (issued 05 February 2020). Major global airlines have canceled their flights to mainland China to contain the spread of the deadly coronavirus, which has so far killed at least 493 people and infected more that 24,000, mostly in China. EPA/ROMAN PILIPEY ROMAN PILIPEY EPA Airports empty as Coronavirus affects aviation industry Daxing International Airport, Beijing This picture taken on February 14, 2020 shows a salesclerk wearing a protective face mask and gloves (R) at an empty duty free shop at Daxing international airport in Beijing, as travel has ground to a halt in the wake of the the COVID-19 coronavirus outbreak. (Photo by NICOLAS ASFOURI / AFP) (Photo by NICOLAS ASFOURI/AFP via Getty Images) NICOLAS ASFOURI AFP via Getty Airports empty as Coronavirus affects aviation industry Haneda Airport, Tokyo An empty departures gate is pictured at Haneda Airport in Tokyo, Japan, March 4, 2020. REUTERS/Stoyan Nenov STOYAN NENOV Reuters Airports empty as Coronavirus affects aviation industry Shanghai Pudong Airport in Shanghai, China epa08194181 Passengers wearing protective masks sit in the empty hall of Shanghai Pudong Airport in Shanghai, China, 04 February 2020 (issued 05 February 2020). Major global airlines have canceled their flights to and from mainland China to contain the spread of the deadly coronavirus, which has so far killed at least 493 people and infected more that 24,000, mostly in China. EPA/ROMAN PILIPEY ROMAN PILIPEY EPA Airports empty as Coronavirus affects aviation industry Noi Bai International Airport, Vietnam Passengers with protective facemasks walk with their luggage in the empty arrival hall of Noi Bai International Airport in Hanoi on February 27, 2020, as the number of air travellers has plummeted amid fears over the spread of the COVID-19 coronavirus. (Photo by Mladen ANTONOV / AFP) (Photo by MLADEN ANTONOV/AFP via Getty Images) MLADEN ANTONOV AFP via Getty

Myllyvirta says that while emissions have rebounded a bit over the past week, “it’s still very far from normal levels”. “Oil demand and demand for things like coal and steel have fallen,” he says. “The impact on many of the major industrial sectors is very profound.” He says sales of real estate are likely to fall sharply over the first quarter of the year in China. The outbreak will affect construction projects and investment decisions for months to come, all factors that could hinder economic growth and slow down emissions.

The effects seen in China may ripple around the world. The International Air Transport Association recently announced that global January air travel, while still showing growth, saw “the lowest monthly increase since April 2010”. And February’s figures could be even worse.

United Airlines recently announced plans to cut domestic flights by 10 per cent and international ones by 20 per cent for April and May. It’s asking staff to volunteer for unpaid leaves to help adjust for the decline in revenue. Aircraft account for roughly 3 per cent of total US greenhouse gas emissions, so changes here could have a major impact.

“I expect where the coronavirus is going to be hitting is one of the more energy-intensive aspects of the economy, which is travel,” says Kenneth Gillingham, a professor of economics at Yale University. “I do expect emissions to decline,” Gillingham adds. “Not that I think that that is a particularly good thing in this context because the coronavirus is an absolute tragedy.”

Meanwhile, the Organisation of the Petroleum Exporting Countries (Opec) and the International Energy Agency both recently lowered their forecasts for oil demand in 2020, thanks to coronavirus. On Thursday, Opec proposed cutting production by an additional 1.5 million barrels a day through the end of the year, which would be the biggest cut since the 2008 financial crisis. The OECD, meanwhile, said that in a scenario of broad global spread of the virus, economic growth could only tally 1.5 per cent in 2020, as opposed to a prior prediction of 3 per cent before the outbreak occurred.

That itself is revealing, though, notes Peters from Norway’s Centre for International Climate Research. “If global growth goes from 3 per cent to 1.5 per cent, then it is very low by historical standards, but nowhere near as low as negative growth from the financial crisis,” Peters says.

There’s evidence of emissions declining from 1918 to 1919 in the wake of the deadly Spanish flu (AFP) (AFP/Getty)

From 2008 to 2009, during that seismic economic event, global emissions declined about 1.4 per cent, according to figures from Peters and the Global Carbon Project. That’s equivalent to a reduction of about 450 million tons of carbon dioxide. But then growth quickly resumed, and 2018’s global emissions, nine years after that downturn in 2009, were 16 per cent higher. That’s equivalent to an additional 5 billion tons of CO2 per year.

The Global Carbon Project’s data show even larger temporary declines, on a percentage basis, in the past during moments of global upheaval.

Take the Great Depression – the longest-lasting and most severe economic decline affecting the United States and the world since 1900. US unemployment climbed as high as 25 per cent and thousands of banks failed. Global emissions, which were then far lower, dropped 25 per cent from 1929 to 1932 and did not exceed their 1929 levels again until 1937.

There’s also evidence of an emissions decline from 1918 to 1919, in the wake of the deadly Spanish flu, the worst pandemic of the modern world – 50 million people around the globe died. At least initially, this looks like a clear case of a biological event, rather than an economic, political or military one, driving down emissions – which shrank by more than 400 million tons of carbon dioxide in just one year.

However, that period came in the immediate wake of the First World War, and it isn’t clear that the decline was solely due to the pandemic. Emissions also fell as combatants laid down arms, explains Robbie Andrew, also a researcher at Norway’s Centre for International Climate Research. Peace also brought an end to wartime spending and a contraction of the emission-intensive steel and arms industries.

“The years immediately after the First World War are likely to show a combination of effects that overlapped,” he says.

Other episodes of emissions declining or flattening underscore that thus far in history, it has generally required a massive societal or economic upheaval for such a decline to occur. In October 1973, Opec retaliated against the United States for its role in the Arab-Israeli war, imposing an oil embargo. The oil cartel slashed production, quadrupling crude prices, fuelling inflation broadly, squeezing consumers and throwing the world into recession throughout 1974. It was then the deepest four-year downturn since the mid-1940s. And greenhouse gas emissions declined slightly for a few years.

In 1978, another “oil shock”, this time stemming from the Iranian Revolution and the drop in its oil output, badly hurt the global economy at the worst possible time. In the face of soaring inflation and the falling value of the dollar, the Federal Reserve slammed on the brakes, raising interest rates as high as 19 per cent in 1981. Inflation eased by the end of 1982. At the time, it was the most severe recession since the Great Depression. Emissions declined for three years and did not exceed their 1979 levels until six years later, in 1985.

In the early 1990s, the world economy suffered from a US slowdown and the collapse of the Soviet Union – leading, once again, to a modest and temporary emissions decline. Myllyvirta says the parallels to past episodes when the world has seen its emissions fall are limited. A pandemic, after all, is hardly a humane, desirable or logical way to count on combating climate change.

“To reduce emissions in a sustained way, you need the world to run in a clean way – and forever,” he says. “You can’t just lock everyone in their homes and say you shouldn’t go to work.”

“A complete switch from coal to low-carbon generation – or a modest carbon pricing policy – can provide emissions reduction on the same order of magnitude as a war, recession or pandemic,” Gillingham added. “This provides at least a sliver of a reason for optimism.”