The streets of Wuhan, China, are deserted after authorities implemented a strict lockdown. In Italy, the most extensive travel restrictions are in place since World War Two. In London, the normally bustling pubs, bars and theatres have been closed and people have been told to stay in their homes. Worldwide, flights are being cancelled or turning around in mid-air, as the aviation industry buckles. Those who are able to do so are holed up at home, practicing social distancing and working remotely.

It is all aimed at controlling the spread of Covid-19, and hopefully reducing the death toll. But all this change has also led to some unexpected consequences. As industries, transport networks and businesses have closed down, it has brought a sudden drop in carbon emissions. Compared with this time last year, levels of pollution in New York have reduced by nearly 50% because of measures to contain the virus.

In China, emissions fell 25% at the start of the year as people were instructed to stay at home, factories shuttered and coal use fell by 40% at China’s six largest power plants since the last quarter of 2019. The proportion of days with “good quality air” was up 11.4% compared with the same time last year in 337 cities across China, according to its Ministry of Ecology and Environment. In Europe, satellite images show nitrogen dioxide (NO2) emissions fading away over northern Italy. A similar story is playing out in Spain and the UK.

Only an immediate and existential threat like Covid-19 could have led to such a profound change so fast; at the time of writing, global deaths from the virus had passed 20,000, with more than 400,000 cases confirmed worldwide. As well as the toll of early deaths, the pandemic has brought widespread job losses and threatened the livelihoods of millions as businesses struggle to cope with the restrictions being put in place to control the virus. Economic activity has stalled and stock markets have tumbled alongside the falling carbon emissions. It’s the precisely opposite of the drive towards a decarbonised, sustainable economy that many have been advocating for decades.

Renewable energy, often referred to as clean energy, comes from natural sources or processes that are constantly replenished. For example, sunlight or wind keep shining and blowing, even if their availability depends on time and weather.While renewable energy is often thought of as a new technology, harnessing nature’s power has long been used for heating, transportation, lighting, and more. Wind has powered boats to sail the seas and windmills to grind grain. The sun has provided warmth during the day and helped kindle fires to last into the evening. But over the past 500 years or so, humans increasingly turned to cheaper, dirtier energy sources such as coal and fracked gas.