These aren’t satellite images and they don’t show evidence of mass cremations in Wuhan

“Chilling satellite pics ‘show extent of corpse burning in Wuhan’”

The Sun, 10 February 2020

“Coronavirus satellite image: Does THIS image show REAL scale of virus cremations?”

The Express, 10 February 2020

Multiple newspapers have claimed that satellite maps showing very high levels of sulphur dioxide (SO2) in areas of China affected by the new coronavirus may indicate the mass burning of dead bodies.

For example, The Sun reported that “Satellite maps in recent days have detected alarming levels of SO2 around Wuhan”, while Metro wrote that “The sheer scale of the number of bodies being cremated in China after the coronavirus outbreak can be judged by the cloud of sulphur dioxide that has appeared above affected cities, it has been claimed.”

These claims are wrong. The maps the claims are based on are not satellite images, and they do not show real, observed data on current levels of sulphur dioxide. NASA, which provided the data in the first place, told Full Fact that they are simply forecasts based on weather patterns and historical information about SO2 emissions.

Where the claim comes from

The claims originated on social media, including one particularly viral Twitter thread. They suggest that an apparent surge in SO2 levels above Wuhan and Chongqing, both cities affected by the outbreak of the new Covid-19 coronavirus, could be evidence of mass cremations, on the grounds that SO2 is released when a corpse is burned.

They are based on screenshots from a weather forecast site called Windy.com. In addition to standard weather forecast features, Windy offers options to display predictions for levels of various pollutants, such as particulate matter, nitrogen dioxide, and sulphur dioxide. The screenshots are of the sulphur dioxide three day forecasts for the Wuhan area from the weekend beginning Saturday, 8 February (you can see the equivalent current forecast here).

But (as was pointed out in a thread on Reddit) that’s all they are: forecasts. They don’t show what actually happened.

The data doesn’t include real-time observations

Windy.com says that the SO2 forecast uses data from NASA’s GEOS-5 atmospheric modelling system. Dr. Arlindo M da Silva, a research meteorologist from NASA’s Global Modeling and Assimilation Office, told Full Fact that the GEOS-5 sulphur dioxide models do not “assimilate real satellite data” into their forecasts, but instead are based on past evidence of emission levels.

“Our forecasts are based on fixed emission inventories,” he wrote in an email. “Although satellite data has been used in the construction of the emission inventories, these emissions do not account for the day-to-day variations in SO2 emissions and as such cannot account for sudden changes in human activity. In GEOS-5, day-to-day variations in SO2 are due to variations in the meteorological conditions, in particular winds.”

In other words, the maps in question are not based on any real-time observations; instead they are simply predictions based on weather patterns. As such they could not possibly show an unexpected event such as a mass cremation.