麻豆社

The space industry is already larger than you might think and it's growing fast.

There were almost 150 launches in 2021 alone, many of which involved deploying satellites to carry out relatively routine tasks like monitoring land-use changes and improving communication links, rather than the more headline-grabbing Moon landings that might first spring to mind.

In fact, the world is currently witnessing a "boom time" for space launches, space tourism and commercial spaceflights in the eyes of aerospace journalist Mike Killian. "Who knows what the tempo will be?" he added. "But we could be looking at 1,000 launches a year around the world, or it could be dramatically more than that."

Ramping up the frequency of space launches could have a significant impact on the environment. Pinpointing what the exact effect will be isn't easy, however, because there are so many variables involved.

A key consideration is what fuel is being used for the spacecraft, as different operators prefer different rockets, each of which rely on different types. Generally speaking though, the most common fuels emit nitrogen oxides and water vapour when the engines are fired up. Some also produce soot particles.

Nitrogen oxides harm the ozone layer, a thin part of the Earth's atmosphere that absorbs most of the damaging UV rays from the Sun. This could have serious consequences for people around the world.

"When nitrogen oxides are released into the stratospheric layer, they can contribute to depletion of ozone, where they can cause increased incidence of skin cancer," said Dr Eloise Marais, associate professor in physical geography at University College London.

It's taken decades of concerted effort to repair the ozone layer. An international agreement to phase out the use of ozone-damaging chemicals was reached way back in 1987 and, in January 2023, a UN-backed panel of experts reported that the ozone layer is on track to recover fully by around 2066. They also said that a 2016 amendment to the agreement, which required a phase down of the production of powerful greenhouse gases called hydrofluorocarbons, is expected to avoid up to 0.5C of global warming by 2100.

But some experts worry that space travel could fritter away these hard-won gains.

"Eloise thinks 30 years of progress to reduce the hole in the ozone layer could be substantially undermined with just 10 years of a large space tourism industry," explained presenter Jordan Dunbar.

The water vapour emitted from space rockets is another cause for concern.

According to Nasa Earth Observatory, water vapour is the most important greenhouse gas in the atmosphere. It traps the Sun's heat, causing the planet's temperature to rise. Put simply, more launches would mean more water vapour in the atmosphere, and consequently more global warming.

The soot particles, or black carbon, produced by some types of fuel also represent a significant risk to the environment.

"They [the soot particles] are about 500 times more efficient at warming the atmosphere than the black carbon that's emitted from surface sources," said Dr Marais. "Because rockets release these pollutants into multiple layers in the atmosphere, they tend to last for longer. And so for soot particles, we're releasing them closer to the Sun, and they don't have to compete with other things for the Sun's rays."

Scientists have been warning for years that soot particles from surface sources like cars, homes and factories contribute to climate change. If soot particles from rockets are 500 times more efficient at warming the atmosphere, even a relatively small upswing in launches could have big consequences for our planet.

Given the threat posed by nitrogen oxides, water vapour and soot particles, you could be forgiven for wondering what lawmakers around the world are doing about it.

"The fundamental rules [governing space] say very little about the environment," revealed Steven Freeland, emeritus professor of international law at Western Sydney University. It's possible the UN could adopt tougher regulations around the pollution caused by rocket fuel, but this would require the agreement of "100-plus countries" according to Freeland, who added: "And to be honest, the countries have other priorities."

Yet it's important to stress that the space industry does have some benefits too.

"We've talked a lot about space and climate harms," said Dunbar. "But it is also a major way for us to monitor things like deforestation, methane leaks and global temperatures, so we actually need the space industry to help fight climate change."

Ultimately, space travel is here to stay, and we can expect to see far more launches in the years ahead. But unless countries and companies take steps to cut emissions, this stellar growth could result in a giant leap backwards for the climate.

Listen to The Climate Question: Is space travel a problem for the climate?