An ambitious new project intends to carry out tests to determine whether seeding the atmosphere with aerosols could mitigate temperature rise in what would be the largest geoengineering study to date.

A couple of small-scale experiments, run by Harvard at a cost of £16 million ($20 million), will test how water droplets (and later calcium carbonates) sprayed in the stratosphere 20 kilometers (12 miles) up will reflect the Sun. The project's ultimate aim is to test whether the aerosol injections could be used as a latch-ditch attempt in the future should climate change spiral out of control. But the project has many people worried, as the impact of such widespread manipulation is so complex that it's difficult to predict the effects.

Harvard professor Daniel P. Schrag admits that the prospect of using solar geoengineering in real life is “terrifying” and the possibility of something going wrong is “really scary”, including a plethora of questions such as who controls it and at what level do you set the thermostat. But the point is we don’t have the answers to these questions and it is always better to be informed than to blindly conduct something as serious as geoengineering in the future.

“We need to find out and try and quantify aspects as soon as possible,” explains Frank Keutsch in a video announcing the study. “The worst scenario that we want to be in is that in 20 years down the road, we find ourselves in a situation where we say that the rate of change from climate change is so big that the cost to humans and the environment is unacceptable, and we are starting to be forced into a situation to do something to try and slow the rate of change.”

The researchers contend that spraying aerosols into the atmosphere could help to protect against the extremes that are likely to be faced if not enough is done to mitigate climate change. Yet other studies, such as one from the Met Office, discuss how seeding the atmosphere could instead induce severe droughts in North Africa, for example.

Whether or not the larger-scale Harvard study goes ahead is still not set. If it does, it will not take place for some time. The researchers first plan to use balloons to spray water into the atmosphere and then other particles such as calcium carbonate. Future research could even investigate whether diamond dust does the job.

But while limiting temperature is one of the major concerns of climate change, it is not the only one. High levels of carbon in the atmosphere are increasing the acidity of the oceans, and geoengineering won’t alter this. The concerns are that this will not stop climate change, just mask its effects.