In June, a team of Harvard scientists is planning to launch a high-altitude balloon from Kiruna in Lapland to test whether it can carry equipment for a future small-scale experiment on radiation-reflecting particles in the Earth's atmosphere.

An independent advisory committee will rule on whether to approve the balloon test flight by 15 February. Swedish environmental groups have written to the government and the Swedish Space Corporation (SSC) to voice their opposition.

In the letters, seen by the Guardian, organisations including the Swedish Society for Nature Conservation, Greenpeace Sweden and Friends of the Earth Sweden said that while the balloon flight scheduled for June does not involve the release of particles, it could be the first step towards the adoption of a potentially "dangerous, unpredictable, and unmanageable" technology.

Stratospheric aerosols are a key component of solar geoengineering technology that some have proposed as a plan B for controlling the Earth's temperature if the climate crisis makes conditions intolerable and governments do not take sufficient action.