Marine Cloud Brightening – This aims to limit the effects of climate change by spraying small particles, such as sea salt, into the air over the oceans, to make clouds brighter. These clouds would reflect sunlight away from the Earth, which could cool temperatures on a local or regional level. Marine cloud brightening might also help to protect ecosystems threatened by climate change. One way to spray the particles would be to use a fleet of ships. But for it to work, we would have to keep doing it continuously. If we stopped, temperatures would rise once again. Also, marine cloud brightening would not do anything to reduce greenhouse gas emissions or help with other impacts, such as ocean acidification.

Space-based Geoengineering – This aims to limit the effects of climate change by putting a giant mirror or other reflective material in outer space between the Earth and the sun. Such a space mirror or sunshield would deflect sunlight back into space. This could cool temperatures on Earth. This would avoid direct changes to the land, oceans, or atmosphere of the Earth itself. But for this idea to work, we would need to be able to build and maintain something in space much larger than ever before. A space mirror would also be very costly to build, given that its location would be about four times as far from the Earth as the Moon. Also, it would not do anything to reduce our greenhouse gas emissions or help with other impacts, such as ocean acidification