Atmosphere / solar radiation

Roughly one-third of the incoming solar radiation is directly reflected back into space by the Earth’s atmosphere and surface albedo. Clouds play an important role in this, although their role is double as water droplets can also interfere with outgoing longwave radiation, thereby contributing to the greenhouse effect. Over open water clouds can make a particularly big difference as the albedo of the water is below 0.1, thereby absorbing most of the sun’s energy.

GHG emissions reductions and future negative emissions are the only sustainable solutions to stabilize or even reverse global warming as they counter the cause of the problem. However, the required actions will likely take time to materialize, and inertia in the climate system and locked-in warming already ensures major changes in global temperatures and the nearing of several tipping points. Solar radiation management (SRM) techniques seek to reduce global temperatures by reflecting incoming solar radiation. They would thereby not fix the underlying issue of the warming effects of GHGs but are, according to the United Nations Environment Programme (UNEP) Review on Solar Radiation Modification Research (2023), 'the only known approach that could be used to cool the Earth within a few years'.

With the exception of some regions like Antarctica, global snowfall amount and frequency have decreased, and the timespan during which snow cover remains has shortened (Zender 2012). This has multiple effects on human and natural systems as it influences widely diverging processes such as reducing surface albedo and changes in the hydrological cycle.