large-scale manipulation of the Earth's environment

The deliberate large-scale manipulation of the Earth's environment, called geoengineering, could be one way to cool the Earth or help reduce levels of carbon dioxide in the atmosphere.

But scientists are aware that these technologies are in very early stages of development and remain untested on a global scale.

Although there are great risks in deliberately interfering with nature to cool the planet, some researchers say that if the concentrations of carbon in the atmosphere reach a critical stage, geoengineering might become the only way to take control of our climate.
On the other hand, others worry that having the technology to "reverse" climate change could be seen as a get-out-of-jail-free card and that more effort should be put on existing ways of reducing emissions.

Steve Rayner of the Oxford Geoengineering Programme, UK, says that there is no easy answer, but it would be "irresponsible for us not to explore the potential to understand the technologies as best we can".

Geoengineering refers to the deliberate large-scale manipulation of the Earth's environment to counteract climate change.

There are essentially two ways of doing this.
The first is called Solar Radiation Management (SRM) and involves reflecting more of the Sun's rays away from the planet back into space.

Model cloud whitening ship Cloud-whitening would aim to reflect more of the Sun's heat back into space

One proposed method of SRM involves putting sulphur aerosols into the high reaches of the atmosphere.

This mimics what occasionally occurs in nature when a powerful volcano erupts. For example, the Mount Pinatubo eruption in 1991 injected huge volumes of sulphur into the stratosphere. The particles produced in subsequent reactions cooled the planet by about 0.5C over the next two years by reflecting sunlight back out to space.

Solar radiation management (SRM)
Albedo enhancement: Increasing the reflectivity of clouds or the land surface so that more of the Sun's heat is reflected back into space

Space reflectors: Blocking a small proportion of sunlight before it reaches the Earth
Stratospheric aerosols: Introducing small, reflective particles into the upper atmosphere to reflect some sunlight before it reaches the surface of the Earth
Carbon dioxide removal (CDR)
Afforestation: Global-scale tree-planting efforts
Biochar: Burning biomass (plant material) and burying it so that its carbon is locked up in the soil
Bio-energy with carbon capture and sequestration: Growing biomass, burning it for energy and capturing and locking away the CO2 generated in the process
Ambient air capture: Building machines that can remove CO2 directly from ambient air and store it elsewhere

Ocean fertilisation: Adding nutrients to the ocean in selected locations to increase marine food production, which draws down CO2 from the atmosphere
Enhanced weathering: Exposing large quantities of minerals that react with carbon dioxide in the atmosphere and storing the resulting compounds in the oceans or soil