Climate engineering

[9][8][10] Climate engineering (or geoengineering) has been used as an umbrella term for both carbon dioxide removal and solar radiation management, when applied at a planetary scale.

Enhancing the solar reflectance and thermal emissivity of Earth in the atmospheric window through passive daytime radiative cooling has been proposed as an alternative or "third approach" to climate engineering[25][49] that is "less intrusive" and more predictable or reversible than stratospheric aerosol injection.

In 2021 the US National Academies of Sciences, Engineering, and Medicine (NASEM) requested $2.5 billion funds for research in the following decade, specifically including field tests.

[64] Enriching seawater with calcium hydroxide (lime) has been reported to lower ocean acidity, which reduces pressure on marine life such as oysters and absorbs CO2.

The added lime raised the water's pH, capturing CO2 in the form of calcium bicarbonate or as carbonate deposited in mollusk shells.

[33] Enhancing the natural marine sulfur cycle by fertilizing a small portion with iron—typically considered to be a greenhouse gas remediation method—may also increase the reflection of sunlight.

[67][68] A proposal from 2018 included building sills at the Thwaites' grounding line to either physically reinforce it, or to block some fraction of warm water flow.

[69][68] They also acknowledged that this intervention cannot prevent sea level rise from the increased ocean heat content, and would be ineffective in the long run without greenhouse gas emission reductions.

[76] However, several public opinion surveys and focus groups reported either a desire to increase emission cuts in the presence of climate engineering, or no effect.

Some religious traditions express views on the relationship between humans and their surroundings that either encourage or discourage explicit actions to affect climate, depending on the objective.

[12][85] Some environmental organizations (such as Friends of the Earth and Greenpeace) have been reluctant to endorse or oppose solar radiation modification, but are often more supportive of nature-based carbon dioxide removal projects, such as afforestation and peatland restoration.

In 2009, the Royal Society in the UK reviewed a wide range of proposed climate engineering methods and evaluated them in terms of effectiveness, affordability, timeliness, and safety (assigning qualitative estimates in each assessment).

[92] Nonetheless, the report also recommended that "research and development of climate engineering options should be undertaken to investigate whether low-risk methods can be made available if it becomes necessary to reduce the rate of warming this century".

The authors found that "[air] capture and storage shows the greatest potential, combined with afforestation, reforestation and bio-char production", and noted that "other suggestions that have received considerable media attention, in particular, "ocean pipes" appear to be ineffective".

The differences between these two classes of climate engineering "led the committee to evaluate the two types of approaches separately in companion reports, a distinction it hopes carries over to future scientific and policy discussions.

"[94][95][96] The resulting study titled Climate Intervention was released in February 2015 and consists of two volumes: Reflecting Sunlight to Cool Earth[97] and Carbon Dioxide Removal and Reliable Sequestration.

[98] In June 2023 the US government released a report that recommended conducting research on stratospheric aerosol injection and marine cloud brightening.

[99] As of 2024 the Coastal Atmospheric Aerosol Research and Engagement (CAARE) project was launching sea salt into the marine sky in an effort to increase cloud "brightness" (reflective capacity).

Planting trees is a nature-based way to remove carbon dioxide from the atmosphere, however the effect may only be temporary in some cases. [ 34 ] [ 35 ]
refer to caption and image description
Proposed solar radiation modification using a tethered balloon to inject sulfate aerosols into the stratosphere
PDRC can lower temperatures with zero energy consumption or pollution by radiating heat into outer space. Widespread application has been proposed as a solution to global warming. [ 51 ]
Video to explain some of the marine geoengineering approaches with a focus on their risks, negative impacts and potential side-effects, as well as on the question of governance of these technologies.
A proposed "underwater sill" blocking 50% of warm water flows heading for the glacier could have the potential to delay its collapse and the resultant sea level rise by many centuries. [ 29 ]