The merits of geoengineering options to stem the tide of anthropogenically induced climate change appear cloudy at best. Ocean upwelling or ocean alkalinization programs would have to be implemented at almost global scales to exert any effect, and any adverse impacts of such efforts are largely unknown. Marine cloud brightening to reflect solar radiation away from the planet has also been proposed but appears to be only a Source: NASASource: NASAshort-term measure to offset global warming.

A recent study examined the costs and practicalities of a large-scale, hypothetical "solar geoengineering" project beginning 15 years from now. The initiative would inject sulfates into the lower stratosphere at altitudes of about 20 km halve any increase in anthropogenic radiative forcing.

The costs of such a stratospheric aerosol injection (SAI) project were deemed relatively inexpensive, averaging $2 billion to $2.5 billion per year for 15 years. However, no existing aircraft design can accomplish this mission, leading researchers to propose specifications for an SAI Lofter (SAIL). The craft would be equivalent in weight to a large narrow-body passenger aircraft but with double the wing area to sustain level flight at the desired altitude. The aircraft would also need double the thrust of an equivalently sized airliner, and four engines instead of two.

A fleet of eight SAILs is envisioned to fly 4,000 missions in the first year, rising to a fleet of 100 that would complete 60,000 missions annually by year 15.

Concerns over the need for international cooperation and funding, secrecy and the potential for rogue actors suggest that the proposed geoengineering program could never get off the ground.

Scientists from Yale College and Harvard University contributed to this study, which is published in Environmental Research Letters.