Daniela Cusack, the study's lead author and an assistant professor of geography in UCLA's College of Letters and Science, said they found that climate engineering doesn't offer a perfect option.
She said that the perfect option is reducing emissions.
Still, the study concluded, some approaches to climate engineering are more promising than others, and they should be used to augment efforts to reduce the 9 gigatons of carbon dioxide being released each year by human activity. (A gigaton is 1 billion tons.)
The first scholarly attempt to rank a wide range of approaches to minimizing climate change in terms of their feasibility, cost-effectiveness, risk, public acceptance, governability and ethics.
Of the five options the group evaluated, sequestering carbon through biological means - or converting atmospheric carbon into solid sources of carbon like plants - holds the most promise. One source, curbing the destruction of forests and promoting growth of new forests, could tie up as much as 1.3 gigatons of carbon in plant material annually, the team calculated. Deforestation now is responsible for adding 1 gigaton of carbon each year to the atmosphere.
The study also advocates a less familiar form of biological sequestration: the burial of biochar. The process, which uses high temperatures and high pressure to turn plants into charcoal, releases little carbon dioxide into the atmosphere. Under normal conditions, decaying plant life inevitably decomposes, a process that releases carbon dioxide into the atmosphere.
But charred plant material takes significantly longer - sometimes centuries - to decompose. So the approach can work to keep carbon that has become bound up in plant life from decaying and respiring as carbon dioxide. And like working slash into the soil, adding biochar to soil can improve its fertility and water retention.