Mammoth, a giant machine in Iceland, will pull carbon dioxide out of the air. Francesca Jones for The New York Times

New climate technology

In the past, investors wrote off technologies that re-engineered the natural environment to counteract climate change. Ideas like sucking carbon dioxide out of the air or adding sulfur dioxide to clouds to block the sun were considered too expensive, too impractical or too sci-fi to be taken seriously.

But as climate dangers worsen and nations fail to meet goals of slashing emissions, some of these technologies are quickly moving to the mainstream despite concerns from scientists.

Some fear that the projects, which are broadly known as “geoengineering,” could distract policymakers from the more urgent work of reducing fossil fuel emissions. Others worry that the interventions could open a Pandora’s box of new problems.