New York

On July 20th, James Hansen, the former NASA climatologist who brought climate change to the public's attention in the summer of 1988, issued a bombshell: He and a team of climate scientists had identified a newly important feedback mechanism off the coast of Antarctica that suggests mean sea levels could rise 10 times faster than previously predicted: 10 feet by 2065. The authors included this chilling warning: If emissions aren't cut, "We conclude that multi-meter sea-level rise would become practically unavoidable. Social disruption and economic consequences of such large sea-level rise could be devastating. It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilization" . . . .

James Hansen, the dean of climate scientists, retired from NASA in 2013 to become a climate activist. But for all the gloom of the report he just put his name to, Hansen is actually somewhat hopeful. That's because he knows that climate change has a straightforward solution: End fossil-fuel use as quickly as possible. If tomorrow, the leaders of the United States and China would agree to a sufficiently strong, coordinated carbon tax that's also applied to imports, the rest of the world would have no choice but to sign up. This idea has already been pitched to Congress several times, with tepid bipartisan support. Even though a carbon tax is probably a long shot, for Hansen, even the slim possibility that bold action like this might happen is enough for him to devote the rest of his life to working to achieve it. On a conference call with reporters in July, Hansen said a potential joint U.S.-China carbon tax is more important than whatever happens at the United Nations climate talks in Paris.

One group Hansen is helping is Our Children's Trust, a legal advocacy organization that's filed a number of novel challenges on behalf of minors under the idea that climate change is a violation of intergenerational equity — children, the group argues, are lawfully entitled to inherit a healthy planet.

A separate challenge to U.S. law is being brought by a former EPA scientist arguing that carbon dioxide isn't just a pollutant (which, under the Clean Air Act, can dissipate on its own), it's also a toxic substance. In general, these substances have exceptionally long life spans in the environment, cause an unreasonable risk, and therefore require remediation. In this case, remediation may involve planting vast numbers of trees or restoring wetlands to bury excess carbon underground.