In a short speech on Rowes Wharf in downtown, Weld, who the Globe recently endorsed in his challenge to the incumbent president, vowed to declare a national emergency and implement a carbon tax in his first 100 days in office if elected.

“This is not something that’s impossible to do and it really is a national emergency. In fact it’s a planetary emergency,” Weld said before criticizing President Donald J. Trump three days before the Massachusetts primary, according to a live-stream by his campaign.


Weld, who served two terms as governor from 1991 to 1997, also chided Democratic presidential candidates for “just throwing money” at the issue by supporting the proposed congressional Green New Deal.

In addition to taxing carbon emitters, Weld proposed rejoining the 2015 Paris climate agreement that Trump administration announced in November it would abandon, encouraging new agricultural practices that release less carbon, planting trees, and buying the debt of heavily forested nations in exchange in exchange for promises not to disrupt the environment.

Former Massachusetts state senator and state secretary of environmental affairs Robert Durand introduced Weld at the waterfront as a “true conservationist,” and said “there is not a presidential candidate, Democrat or Republican, that has the kind of passion for the environment that Bill Weld does.”