SEEKONK, Mass. — It wasn’t intended to be a debate, but Greg Gerritt, Rhode Island’s unofficial grassroots environmental leader, and Sen. Sheldon Whitehouse, D-R.I., Washington’s leading climate hawk, spoke back to back at a recent sustainability summit. Their dissimilar views underscore the divide in the environmental movement: a top-down, policy-driven approach vs. a populist reshaping of economics and equality.

The themes of food, energy and compost served as the backdrop for their presentations, but they mostly spoke about broad-based plans for addressing fossil fuels, the economy, exploitation of natural resources and the forces that pursue them.

Climate-change-driven drought means that most food must be locally grown, Gerritt said. Notions of high GDP can no longer exist, while consumption must decline, he added.

“We have this system that is guaranteed not to be sustainable,” said Gerritt, noting that the planet’s ecosystems are already in collapse. “That’s the reality we live in.”

To fix it, he said, you have start reversing the damage to ecosystems by paying attention to justice and democracy. “We need a new plan.”

The challenge is finding solutions that reduce consumption of natural resources such as trees, fish, minerals and land. “How do you figure out a way to use less that is going to be just?” Gerritt asked.

Whitehouse spoke about his carbon tax plan and the $200 billion to $700 billion subsidies the fossil-fuel industry is fighting to protect in Congress. His carbon fee, he said, should be charged on oil and gas, as well as on methane emissions from livestock. The tax, he said, would encourage fossil-fuel companies to diversify into renewable energy and seek new technologies to reduce or capture their emissions.