It’s a big week for Boston Mayor Marty Walsh. He's hosting the U.S. Conference of Mayors in Boston over the weekend, and on Thursday, leading what’s being dubbed an international climate-change summit for mayors at Boston University.

But as Walsh gets a platform to discuss an issue he's identified as crucial for Boston's future, some local activists are urging him to act far more decisively.

A few days ago, one of them, Kannan Thiruvengadam, gave me a tour of the Jamaica Plain Green House — a once-derelict 100-year-old home that now houses an alternative school and has been radically rejiggered so it actually creates more energy than it uses.

"The light is turned into heat inside, and the heat is kept inside because the insulation is good," Thiruvengadam said. "You can probably tell, it’s more than a foot of insulation."

For Thiruvengadam, the Jamaica Plain Green House embodies both how much can already be done to fight climate change, and how much the city of Boston isn’t doing that it could be.

Ideally, he said, "Boston should be building 21st-century buildings, kind of like the one we’re sitting in. It could be passive solar, it could be zero carbon, it could be near zero carbon."

"These huge buildings that are going up all over the place ... isn’t this also an opportunity to build these buildings in a way that would be a model?" he asked.

But right now, Thiruvengadam said, the new developments dotting Boston’s skyline aren’t especially green at all. And while Mayor Marty Walsh has pledged to make Boston carbon-neutral by 2050, the details are still being hashed out.

"While you’re doing research, you’re not making any change," Thiruveengadam said. "You’re not cutting carbon. You’re not adding more renewable energy. You’re not moving the needle."

That isn’t the message Walsh will deliver at BU tomorrow when he hosts the aforementioned summit, which is slated to feature John Kerry and former EPA head Gina McCarthy.

In the past, Walsh has called Boston “America’s climate champion." And he says that, right now, the city is already responding to the challenges posed by climate change in a number of meaningful ways.

"In this year’s budget, we have money for sea walls to be put up in East Boston," Walsh told WGBH News recently. "We’re looking at designing our park system— Langone and Puopolo in the North End, we’re going to be raising it 40 inches for sea level rise. We’re designing, right now, Moakley Park in South Boston; we’re also taking into account what’s happening over there."

To Emily Norton, the Sierra Club's Massachusetts director, those steps don't go far enough.

"We're not seeing the action match the rhetoric," Norton said.

She cites what she considers the Walsh Administration's slow pace implementing Community Choice Energy, a program that was unanimously backed by the Boston City Council several months ago and would increase the energy from renewable sources by city residents and businesses. And she points to the Seaport, which suffered dramatic flooding this past winter, but where a massive construction boom still continues.

"What happens when sea level is three feet higher, five feet higher, ten feet higher?" Norton said. "What happens when the roads to those buildings are chronically inundated? What does that do to the infrastructure underground — the sewer, the water, the subway?

"We know these problems are coming, so let’s act now."

The good news, for advocates who think the city is falling short, is that Walsh says he welcomes public pressure in this area — and that big changes to the way the city operates are coming. Soon.

"I’m not going to take the criticism as a bad thing," Walsh said "It’s a challenge to us to move faster.

"In the city, at least under my administration and the administration before me, there was a lot of work put into this, a lot of planning," he added. "I think now it’s coming down to actually laying the foundation and doing the work.

And if there's one thing the mayor and climate-change activists seem to agree on, it's that plenty of difficult work remains to be done.