Climate change is a threat multiplier.

Many of the things happening — storms, wildfires, intense heat — have always happened. Now they are happening with greater frequency, said Raymond Najjar, professor of oceanography at Penn State, in his opening address at the Climate Action Summit yesterday.

“There are twice as much burning of forests in the west because of climate change,” he noted.

“The wrong question is: Has climate change made xyz? The right question is: How much worse has climate change made xyz?”

A sold-out, invitation-only crowd filled the main room of the David L. Lawrence Convention Center for the all-day summit hosted by p4 and The Heinz Endowments in partnership with Sustainable Pittsburgh.

Keynote speaker David Wallace-Wells, author of “The Uninhabitable Earth,” set the tone for the summit with a dire assessment of what’s happened in the past 30 years to change everything.

“Half of all emissions in the history of the world have been in the last 30 years. We’ve done more damage since then than we did in all the centuries before it,” he said at the start.

A few examples:

Wildfires, he noted, are five times worse since 1972.

Houston has been pummeled by five, 500-year storms in the past five years.

Heat waves in Europe broke records in June and again in July and were close to breaking records again in August.

“I am 37 years old,” said the author, “born at a time when the climate seemed stable. Today, we are on the brink of catastrophe because of what has been done in just those 30 years. Climate change is the work of a single generation. Ours.”

“All of us are holding the fate of the planet in our hands,” he continued. “We have 30 years. What happens next? What would a positive outcome look like?”

His answer ranged from “solar arrays everywhere you look to a new electric grid that didn’t waste so much power, a new kind of plane that doesn’t produce carbon and a new way of raising agriculture and meat.

“We can feed our cattle seaweed to reduce methane by 95%.”

“The problem is too big to solve in any one single-bullet way,” he said. “We probably won’t be able to do enough. That’s the terrifying math we face. We’re going to learn to live with it and limit it. We need billions, trillions of trees to suck out carbon dioxide, and seawalls and levies to protect people living on coasts.”

But the only obstacles are human ones, he said. “We have the tools we need. We also have the tools we need to end global poverty and epidemic disease.”

On a more positive note, he said more is being done now to combat climate change, from the Extinction Rebellion to the Democratic candidates “competing to outdo each other” on the issue, than ever before.

So what will it take? Ultimately, “We need a new politics,” he said.

As if on cue, Mayor Bill Peduto hit the stage next — he was scheduled to appear before the author but was running late — and made an announcement that stunned the crowd.

“I talk with business executives every week — people from around the country and from around the world,” Peduto said. “And what they say is very clear: ‘Clean your air and clean your water.’ … “So, let me be the first politician to say publicly: I oppose any additional petrochemical companies coming to Western Pennsylvania.”

Read more about the mayor’s talk here and check back with NEXTpittsburgh for more news from the Climate Action Summit.