Former Vice President Al Gore came to the Temple Emanu-El Streicker Center on Wednesday evening to discuss the future — mainly the global climate crisis, a condition he first warned of as a U.S. senator in 1976.

But one sensed among the 2,200 people who filled the sanctuary an air of nostalgia, a “what if?” element harking back to Gore’s narrowest of losses in the 2000 presidential race, given what’s happened since.

He received a prolonged standing ovation on taking the stage, looking grayer and more bulky with age. At the outset he shared a comment from a woman who he said had been staring at him at a restaurant recently: “If you dyed your hair black,” she said, “you’d look like Al Gore.”

It was one of the few light moments in an evening highlighting the “existential” danger to the planet from fossil fuels and other elements poisoning the atmosphere. Over the last decade, since his Academy Award-winning documentary, “An Inconvenient Truth,” was released, Gore has made his case more than 1,000 times to audiences around the world. (A movie sequel and new book are due out this year.)

But he brought fresh energy and passion to his presentation, standing beneath a large screen and narrating scores of slides and offering video footage that showed the ravages of global warming.

Gore focused on “the only three questions” to be asked about the climate crisis: Do we really have to change? Can we change? And will we change?

The “bad news,” he said, was the urgent need to address the problem, noting that “99.9 percent of the scientific community” agrees about the danger to the planet. He offered vivid evidence of the resulting heat waves, floods, typhoons, rain storms, droughts and other weather crises already occurring, and certain to grow in scope and frequency unless current trends are reversed.

Gore spoke of the wide-ranging effects of these natural catastrophes, such as droughts causing food shortage and starvation, which in turn can lead to political crises. He pointed out that the Arab Spring uprising began with a Tunisian man setting himself on fire in frustration over his failing vegetable business, and how drought in Syria led to masses of refugees fleeing to the cities before the civil war broke out.

In addition, infectious diseases like the zika virus can be traced to dramatic changes in the environment.

But while acknowledging that “yes, there is an existential threat to civilization,” Gore told the rapt audience, “don’t get depressed.” He cited as reasons for optimism the strong economic and business incentives in going green, the desire among millennials to be aligned with the cause, and that various forms of renewable energy are gaining acceptance.

“This is our home,” he said of Planet Earth, “and we have the moral obligation to those who come after us to wake up and act now.”

In an interview segment with New York Times science reporter Justin Gillis, Gore was asked about his response to the Trump administration’s views — skeptical at best — on the climate crisis.

He said that “partisan politics can be highly destructive,” and asserted that “our democracy has been hacked.” But he added that “we still have checks and balances, and maybe there are enough senators to limit the damage to our environment.”

Gore urged his audience to become knowledgeable about the issues: “Win the conversation,” he said, by not allowing “climate denial to go unchallenged”; be a “green consumer” and be politically active.

Despite the bleak situation, “we can turn this political process around,” he said.