PORTSMOUTH — People who live in a low-lying area of the city like the South End should consider selling their house — “and I’m not kidding,” said Cameron Wake, University of New Hampshire professor of climatology and glaciology.

If there is a big coastal storm like Hurricane Sandy, “those houses are at risk of flooding” today. And it won’t get any better in the years to come, as sea levels inevitably continue to rise.

“My recommendation is why deal with the headache? Sell now while you can still get money out of the home,” he said.

As for Hampton Beach, he said, the town’s move toward making the beach a 5-star resort area is misguided at best. “Hampton Beach is so at risk, so vulnerable, so exposed” that it makes no economic sense to continue on that path.

Wake spoke to the Herald editorial board Wednesday, in advance of his talk next week at 3S Artspace in Portsmouth. He said sea level rise from climate change is occurring now and its trajectory is inevitable. The question is how quickly will we curtail human activities that contribute to global warming?

Will carbon emissions continue unabated at current levels — in which case sea levels could rise as much as 6 feet in the next 80 years, leaving Hampton Beach, Strawbery Banke Museum, Portsmouth Middle School and South Mill Pond homes in Portsmouth under water? “I don’t mean to be hyperbolic here, but that’s the picture,” said Wake.

Or will there be a serious and immediate commitment to reducing carbon emissions by systemically investing in renewable energy sources, weaning off high carbon use, implementing energy efficiency measures and instituting a carbon tax? In the most optimistic case, then, sea levels would rise 2 feet over the next 80 years, “something we can adapt to, something we can survive.”

Wake sees reasons for optimism amid concerns that the planet could be facing “a whole suite of nasty surprises” in the future — including the possibility of more accelerated melting of the Greenland and West Antarctic ice sheets than had previously been anticipated. Former NASA scientist James Hansen in a study released this week predicted even if the Earth warms by a modest 3.5 degrees Fahrenheit by 2100 — as agreed to by the nations of the world in Paris last December — it will be too warm to stop the sheets from melting. That would cause sea levels to rise quickly and precipitously, the study argues.

“The conversation we’re not having is the conversation Jim Hansen wants us to have,” said Wake. “We had to get over the denial, and we’ve done that. Now we need to take a hard look at where we go from here.”

Wake was asked what number he would assign the world today, if zero was the worst carbon pollution possible and 10 was the perfect climate world.

“I think we’re at about a 1," he said. "The developed world needs to be carbon neutral by 2050. We need to get to 10 really quickly,” he said, and then help developing countries reach that goal in the decades to follow. “But when you look at the rate of change today, we’re headed in the right direction.”

That’s where the optimism comes in, he said. It’s become clear in recent years that a solution to global warming is becoming cost effective, he said. The cost of wind and solar has come down, for instance.

“We can see a pathway to a clean energy revolution that wasn’t there before. The tipping point is where capital, interest and technology all meet. I’m optimistic because solutions line up with profit motives,” he told the Herald last December.

He likened it to the Internet. Early on, comparatively few people used the Internet, but then it reached the same critical mass “and took off exponentially. That same exponential curve is happening now” with renewable energy.

In order for this trajectory to continue, people need to incorporate changes in their personal lives, and begin demanding their elected leaders from town hall to Congress deal with this issue. “Once politicians hear from many people, I think they will start to get much more serious.”

While there are many challenges ahead, he said, he said “it’s not too late. There is an amount of climate change we are going to have to adapt to. We have already committed to a warmer world. But if we can act now, in the next decade, and the developing world in the next two or three decades, I do think we can salvage this.”

Want to learn more?

Cameron Wake will be speaking at the 3S Artspace on Vaughan Street in Portsmouth on Tuesday, March 29, at 6:30 p.m. The event is free. To reserve a seat, visit www.ps21.info. The talk is being presented by Portsmouth Smart Growth for the 21st Century.