President Trump touted infrastructure in his State of the Union address last night without mentioning climate change.

But the two issues are intimately related.Experts say the impacts of climate change—including floods, wildfires and sea-level rise—could place a big strain on the nation’s aging infrastructure.

They caution that the country’s roads, highways and bridges must be rebuilt in a resilient manner so that they can withstand the consequences of a warming world.

Otherwise, experts say, billions of dollars could be wasted on infrastructure projects that get swept away by the next major hurricane or other extreme weather event.

Trump didn’t utter the words “climate change” or “resilience” last night. His remarks on infrastructure were largely confined to pleas for Democrats and Republicans to work together on a broad legislative package.

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“Both parties should be able to unite for a great rebuilding of America’s crumbling infrastructure,” the president said. “I know that Congress is eager to pass an infrastructure bill—and I am eager to work with you on legislation to deliver new and important infrastructure investment, including investments in the cutting-edge industries of the future.”

Trump added, “This is not an option. This is a necessity.”

The National Academies of Sciences, Engineering and Medicine also used the word “necessity” in a recent report, but in relation to rebuilding large portions of the Interstate Highway System to account for climate change and other challenges that have risen since the system was built in the 1950s.

“The need to make the Interstate System and other transportation assets more resilient to the consequences of climate change is now widely recognized,” the report says, “in part because of recent experience and in part because of forecasts by much of the science community.”

The report goes on to cite several examples of how climate change is already chipping away at surface transportation infrastructure across the country.

In Alaska, thawing permafrost is threatening the structural integrity of bridge supports. And in Houston, three major storms have occurred since 2015, with Hurricane Harvey inflicting more than $125 billion in damage.

“Climate change is upon us, and we need to consider that in building or rebuilding infrastructure,” said Vicki Arroyo, executive director of the Georgetown Climate Center and a contributor to the report.

It’s unsurprising that Trump neglected to mention climate change in his second State of the Union address, given his track record of calling global warming a “hoax,” Arroyo said. The speech was Trump’s third address to Congress.

More important than the president’s rhetoric, she said, is whether Congress ends up incorporating climate concerns into a broad infrastructure package.“Investing in infrastructure is long overdue. But any infrastructure bill MUST confront climate change,” Markey said on Twitter shortly before the State of the Union concluded.

“We have a once-in-a-generation opportunity to literally rebuild America and pave the way for an efficient, resilient, vibrant future. We cannot afford to miss it. #SOTU.”

Said Arroyo: “Whether or not Trump says it in the State of the Union, the most important thing is that the legislation allows for considering that the future will look different than the past.”

To be sure, the Trump administration has set aside record funding for pre-disaster mitigation projects. The Department of Housing and Urban Development last spring prepared to provide a record $28 billion to support long-term disaster recovery in nine states, Puerto Rico and the U.S. Virgin Islands. Of that, a whopping $16 billion was earmarked for risk mitigation.

But there’s a catch: The money hasn’t been allocated yet. That leaves vulnerable communities in limbo as they wait for help from the federal government to prepare for the next Hurricane Harvey

“For risk mitigation, I would just say that being able to release that funding, with criteria that really prepares us for the next disaster, is critical for this administration to take action on,” said Stephanie Gidigbi, infrastructure lead at the Natural Resources Defense Council.

Gidigbi said she too ws unsurprised that climate change didn’t get airtime in the State of the Union. But she said the status quo of making costly repairs after disasters would be untenable going forward.

“To date, our nation has spent $1.5 trillion on disaster-related events due to extreme weather,” she said. “And so we simply can’t afford more of the same.”

Infrastructure was far from the main theme of Trump’s address last night. The president spent more time on topics like border security, national security and trade.

Still, some groups said they were pleased that Trump used the high-profile address to mention infrastructure at all.

“The president’s State of the Union address is once again making transportation infrastructure investment a top national priority,” Jim Tymon, executive director of the American Association of State Highway and Transportation Officials, said in a statement.