Mike Rowe, the host of TV show Dirty Jobs, recently offered a sobering diagnosis for the state of skilled trades jobs today: “For every five tradespeople who retire this year, two replace them.” “Five out, two in,” Rowe said during a Ford Pro Accelerate panel on workforce development. “I don’t care how you vote. I don’t care what your politics are. Math doesn’t care either.

“How long do you want to wait for your toilet to get fixed?” he added. “How long do you want to wait for the lights to come back on when you flip the switch?”

Now economists are putting a number to just how big this shortage is—and what exactly it takes to fill it. The recent State of America’s Skilled Trades report, published by nonprofits Jobs for the Future and the Burning Glass Institute, found there will be 1.7 million skilled trades job openings every year through 2035, including 600,000 new net positions added through the same time period.

The surge bucks the trend of sluggish job growth and unemployment, which ticked up to 4.2% in September, according to Bureau of Labor Statistics data. Trade job opportunities have exploded in the latest era of technology, in large part a result of the growing AI boom demanding the construction of data centers, as well as increased defense production, and even the growth in demand for affordable housing units. These tradespeople are part of a 18-million strong workforce who added an estimated $3.8 trillion to the U.S. GDP last year.

But these trade industries are facing a twofold problem, as Rowe alluded to: More tradespeople are retiring, leaving experts and employers scratching their heads about how to recruit enough young people to not just replace this graying workforce, but meet the growing demand for these types of jobs.

“You have to think about this like a bathtub with a faucet and a drain,” Matt Sigelman, president of Burning Glass Institute, told Fortune. “We also have a very leaky pipeline.”

Reversing a graying workforce

Nearly one-quarter of skilled trade workers are 55 or older, according to the report, and only 11% are under 25. For some trades, like tool and die makers, nearly half the workforce is over 55.

In the mid-to-late 20th century, trade jobs were prized. The baby boom gave way to around 77 million people added to the U.S. population, many of whom entered the workforce in the 1960s and ’70s, when public works and suburban housing projects soared in demand. An influx of funding for vocational training in schools helped bolster this workforce. However, manufacturing jobs peaked in 1979, and the rise of a service-based economy in the U.S. coincided with the increasing affordability of college, leading to shrinking opportunities in the trades by the end of the century.

The result is the winding-down workforce that took advantage of the postwar need for housing and infrastructure, and a workforce today that is trained to contribute to the service economy. All the while, the growing need for trade roles across industries has escalated the shortage.

“We have a growing need for tradespeople, and one of the things that we’re studying now is how an array of different national priorities … have overlapping demand for the same skill trades,” Sigelman said. “There’s significant overlap in the nature of the tradespeople that are needed for each of these kinds of priorities and many others, and so those shortages can easily compound.”

Trade industries’ retention problem

Tides are beginning to change. Gen Z has become decidedly frustrated with the often prohibitive costs of higher education. Inundated with messaging around AI displacing entry-level, white-collar work, many have sought refuge in trade positions. Industry giants are working to meet the growing interest in trade roles. General Motors has invested nearly $200 million in the past year to modernize internal skilled trade careers and manufacturing, engineering, and technician roles. Technicians, on average, can make between $80,000 to $90,000.

“[We need to] really make sure high school students understand this is a great career and frankly maybe a little more AI-proof than some others,” CEO Mary Barra told Fortune last month.

But getting young prospective workers interested in skilled trades is only half the battle. While recruitment is crucial for filling increasing trade roles, “part of what exacerbates the need for us to do that work is that so few people who start a program finish,” Sigelman said.

Of 100 people who start an apprenticeship or community college workforce program, Sigelman noted, only about 48 finished. While higher education institutions like four-year colleges also face retention challenges, they have the financial and staff resources to intervene and slow attrition rates. Smaller trade and vocation programs lack these same resources, Sigelman said.

Sligelman noted that one solution to increasing the network of skilled tradespeople is expanding who believes they can have a trade position. A recent study by the Ad Council Research Institute of more than 3,000 high school students and 25,000 parents of high school students found 71% of teens said they would be proud of attending a trade school, but just 9% considered a postgraduate career in trades. The problem, according to Sigelman, is one of exposure: Many people who become plumbers go into the field because their parent or neighbor was a plumber.

“We’ve yet to see the network broaden, even as awareness is rising,” he said. “It’s not an awareness gap; it’s a navigation gap. How do we help people navigate to these fields?”