I wasn't the only politician who understood mass immigration's effects on the environment when I left the Colorado governor's house in 1987, but there was certainly a lot more when I started.

Since the nineties onwards, the silence on the negative effects of runaway population growth in America has been deafening. This is why I've joined a lawsuit filed this week challenging our immigration authorities on failing to calculate the costs of their population growth-inducing policies.

Under the National Environmental Policy Act (NEPA), all federal agencies must take a "hard look" at every "major federal action" they commit to.

While it's apparently been well-understood that, for instance, the Department of Transportation must analyze the environmental effects of any highways and byways it commissions, for the Homeland Security department, which implements policies that make those highways and byways necessary, it apparently isn't. In fact, they've never made such an analysis on the effects of immigration. And they've been violating environmental law ever since.

I've lived in Colorado continuously since 1961. I was in the Colorado state legislature from 1967 to 1974, and I served as the governor of Colorado from 1975 to 1987, in both capacities as a member of the Democratic Party.

I've watched Colorado go from a lovely state with a high quality of life to a Colorado whose front range (from Pueblo to Fort. Collins) is rapidly becoming a Los Angeles of the Rockies. That unspoiled, beautiful Colorado that stirred me so deeply growing up has fallen prey to unchecked, immigration-induced population growth.

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The environmental damage that results from population density hits semi-arid Colorado worse than other places of the country. We are an oasis civilization, living on the snow that collects in our high mountains in the winter. Denver would not exist but for the snows in our mountains.

Now, with our population having grown 150 percent since 1970, these resources are becoming pressured, similarly to other high-immigration states, like California, which has grown so fast due to immigration, Denver's become a magnet for it crowded-out and exasperated residents.

When I started my political career, politicians like Nelson Rockefeller and Gaylord Nelson, popular scientists like Paul Ehrlich and John Holdren, and bellwether environmental groups like the Sierra Club, all understood the harmful effects of unregulated immigration.

They understood, for instance, that the environmentally destructive effects of urban sprawl is directly related to immigration-induced population growth. And while runaway population growth is bad for America, it's also bad for the world. Take greenhouse gases - because America produces so much more than the rest of the world, more Americans equals more strain on the planet.

The NEPA was supposed to have stopped this kind of ill-considered population growth. In the sixties and seventies, the environmental movement understood how important population stabilization was to everything it stood for.

The NEPA, the bedrock of our environmental law, was designed to provide for environmentally informed decision-making and public outreach on the part of federal agencies. All the consequences and potential environmental problems of an agency's actions must first be carefully considered, that was the logic of the statute.

Can the mass importation of people into this country (people, of course, being the very agents of pollution), not lead to negative environmental effects? Especially when half of all immigrants go to just five metropolitan areas? It's no coincidence that two of those sprawl centers (apart from New York, Chicago and San Francisco-Oakland), the migrant-havens of Los Angeles and southern Florida, contain the largest number of species now on the national endangered list.

In the days when the NEPA was passed, population growth was not substantially a matter of immigration, but now immigration is our population's primary driver. It's also the primary driver of population growth that's most within the federal government's control.

The level of immigration is a policy choice and not an inevitability like plate tectonics. If the numbers are becoming an environmental problem, they must be cut. But neither DHS, nor its predecessor agency, the Immigration and Naturalization Service (INS), has ever committed to a single environmental review of its immigration-related actions. Absolutely none.

If DHS/INS had followed the NEPA, as it was supposed to, perhaps our relentless pursuit for "smart growth," "new urbanism," LEED building strategies, or sustainable water and energy policies might actually start baring some real fruit. In other words, perhaps we wouldn't be running so hard environmentally just to stand still.

For this reason, I, along with several other concerned citizens and activists, have joined the lawsuit filed by the Immigration Reform Law Institute in the U.S. District Court for the Southern District of California against the DHS. Our government can no longer ignore its moral and legal responsibility to protect the environment from our growing and excessive population.

Lamm, professor of Public Policy at the University of Denver and former Governor of Colorado

The views expressed by contributors are their own and not the views of The Hill.