Earlier this week, for the first time in at least eight years, I revisited one of my favorite places on the Earth that I’ve yet experienced. It’s a snowmelt-filled, glacier-carved alpine lake just below treeline in Rocky Mountain National Park. It’s surrounded by tall cliffs and you have to scramble over boulders to get to it (something that my wife didn’t exactly appreciate when I tried to show it to her). Sure, it’s close to one of the favorite places for tourists in the park, but most of the time I don’t mind a few other people so long as they’re being polite and not too noisy, and the people eating lunch around the lake were generally OK.

This lake and I go way back, back to when I abandoned my Catholicism in favor of a neo-paganism of my own creation. It helped me find myself and a new spirituality in a period of my life when so many things were changing that it felt like the best I could do is hang on. And I feel that it was this lake that saved my life one very, very strange night in a strange town in central Pennsylvania.

I feel a spiritual connection to this lake, like I can feel its presence with me when I concentrate.

When I arrived at the lake, though, I discovered something that saddens me. Eight years ago the lake looked like liquid glass it was so pristine and clear. But yesterday it was green.

Algae hasn’t grown in my high alpine lake. The temperatures stay too cold and there’s not enough nutrients in the surrounding terrain for algae to grow thick enough to turn the water green. But Rocky Mountain National Park is one of the most heavily visited parks in the United States because it’s so close to Denver. In 2008, it was the 7th most visited park, with almost 2.8 million visitors. For comparison, the Grand Canyon and Yellowstone saw 4.4 million and 3.1 million visitors, respectively, in 2008. All those cars emit pollution that contains nitrogen oxides, and the rain washes all that extra nitrogen into the streams and lakes in and around the park.

But as polluting as all those cars are, they’re not the only source of nitrogen that the park has to deal with. Winds from the Denver metropolitan area sweep up into the park where rain and snow drop the nitrogen into the ecosystem.

All that nitrogen isn’t just turning alpine lakes green, it’s also changing the alpine tundra ecosystem, replacing native tundra plants with cold-tolerant grasses that previously couldn’t survive in the nitrogen poor soils above treeline.

But the extra nitrogen is only part of it. Something else that affects water quality in alpine lakes is warming temperatures, and the temperatures have been rising. This is especially true of winter temperatures. Greening alpine lakes isn’t the most obvious evidence of this change – that would be the large-scale killing of evergreen trees due to a pine beetle infestation.

Thankfully, the changes needed to clean up my high alpine lake are the very same changes that the global climate needs to address climate disruption. Less nitrogen pollution from industry and transportation. Fewer carbon emissions from all energy sources. Less ozone. Less sulfur dioxide. And conveniently enough, all of those things help not just alpine lakes, but also public health in general. Ozone triggers asthma attacks. Nitrogen oxides create choking smog. Sulfur dioxide makes acid rain. And lowered carbon emission, applied globally, will keep the health effects of climate disruption from becomming even worse (tropical diseases in temperate areas, fatal heat waves, more intense precipitation causing more deaths from injury, and so on).

I hope my lake will return to being liquid glass again, but it will take concerted action by people living along the Colorado Front Range. First and foremost it’ll take mass transit and the abandonment of coal, both for electricity and industry. At the moment, Denver is building a large mass transit system that will help greatly, but only if it’s finished, and finishing it will take more money than voters originally approved. But while the coal power plants that power the city are all old enough that they could be replaced, replacing the plants with cleaner sources of electricity will be much more expensive than upgrading without federal legislation enacting a price on carbon.

I’ve known about the transit and energy changes along the Front Range for at least a decade, and I’ve written about the science underlying the broader, global trends for years now. I’ve voted in support of the changes over at least six election cycles even though doing so occasionally put my employment at risk indirectly. But most of the time I was voting and writing on environmental and climate changes that were largely impersonal.

Earlier this week I discovered that it had become a bit more personal for me.