How comfortable have we become with national park settings? With the big sweep of granite that frames the Yosemite Valley, with Old Faithful's not-quite-so-faithful demonstrations of steam and hot water, with fall's colorful deciduous forests of Great Smoky and Shenandoah?

Do we take these settings for granted? Have we, perhaps, gotten too comfortable with driving through the tunnel of trees that lines Yellowstone National Park's South Entrance Road, too used to viewing the Yosemite Valley from the mouth of Wawona Tunnel and too accustomed to the kaleidoscope of fall that can be found in Shenandoah and Great Smoky because, after all, our lifetimes are but a blink in geologic time.

We don't live long enough to witness significant change, geologic or otherwise, in the national parks. We weren't around when the glaciers cut Yosemite's fantastic valley, when they sculpted Logan Pass in Glacier National Park, or when they bulldozed down the Mid-Atlantic region and left forests of spruce and fir along the roof of Great Smoky.

And so it's understandably difficult to envision significant change in the National Park System (although many of us will be around when Glacier's rivers of ice are gone, an occurrence that's right around the corner). Change not so much geologically, but in wildlife, vegetation, even fish.

It's coming.

Already moose are said to be heading north out of Isle Royale National Park because it's getting too hot for their comfort. The colorful reefs that time and marine-life built in Biscayne, Dry Tortugas, and Virgin Islands national parks are on the decline, victims of disease, too-warm waters, and, in the not too distant future, waters turned acidic. At Joshua Tree National Park there are fears the climate will grow so hot that the namesake trees won't be able to stand it.

Look close the next time you visit Sequoia or Kings Canyon, any of the national parks in California for that matter, and you just might notice the subtle changes the latest drought is exacting. More dust in the air, shrubs encroaching onto meadows, trees on southern exposures that are dying of thirst, wildfires that are more prevalent. At Rocky Mountain National Park, crews are in a battle with bark beetles.

These and other changes, some subtle, some not so, are on their way and spreading across the park system, courtesy of rising temperatures. They say the way you boil a frog is put it into a pot of cold water and slowly heat it up. Well, you might say the Earth is in a pot of cold water and there's fire down below.

“I feel very strongly that we’re on the edge of a mass extinction. If we go up by 2 degrees Celsius, we could lose as many as 20 percent of the known species," says Dr. Terry Root, a senior fellow at the Woods Institute for the Environment and a professor at Stanford University who specializes in the area of wildlife population and distribution response to changing climate. "The known number of species is 1.8 million, so that’s about 400,000 species. Are we going to hit 2 degrees? In my opinion there’s no way we’re not going to hit 2 degrees."

Where do you begin to imagine a loss of 400,000 species? What might blink out? Plants that you've grown accustomed to see bloom? Bees that pollinate those plants, along with most of the crops society has come to take for granted? Cutthroat trout whose waters have become too warm?

Such a great effect on the biology, and biodiversity, of national parks likely will have a surprising effect. Oh, places like Arches and Canyonlands national parks, and surely Death Valley as well, more than likely won't change too much, outwardly, under climate change. But head north into the woodland and riverine parks and the impacts could very well prove shocking. Can you imagine Redwood National Park without redwoods?

"If you’re talking about forests, or certain kinds of mountain ecosystems, or river ecosystems, I think that the biology has a lot to do with the landscape form," Dr. Philippe Cohen, executive director of the Jasper Ridge Biological Preserve at Stanford. "And if you see a real significant biological shift, you will also see real significant shifts in how those landscapes are experienced and appear."

Now, the Earth is a very dynamic place. There's a long, long history of climate change, and some of it fairly recent. The Little Ice Age, for instance, which chilled the mid-19th Century. But climate scientists tell us the difference with the change we're entering into is not natural, but rather driven by humankind. One of the most recent reports underscoring that, Ecological Impacts of Climate Change, was published by the National Academies of Science last year. Written by the Committee on Ecological Impacts of Climate Change, National Research Council, the report notes that:

Both natural variability and human activities are contributing to observed global and regional warming and both will contribute to future climate trends. It is very likely that most of the observed warming for the last 50 years has been due to the increase in greenhouse gases related to human activities (in Intergovernmental Panel on Climate Change reports, "very likely" specifically means that scientists believe the statement is at least 90 percent likely to be true; "likely" specifically means about two-thirds to 90 percent likely to be true.) While debate over details is an important part of the scientific process, the climate science community is virtually unanimous on this conclusion.

Not only is humankind a key player in climate change, but we've reached the point where no matter how hard we work at reducing greenhouse gases and slowing climate change, Baby Boomers almost assuredly won't live to see the fruits of those efforts.

“I think the next 40 or 50 years are a done deal. I don’t think that’s what we’re talking about here. I think we’re talking about the ensuing 50 years," says Dr. Cohen. "But the next 50 years are a done deal. We could stop carbon emissions today, flat, the next 50 years are done. Whatever is going to happen is going to happen the next 50 years, and I think we’re going to have very little to say how it gets played out. I think the perturbations that are coming are going to happen no matter what.

"I think the real issue is what happens after. And I think that the issues are profound enough that they really are a substantial threat to civilization. When all is said and done, it’s not what happens in the next 50 years, it’s whether there’s going to be anything worth having in 100 years," he says. "So, yeah, I think it’s serious stuff. And humans are terrible at long-term thinking, but this is a long-term issue."

Perhaps, though, the key is to not think long-term, but rather to think what we can do in the short-term to benefit our children and grandchildren in their lives.