This was in the last week of March, a bit premature for backpacking into the world's most famous canyon precisely because of the likelihood of encountering ice on trails at the rim. The ranger at the park's backcountry desk had told us emphatically that the Grandview Trail was "treacherous" and that MICROspikes—mini-crampons with small metal points that slip over backpacking boots—were "absolutely mandatory." I had the spikes for myself, my wife, Penny, and our nine-year-old son, Nate—who I nonetheless also led by the hand across every narrow, icy section. But I had none small enough for Alex's boots.

It was our kids' spring break from school, and with the huge range of elevation in the Big Ditch and its desert climate, we knew that while we'd see snow on the South Rim, we'd hit shorts-and-T-shirt weather down in the canyon. If we waited until school was out in June, the canyon's interior would be too brutally hot for backpacking; some seasonal springs that we'll rely on for water over this four-day, 29-mile trek would dry up by June, forcing us to carry a lot more water in our packs. As it was, even with all of the creeks fat with runoff, we had to carry all of the water our family would need for the hike's last 24 hours or so. I left the hike's last reliable spring with 13 liters—27.5 pounds—of water in my pack, bumping its weight up north of 60 pounds, which probably closely approximated what it might be like to carry Nate piggyback for several hours.

We did get the kids down the Grandview's icy sections without any incident that might prompt a visit from the state division of Child Protective Services. We had a wonderful adventure, full of incomparable scenery, lots of play time in streams and campsites, and the kind of challenges endemic to a Grand Canyon backpacking trip. For example, on our second day, we found a dry creek bed where we'd hoped to find water; we had to push on, hiking into early evening with tired but uncomplaining kids, and eventually logged more than 10 miles that day. Watch a video of our adventure here.

The story of that trip will comprise a chapter in my book Before They're Gone, due out from Beacon Press in spring 2012. The book is about taking my kids on wilderness adventures in a number of national parks facing severe climate-change threats. The Grand Canyon's climate forecast lacks the drama and finality of disappearing glaciers or island nations inundated by rising seas; but by the time Nate and Alex are my age, carrying 27 pounds of water may become more the norm than the anomaly.

The Colorado River basin has warmed more since the 1970s than any other part of the United States outside of Alaska; the average temperature in 2003-2007 was 2.2° F. hotter than the 20th-century average. The river is in the 11th year of its most severe drought in more than a century of recordkeeping—consistent with projections that the Southwest will dry out more than any other region of the country. Researchers have only begun examining what that will mean to ephemeral Grand Canyon streams and springs critical to backpackers, to the plants and animals that rely on those scattered water sources, and not to mention to future rafters and kayakers descending the canyon. If my kids want to repeat this trip someday with their children, they might have to be ready to carry a lot more water for a much longer distance—something that may be physically impossible for a family, or for all but the strongest hikers.