No matter who occupies the halls of Congress, no matter what transpires at U.N. conferences, the physics of climate change remains the same. Climate scientist Lonnie Thompson, the world's leading expert on high-altitude glaciers, likes to cite this observation from the geophysicist Henry Pollack: "Ice asks no questions, presents no arguments, reads no newspapers, listens to no debates. It is not burdened by ideology and carries no political baggage as it changes from solid to liquid. It just melts."

After talking with Thompson, our articles editor, George Black, bore this in mind during his recent reporting journey to Peru for our cover story, "Life and Death in a Dry Land." Andean glaciers are melting away, and their gradual disappearance inevitably dims the prospects of a country whose 30 million inhabitants depend on this water supply for agriculture, hydropower, and basic human needs. Peru's glaciers also offer scientists like Thompson an extraordinarily rich opportunity to understand the past, present, and future of climate change, while the country's ancient archaeological record yields evidence of another sort: that thriving civilizations have collapsed in the wake of a climate catastrophe. Could this happen again? Peru's problems may seem distant from our own, but the consequences of climate change so starkly apparent in the Andean peaks and in a desert city like Lima are strikingly similar to threats we face closer to home -- say, in Los Angeles or San Diego, otherwise thriving cities in water-starved landscapes.

The monumental challenge before us is to both drastically reduce greenhouse gas emissions and to strike a more sustainable balance between energy consumption and natural resources. Regarding the former, Daniel Grushkin and illustrator Gary Hovland team up to create a "Road Map to the Future,” which shows how the U.S. transportation system could decrease carbon pollution by millions of tons per year. Bob Deans, a veteran White House reporter and now associate communications director at NRDC, examines a similar approach in his Eye on Washington column.

The other side of the equation -- adaptation -- is explored by contributing editor Tim Folger in a sober essay on a new book, The World in 2050, which, according to its author, Laurence C. Smith, will be shaped by rising temperatures, a melting Arctic, shrinking water supplies, increased fossil-fuel consumption and pollution, and three billion more inhabitants competing for the planet's finite resources.

Although the courage to address climate change has flagged (temporarily, I hope) in Congress, other public officials, as well as entrepreneurs, business leaders, scientists, and ordinary citizens, are acting with urgency and creativity. You'll meet a number of them in this issue: the pioneering biologist E. O. Wilson, who tells Elizabeth Kolbert of the need for humans to cultivate "a new kind of self-understanding"; "water harvesters" in the slums of Lima; a young American woman who is converting human waste (literally) into hope in Haiti; and a schoolteacher in Redmond, Washington, whose innovative Cool School Challenge offers climate solutions to high school classrooms around the world. All in all, these stories suspend us in a rough equilibrium between alarm and hope that seems appropriate for our times.