As I type this column, several recent storms are weighing on my mind. Winter snowfalls around the country have sparked questions about climate change yet again. Skeptics ask, How can warming be happening if we’re getting big snows? As if we could determine the world’s condition during a single season. In fact, one symptom of a changing climate could be more varied or more extreme weather—but a couple of heavy snows wouldn’t prove that either. January was slightly warmer in the U.S. than average, in any case.

Another storm surrounds “Climategate.” More than 1,000 private e-mails were stolen from the University of East Anglia’s Climatic Research Unit and publicly released last November. Climate doubters have asserted that the e-mails prove that science surrounding global climate change is not settled and that the data in favor of it were misrepresented.

Disturbingly, a few mistakes were also recently uncovered in the second of the climate research reports produced in 2007 by the Intergovernmental Panel on Climate Change; the second report examines the current effects of climate change and forecasts future effects. (No errors have been found in the first, and most often quoted, report, which says that the evidence is incontrovertible that human activity is causing the atmosphere to warm and the seas to rise.)

Last, in December, the much anticipated climate summit in Copenhagen failed to produce a significant agreement to curb greenhouse emissions; at the same time, U.S. legislation on those fronts has stalled.

As we mark the 40th anniversary of Earth Day this April, what are we to make of these events? It is true that atmospheric science is complex and climate models are imperfect. Clearly, scientists, who are only human after all, are also imperfect. But the advancement of science involves a preponderance of evidence. Thousands of studies, conducted over decades, indicate that humanity’s thumbprints are molding the planet. Readers of Scientific American first learned that excess carbon dioxide could detrimentally affect climate in a feature article that ran back in 1959— that’s right, 50 years ago. Today science is still grappling with uncertainties over the degree of human influence, but the work of thousands of researchers before and since that 1959 article shows that it does exist.

In this issue, a special report reveals how we have fundamentally altered Earth—its climate, its resources, its ecosystems—and offers ideas for what we can do about it. “Boundaries for a Healthy Planet,” by atmospheric scientist Jonathan Foley, explains the safe thresholds for environmental processes that profoundly affect sustainability. Then, “Solutions to Environmental Threats” provides a set of experts’ takes on approaches we could employ to keep those processes within limits. Next, in “Breaking the Growth Habit,” Middlebury College scholar in residence Bill McKibben contends that, to survive, society must end its addiction to economic growth in favor of smart maintenance of wealth and resources. Skeptical? Staff editor Mark Fischetti questions such assertions in “Bill McKibben, Challenged.” Whether you agree with the notions or not, we hope you will find the exchange, and the special section as a whole, informative and thought-provoking.