For many environmentalists, all human influence on the planet is bad. Many natural scientists implicitly share this outlook. This is not unscientific, but it can create the impression that greens and environmental scientists are authoritarian tree-huggers who value nature above people. That doesn't play well with mainstream society, as the apparent backlash against climate scientist revels.

Environmentalists need to find a new story to tell. Like it or not, we now live in the anthropogene—an age in which humans are perturbing many of the planet's natural systems, from the water to the acidity of the oceans. We cannot wish that away we must recognize it and manage our impacts.

Johan Rockstrom, head of the Stockholm Environment Institute in Sweden, and colleagues have distilled recent research on how Earth system work into a list of nine "planetary boundaries" that we must stay within to live sustainably. It is preliminary work, and many will disagree with where the boundaries are set. But the point is to offer a new way of thinking about our relationship with the environment—a science-based picture that accepts a certain level of human impact and even allow us some room to expand. The result is a breath of fresh air: though we are already well past three of the boundaries, we haven't trashed the place yet.

It is in the same spirit that we also probe the basis for key claims in the Intergovernmental Panel on Climate Change's 2007 report on climate impacts. This report has been much discussed since our revelations about its unsubstantiated statement on melting Himalayan glaciers. Why return to the topic? Because there is a sense that the IPCC shares the same anti-human agenda and, as a result, is too dangerous of unverified numbers. While the majority of the report is assuredly rigorous, there is no escaping the fact that parts of it make claims that go beyond the science.

Above all, we need a dispassionate view of the state of the planet and our likely future impact on it. There is no room for complacency; Rockstrom's analysis shows us that we face real dangers, but exaggerating our problems is not the way to solve them.