April 22 marked the 45th anniversary of Earth Day, established in 1970 to draw attention to environmental challenges. Never have those challenges been greater or more urgent than they are today. A combination of climate change, erosion of biodiversity and depletion of natural resources is propelling Earth toward a tipping point, beyond which objectives like sustainable development and poverty reduction will be more difficult than ever to achieve.

Since 1970, scientists have learned not only that human activity is the primary driver of environmental change, but also that it is pushing Earth beyond its limits. If we do not make big changes fast, the results could be devastating.

Global leaders seemed to recognize this when they agreed five years ago to limit global warming during this century to 2 Celsius above pre-industrial levels — the threshold beyond which we risk triggering more devastating consequences of climate change. But strong action to reduce emissions has not been taken. On the contrary, emissions have increased markedly.