Human-induced climate change, with such rapid and continuing global-scale warming, is historically unprecedented and signifies that human pressures on Earth's life-supporting natural systems now exceed the planet's bio-geo-capacity. The risks from climate change to health and survival in populations are diverse, as are the social and political ramifications. Although attributing observed health changes in a population to the recent climatic change is difficult, a coherent pattern of climate- and weather-associated changes is now evident in many regions of the world. The risks impinge unevenly, especially on poorer and vulnerable regions, and are amplified by pre-existing high rates of climate-sensitive diseases and conditions. If, as now appears likely, the world warms by 3-5oC by 2100, the health consequences, directly and via massive social and economic disruption, will be severe. The health sector has an important message to convey, comparing the health risks and benefits of enlightened action to avert climate change and to achieve sustainable ways of living versus the self-interested or complacent inaction.