The focus of World Environment Day this year is on the impact of climate change on the polar regions, their ecosystems and communities, and the consequences that will have for the world.

There is a close and complex relationship between health, health security and our changing environment. Limiting the impact of climate change is about saving lives and livelihoods, as much as it is about protecting the natural environment. More than 35 000 people died in the summer heatwave in Europe in 2003, while in 2005 Hurricane Katrina in the United States caused significant death and destruction. It is estimated that 60,000 deaths from climate-related natural disasters occur every year, the majority of them in the developing world.

Even these dramatic numbers do not adequately reflect the potential indirect impact of climate change on health. Many of the most important global killers are highly sensitive to climatic conditions. Malaria, diarrhoea and malnutrition kill millions of people every year, most of them children. Without effective action to mitigate and adapt to climate change, the burden of these conditions will be greater, and they will be more difficult and more costly to control.

As the climate warms, icecaps and glaciers retreat and sea levels rise. This threatens the health of those who live in coastal areas, or in cities where the only freshwater comes from predictable seasonal melting of glaciers. At the same time, rains become less predictable and evaporation increases, reducing the quality and the quantity of drinking water, and eventually bringing drought. Together, these changes threaten the health of millions of people.

There are two things that we can and must do to respond to this challenge. First, we need to strengthen public health systems, which are the first line of defence against climate-related health risks. Second, we need to remember that prevention is just as important as cure. Health outcomes benefit both from reducing climate change and adapting to it. Many of the actions that are necessary to reduce our impact on the global climate can also reduce pollution and save lives now.

Reducing our impact on the global climate requires individuals, communities and governments to make the behaviour and policy changes - such as cleaner energy and more sustainable transport systems - that will also bring immediate health benefits.

Together, we must act to reduce the impact of climate change, for healthy populations and a healthy planet. Dr Margaret Chan Director-General, WHO, 05/06/07.