It was the French novelist, Victor Hugo, who said: "There is nothing so powerful as an idea whose time has come". That idea is the role of nature and natural capital in overcoming poverty and underpinning the wealth of nations.

2005 has witnessed unprecedented interest in the economics of the environment and the goods and services that nature provides. The wealth of nature was emphasized by, among others, the Millennium Ecosystem Assessment (MA), the findings of the Millennium Project - the initiative of the Secretary-General designed to inform the review of the Millennium Development Goals (MDGs) - and the 2005 World Summit.

The message emerging from these different processes, quite clearly, is this: targeted investments in the environment and in the restoration of damaged and degraded ecosystems have enormous long- and short-term economic benefits. As the 2005 Overview of this GEO Year Book points out with regard to the findings of the MA, although many of the benefits that ecosystems provide do not pass through the formal market system, they are often among the most valuable to societies.

The MA findings also point out that the economic and public health costs associated with damage to ecosystem services can be substantial. This was clearly demonstrated in 2005 - for several regions of the world where the impact of diverse natural disasters were worsened because environmental buffers had been previously removed.

The Feature Focus this year elaborates on the environmental, socio-economic and public health impacts of energy-related air pollution. There are many reasons why air pollution needs to be addressed urgently - not only because of its huge toll on human health in areas where it originates but also because it is too often an uncontrolled and unwelcome export to neighbouring countries. Associated with the energy consumption that contributes to air pollution are increasing global concerns over climate change, and energy security and access. On the other side of the coin, cleaner energy technologies are now available but are not always being widely adopted. These issues will be discussed at the annual UNEP Global Ministerial Environment Forum (GMEF) in 2006. A key challenge will be to identify ways in which the global community can continue to meet the rising demand for energy without compromising energy needs - particularly those of the poor - and still address the negative impacts of energy-related emissions.

In the past, the goods and services delivered by nature have often been seen as free and available at little or no cost. This will have to change as these resources become increasingly scarce and society demands higher standards of environmental care. The chapter on Emerging Challenges addresses two topics of policy interest related to food security.

The first topic explores the issue of crop production in a changing climate. Global warming could seriously compromise the ability of the environment to meet food requirements in the future. Action is needed at the national and global level to ensure that we adapt as best we can to the changes that are already taking place, while addressing the root of the problem by reducing harmful greenhouse emissions in the future. The entry into force of the Kyoto Protocol earlier this year is a first historic step, but we still have a long way to go.

The second topic identifies environmental effects and best practices related to fish and shellfish farming in marine ecosystems. Caution, planning and good management is needed to ensure that current practices do not compromise the services provided by marine ecosystems in the future.

The GEO Indicators depict major developments and trends. They support the findings reported elsewhere in the Year Book that rising greenhouse gas emissions are resulting in ecosystem change, such as accelerating ice thickness losses of mountain glaciers, and that increasingly intense exploitation of fisheries stocks is leading to serious depletion.

However, the Indicators also show that there is hope. Where action has been taken, there are positive results. The global consumption of chlorofluorocarbons continues to decrease. The proportion of the Earth's surface affording some form of environmental protection to biodiversity continues to increase.

The GEO Year Book is intended to provide a bridge between science and policy. More than 140 experts were involved in preparing the sections of this Year Book. Previous volumes have stimulated calls for action - including by UNEP's Governing Council. I hope that you will find this edition both stimulating and informative. Your feedback is very welcome.