The world's poor will bear the brunt of the impact of global climate change. As the planet warms, rainfall patterns shift, and extreme events such as droughts, floods, and forest fires become more frequent. Millions in densely populated coastal areas and in island nations will lose their homes as the sea level rises. In Africa, Asia, and elsewhere, poor people face prospects of tragic crop failures, reduced agricultural productivity, and increasing hunger, malnutrition, and disease. It will become even harder to attain the Millennium Development Goals - and ensure a safe and sustainable future beyond 2015.

For the people of the developing world - even as they strive to overcome poverty and advance economic growth - climate change threatens to deepen vulnerabilities, erode hard-won gains, and seriously undermine prospects for development. At the same time, they fear limits on their critical call to grow their economies, expand opportunity, and develop energy or new rules that might stifle their many needs, from infrastructure to entrepreneurism.

Climate change is one of the most complex challenges of our young century. No country is immune. Alone, no country can take on the interconnected challenges posed by climate change, which include controversial political decisions, daunting technological change, and far-reaching global consequences.

A "climate-smart" world is possible in our time. Yet, as the World Bank Group's new World Development Report argues, effecting such a transformation requires us to act now, act together, and act differently.

We must act now, because what we do today determines both the climate of tomorrow and the choices that shape our future. Today, we are emitting greenhouse gases that trap heat in the atmosphere for decades or even centuries. We are building power plants, reservoirs, houses, transport systems, and cities that are likely to last 50 years or more. The innovative technologies and crop varieties that we pilot today can shape energy and food sources to meet the needs of 3 billion more people by 2050.

We must act together, because climate change is a crisis of the commons. Climate change cannot be solved without countries cooperating on a global scale to improve energy efficiencies, develop and deploy clean technologies, and expand natural "sinks" to grow green by absorbing gasses. We need to protect human life and ecological resources. Developed countries have produced most of the emissions of the past, and have high per capita emissions. These countries should lead the way by significantly reducing their carbon footprints and stimulating research into green alternatives. Yet most of the world's future emissions will be generated in the developing world. These countries will need adequate funds and technology transfer so they can pursue lower carbon paths - without jeopardizing their development prospects.

We must act differently, because we cannot plan for the future based on the climate of the past. Tomorrow's climate needs will require us to build infrastructure that can withstand new conditions and support greater numbers of people; use limited land and water resources to supply sufficient food and biomass for fuel while preserving ecosystems; and reconfigure the world's energy systems. This will require adaptation measures that are based on new information about changing patterns of temperature, precipitation, and species. Changes of this magnitude will require substantial additional finance for adaptation and mitigation, and for strategically intensified research to scale up promising approaches and explore bold new ideas.

At this point, the diverse countries of the world have not sufficiently curbed emissions or financed developing countries. We need a new momentum. The current global economic turmoil must not hold us back - rather, it presents an opportunity to think anew. "Green" stimulus funds in many countries may jumpstart the innovation needed to address climate change problems. It is crucial that we reach a climate agreement in December in Copenhagen that integrates development needs with climate actions.

As a multilateral institution whose mission is inclusive and sustainable development, the World Bank Group has a responsibility to try to explain some of the interconnected challenges posed by climate change - challenges in development economics, science, energy, ecology, technology, finance, and effective international regimes and governance - and to build cooperation among vastly different states, the private sector, and civil society to achieve common goods.

The World Bank Group has developed several financing initiatives to help countries cope with climate change, including our carbon funds and facilities, which continue to grow as financing for energy efficiency and new renewable energy increases substantially. We are trying to develop practical experience about how developing countries can benefit from and support a climate change regime - ranging from workable mechanisms for afforestation and avoided deforestation through carbon trading systems, to lower carbon growth models and initiatives that combine adaptation and mitigation. In these ways, we can support the UN Framework Convention on Climate Change process and the countries devising new international incentives and disincentives.

Much more is needed. We need action on climate issues before it is too late. If we act now, act together, and act differently, there are real opportunities to shape our climate future for a safe, inclusive, and sustainable globalization.