All of us are aware of the changing climate. We all have our anecdotes about how different the weather was in the past. We saw it again in the unseasonably warm Thanksgiving weekend. And “Climate-gate” notwithstanding, there are many datasets, from different sources, using different methodologies, that show that the last years have been the warmest on record.

Does it matter? The warm Thanksgiving weather was pleasant…but let me quote Mercy Karunditu whom we met in Kenya: “We used to be very sure when the rains would come....now we are not sure and when they come they are strong and in a very short period of time.” High income countries are threatened, we know that. But developing countries are much more vulnerable: According to studies reviewed for the World Development Report, looking forward, developing countries will bear some 80% of the costs of the damages of climate change. Yet they have contributed only about a third of the greenhouses currently in the atmosphere.

So what to do about climate change? Poor countries are confronted with so many immediate development challenges. High income countries are tackling a financial crisis. Yet the World Development Report 2010 argues that we have to “Act now, act together, and act differently.”

What does this mean for us as individuals? Well, as consumers we directly determine about 40 percent of emissions through our daily decisions on how to move around (SUV, bus, bicycle), where to live, and what to consume (meat eating is a source of substantial methane emission, with methane a very potent gas). And as citizens, we determine whether politicians are willing to vote on an ambitious climate bill. Politicians though are worried individuals aren’t willing to pay to control climate change. They are wrong: a recent poll done for the WDR shows that 63% of people polled across 15 countries (most developing) were willing to spend an amount equivalent to 0.5-1% of monthly national income to combat climate change. In poor Viet-Nam, nearly 60% were willing to spend 1%. Are you?

High-income countries can easily reduce their high-carbon footprint without dramatically affecting their lifestyles. For example, replacing the fleet of SUVs currently on the road in the United States with sedans that have European fuel efficiency standards would reduce global emissions by an amount equivalent to the emissions produced by providing electricity to the 1.6 billion people currently without. And rich countries adopting stringent emission targets will trigger the kind of investments we need in clean technologies. (For your information: annual global public investments on energy Research and Development today is equivalent to what US families spend on pet food, and French families on cheese. And private energy Research and Development amounts to 0.5% of energy companies’ revenues. Innovative sectors like telecom and pharmaceuticals spend 8 to 15% of their revenues on Research and Development.)

So….

Act now, because otherwise it will be too late. The climate system is characterized by tremendous inertia: carbon dioxide stays in atmosphere for decades to the century so that today’s action determines tomorrow’s options. If we wait too long it will be too late: scientists tell us that if we fail to act in the coming decade, we will overshoot the 2°C warming that prudence recommends not exceeding.

Act together, because all have a role to play. Developing countries will be responsible for some 90% of emission increases looking forward so they must be part of the effort to act (though they will need financial support). And, like richer countries, they have lots of opportunities to cost-effectively reduce emissions.

Act differently, or else we will repeat the mistakes of the past. To stabilize warming around 2°C we will need to fully decarbonize the world economy by the end of the century. That requires massively transforming our energy systems, and massively increasing our energy efficiency. It also requires major changes in how we manage our land and agriculture (land use, land use change and forestry accounts for some 20 percent of global emissions).

This special article was received from Marianne Fay, Chief Economist, Sustainable Development Network, who is also the Co-Director, World Development Report 2010 “Development in a Changing Climate.” The WDR is one of the flagship publications of the World Bank Group.