Such efforts should be coupled with targeted climate adaptation that improves the resilience of poor communities, such as the introduction of heat-resistant crops and disaster preparedness systems. We know that such measures can save many lives. When Cyclone Phailin made landfall near Gopalpur in India in 2013, it killed fewer than 100 people. A similar storm that hit the area in 1999, before early warning systems and evacuation plans were put in place, had caused 10,000 deaths.

Over the longer term, only rapid, sustained international action to reduce harmful greenhouse gas emissions will keep millions of people from being pushed back into poverty. And climate mitigation policies can be designed to help, rather than burden, the poor. For example, revenue generated by reforming fossil fuel subsidies could be plowed back into social safety nets. Data show if the resources currently used for energy subsidies in 20 countries were distributed instead as universal cash transfers, most people would benefit, and the poorest people - who consume almost no energy - would be the main beneficiaries.

For poorer countries, international support will be essential to support the measures needed. This is particularly true for investments in long-term sustainability, like urban transport systems and resilient energy infrastructure, which have high up-front costs but cannot wait.

The potential costs of not acting are huge. The new World Bank report estimates that based on poor people's vulnerability to natural disasters, losses of crops, hikes in food price, and increased incidence of disease, more than 100 million people could be pushed back over the poverty line by 2030 - most of them in South Asia and Sub-Saharan Africa.

For those gathering in Paris, the stakes are high. But they are even higher for the hundreds of millions of low-income people around the world who live in floodplains, along vulnerable coastlines, in fragile ecosystems, and on marginal agricultural land. We must continue to act, and act fast, to protect them.

The author is senior economist in the Climate Change Group of the World Bank Group.