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Scientists should do the research to help mayors prepare for a warming world, say Cynthia Rosenzweig, William Solecki, Stephen A. Hammer and Shagun Mehrotra.
For years, the focus on the world's response to climate change has been on nation states, which have been mostly unsuccessful in brokering comprehensive agreements or taking action. Cities, by contrast, are preparing risk assessments, setting greenhouse-gas emission reduction targets, and pledging to act. Urban areas, home to more than half of the world's people, are emerging as the 'first responders' in adapting to and mitigating climate change.
Cities were initially ignored by most climate- change scientists. Early impact studies focused on ecosystems and agriculture. Many researchers assumed that cities in developed countries were inherently 'adaptable' - an assumption shattered by Hurricane Katrina's devastation of New Orleans in 2005. Furthermore, researchers needed complex models on small scales to examine the combined effects of heat islands, air pollution, engineering, architecture and urban design - models that haven't been possible until recently.
What the world needs is the same sciencebased foundation for cities that the Intergovernmental Panel on Climate Change (IPCC) provides for nations. Scientists including ourselves are now coming together to provide this information, with several groups formed in recent years and influential publications due out soon. Physical scientists, health scientists and engineers are starting to answer specific questions about how cities and the urban environment will interact in the face of climate change. Social scientists are addressing the human and economic costs, specifically for at-risk populations. And all are learning to take a more holistic approach, considering mitigation alongside adaptation and disaster planning.
Cities are crucial to global mitigation efforts. The International Energy Agency estimates in its most recent survey that urban areas are responsible for 71% of global energy-related carbon emissions, although the numbers vary widely depending on how cities or urban areas are defined. This percentage will grow as urbanization trends continue. The United Nations estimates that by 2050, the world's urban population will almost double from 3.4 billion to 6.3 billion, representing most of the global population growth over that time1. Cities are also centres of wealth and innovation, and so have the tools and resources with which to tackle climate-change challenges.
At the same time, cities,...