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Scientists are city people. More than one-tenth of the workforce in the Washington DC metropolitan area are scientists and engineers. Beijing has more than 160,000 professionals in research and development. Worldwide, resources such as universities and researchers are concentrated in urban areas. So why do so many scientists ignore the needs of our cities? It is time to encourage scientists and universities to pay more attention to urban areas, and Nature this week includes a package of articles about researchers and cities (see page 899).

Statistics reveal that cities are the most productive regions in terms of numbers of papers and their scientific impact. Tokyo, London, San Francisco, Paris, New York, Boston and Beijing all score highly on these metrics, and they each hold vast populations. These urban centres not only provide ample opportunities for scientific collaboration, but also contain a wealth of nonscientific resources, such as centres of the arts, entrepreneurship and financial markets.

Researchers who benefit from opportunities in cities should ask what they can give back. More than half of the world's people live in cities, and that number is growing rapidly. So if scientists want to help the majority of the population, they need to turn their attention to urban areas.

Metropolitan concerns should also draw the focus of scientists for other reasons. Cities suffer from pollution, poverty, insufficient health resources and vulnerability to climate change and natural disasters; just look at the situation in Port-au-Prince after the Haiti earthquake in January, or Dhaka after this year's floods in Bangladesh. At the same time, cities are the unit of government with the greatest chance of managing problems such as climate change. More than 40 of the world's large cities are setting voluntary goals to reduce their own emissions. If researchers can help to solve the problems of cities, they will go a long way towards tackling these issues on a bigger scale.

Individual scientists and organizations have been slow to realize this. The Intergovernmental Panel on Climate Change, for example, has over the past two decades produced four major assessments and many smaller reports on the causes and effects of global warming, but it has focused its analyses on the national level and has not conducted any extensive studies on cities — even though they are responsible for the vast majority of carbon dioxide emissions and will suffer from shifts in climate.

This negligence is now being addressed. Several universities — such as the University of Colorado Denver and Newcastle University, UK, are building doctoral programmes in urban sustainability.

Individual scientists can make a difference, too. Cynthia Rosenzweig, for example, has worked in New York City for more than 20 years to help assess the risks of climate change and plan how the city can prepare for coming hazards (see page 909). She co-chairs the New York City Panel on Climate Change, and has helped to develop a sustainability plan for the city. In China, scientists are often consulted by mayors trying to meet goals for energy efficiency and other green metrics.

Scientists who have been involved in helping cities prepare for the future say that researchers need to venture outside their comfort zones. Too often, scientists simply publish their findings and assume that the information will reach the policy-makers who need it. But information does not flow on its own. Researchers should create opportunities to provide information in clear language directly to officials, through meetings and in the form of reports and websites such as the 2008 assessment Climate Change and Chicago (see When they do sit down with policy-makers, scientists may learn that the information they provide is not always what is most needed. Water managers, for example, require projections of shifts in precipitation patterns and temperature trends over the next decade — a level of specificity that might be beyond the current capabilities of climate models. But interactions between scientists and information users can help to shape how researchers plan their future work.

Scientists who don't study topics with obvious urban connections may wonder what they can do. Those from many disciplines can chip in; on page 916 of this issue, synthetic biologists argue that their community could help, for example, by developing engineered molecules to cover buildings and provide protection from the elements while absorbing carbon dioxide from the environment.

Researchers could also assist urban communities through appearances in classrooms. Many cities suffer from a lack of resources and can't give students adequate instruction in science and mathematics. Scientists can tutor students, help with science fairs or just talk about their work. In the most crowded places on the planet, there is often a shortage of inspiration. Scientists can help to fill that gap.