State of the Planet

News from the Columbia Climate School

Cities: the Vanguard Against Climate Change

New York City Photo: Daniel Schwen
New York City Photo: Daniel Schwen

By 2050, two-thirds of the global population will likely live in cities. Temperatures in cities around the world are already rising due to climate change and the urban heat island effect, and are projected to rise 1.3 to 3.0°C by the 2050s in 100 global cities. By then, it’s also projected that half of the world’s urban population will live in coastal cities, which are especially vulnerable to climate change because of storm surges and sea level rise.

The election of Donald Trump, who has called climate change a hoax, has said he would cancel the Paris climate deal, block Obama’s clean power plant, and abolish the Environmental Protection Agency, will likely hamper our nation’s efforts to combat climate change. Moreover, a new UN report  says that even if the 197 countries at the Paris climate conference meet the pledges they made there, they are not ambitious enough to stop global temperatures from rising to 3° C above pre-industrial levels, a possible tipping point that could unleash the most devastating effects of climate change. These developments are troubling, but regardless of how the climate commitments of the U.S. and other nations play out, cities are becoming the vanguard in the fight to stem climate change. Before the Paris climate conference in December 2015, nearly 400 mayors of cities signed onto the Compact of Mayors, pledging to reduce their cities’ greenhouse gas emissions, make their cities more resilient to the effects of climate change and monitor progress.

Cities are responsible for 60 to 80 percent of the world’s greenhouse gas emissions, consume 75 percent of the world’s resources and because of the size of their populations and their infrastructure, are especially vulnerable to the effects of climate change.

Traffic in Bangkok, Thailand. Photo: Armin Wagner
Traffic in Bangkok, Thailand. Photo: Armin Wagner

“Cities are on the front line of both the cause and effect of climate change,’ said Somayya Ali Ibrahim, program manager for the Urban Climate Change Research Network based at Columbia University’s Earth Institute. “Cause—because if there are so many people gathered in one spot, there are more emissions and more energy is used. And on the converse side, they will be most affected by climate change because of coastal flooding, heat waves, urban heat island effects, epidemics, [and impacts on] water and sanitation systems, and transport systems. So most of the people affected [by climate change] will be in cities.”

The density of cities, however, also affords them myriad opportunities to lower their carbon footprints. And while no two cities are identical in their infrastructure, governance, technical sophistication or needs, they can collaborate and share knowledge, because most urban emissions arise from the same sources: buildings that are not energy efficient, landfills that emit methane, street lighting that produces waste heat, traffic emissions and wasteful water systems.

Cities are able to coordinate the efforts of citizens, businesses, institutions and government more easily than nations can. It is also less complicated for mayors to meet up and work together than it is for heads of state.

“And in terms of passing climate change laws or policies, national governments can get bogged down in politics, in lobbying, in different interests, as we all know,” said Ali Ibrahim. “Cities are able to very quickly pass legislation or to have a policy in place within weeks and months.”

Cities around the world are joining forces. The Global Covenant of Mayors for Climate and Energy, formed in June from the merging of the Compact of Mayors and the EU Covenant of Mayors, now comprises 7,100 cities from six continents. The largest coalition of cities fighting climate change, it is co-chaired by former NYC Mayor Michael Bloomberg and European Commission Vice President, Maros Sefcovic. The participating cities set targets that will eventually be more ambitious than the pledges their countries made under the Paris agreement. The initiative will centralize data on the cities’ climate actions, enable them to compare their efforts, foster greater collaboration and increase funding for climate actions.

Paris, France. Photo: taxiarchos228
Paris, France. Photo: taxiarchos228

Established in 2005 and chaired by Paris Mayor Anne Hidalgo, C40 coordinates the efforts to reduce greenhouse gas emissions and climate risks of over 80 megacities. Together they have committed to actions that will reduce CO2 emissions by three gigatons by 2030—the equivalent of removing 600 million cars from the road. The C40 Mayors Summit will be held in Mexico City from Nov. 30 to Dec. 2.

ICLEI – Local Governments for Sustainability is a network of over 1,500 global cities and towns that provides consulting and training to help local governments with sustainable development.

In the U.S., the City Energy Project, a joint effort of the Natural Resources Defense Council and IMT, the Institute for Market Transformation, works with 20 American cities to promote innovative solutions that reduce pollution, save money and improve the quality of life for residents. Its efforts set aggressive targets, improve the energy efficiency of buildings, and create financial vehicles to facilitate investment in energy efficiency.

Aspen, Colorado
Aspen, Colorado

The Sierra Club’s new campaign, Ready for 100, challenges 100 U.S. cities to commit to 100 percent clean energy. Burlington, Vt.; Aspen, Colo.; Columbia, Md.; and Greensburg, Kan., already get 100 percent of their energy from renewable sources. The recent Ready for 100 report highlights the achievements of 10 exemplary cities.

The Urban Climate Change Research Network provides climate science information to cities around the world. Established in 2007, the network brings together over 800 climate scientists, social scientists, political scientists, economists, planners and urban designers to study climate change mitigation and adaptation from a specifically urban perspective and share their knowledge with city leaders. It is co-directed by Cynthia Rosenzweig, senior research scientist at the NASA Goddard Institute for Space Studies where she heads the Climate Impact Group, and William Solecki, director of the CUNY Institute for Sustainable Cities.

The network’s new report, Assessment Report on Climate Change and Cities (ARC3.2) presented at Habitat III, the recent UN Conference on Housing and Sustainable Development in Quito, Ecuador, examines the latest scientific information on climate change and cities. It also describes the efforts of cities to reduce their carbon emissions and adapt to the impacts of climate change. The network’s Case Study Docking Station provides access to more than 115 examples of climate actions.

The report recommends five strategies that cities should adopt to deal with climate change.

  1. Disaster risk reduction and climate adaptation need to be integrated in development policies.
  2. Reduction of greenhouse gas emissions must be combined with increasing resilience.
  3. All stakeholders and scientists should be involved in developing action plans because cross-disciplinary collaboration is most effective.
  4. The most disadvantaged and vulnerable need to be considered when developing climate actions.
  5. Cities should access municipal and outside financial resources, develop sound urban governance for long-term planning and share knowledge with other cities.

The Urban Climate Change Research Network is a global resource, providing experts on specific aspects of climate science where they are needed. And expanding on its role as a knowledge provider, it recently launched Regional Hubs in Europe, Latin America, Africa, Australia, South and East Asia and North America with the mission to enhance the involvement and skills of local scientists, and share knowledge with cities. The hubs will be linked to one another and to other resource organizations so that reports and information can be distributed to local scientists and mayors.

“The purpose of the hubs is to develop capacity in the region,” said Ali Ibrahim. “For instance, Brazilian scientists might want to work with other cities, but due to language barriers they often can’t. Or they don’t have the connections…how do they reach someone in Australia to learn from them? So the hub director holds workshops, has events, and recruits her colleagues…it’s capacity building for the scientists in the region. …The hubs will also help us translate our knowledge into local languages.”

Here are examples of what some forward-looking cities are doing to reduce greenhouse gas emissions and/or increase their resiliency.

More Energy Efficient Buildings

Seattle, WA Photo: Daniel Schwen
Seattle, WA Photo: Daniel Schwen

Seattle, which has its sights set on being carbon neutral by 2050, adopted a Building Tune-ups policy in March 2016. Beginning in 2018, nonresidential buildings larger than 50,000 square feet will be required to have tune-ups to optimize their energy and water efficiency, and identify low-cost measures that can save 10 to 15 percent in energy per building. The city is aiming to reduce building emissions 39 percent by 2030 and 82 percent by 2050.

By 2030, Portland, Ore.’s goals are to reduce the energy consumed by buildings built before 2010 by 25 percent, make all new buildings and homes net zero, and get 50 percent of the energy used by buildings from renewable sources. The new Home Energy Score policy requires sellers of all single-family homes to do a home energy performance report and share the results when selling the house. The policy builds on the city’s mandatory energy scoring for large commercial buildings.

Clean Energy

Reykjavik, Iceland’s goal is to be fossil-free by 2050, but already gets only 0.1 percent of its electricity from fossil fuels. Most of its buildings are powered by geothermal energy and hydropower. The city has used hot water from under the earth to heat homes since 1930, and today produces much of its electricity from geothermal steam. It is the only city in the world with a district wide heating and electrical system run mainly on renewable energy.

Krafla Power Station, Iceland's largest geothermal facility. Photo: Jonathan
Krafla Power Station, Iceland’s largest geothermal facility. Photo: Jonathan

The geothermal heating system saves up to four million tons of CO2 yearly. Hellisheidi, the second largest geothermal plant in the world, is where the innovative CarbFix technology to capture its carbon emissions has been successfully demonstrated. Captured CO2 is injected back into the basaltic rock of the geothermal system and reacts with the basalt to form rock that is stable for centuries or longer.

Vancouver, which is one of the lowest per capita carbon emitters of any large city in North America, aspires to be the greenest city in the world by 2020. One neighborhood utility derives thermal energy from sewage to provide heat and hot water to nearby buildings, saving over 60 percent of the greenhouse gas emissions associated with heating buildings. When people use hot water in their homes, most of the heat is still there when the water is discarded. The facility runs the warm wastewater through a heat pump that extracts the heat, cooling the sewage. Next, it boosts the temperature of the product water, which is then pumped through the neighborhood, and at the buildings, heat is taken out and used.

Solid Waste Management

Since 2000, London, has decreased its municipal solid waste by 20 percent. Raising its landfill tax in 2011 spurred the implementation of more sustainable waste management strategies. London now incinerates 44.1 percent of its municipal solid waste in waste-to-energy plants, recycles and composts 30.4 percent of it and landfills 25.5 percent. Since 2000, landfilling has decreased 72 percent, waste-to-energy has increased 65 percent, and recycling and composting has grown 216 percent, saving the equivalent of 4.3 million tons of CO2.

Recycling in San Francisco Photo: Walter Parenteau
Recycling in San Francisco Photo: Walter Parenteau

San Francisco recycles over 75 percent of its waste, and is well on its way towards its goal of zero waste by 2020. Everyone is required to separate recyclables, compost and trash. From 1990 to 2010, landfilling went from 65 percent of solid waste to 20 percent. Mandatory composting increased 50 percent, to over 660 tons a day, more than any other U.S. composting program. The city has also banned plastic bags and charges 10 cents per checkout bag.

New Songdo City, South Korea, a brand new eco-city being built for 210,000 people, has a unique pneumatic waste collection system that sucks garbage from homes and businesses through a system of underground pipes and sends it directly to the waste collection plant. This avoids the carbon emissions and congestion that garbage trucks would produce.


This past summer, Taiyuan, China replaced its taxi fleet of 8,292 vehicles with all electric vehicles. It has over 2,451 40kW high-power charging outlets for the taxis and plans to have 6,000 by the end of this year. The city will also build 18 charging towers around the city that could charge 7,200 taxis at the same time.

New BRT in Rio Photo: EMBARQ Brasil
New bus rapid transit in Rio
Photo: EMBARQ Brasil

Rio de Janeiro is reducing emissions by creating four new bus rapid transit systems and expanding its subway system. In 2009, only 18 percent of its population had access to mass transit; today over 60 percent have it. The city has also enhanced its biking culture with Bike Rio, a shared bicycle rental program, 450 kilometers of bike paths and increased bike parking infrastructure.


About 80 percent of Rotterdam is below sea level. Faced with sea level rise that could exceed 4 feet by 2100, the city is climate-proofing itself by reinforcing dikes, building new moveable flood barriers, and making plans to accommodate the water.

The Floating Pavilion Photo: Rick Ligthelm
The Floating Pavilion
Photo: Rick Ligthelm

A Floating Pavilion, a floating hotel and plans for a floating dairy are precursors to Rotterdam’s vision of future floating urban districts with office complexes and parks. The city has also constructed green roofs throughout the city and water squares and underground parking facilities that can hold excess rainwater. Pavement by riverbanks has been replaced by grass to absorb water.

The number of Chinese cities affected by floods has more than doubled since 2008, because urban sprawl with expanses of impermeable concrete has overwhelmed drainage infrastructure. In 2015, the government launched a plan for 16 pilot sponge cities that will be retrofitted to hold, clean and drain water naturally. Each city will receive $60 to $90 million to construct ponds, filtration pools, wetlands, and permeable roads and public spaces that absorb stormwater. Analysis of the pilot projects in Beijing, Shanghai and Xinjiang found that 85 percent of runoff could be controlled to help prevent flooding. The sponge cities also helped conserve and purify water; the moist soil and foliage lessened the urban “heat island” effect, cooling the air several degrees.

New York City’s Staten Island Bluebelt is a stormwater management system based on the natural ecosystem instead of the usual hard infrastructure. A system of created wetlands linked with streams, existing wetlands, parks and natural areas slow, store and treat stormwater. The system also improves water quality, provides habitat for wildlife and creates opportunities for recreation. Streambeds and slopes are planted with native wetland vegetation that stabilizes and enhances the soil. Because the bluebelt concept has been so successful, it will now be employed in other boroughs.

Staten Island Bluebelt Photo:dgphilli
Staten Island Bluebelt

New York City is one of the most energy efficient cities in the U.S. New Yorkers per capita contribute far less to climate change than do Americans in other parts of the country, because we live in small spaces and travel via mass transit.

The city’s climate goals are ambitious: By 2050, greenhouse gas emissions will be 80 percent lower than they were in 2005. To achieve this, the city plans to reduce emissions from power production, vehicles and waste disposal, and reduce building emissions by 30 percent by 2025. The city’s goal to send zero waste to landfills by 2030 will be achieved through increased recycling and composting, expanded textile and electronics recycling, reduction of commercial waste disposal and making all schools zero waste.

New York City’s $20 billion resiliency plan includes building dunes to protect the coasts; storm water management, more bluebelt projects, and over $3 billion for reconstruction and resiliency projects across New York City housing.

“We’re going through a paradigm shift,” said Steve Cohen, executive director of the Earth Institute. “We have to change the entire nature of cities from being places where we collect people and don’t care much about the environment to places where we’re paying attention to that…It will take decades to do what we need to do. We need to work on our water system, we have to improve the issue of combined sewer overflows, we have to build more green infrastructure, we have to use more renewable energy inside the city and set up the grid in such a way that we have microgrids and smart grids to use energy more efficiently. There’s still a lot to be done, but we’ve taken some significant first steps.”

Cohen is optimistic that we will be able to head off the dire impacts of climate change through ingenuity. Reflecting on other critical moments in history, he maintains that human beings have always been resourceful enough to marshal the necessary forces to avoid catastrophe.

“What will happen ultimately, and we’re already starting to see it, is that renewable energy and electric cars and mass transit will create an effective competitor for the big suburban house, the use-up-a-resource, chew-it-up-and-throw-it-into-a-hole type of economy we’ve had,” Cohen said. “Our capacity for responding when things are bad should not be underestimated.”



Banner featuring a collage of extreme heat images.

Recent record-breaking heat waves have affected communities across the world. The Extreme Heat Workshop will bring together researchers and practitioners to advance the state of knowledge, identify community needs, and develop a framework for evaluating risks with a focus on climate justice. Register by June 15

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