Cities are increasingly moving ahead of countries in setting carbon-reduction goals and initiatives, according to a new report from banking giant HSBC.

More than 2,500 cities have now listed climate-change pledges on the Non-State Actor Zone for Climate Action (NAZCA) portal launched as part of the 2014 Lima-Paris Action Agenda, HSBC notes.

“We think this is extremely important because NSAs [non-state actors] can move quicker in implementing climate change policies and measures,” reads the report.

Cities and other NSAs tend to be faster than countries at making decisions, and are more accountable to their local electorates. They may also have greater control over which budgets can be assigned to climate-change mitigation policies. (Some experts, however, warn that cities are having serious problems implementing their own climate goals.)

Metropolitan centers have much to lose from inaction. Cities account for up to 70 percent of all greenhouse gas emissions, and many are already experiencing major levels of pollution. This causes 3 million deaths a year, according to the World Health Organization.

Dangerous levels of airborne particulate matter are a common feature of emerging market cities such as Gwalior or Allahabad in India, or Riyadh in Saudi Arabia. But they are also found in major financial centers such as Paris, London or Stuttgart.

Dealing with air pollution is a pressing problem, but one that may pale compared to the looming risks associated with global warming.

With many major cities in coastal areas, 71 percent of the world’s population might be exposed to rising sea levels by 2025. In Latin America, the proportion of the population living in low-elevation coastal zones could be as high as 90 percent.

City populations will also be more prone to higher urban temperatures, vector-borne diseases and allergen levels, HSBC predicts.

Health aside, the investment bank cites OECD data showing that by 2070 up to $35 trillion in assets could be at risk from coastal flooding in large cities.

Given the magnitude of these threats, it is not surprising that many cities have opted to take climate-change mitigation measures into their own hands.

The Paris Agreement prompted a 70 percent increase in the number of cities disclosing climate data, with urban centers such as Copenhagen, Melbourne and Stockholm announcing plans to become completely carbon neutral.

“In the U.S., where President Trump has signed an executive order to pull out of the Paris Agreement, it is encouraging from a climate standpoint that 93 cities have pledged commitments to climate action through the NAZCA portal,” reads the report.

It lists 28 countries that now have 10 or more "climate-smart cities" with city-level climate pledges. Europe leads the trend, with 646 cities lining up to cut emissions in Italy alone.

Elsewhere, there are significant climate-smart city movements in nations from Mexico to Japan. One country that stands out, HSBC says, is Canada. There, 21 cities have made climate pledges.

Canada’s 10 largest cities account for around half of the country’s population and are on a path to achieve a 40 percent emissions reduction by 2030, on average. This would achieve 17.2 percent of Canada’s national target of a 30 reduction by 2030, according to HSBC.

Jonathan Walters, a former World Bank director who now works as an independent economic consultant on energy and climate finance, said the incentives for cities to deal with climate-change mitigation are very strongly linked to local pollution and economic growth factors.

“If you look at China, large city administrations have a very strong incentive to tackle climate-change mitigation because the things you need to do are ones they want to do for other reasons,” he said. “A lot of people are dying from coal pollution, so if you replace coal, you save people from dying and save the planet at the same time.”

In addition, cities are often able to wield significant power over local transport, which the United Nations Human Settlements Program says accounts for 23 percent of city greenhouse gas emissions.

Thus, city planners can help speed up the implementation of electric vehicles and possibly even self-driving vehicle programs, unlocking “enormous gains in energy efficiency of transport,” Walters said. “It changes things dramatically.”