What do Glasgow, Edinburgh, Manchester, Nottingham, Bristol and London have in common? They have all set themselves the target to become carbon-neutral, with plans to dramatically reduce emissions from housing, transport and energy systems. Though target dates so far range from 2030 to 2050, all have recognised the severity of recent scientific warnings that climate change needs to be treated as a state of emergency.

In Denmark, Copenhagen has been working on similar plans since 2012, when the city council adopted its CPH 2025 Climate Plan. This aims to make the city carbon-neutral by 2025, which – if successful – would make it the first capital city in the world to achieve such a goal.

Copenhagen has reduced its emissions by 42% since 2005, according to Jørgen Abildgaard, director of the city’s climate programme. This reduction took place at a time when the population grew by 16%, and was mainly attributable to the increased use of biomass in combined heat and power production, and a growth in wind power to generate energy.

Some 20,000 street lamps in the city have been replaced with LED bulbs, saving 57% of energy compared to 2010. The 100-year-old district-heating network – through which heat is produced and supplied from one neighbourhood plant, instead of within each household – has achieved major energy savings through the replacement of steam with hot water in its system and a reduction in the temperature of the supply pipe.

Already a cycle-friendly city, Copenhagen has built new cycle lanes and walkways over the harbour to provide better links between parts of the city. Since 2010, CO2 emissions from transport have fallen by 9%, while the number of kilometres driven on the city’s road network has fallen by 3%, and cycle traffic has risen by 12%.

However, as the plan moved into its second phase, covering 2017 to 2020, the city recognised that far more needs to be done, since the cheap and easy options for cutting CO2 emissions have been all but exhausted. According to Abildgaard, there are particular challenges when it comes to traffic congestion, converting vehicles to new types of fuel, and reducing energy consumption in the city.

Indeed, the city admits that the transition has been slower than expected, with national measures such as congestion zones and changes to energy taxes failing to materialise. Car ownership is expected to rise, exacerbated by the city’s population growth.

One idea under consideration is “mobility as a service”, which would introduce a subscription scheme to provide residents and visitors with easy access to ordering and paying for their daily transport by bus, train, car sharing, bike and taxi as a flexible alternative to private cars. This is being piloted with 200 families, and officials intend to roll it out city-wide if successful.

Ultimately, Abildgaard says, the key to the success of Copenhagen’s plan will be collaboration – with citizens, internationally, and with the private sector. “One of the preconditions in a city is close collaboration with stakeholders. We can set up a programme but it’s really the private sector that needs to implement it. They have the investment power,” he explains.

For example, the city has been working with businesses including its district-heating operator HOFOR and energy companies Ørsted and ABB to test and demonstrate solutions and products that integrate energy production and use in buildings and the transport sector in Nordhavn, a new part of the city under development. The projects will use real-time data to intelligently control subsystems and components in order to improve energy flexibility, making renewable energy more efficient.

Projects have been initiated with towns and cities around the world, such as climate adaptation with New York, and water and district-heating projects with Beijing. “We need to have international cooperation,” Abildgaard says. “We are too small on our own.”

Catherine Early is chief reporter for The Ecologist