Brussels: Cities are climate change's engine rooms — consuming 65% of the planet's energy and producing 70% of the greenhouse gas emissions responsible for heating up the planet.
And they are often one of its biggest casualties: residents swelter in dense, concrete environments due to the "heat island effect".
By 2050, urban populations are expected to double, meaning the climate footprint of cities could balloon unless the way we plan, power and move around them is reconfigured.
Can European cities lead on climate action?
As part of an EU initiative, 112 cities are hoping to rise to the challenge.
100 from across the European Union and 12 from associated countries such as the United Kingdom and Turkey were selected to receive support in their efforts to rapidly
reduce fossil fuel use and ensure any unavoidable emissions can be absorbed by nature or removed via carbon capture technologies. In other words, to reach net zero by 2030.
By comparison most countries around the world are falling short of the 45% reduction in emissions that scientists say are needed by the end of the decade if the world is to avoid the most catastrophic impacts of climate change.
Mission cities receive technical help and support in attracting investment. They are also encouraged to develop detailed roadmaps, which the EU estimates will require an estimated €650 billion (over $700 billion) in investments, mostly from the private sector, to achieve.
Thomas Osdoba, program director of NetZeroCities, an EU-funded project supporting the cities mission, says many of those selected share similar challenges. These include old buildings that are difficult to retrofit, car-centric urban planning, limited renewable infrastructure as well as the constraints of national policies and slow investment cycles.
Helsinki closes coal plants
However, Osdoba highlights the Finnish capital, Helsinki, as a leading example of turning climate ambitions into reality.
While Finland has committed to climate neutrality by 2035, Helsinki is aiming to reach this in 2030 by an 80% reduction in greenhouse gas emissions. So far, the city has almost halved emissions since 1990.
As is the case for most cities, heating and transport are the main sources of Helsinki's emissions. Over the next year, after closing the second of its two coal plants, the Finnish capital is set to slash its heating emissions and switch to keeping the city warm through a combination of electric boilers, bioenergy and heat pumps .
The energy company in charge of district heating is owned by Helsinki, and the decision to close plants illustrates how "agile" cities can be in climate action, explained Hanna Wesslin, climate director of the city of Helsinki.
The capital is also aiming to tackle transport, the second biggest emission source, by promoting electric vehicle use and developing the charging network, as well extending its public tramway system.
Free public transport for youth in Porto
In Porto, a coastal city in northwest Portugal, changing attitudes towards public transport is a big focus, explained Filipe Araujo, the city's vice-president responsible for the environment and climate transition office. Transport makes up 40% of the city's emissions.
Araujo said the biggest investments over coming years will be in mobility, including expanding the metro system with two new lines and making 40% of public buses electric by 2027.
He added that reducing the cost of a monthly transport pass to €30 and making it free for people under 23 has had a huge impact, doubling the number of 13–18-year-olds using public transport in recent years.
Porto has attempted to reduce its energy consumption. Switching to LEDs in street lighting, for example, has more than halved energy use. And while overall, Portugal generated a record 60% of its electricity from renewables last year, Araujo said their goal is "to produce much more energy in the city."
He said most public buildings such as schools and libraries now have solar panels, and the city is encouraging the private sector to further invest in solar by offering property tax benefits.
Porto is also investing in ensuring all social housing has solar on its rooftops so it can produce its own energy, Araujo added. "This one is very important for us because it also tackles energy poverty."
Millions of people across Europe are unable to afford enough energy to adequately power basic services in their homes such as heating, hot water and lighting.
Greening homes and streets in Leuven, Belgium
Leuven, Belgium, may be one of the smaller mission cities but is advancing quickly on a plan already 10 years in development, says Osdoba.
Jessie Van Couwenberghe, leader of Leuven's Climate Neutral mission says the city has worked hard to engage all elements of society so there is a sense of ownership in its plans.
As heating buildings is currently the biggest source of energy consumption in Leuven, the city is prioritizing retrofits to curb energy use and boost renewables. As part of this Leuven has created a "Climate House", which the public can visit for information on renovating their homes, including advice on where to find subsidies.
And while massive emissions cuts are needed, it is also addressing what is happening street by street.
For local communities this includes grants for projects related to nature-based solutions and asking the public to suggest areas for so-called depaving, which is the process of replacing concrete and asphalt surfaces with carbon absorbing plants and soil.
Will cities be able to do it?
But with only a few years left and much of the funding yet to be invested, how realistic are these goals?
Osdoba is optimistic a good number will hit net zero by 2030, and those that don't will be much closer to it than they would have otherwise.
Warsaw, one of five Polish cities on the EU mission, is a case in point.
"Frankly, it's impossible for us to be climate neutral by 2030," said Jacek Kisiel, deputy director of Warsaw's air protection and climate policy department, explaining the city is reliant on a state-owned heating network powered by fossil fuels, which continue to produce most of Poland's energy.
"But still, we have the ambition," said Kisiel.
He has high hopes for a proposed green construction standard requiring all new city buildings to be powered by renewables and collect and reuse rainwater. Warsaw is also aiming to retrofit 40% of city owned buildings by 2035 so they consume less energy.