When it comes to fighting climate change, every bit counts. At least, that was the thinking behind a small test project last summer at a metro station in Paris, the city where the world’s first legally binding climate accord was signed.

Commuters who went through turnstiles at the Miromesnil station in central Paris powered mini turbines, converting kinetic energy into electricity. During the two-day pilot project, 27,000 people crossed six turnstiles — a tiny fraction of the more than 1.5 billion passengers who use the French capital’s metro system annually. The energy produced was minuscule, but if installed across the city’s metro network, these turbines could produce 136 megawatts a year, saving 30,000 tons of CO2, according to Iberdrola SA, the Spanish energy company in charge of the project.

An upgrade across the metro system won’t happen anytime soon since it’s deemed too expensive, but the trial is an indication of emerging climate ideas. Iberdrola partnered with students at French engineering school JUNIA to design and install the mini turbines for the pilot project. The students are now working on developing more viable future iterations of the technology that can be used in metros in Paris, Madrid, Santiago and beyond, said Victoire Talleux, one of the four students on the project.

“If we transform an object into an autonomous energy generator, we can have a much lower carbon footprint than today, even if each singular object does not produce a ton of energy,” Talleux said. The turnstiles at Miromesnil powered signs in the metro station, but energy generated from future projects could be more widely used.

The project is among dozens of ideas being tossed around as Paris — which has already warmed 2.3 degrees Celsius from the pre-industrial era — seeks to transition to cleaner power and more efficiently use its energy resources. Other plans include using water from the Seine river to create a “cooling network” and reduce the effects of “urban heat islands”; or creating a new river in the bois de Vincennes fed by non-potable water that already feeds the area’s lakes and rivers. Still other projects envisage reopening the Bièvre river, which was covered in the early part of the 20th century, or adding vegetation to the rebuilt Parvis de Notre Dame forecourt.

Paris is one of the few cities in the world that calculates the carbon footprint of its territory, including emissions from air traffic and food consumed by residents. In 2021, the city’s carbon footprint was 18.4 million tons of CO2, down 35% from 2004. A new climate plan unveiled in November targets carbon neutrality by 2050, with measures including a commitment to using 100% renewable energy to power all municipal public facilities by 2040 and the phasing out by 2030 of all internal combustion engines in public vehicles — including garbage trucks and ambulances.

With traffic jams accounting for 13% of CO2 emissions in Paris, the city is adding more bike lanes, new stations for the Velib shared-bike system and 3,000 more Velibs. It’s working on the pedestrianization of big squares like Trocadéro, Iéna and Concorde, and increasing the number of lanes dedicated to buses, cabs and carpooling. After the Olympic Games in the city this summer, Paris plans to implement a Limited Traffic Zone in the city center, with travel restricted to pedestrians, cyclists, public transport and certain authorized vehicles.

As the city works toward its climate targets, some key themes have emerged. Like elsewhere in France, saving energy, particularly through insulating buildings, has become critical. Buildings are the biggest source of CO2 emissions in the French capital, accounting for a whopping 72%. Most of these emissions are from the “energy combustion” used to heat buildings.

The classic Haussmannian buildings — with stone facades, gray zinc roofs, balconies and French windows — that are a quintessential part of Paris’s iconic identity and give the city its beauty, have very poor insulation. Keeping the heat in during the winter and cooling interiors in the summer remain challenging. One in two buildings in Paris is over a century old.

The city has a goal of renovating all existing buildings to “low energy consumption” by 2050, starting with government offices, including City Hall in the center of Paris. For residential buildings, the goal is to reduce emissions by about 43% compared to 2004 levels by 2030. This includes 5,000 social housing units renovated annually and 40,000 private homes or apartments. The city plans to set up a system so lower income households can ecologically modernize their living spaces at little to no cost.

The efforts in Paris come against the backdrop of similar measures unveiled nationally. Across France, there are financial incentives for people to make homes and businesses more energy efficient, however the process is not yet user friendly, according to Michel Dubromel, head of the energy network for France Nature Environnement (FNE)—a federation of environmental protection associations.

“The government has set up a very complex financial system that people don’t understand,” he said. “Since thermal renovation costs money, people don’t commit.”

The country is also planning to double renewable energy production by 2030 to 40%. France already relies less on fossil fuels than its neighbors because of its nuclear network, giving it one of the lowest CO2 emissions relative to the size of its economy, Lamis Aljounaidi, director of Paris Infrastructure Advisory, said in an interview.

“But all our nuclear power plants are starting to age and will need to be replaced,” she said.

Renovating nuclear plants requires time and resources, which could take funding away from other forms of renewable energy, Dubromel said. Unlike the current centralized system, wind, solar and hydropower production will need to be decentralized and be overseen by regional and local authorities, he said.

Between 2004 and 2021, Paris’s energy consumption fell by 15%, with local renewable energy production going to 7% from 2.3%. To make the French capital a 100% renewable city by 2050, Paris plans to tap photovoltaic solar energy, solar thermal, geothermal, waste heat recovery and hydrothermal heat recovery.

On a national level, however, things aren’t moving fast enough, says Andreas Rüdinger, the energy transition coordinator for the Institute for Sustainable Development and International Relations (IDDRI), a French think tank. The French government, without an absolute majority in parliament, hasn’t introduced strong climate-related legislation, slowing the transition and preventing proposals from being implemented, he said. A plan to ban gas boilers was rejected by the government, which has also delayed certain measures to create low-emission zones.

“The government has trouble implementing more regulatory measures,” he said. “But it is wishful thinking to convince people that we can get through this without some drastic measures.”