Environment & climate
Climate, pollution, waste and nature. Real interventions, each with its sources: what worked, what didn't, and why.
9 worked5 mixed2 didn't work
What worked
- WorkedEnvironment & climate
Sweden's carbon tax
ChallengeSweden needed to cut carbon emissions without damaging its economy.
One of the world's first and highest taxes on carbon emissions, introduced in 1991.
Almost −11%transport CO2 after the carbon tax and fuel VAT, mostly due to the taxQuasi-experimentalRead case - WorkedEnvironment & climate
The EU Emissions Trading System
ChallengeEurope needed to cut emissions from power plants and heavy industry.
A cap on total emissions from power plants and heavy industry, with tradable permits.
~−47%emissions under the system, 2023 vs 2005ObservationalRead case - WorkedEnvironment & climate
Costa Rica's payments for forest protection
ChallengeCosta Rica was losing its forests to one of the world's fastest deforestation rates.
Paying landowners to protect and restore forests, funded partly by a fuel tax.
1,052,867.40 haprotected, managed, restored or reforested under the program, 1997–2014 (FAO)ObservationalRead case - WorkedEnvironment & climate
Ireland's plastic bag levy
ChallengePlastic bags were a major and highly visible source of litter.
A 15-cent charge on every plastic shopping bag, paid by the customer.
−90%plastic bag use almost immediatelyObservationalRead case - WorkedEnvironment & climate
Global phase-out of leaded petrol
ChallengeLead from petrol harmed children's brain development and caused heart disease and early deaths.
A UN-hosted partnership helped the last countries stop selling leaded petrol, ending its use in 2021.
1.2mpremature deaths prevented per year (UNEP estimate)ObservationalRead case - WorkedEnvironment & climate
Breathe London hyperlocal air quality sensors: London
ChallengeAround 100 official monitors could not show pollution street by street, outside schools or in outer boroughs.
London placed 100+ low-cost air sensors at schools, hospitals and hotspots and published the data live.
40%share of Breathe London sensors detecting likely illegal pollution, first 8 monthsObservationalRead case - WorkedEnvironment & climate
Energy retrofits of social housing: Paris
ChallengeHousing produces a third of Paris’s emissions, and many social tenants face high heating costs.
Paris has co-funded deep energy renovations of social housing with landlords since 2008.
−56%average cut in greenhouse gas emissions in renovated Paris social housingObservationalRead case - WorkedEnvironment & climate
Air sensors at schools and children’s centres: Lima
ChallengeLima had some of Latin America’s worst traffic air pollution and few monitors near young children.
Lima put low-cost air sensors at schools, shelters and child health centres and redesigned nearby spaces.
45%maximum air quality improvement reported in redesigned spaces near a Lima schoolObservationalRead case - WorkedEnvironment & climate
Recycling cart ‘Oops’ tags: San José, California
ChallengeOver half of single-family recycling was contaminated, driving up the city’s hauling costs.
City ambassadors checked recycling carts and left ‘Oops’ or ‘Good Job’ tags with personal feedback.
−18.9%contamination in tagged households’ recycling carts, 1–2 weeks after one tagQuasi-experimentalRead case
Mixed results
- MixedEnvironment & climate
London's Ultra Low Emission Zone
ChallengeAir pollution from vehicles was harming Londoners' health.
A daily charge for the most polluting vehicles driving in London.
19.6%drop in NO₂ at central London traffic sites, 3 months after 2019 launchQuasi-experimentalRead case - MixedEnvironment & climate
Kenya's plastic bag ban
ChallengePlastic bags were clogging drains, polluting land and harming livestock.
One of the world's strictest bans on making, selling or using plastic bags.
80%of Kenyans stopped using plastic carrier bags, per environment agency estimateObservationalRead case - MixedEnvironment & climate
Insulated ceilings for low-income homes: Cape Town
ChallengeMany cold, damp RDP houses had no ceilings, pushing poor families to spend more on heating.
Cape Town fitted insulated ceilings to government-built RDP homes that were built without them.
64%Mamre households needing less electricity to heat their home after the retrofitObservationalRead case - MixedEnvironment & climate
Sustainable school menu with local farm produce: São Paulo
ChallengeFeeding about a million students daily with high-carbon menus and little local, sustainably farmed food.
São Paulo buys organic and family-farm food for city school meals and plans lower-carbon menus.
30%at least this share of São Paulo school-meal ingredients now from local family farms (WFP, 2024)ObservationalRead case - MixedEnvironment & climate
Bringing informal waste collectors into the system: Accra, Ghana
ChallengeTwenty years of formal private contracts had left a quarter of Accra’s waste uncollected and little recycled.
Accra partnered with informal waste collectors and recyclers instead of relying only on formal contractors.
90%waste collection coverage in Accra after informal collectors were included (from 75%)ObservationalRead case
What didn't work
- Didn't workEnvironment & climate
Cash for Clunkers
ChallengeCar sales had collapsed in the recession and old cars polluted heavily.
Payments to trade in old, fuel-hungry cars for more efficient new ones.
370,000extra cars bought July–August 2009, mostly offset within 10 monthsQuasi-experimentalRead case - Didn't workEnvironment & climate
France's 2018 fuel tax increase
ChallengeFrance needed to cut emissions from road transport to meet its climate goals.
A planned rise in fuel taxes for climate goals, dropped after the 'yellow vest' protests.
€44.6/tCO₂carbon tax frozen at 2018 level; planned rise to €86.2 by 2022 abandonedObservationalRead case