How little nudges can help win the fight against climate change

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Four years ago, Cape Town was on the verge of running out of water. Facing the city’s worst drought on record, it was able to back away from the cliff edge thanks, in part, to a number of smart behavioural interventions.
Despite the municipal government implementing a number of measures to try and get its 4.7 million residents to cut down their water consumption, more than 60 per cent of Capetonians were still ignoring the call to action. The city then introduced restrictions on the amount of water each resident was allowed to use per day, dialled down water pressure, hiked up tariffs and fines, and installed water restriction devices at households who weren’t complying. Despite all that, consumption rates were still high.


That finally changed in 2018, when the city was faced with the real possibility that its homes’ taps could run dry. In January, the government launched a city-wide water saving campaign underpinned by behavioural science. Ever since, academics have been poring over data collected during the water crisis to find out how exactly it succeeded. Confronting the Cape Town water crisis was, in a way, a lot like confronting climate change – which means better understanding how it was solved might hold some important clues about how to handle this much bigger crisis.
“Because the drought approached and crept up on us, many people weren’t really sufficiently worried,” says Thinus Booysen, an engineering professor at Stellenbosch University in South Africa. “It was like this slow thing, like a frog in warm water.”
This is something that psychologists call “present bias”, and leads to people prioritising present-day needs over future ones. Booysen observed in a retrospective paper published in 2019 that even though the government continued to limit people’s water usage to 100 litres, and then to 82 litres, residents were still using more water than advised, possibly due to confusing messaging from the government. Even though the municipality applied considerable water fines and tariffs, they didn’t have a huge impact on the consumption habits of Cape Town’s wealthier individuals. “People who could afford to just kept on using water,” Booysen says.
Then, in January 2018, the municipal government asked residents to cut down its water usage to 50 litres a day. It announced that if Capetonians didn’t act to avert the water crisis, the taps would be turned off on April 21 – an ominous date known as Day Zero, when everyone would be forced to queue at one of 200 guarded collection points to receive a daily 25-litre water ration.


It was a wakeup call for all of Cape Town’s residents. That same month, the government collaborated with the University of Cape Town’s Environmental Policy Research Unit (EPRU) to roll out a series of measures to subtly nudge people into changing their behaviour.
The EPRU had already been investigating how it could nudge people to conserve more water prior to the drought. Between 2015 and 2016, it had conducted an extensive study on 400,000 households in Cape Town aimed at finding out what the best way was to nudge people into reducing their water consumption. During the study, researchers implemented pro-social measures like comparing a household’s water usage to its neighbours’, and financial nudges informing people of how much money they would save – or lose – depending on their water usage.
One of the most significant nudges was the publication of the names and addresses of the top water savers on the city’s website. Those targeted with this message – a mix of demographics – reduced their water use by 1.9 per cent. “We found that the high income groups responded better to the pro-environmental, prosocial, public good – specifically the social recognition type – measures – and not so much to the financial ones,” says Martine Visser, a behavioural economist at the University of Cape Town, who spearheaded the development of the nudges behind the Day Zero campaign. “For middle and low-income households, we did see that price and financial nudges mattered more.”
At the start of the Day Zero campaign, the government rolled out an online water map devised by Visser and her team. The map publicly acknowledged households that were achieving water-saving targets. If a household reached its target, it was rewarded with a green symbol displayed on their property. The map was designed with the knowledge gained from the 2016 study, which highlighted how effective it is to recognise people socially when it came to incentivising water scarcity.


Messages were also employed to help residents frame water targets as more understandable units of measurements. The city released infographics of how much water one flush of the toilet would use, or how many litres of water a two-minute shower would use. Making information clearer, Visser says, is a lesson that can be applied to climate change more broadly. Messaging needs to be delivered in a way that everyone can understand. “It took us almost going to the brink for the government to really understand the extent to which communication needs to improve to make people respond to the crisis,” she says.
Booysen also led the installation of smart water meters across 345 schools in the Western Cape, turning water conservation into a competition between the schools. Some schools were also given weekly report cards with their water usage, defined by multiples of bottles of coke or swimming pools. Overall, the interventions led to a 15 to 26 per cent water usage reduction.
Booysen admits that the strongest intervention was the “fear factor” – residents being told that they were going to have to queue up for water. “That is the moment when the penny dropped,” he says. “What our analysis of smart metre water data showed is that was the exact point when usage substantially dropped.”
While Day Zero was eventually postponed indefinitely thanks to the city pulling together to conserve water, disastrous droughts as seen in Cape Town are going to become more common in a warming world. According to a study from Stanford University, man-made climate change made the Day Zero drought five to six times more likely.
The success of nudging people to make small but significant changes has been seen in a number of local communities around the world. In the Indian city of Mumbai, restaurants began serving half glasses of water after they found that patrons were only taking a few sips and throwing the rest away. In California, restaurants are not allowed to serve water unless the diners explicitly ask for it.
The above are all examples of what behavioural psychologists call a “default”, a mechanism that works by taking the choice out of people’s hands – a real timesaver given we make 35,000 decisions each day. Toby Park, principal advisor of energy, environment and sustainability at the British consultancy Behavioural Insights Team says that nudges work best when they reduce friction and make things as easy as possible for people. “Often we don’t make an active choice; we just stick with the default option. That can have really profound impacts on the energy tariff we use, whether we offset our flights, the food we eat and so on,” he explains.
Park points to another study in which food wastage was reduced in school canteens when plastic trays used to carry food were removed, forcing people to carry their plates. “It really comes down to creating a world in which the sustainable choices are the easy choices, the popular, readily available choices, the default choices,“ Park says.
Pro-social nudges, such as water usage maps and utility bill comparisons have proven effective in other contexts. When energy customers living in low-value homes in the US were sent monthly letters outlining how much energy their neighbours were using, those who were overusing cut their consumption by up to two per cent.
But Cape Town’s success story also shows that change has to happen on many levels. While citizens were trying to reduce their water consumption, the municipality was also busy building new water sources, reducing water pressure across the city, and blasting out information on the importance of water conservation over the television and radio. “Nudges can be used in a very successful, complementary way,” Visser says. But they work best when paired with regulation.
While pro-social behavioural nudges and default changes might help with small shifts to individual behaviour, it doesn’t tackle the real systemic changes needed to deal with climate change, which needs the input of a number of different parties. The thing about behavioural nudges, is that you don’t have to think about them.
A joined up approach which utilises smart nudge interventions might be what sets us on the course to solving climate change. “It feels like maybe we should be having a much larger conversation about what activities are most polluting. Should you nudge people into buying the carbon offset for a distance flight? Or should we just ban business class travel?” Shreedhar asks. “The big challenges will be going after highly polluting activities, and balancing voluntary action and regulation”

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