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Nudging for a sustainable future

Updated: May 24, 2021

Raising awareness about sustainability and ecological alternatives is taking an increasingly important role throughout time. Planet earth is facing major environmental issues due to carbon dioxide emissions and to careless human environmental destruction. Consequently, behavioural economics may be a tool to influence the decisions of the everyday person to enhance sustainability and to solve some of the great challenges of fighting climate change.

What is a green nudge?

Green nudges are designed to encourage environmentally sustainable behaviours. Green nudging practice can be divided into three main categories:

- nudges that appeal to the consumers’ desire of maintaining an attractive self-image,

- nudges that appeal to people’s tendency to social conform and nudges that re-set the default choice.

As claimed by Niklas Hagelberg, a United Nations climate change expert, the use of the behavioural science is fundamental to tackle environmentally exhausting behaviours. Therefore, green nudges seem to be an encouraging way to change human conduct towards a more sustainable one.

In fact, they have already been tested, both in experimental and real-life settings, and have exhibited positive outcomes. But how is it applied to everyday life?

Green nudges in everyday life

Meat vs vegetarian

According to Tackling Climate Change through Livestock, the livestock sector contributes approximately 14.5 % of global human-induced greenhouse gas emissions yearly. Also, meat consumption is causing about one-third of food-related greenhouse emissions emerging from consumption in countries such as Sweden and the United States. When talking about sustainability, it is also important to mention that when reducing meat consumption, it may also be a way to improve and protect biodiversity, reduce the consumption of water and can lead to significant benefits for public health as well.

As stated by Swedish Agricultural Board in 2017, the ordinary Swedish person eats an average of 87.7 kilograms of meat per year. This translates to roughly a quarter pound of meat per day. It became specially alarming since it reached an all-time high in 2016.

Lunch default option experiment

A study (Hansen et al. 2019) investigated a green nudge to promote healthier and more sustainable food choices. This comprised of using a vegetarian lunch-default at conferences. The experiment consisted into three rounds of two randomized groups:

- Group 1 received a non-vegetarian buffet as default but allowing to change to a vegetarian option (standard lunch registration).

- Group 2 received a vegetarian buffet registration also allowing the change to a non-vegetarian option.

The results were impressive as the vegetarian choice, by using the opt-out nudge, increased in every experiment by more that 70%. Changing the lunch-default to a vegetarian option turned out to be an effective, cheap, easy, and well-accepted nudge to promote healthier and sustainable food choices at conferences.

Green energy as a default rule

Producing energy from fossil fuels releases air pollutants, such as carbon and sulfur dioxide, contributing to the increase of greenhouse effects. As the seas absorb some of man-made carbon emissions, fossil fuels are also responsible for ocean acidification. Green energy, on the other hand, is produced from renewable resources, for example from wind, sunlight and water, being a cleaner way of producing energy.

Evidence from a German village initiative

During the 80’s in the town of Schönau, Germany, it was voted to put a green energy coalition in charge of the town’s power grid. This way, they set a green energy contract as the default option for residents of Schönau.

The results were quite positive, in 1996, 8 years after changing the default option, 99% of residents were still with the green energy contract. By comparison, other German towns who have non green energy contracts as the default option, have around 1% of the population shifting to a green contract.

Plastic recycling

The production and evolution of plastic products accelerated after World War II and it revolutionized many aspects of life as it is known today. Although having advantages and being useful in producing many equipment, plastic pollution is nowadays amongst the most serious environmental challenges, as 40% of the plastics produced per year are single-use products and disposable items.

An experiment conducted at the School of Advanced Studies Sant’Anna, in Pisa, explored how green nudges could promote plastic cups recycling.

The experiment was divided into three parts, the control period where the number of recycled plastic cups was measured without implementing any intervention. After two weeks in the control period the first treatment was implemented, it consisted of showing a message, near the garbage bins, that emphasized the importance of recycling and said that about 70% of Harvard students recycled. Subsequently the second treatment was implemented, where the recycling-bin-to-garbage ration was altered, having then a bigger plastic recycling bin.

The results showed these nudges were effective, as in the control group only an average of 3.9% plastic cups were recycled and after the first treatment this percentage increased by 36%. The second treatment was even more effective as the experiment concluded that approximately 100% of the cups were placed in the correct bin.


In terms of the outcomes for promoting sustainable behaviours, green nudges are well worth the effort. People must have the option to choose an alternative, even if it is unsustainable. By using behavioural science, it can often impact the decision process and contribute to a better and more sustainable society. Every effort is important to enhance sustainability and to answer to the important and urgent challenges of fighting climate change.


Sofia Murça - Research Analyst Catarina Chambino - Research Analyst


Hansen, Pelle G, Mathilde Schilling, and Mia S Malthesen. 2019. "Nudging Healthy And Sustainable Food Choices: Three Randomized Controlled Field Experiments Using A Vegetarian Lunch-Default As A Normative Signal". Journal Of Public Health. doi:10.1093/pubmed/fdz154.

Kurz, Verena. 2017. "Nudging To Reduce Meat Consumption: Immediate And Persistent Effects Of An Intervention At A University Restaurant". SSRN Electronic Journal. doi:10.2139/ssrn.3067940.

Nudge To Action: Behavioural Science For Sustainability". 2017. UN Environment.

Koomen, Rebecca. 2020. "What’S A Green Nudge? - The Behaviouralist". The Behaviouralist.

Schubert, Christian. 2016. "Green Nudges: Do They Work? Are They Ethical?". Econstor.Eu.

Denchak, Melissa. 2018. "Fossil Fuels: The Dirty Facts". NRDC.

Parker, Laura. 2019. "Plastic Pollution Facts And Information". Environment.

Cosic, Ajla, Hana Cosic, and Sebastian Ille. 2018. "Can Nudges Affect Students’ Green Behaviour? A Field Experiment". Sabeconomics.Org.

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