The Spillover Effect: What is it and can it promote pro-environmental behaviour change?

In general terms, a ‘spillover’ is the unintended effect of an action or event. It is often beyond the original scope of impact that was envisioned. In behavioural science, there are two types of spillovers: positive and negative. 

Looking at this through an environmental lens, we talk about positive spillover when the adoption of one pro-environmental behaviour leads to the increased probability of adopting more pro-environmental behaviours, especially if they are similar. For example, a change in recycling behaviour that leads to reusing otherwise thrown away items. 

On the other hand, negative spillover is when the adoption of one pro-environmental behaviour leads to the decreased probability of adopting more pro-environmental behaviours. For example, newly adopted recycling at home that leads to an increase in buying behaviours.

How can the adoption of similar pro-environmental behaviours lead to different outcomes? According to Dr Nita Lauren, there are a few spillover ‘influences’ that we have been able to observe:

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Factors influencing negative spillover:

Two scenarios have been observed where negative spillover is more prone to occur:

Making the better item more affordable does not always lead to better behaviour change

Let’s use car petrol as an example. Hypothetically, if a new ecological gas enters the market at 50c less than your usual petrol, people are generally more prone to ‘feel better’ about purchasing more petrol, which in turn leads to more private vehicle use, and less savings.

Giving yourself a “one-off” (or a two, three, or more) based on past pro-environmental behaviours

The second one is related to a moral licensing,which is giving yourself permission to behave ‘less’ morally (or sustainability) based on past actions of behaving morally.

For example, an individual giving themselves a “one-off” to not recycle for a whole week, or month, based on previously good recycling behaviours. Or when an individual chooses to ignore certain pro-environmental behaviours (e.g. bringing reusable bags to the grocery store) based on the fact that they are already doing other pro-environmental behaviours and are “already doing their part”.

In both cases you feel you have ‘permission’ to do environmentally unfriendly behaviours, either because you have already done “the right thing” or because you are already doing “other right things”.

Factors influencing positive spillover:

Here are two instances where spillovers can create positive outcomes:

Joining a community of like-minded individuals

When a person identifies with a group, say a sustainability group, there is a sense of obligation to act towards the group’s goals.  In addition, the initial behaviour change affects self-perception, thus changes in their behaviour occur in accordance with how they now perceive themselves.

Reminding a person of their past pro-environmental behaviours also works to increase identity towards pro-environmental goals. This is especially the case when the alternative behaviour is costly or difficult, as it prompts individuals to reflect on their actions.

Taking baby steps

When doing one thing for long enough, you build a sense of confidence or capability to do that one thing. The longer a person continues to do that one thing, the more likely they are to adopt similar behaviours. With time it could even lead to doing more difficult behaviours. For example, remembering to always bring a reusable bag to the grocery store could lead to always bringing a reusable coffee cup. In time, this could lead to cycling to work, using other forms of active transport, taking shorter showers, or even joining a local sustainability group.

However, the determination of either positive or negative spillover occurring doesn’t rely only on these factors. According to Nita, spillover is complex and relies on a multitude of things:

“Behaviour cannot be explained only by one mechanism but instead many mechanisms are required. It is not only one behaviour that leads to another, it’s a whole range of factors and behaviours that leads to other behaviours.”

It is also important to consider that not all pro-environmental behaviours are equally likely to be adopted. It also depends on the level of difficulty of the behaviour: more difficult behaviours are more likely to be adopted by people with a higher level of attitude. 

For positive outcomes for our planet, we need more people to adopt more pro-environmental behaviours. Engaging positive spillovers could be one way to achieve this. Dr Sarah Kneebone explored over 150 water saving behaviours in Australian households. She noted ‘similarities’ across these different behaviours, and, to what extent, the spillover effect can be applied to households adopting more of these behaviours. Watch this episode of Pocket Change to find out more.

Nonetheless, spillover is a complex process. Activities or campaigns to promote positive spillover must be specific, targeted and evidence-based.

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