Climate change has returned to the big screen with the release of Al Gore’s An Inconvenient Sequel: Truth to Power. It’s the follow-up to his Oscar-winning documentary from 2006, An Inconvenient Truth, which raised awareness about global warming and encouraged us to reduce our carbon footprints.

The sequel puts the spotlight on climate change once again and will likely re-ignite the debate in popular culture for a whole new generation of moviegoers.

Read more: Ten years on: how Al Gore’s An Inconvenient Truth made its mark

While “big issue” documentaries do a great job raising awareness and developing attitudes on important issues, they often don’t go far enough in inspiring a “call to action” – especially one that leads to long-term behaviour change. Gore’s first film did inspire short-term action on climate change, but the effects soon faded.

As well as being artistically engaging, a successful advocacy film should encourage viewers to do something. This might be to reduce their consumption of fast food (as in Super Size Me), petition for the protection of threatened wildlife (The Cove), or adopt a whole-food plant-based diet (Forks Over Knives).

Media influence

Media can and do affect our behaviour. There is a well-established link between violent media and aggressive behaviour. Smoking in movies can encourage teenagers to take up smoking.

Less is known about the media’s ability to have a positive influence – such as encouraging environmentally friendly behaviours. Even when research is conducted, the long-term effects are rarely considered.

Read more: Al Gore Q&A and video interview: Fixing democracy to combat climate change

Some studies have looked for a direct link between viewing an environmental documentary and environmental donations. One study found that twice as many people donated to an environmental cause after watching a seven-minute environmental clip. Another found that after watching a full-length dolphin documentary, almost everyone donated to a related cause.

These studies might seem encouraging, but in both cases money was given to participants and they were asked to donate it to one of a predetermined list of charities. Sadly, this means the behaviour is unlikely to translate to the real world.

Short-lived success

In the case of Gore’s An Inconvenient Truth, individuals who watched the film reported an increase in knowledge, environmental concern, and willingness to act. Another study found that two months after the film was released, the purchase of carbon offsets increased by 50% in suburbs near cinemas that screened it.

After watching the documentary Food, Inc., which takes a critical look at America’s industrialised food industry, one of us (Kim) personally took up the challenge of avoiding processed foods. She stocked her fridge with local produce and started eating more fresh fruit and vegetables. Her friends and family also copped an earful about the difference between “food” and “food-like products” – some even adjusted their behaviours as a result.

It appears Kim wasn’t alone in her response. A study by the Norman Lear Center found that people who saw Food, Inc. were more likely to do as she did, at least in the short term (there was no follow-up study). The real challenge is in creating long-term sustainable change. Kim’s Food, Inc.-induced commitments faded within six months.

This seems to be the common trend with “big issue” documentaries. While more people intended to reduce greenhouse gases after watching An Inconvenient Truth, a survey a month later showed few had followed through.

Similarly, the increased purchase of carbon offsets failed to translate into a repeated behaviour. If customers had renewed their film-inspired purchase, the notable spike two months after its release should have been observed the following year, but this was not the case.

An unexpected win

One success story was the “big issue” documentary Blackfish, which centres on the plight of captive orcas in parks like SeaWorld. The film didn’t tell people how to feel or how to respond (it didn’t include a specific “call to action”), but since its release in 2013 SeaWorld has reported a consistent drop in visitors and revenue. In 2016 Seaworld discontinued its orca breeding program and recently discontinued the orca show itself.

Apart from its strong emotional appeal, part of the film’s success is credited to the distributor, CNN, for capitalising on the growing popularity of social media. As a result, Blackfish became the most-talked-about show on Twitter, achieving almost 70,000 Tweets on the night it was released in the US. It sparked a fierce online debate, which included celebrities and media personalities, further stimulating its reach and success.

Making change last

If documentary makers want to create long-term change, they need to do more than just pull at our heartstrings. They must include a solution message and an achievable “call to action”. Without telling viewers how they can help, they can be left feeling that it’s a lost cause and that everyone is doomed.

Advocacy documentaries should also be coupled with other behaviour change techniques to increase their chances of success. For instance, they should ask viewers to publicly pledge to change their behaviour or to set goals, give them tools to help form a new habit, or tell them exactly how to petition organisations and governments to make structural changes.

Gore’s latest film ends with a brief “call to action” – urging viewers to encourage local governments and institutions to switch to 100% renewables. It even asks for a public pledge on Twitter using the hashtag #beinconvenient. But these requests seem like an afterthought. Although the doom and gloom message is paired with glimmers of hope, watching Gore’s personal struggles against big business and politics did not leave Kim, an everyday citizen, feeling empowered.

Documentaries can be a useful instrument in the behaviour change toolkit. But lasting change needs more than an engaging story on its own.