Dead plants encourage belief in global warming

In 2006, the Conservative party in the UK unveiled its new logo – a scribbled sketch of a healthy-looking oak tree. The image was intended in part to communicate the party's renewed dedication to environmental causes. A new study by French psychologist Nicolas Guéguen suggests that if the Conservatives want to help change people's attitudes towards the environment, they should consider adapting their logo to one of a dying tree. Why? Guéguen has shown that the presence of dead plants strengthens people's beliefs in global warming.

In the first of two studies, Guéguen had 60 participants fill out a questionnaire about current affairs, including four questions about global warming, such as: "It seems to me that the temperature is warmer now than in previous years." Crucially, half the participants filled out the questionnaire in a room in the presence of a 150cm tall ficus tree with luscious green leaves; the other participants in a room in the company of a dead ficus tree. The finding: participants in the dead tree condition expressed far stronger beliefs in global warming than the participants in the other group, whilst their answers to the remaining questions were no different.

In a follow-up study, Guéguen introduced a no-tree condition, to make sure that it's not the case that the presence of a healthy plant weakens beliefs about global warming. He also featured a condition with three dead or healthy plants – a ficus, a bonsai and a dracaena. The presence of healthy plants made no difference to global warming beliefs versus the no-plant control condition. Once again, however, the presence of a dead plant strengthened beliefs in global warming, and more dead plants meant even stronger such beliefs. No students in either study guessed the aims of the research.

Guéguen speculated that the sight of dead plants probably triggered in participants' minds concepts associated with global warming, such as heat and drought, without them being consciously aware of this effect. The new findings chime with earlier research showing how incidental circumstances influence people's belief in climate change – for example, people are more likely to say they believe in climate change on warmer days. A weakness of the study is that there's no mention of whether the female experimenter who dealt with the participants was blind to the aims of the research – might she have affected their results through her own behaviour?

Notwithstanding that issue, the study has obvious practical implications. Guéguen suggested that in public toilets, for example, the presence of plants without foliage could encourage less water consumption when washing one's hands (though that might harm hygiene initiatives!). More generally, Guéguen advised, "people who want to heighten public awareness on the topic [of global warming] could profitably use photographs or videos of dead plants, or plants without foliage, thus increasing the effectiveness of public awareness campaigns."

Further reading

Guéguen, N. (2012). Dead indoor plants strengthen belief in global warming. Journal of Environmental Psychology, 32 (2), 173-177 DOI: 10.1016/j.jenvp.2011.12.002