If you need a cheap way of warming up during the colder months, then we might have a solution.
According to psychologists, doing an environmentally good deed gives you a warm feeling - quite literally.
A study found that when volunteers thought they were helping the environment, their perception of temperature changed. It was as if they were enveloped in a "warm glow".
People classed as environmentally "friendly" estimated the temperature around them to be around 1C higher than those led to believe their behaviour was environmentally "unfriendly".
The report authors, led by Danny Taufik, from the University of Griningen in the Netherlands, wrote in the journal Nature Climate Change: "Acting environmentally friendly boosts a person's self-concept, which is reflected in a literal warm glow.
"We also explored whether physical warmth (skin temperature) is affected by acting environmentally friendly, but we found no consistent evidence for this."
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Students taking part in the study completed a questionnaire about their carbon footprint, and were told that lower scores indicated environmentally friendly behaviour.
They were then given a fake carbon footprint score for the "average" student, against which their own scores were compared.
Participants were also asked to guess the temperature of the room in which they were sitting.
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Those whose carbon footprints appeared to be more environmentally friendly than average rated the room significantly warmer than students whose scores were less friendly.
The researchers concluded that helping the environment was intrinsically rewarding, which was something that should be recognised by "green" campaigns.
For instance, informing people they could help protect the environment by unplugging unused electronic devices may be a better strategy than telling them it will save money.
Future research could explore the extent to which acting in an environmentally friendly way might influence warmth-related behaviours such as setting central heating thermostats, said the scientists.
They added that other work had shown a negative psychological state caused by feeling lonely resulted in lower perceived temperatures, and also prompted people to take warmer showers "presumably to make one feel better".