A study of 2,000 adults found carnivorous Brits usually only manage to ditch their favourite foods for a plant-based diet for 12 days in total.
Using eco-friendly products is a behaviour people can keep longest, but even that starts to wane after 15 days.
While measures such as using the food waste bin, using eco settings in the home, and only boiling the water required, last for just two weeks.
It emerged 55 per cent of people have not seen positive changes following their actions, while more than half feel disheartened because it seems no matter what they do, the climate emergency isn’t improving.
The study was commissioned by Utilita, as part of its Planet Pledge campaign which invites people to take part in a 66 day pledge to do something good for the environment - the time it takes to form a new habit effectively.
Sustainability Lead, Archie Lasseter, said: "While it can feel like we're fighting a losing battle, it's so important to remember that even the smallest changes can have a massive impact, and will.
“There are 67 million people living in the UK, and if each person made a small change, the impact would be huge.
“It is sad to see how quickly us Brits give up on our attempts at being green, lasting a little under two weeks for most of us – but it’s reassuring to see that some people are winning, and are able to carry them on indefinitely.”
The study found 24 per cent of adults have been inspired to live a greener lifestyle and take on new habits because someone they knew was doing so.
However, those who decide to get into composting will pack in the new habit after just 14-and-a-half days on average, but will last a little longer before going back to buying non-sustainable fashion.
Other green goals that fall by the wayside early include walking short distances rather than driving and cutting down on using the tumble dryer.
While 22 per cent of adults don't believe they will reduce the amount they fly despite the climate crisis.
More than a fifth (22 per cent) of respondents have been told a green habit they were trying to maintain was ‘pointless’.
And another 21 per cent confess they don’t really live a sustainable lifestyle at all, according to the OnePoll figures.
Three in 10 say it’s simply too expensive to live as sustainably as they would like, and when it comes to winter, 27 per cent can’t resist taking the car instead of walking.
Another quarter found that ‘green alternatives’ to things they were used to were simply not good enough to switch to full-time.
And of the 24 per cent who do believe they’ve seen a tangible benefit to their new green lifestyle, some of the top changes have been noticeably putting less into landfill (50 per cent) and an improvement in health (45 per cent).
Four in 10 have seen their energy bills go down, and 31 per cent feel their personal energy levels have gone up since their reliance on unsustainable food decreased.
Just under half (49 per cent) believe they need ‘help’ when it comes to being motivated to live more sustainably.
In fact, on a scale of one to five, the average adult only rates their motivation for green-ness at a fairly low 3.2.
But 47 per cent feel they don’t live as green as they could because they’re just not sure how to turn their passion for sustainability into tangible changes.
Dr Pippa Lally, a behaviour scientist from University College London, said: “Utilita’s study confirms that some people are giving up on their new behaviours before they have had a chance to form into strong habits.
"The time it takes to form a habit varies for different people and different behaviours but in our research the average time it took to form a habit was 66 days, and this can be a useful target for people to aim for."
The Planet Pledge campaign is designed to help people in every household in the UK to form as many as nine new eco-friendly behaviours.
Each new behaviour comes with an annual carbon saving and cost saving, as well as prizes, which, together, should incentivise people to make some pro-planet habits.
To find out more and join before 17th Jan, visit www.planetpledge.co.uk
HOW LONG IT TAKES BRITS TO GIVE UP ON SUSTAINABLE HABITS
Have ‘meat-free days’: 12.8 days
Turning electricals off at the mains rather than leaving them on standby: 12.9 days
Setting the heating at a lower constant temperature: 13.3 days
To walk all short distances instead of driving: 13.3 days
To go a whole year without putting anything in a black bin bag: 13.3 days
Not using the tumble dryer: 13.4 days
Unplug items to avoid using vampire energy: 13.4 days
Putting on more layers instead of turning the heating on: 13.4 days
Not using the tumble dryer: 13.4 days
To have shorter showers: 13.9 days
Checking the labels of everything in the supermarket: 13.6 days
Washing clothing on lower temperatures: 13.9 days
Stop buying new clothes and get second-hand instead: 14 days
To use eco settings where possible at home: 14 days
To not buy any food with too big a ‘food mile’ footprint: 14 days
Put food in the food waste bin, not the regular bin: 14.2 days
To buy only from sustainable brands: 14.2 days
Avoiding boiling more water than needed: 14.3 days
Remember bags for life at the supermarket: 14.3 days
Drive less in general: 14.3 days
Turn off lights in unoccupied rooms: 14.3 days
Eat meat substitutes: 14.4 days
Remembering to turn off lights in the house: 14.4 days
To only buy organic fruit and veg: 14.4 days
Not to use cotton buds: 14.4 days
Compost more food: 14.5 days
Cycle more: 14.5 days
Grow your own fruit and veg: 14.5 days
To not use any single use plastic: 14.5 days
Not to book a holiday that required a flight: 14.6 days
Buying sustainable fashion: 14.8 days
Always wash and recycle everything possible: 14.9 days
Switch energy supplier: 15 days
Use eco cleaning products: 15.1 days
