Illegal Cannabis Farms Are Making the Climate Crisis Worse

Every kilo of weed grown in UK illegal cannabis farms produces the same carbon emissions as a return flight from London to New York.
Police load up cannabis plants after a raid on a large indoor cannabis farm in Glasgow. PhotoAndrew Milligan/PA Images via Getty Images

Residents of Doncaster in South Yorkshire had wondered why their town had been experiencing random power outages over the last year. But then the answer came when police discovered a huge cannabis farm in an abandoned bingo hall on the outskirts of the town. Kitted out with high-tech equipment and 1,000 watt lamps, it contained over 2,000 plants worth more than £2 million and would have cost as much as £50,000 to install. 


The monster grow was typical of the UK’s blossoming £2.5 billion illegal cannabis industry. British growers produce hundreds of tonnes of black market weed each year to cater for the country’s estimated 2.6 million cannabis users, most of it grown inside buildings under high-powered lamps. Setting up behind closed doors in abandoned warehouses and repurposed homes – recent busts include old cinemas and suburban houses – helps keep a low profile from police and thieves

Due to its illegality, the hidden nature of the cannabis cultivation industry comes at huge cost. It has fuelled slave labour and escalating violence by the criminal gangs which run many of them. Yet one harm of this industry remains little-understood: its pernicious impact on the environment. 

Cannabis grown indoors needs a narrow set of conditions if it is to produce multiple potent harvests a year. Most prominent are the intensely bright lamps, which run for at least 12 and up to 24 hours a day to mimic the sun. But there’s more: air conditioning keeps the room at a constant humidity and temperature of 25-30 degrees, large extractor fans ventilate the plants and carbon scrubbers pull tell-tale smells from the air. Sophisticated growers may even pump rooms with bottled CO2 to make the plants grow faster.


Cannabis farms are far from green. Many burn through up to 50 times more power per square metre than homes and offices. In 2012, UK weed growers stole £200 million worth of electricity

“It's an incredibly, unusually energy intensive activity,” said Dr Evan Mills, a Californian energy scientist who was one of the first to examine the environmental impact of indoor cannabis cultivation. 

In a landmark study in 2011 Mills estimated that each kilo of weed grown indoor in the U.S. takes 6,074 kilowatt-hours of electricity to produce. He worked out that at the time America’s largely indoor-grown cannabis industry was using one percent of all the electricity generated in America. 

In terms of carbon emissions emitted by electricity generation on the UK grid, every kilo of weed grown in indoor UK cannabis farms produces just over one tonne of carbon emissions, around the same as a return flight from London to New York. Producing just one joint’s worth of weed has the same carbon footprint as leaving an LED light bulb on day and night for 15 days. An operation the size of the Doncaster farm would be responsible for almost 5,000 tonnes of greenhouse gases per year. 


Estimates for the UK’s total illicit cannabis production range from between 255–735 tonnes annually. With most of this grown in professionally-run weed farms, this could mean as much as 950,000 tonnes of CO2-equivalent gases pouring into the atmosphere each year from British grow ops – the same as running nearly half a million cars for a year. 

The environmental impact doesn’t stop there.

“A lot of small scale growers are concerned about environmental issues and some of them will deliberately choose organic methods,” said Dr Gary Potter, a cannabis production expert at the University of Lancaster. “But if you’re a large-scale commercial grower, you’re using chemicals, whether that's fertilisers or insecticides or herbicides. The chemicals themselves are not very well regulated and labelling is poor. So even when people do care, they are not necessarily aware of the impact of some of the things that they’re using.”

Some of the most concerning chemicals are synthetic Plant Growth Regulators (PGRs), which are commonly used to increase bud size despite being banned from food crops. When ingested over a long period of time, these “plant steroids” can cause cancer, liver problems and infertility


Rat and insect poisons are widely used by growers to keep pests at bay, but can leach into the environment when waste materials from grow ops are dumped, harming wildlife and humans. Any residue from these chemicals left on weed may be consumed by users. A recent study recommended pesticide controls for weed “go beyond those of normal agriculture… as they may be inhaled at high temperatures or ingested”. 

Unlike in the US, where weed farms have been blamed for drying up streams, water use is not so much of an issue in the UK’s rainy climate. Yet bizarrely, the plant itself causes air pollution. Cannabis leaves release toxic compounds called terpenes which can build up indoors if not properly filtered, causing potential harm to cannabis farm workers who are with plants in enclosed areas for long periods of time. In urban areas, these gases react with traffic fumes to form ozone, a gas which is useful in the stratosphere, but harmful when we breathe it in.

Britain’s illegal cannabis industry isn’t even the largest in Europe. Spain, the Netherlands, Albania and Italy are all major producers of black market weed, with Europe as a whole churning out 2,500 or so tonnes per year. Power outages caused by Dutch grow ops are common, where they use as much power as the entire city of Leeds. In Morocco, illegal plantations are causing widespread deforestation, soil erosion and water stress in the Rif region. 


None of this meshes well with the image of cannabis as a green, natural drug. Heavy electricity use is a relatively new phenomenon, born in the mid-2000s when super-strength skunk became popular and extremely profitable. As recently as 1997, 70 percent of British cannabis growers used only natural light and the majority of weed consumed here was grown outdoors in warmer countries. 

“With technical innovations like hydroponics and new strains of seeds, suddenly it became possible to make £10,000 or £20,000 from your spare room,” said Steve Rolles from drugs policy think tank Transform.

Now only a small proportion of the UK’s crop is grown outside and organised crime groups have taken a large share of the market. For Rolles, the environmental damage of nefarious indoor weed grows is an argument for legalisation and regulation. 

“Illegal producers do not bear the costs to the environment of what they’re doing, because there's no accountability or regulatory structures around them. They just make their money.

“Within a legal market, the electricity use can be dealt with by establishing controls on the amount of power that can be used per volume of cannabis production and mandating outdoor or greenhouse grows… It becomes just like growing tomatoes.” 

Until then, if you’re concerned about your own consumption there are steps you can take. “It is possible to get environmentally sustainable illegal cannabis in a way that it's not possible for cocaine,” said Rolles, “by either growing your own, or getting it from a small-scale grower or cooperative who could vouch for the provenance of a particular crop.”


Greenhouses, common in Britain’s burgeoning medical cannabis industry, use significantly less energy than fully-indoor production. Even better, when grown in the open air (or a back garden polytunnel), weed is considered eco-friendly for its ability to suck carbon from the air and store it in the soil. This is the ethos of the “guerilla growers” movement which plants in secret, open-air sites, or non-profit cannabis social clubs.

Jouke Piepenbrink of Dutch Passion, a Dutch cannabis seeds company, told VICE World News“many” home growers actually have a carbon-negative footprint. “Innovation and legalisation are definitely ways to improve the sustainability of cannabis production, but that doesn’t mean all unregulated production is bad. We have a segment of seeds which are only suitable for outdoor growing. They are very popular in central and northern Europe, including the UK.”

He also points to the increasing use of LED lights among both black market and legal producers as a positive sign. “Lights which consume less energy produce less heat, which makes the grow set up easier to control. Less or even no cooling is needed.

“On top of that, cannabis produced under LED is in my opinion of higher quality, it usually has more cannabinoids and a better and stronger bouquet of taste and aroma.”

It is only by being brought out of the closet and into the open, away from the criminal world, that the cultivation of this plant can once again become a truly green endeavour.