The UN expects that the world population will reach seven billion on 31 October, and experts predict that there will be at least nine billion humans on the planet by 2050. Global meat consumption is projected to double by 2050, too - a frightening prospect, considering the factory-farming nightmare required to raise and slaughter more than 55 billion animals and meat production's impact on nearly all environmental problems from climate change to deforestation to pollution.

The Worldwatch Institute estimates that the global livestock population has already increased 60% since 1961, and while people grow fat on bangers and bacon butties, countries around the globe are bulldozing huge swaths of land in order to make room for more factory farms to house all the additional chickens, cows, and other animals as well as for the huge quantities of crops needed to feed them.

Many more people can be fed from a given area of land if the crops aren't first fed to animals in order to produce meat. Animals require large amounts of food and resources but produce very little food in return. It takes three and a quarter acres of land to produce food for a person who eats meat and dairy products, while food for a vegan - someone who doesn't eat any animal products - can be produced on just 1/6 acre of land.

Even beyond the basic inefficiency of funnelling crops through animals, more fossil-fuel energy is used in meat production to operate feed mills and factory farms; transport animals many miles to slaughter in petrol-guzzling, pollution-spewing lorries; operate abattoirs and then transport the meat to processing plants.

And then there's water. The United Nations Environment Programme (UNEP) reported that 200 scientists in 50 countries have identified water shortage as one of the two most worrying problems for the new millennium (the other was global warming). Between watering the crops grown to feed farmed animals, providing drinking water for the animals and cleaning away the filth in factory farms, trucks, and abattoirs, meat production places a serious strain on our water supply. It takes about 15,500 litres of water to produce 1 kilogram of beef, compared with just 1,000 litres to produce 1 kilogram of wheat.

And as if that weren't enough, climate change experts have produced overwhelming evidence that meat production causes climate change. Worldwatch Institute researchers estimate that raising animals for food causes 51% of global greenhouse-gas emissions each year. A 2006 United Nations report, Livestock's Long Shadow: Environmental Issues and Options, concluded that the livestock sector is a significant source of climate change and that the meat industry is "one of the top two or three most significant contributors to the most serious environmental problems, at every scale from local to global."

We can't expect to have a liveable environment if we continue to squander the Earth's resources, pollute the environment, lay waste to arable land, and abuse animals to feed our unhealthy appetite for meat. I say "unhealthy" because diets rich in animal fats have been conclusively linked to higher rates of obesity, heart disease, diabetes, strokes and cancer. We'd do well to adopt vegan diets ourselves. Vegan foods provide all the nutrients that we need, minus the saturated fat, cholesterol and contaminants that are found in meat, eggs and dairy products.

Adopting a plant-based diet, in addition to safeguarding the increasingly populous planet and its inhabitants, would spare billions of animals the horrors of the meat, egg and dairy industries. In the UK, piglets have the tips of their teeth and their tails cut off without any pain relief. Chickens live in cramped cages or in filthy sheds, and animals have their throats cut at slaughter, often while still conscious. Animals are kept indoors, denied everything that is natural and important to them, and the first and only time most of them will breathe fresh air or feel the sun on their backs is when they're loaded onto lorries bound for slaughter. In other places around the world, the treatment of animals is even more horrifying.

If we are ever to create a cleaner - and kinder - world fit to support the many billions of us on this planet, we can't carry on the way we are going.

The logic against eating animals is irrefutable. In fact, the UN has made it clear that a global shift towards a vegan diet is vital to save the world from hunger, poverty and the worst effects of climate change. A 2010 UN report titled Assessing the Environmental Impacts of Production and Consumption: Priority Products and Materials states, "Impacts from agriculture are expected to increase substantially due to population growth" and "a substantial reduction of impacts would only be possible with a substantial worldwide diet change, away from animal products".

There have never been so many people on this planet, and now is the time to make the changes necessary to ensure a sustainable future for everyone.