"What we need to remind everybody is: these are things that are happening now," Prince Harry told ethologist Dr Jane Goodall in a recent interview in British Vogue. "We are already living in it. We are the frog in the water and it's already been brought to the boil. Which is terrifying."
After expressing his fears for the future of the planet, the Prince said that he and his wife Meghan Markle will only have "two children, maximum".
The idea that the climate crisis should make you pause for thought when deciding whether or not to have a family is nothing new, but as its scale has become more obvious and solutions have become seemingly more out of reach, the thought process has become more mainstream.
There is a growing scientific consensus that the lives of people born today will be harder than those from previous generations. That resources will be more scarce and that natural disasters and extreme weather events will be more frequent.
So: is it still OK to have children?
On Reddit, a large group of people discuss this question every day. A thread dedicated to "anti-natalism" – a philosophy built on the idea that people shouldn't have children because life is full of pain – has over 34,000 members. The current top post on the thread is titled: "Nothing triggers me more than parents saying they 'sacrificed so much' despite giving conditional love."
The idea that people shouldn't have babies dovetails with another concept that regularly crops up online: that there are already too many people in the world.
Working in environmental journalism, you see this everywhere. It's the topic you're asked about most at events, as well as in the comments underneath your articles. David Roberts, the environment reporter at Vox, grew so exasperated with the overpopulation argument that he wrote a whole essay explaining why he doesn't discuss it in his work.
Overpopulation is a simple enough concept. Human beings cause climate change by pumping greenhouse gases into the air. If you have fewer humans, you reduce emissions. Added to that, it is believed that the planet can only properly support so many people. One study in the 1990s put the optimal human population – the figure to sustain ecosystems – at between 1.5 and 2 billion. There are currently over 7.5 billion people on earth. The UN estimates that this number will rise to 9.7 billion in 2050.
In an interview with the Telegraph in 2013, Sir David Attenborough said: "What are all these famines in Ethiopia? What are they about? They're about too many people for too little land. That's what it's about. And we are blinding ourselves. We say: get the United Nations to send them bags of flour. That's barmy."
Firstly, wow. Secondly, what Sir David and the people who comment underneath articles like this one miss is a fact even simpler than the one underpinning their whole idea. Namely, that some people consume a lot and others don't consume very much at all.
To put it another way, if you're a wealthy man living in Hampstead Village, eating strawberries at Christmas, enjoying a steak flown in from Brazil and travelling business class to Hong Kong every month, your carbon footprint will be a lot bigger than a subsistence farmer in rural Malawi.
The fact that birth rates are higher in poorer countries, and generally declining in the wealthy world, should also make us stop and think when we hear people talk about the problem of overpopulation. The UN estimates that half of the world’s population increase by 2100 will be due to growth in just nine countries, including India, DRC and Nigeria. The United States is the only one of the nine countries that's a member of the G7.
Climate change is the biggest crisis of our age. It will shape the 21st century in the way the Second World War shaped the 20th.
We've already seen the overpopulation argument feed into this with the rise of eco-fascism – a violent ideology that in part inspired the El Paso shooter. As with any geopolitical problem, the marginalised and disadvantaged will be blamed for causing climate change. These ideas will permeate as they always have done. And they will be dangerous and wrong, as they as they always have been.
Famines do not occur because there's not enough land to farm, but because the world's resources are so unfairly distributed.
The world needs to change if we are to stop climate change. But it's the way we use natural resources, not how many people use them, that will solve this crisis. A major new report by the Intergovernmental Panel on Climate Change last week warned that the way the world uses land is threatening the survival of humanity. Scientists revealed that 72 percent of the ice-free surface of the planet is used to feed, clothe and support humanity, yet so much of the global population is not adequately supported.
There are ways of changing this. Instead of using huge amounts of land to grow crops to feed livestock, we could eat less meat and use the land to feed humans. Instead of encouraging people to travel by airplane, through cheap flights and frequent flyer schemes, we could invest in trains and other low carbon public transport. Instead of incentivising farmers to use pesticides, we could encourage organic farming.
If the world as it is does have an overpopulation problem, it's that there are too many rich people using too much stuff.