By 2050, there could be 10 billion humans living on Earth. It's a prediction Chris Packham, who's dedicated his life to championing the natural world, is gravely concerned about.
We're all aware of the climate and environment emergency, suggests the Southampton-born broadcaster (58), and there are plenty of conversations about biodiversity loss taking place.
But the massive threat posed by human population growth is the "elephant in the room".
So, he decided to make a documentary for BBC Two, titled Chris Packham: 7.7 Billion People & Counting.
"If people watch this and they don't think, then we are doomed," muses Packham. "We did everything we could to make this a programme which would prick up people's ears."
Packham travels around the globe in the one-off film to see the impact that our rapidly growing population is having.
He visits Brazil, investigating how Sao Paulo is a mega-city on the verge of running out of water.
"The human species is not particularly good at change, but we've reached a point in our history when, confronted with a number of serious problems, people are still putting their heads in the sand. My duty is to pull people's heads out of the sand," he says.
"There's an ongoing raft of programmes that are trying to generate awareness, but I think what is missing is the urgency that is required and the one that is lagging is the conversation about population growth.
"Unfortunately, when it comes to addressing these issues, the finger is often pointed at sub-Saharan Africa, because that is where the human population is growing most rapidly.
"We were very keen to address the fact that you can't point the finger at large families with poor black children as being the problem. Actually, at this point, we (in the UK) are the problem."
In exploring how the world can re-balance its consumption to accommodate the needs of more than two billion more people, Packham even analyses his own lifestyle choices.
"One of the crucial points in the film is where I honestly, and embarrassingly, point out that I've got 10 hoovering devices. That is exactly the root of the problem: I've got 10 hoovers and the cost of producing those and the batteries in them and replacing them - that's the damage we are doing," he says.
A particularly memorable segment of the documentary sees him interview a couple going through IVF treatment.
Did that meeting have any impact on him, considering his decision not to be a father?
"Not personally; I'm 58," says the presenter, who's stepdad to 24-year-old Megan (her mum is a former girlfriend; he's now in a relationship with Charlotte Corney, owner of Isle of Wight Zoo).
"Would it have made a difference when I was 25, when I might have been thinking about that? Maybe.
"But moving forward - and certainly when I met Megan - I was faced with another question of investing a considerable amount of time and money into another organism.
"Are they going to have a secure future? What is the future going to be like for them? Do they have the potential to be happy, comfortable and healthy?
"I've always been worried about that. And I think that's because I've been drawing my fear from the declines that I've been seeing in the environment and the natural world."
However, he adds candidly, witnessing the couple's drive and profound desire to go through the birth process was "actually quite awesome".
"It was alien to me, but nevertheless awesome. And I genuinely hope that they succeed, because it was something that they wanted so badly," he adds.
When he was in his 40s, Packham was diagnosed with Asperger's, a lifelong disability that affects how a person makes sense of the world.
The condition, which is a form of autism, wasn't really an issue when filming this most recent show, he reflects.
"It's something I can almost invariably cope with. If you're going to go into a situation that you know is not your comfort zone, then you can prepare yourself," he says.
"What was an issue was this programme was bound to expose me to the worst excesses of the things that I fear most. I'm a pragmatist. I have to remain in a position where I'm not going to give up. Because I'm determined to make a last stand, if that's what it comes to, for our environment. Not being overwhelmed by pessimism is something I have to constantly guard against."
Chris Packham: 7.7 Billion People & Counting, BBC Two, Tuesday, 9pm