A young Attenborough pedalled his Raleigh junior bike uphill and down dale before the Second World War, a time when, he admits, there was less traffic on the roads and less to distract children from the wonders of the natural world (including television documentaries). As he looks around him now, approaching his 94th birthday, he sees a very different world.
Swathes of rainforest in Borneo where he made his early films have been burnt and bulldozed to make way for palm oil plantations. Arctic sea ice has shrunk by a third. Some of the reefs where he dived for his first underwater series are lifeless.
This, he explains, is why he's still campaigning when he could be putting his feet up. Against stereotype, he's grown more outspoken as he's grown older.
"I belong to the generation that really created all this stuff. We had no concept that we were ruining the world, none. I suppose you can say, 'well, you were very insensitive, you should have realised', but I don't think many people did."
His latest film, A Life on Our Planet, made in partnership with the World Wide Fund for Nature, borrows the cadence of Life on Earth, but shows the world in a different light. Instead of the pristine habitats and unspoilt wildernesses of the 1979 series, it aims to show the monumental scale of humanity's impact on nature. It will premiere next month simultaneously in the UK, Netherlands, Ireland, Norway, Sweden, Denmark, Iceland and Finland, part of an international campaign before World Environment Day in June.
It is his most political film to date. Not only is the Earth gaining humans and losing animal and plant species at a pace it can't sustain, he says, but it is also heating up at a rate that could tip it into sudden, catastrophic disaster.
At the start of the film, we see him stepping gingerly through the ruins of the Ukrainian town devastated in 1986 by the Chernobyl nuclear power station meltdown. The message that unfolds during the next 83 minutes is just how destructive mankind can be as we see rainforest torn down, slabs of polar ice collapsing and lifeless coral. At the end he returns to the long-abandoned town to show how nature has reclaimed it. If we are intent on destroying our own species, it will eventually happen. Nature will find a way to carry on, even though humans may no longer be around.
The theme is that such destruction is a modern phenomenon, brought about by the boomer generation and its excesses, and it's generation Z that is paying the price for their sins. In Britain, the film will have a special screening at the Royal Albert Hall where 500 places are reserved for young people, giving the event the flavour of a political rally. Attenborough endorses this view, declaring that he and his generation have "done terrible things" and that the future is in the hands of young people who understand "science and our dependence upon the natural world".
Probably no one else alive has seen as much of the Earth's surface over such a long period of time as Attenborough. To make just that one series of Life on Earth he travelled 1.5 million miles to 30 countries and filmed more than 600 species. Audiences have voted him the greatest broadcaster of all time; cooler than David Beckham in a poll of coolest men; and, most recently, the person they trust the most on environmental matters, more than Greta Thunberg.
People listen when he sounds the alarm. Like a world-weary Yoda admonishing Luke — "Do or do not. There is no try" — he's telling us we must act, and act now. But he also has an upbeat message about how we can help save the planet. A first step is to eat less meat. "The big demand that we've imposed on the planet is to get meat. That's what's taken over so much of our countryside. That's what's causing the Brazilian rainforest to be knocked down, to turn it into grazing — for more hamburgers. We can't afford to do that any more and sustain the number of people we've got."
A government-funded report published this month said Britain will have to reduce its meat consumption by half if it is to meet climate targets and be carbon neutral by 2050. Is he vegetarian? "I don't eat meat. That's not entirely true, I eat fish. It wasn't a great sort of decision and I can't pretend that it was motivated by any ecological conscience, but I now avoid red flesh."
The other thing we can all do is live modestly. Even small changes make a difference. If we avoided food waste, we could feed five instead of four. "I try to recycle," he says. "It's more like a religious practice, a kind of ritualised thing."
Does he drive an electric car? "I don't drive. I've never driven. Well, that's not true, I can drive, but I've never driven. Never had a reason, never had a car.
"My daughter drives and we're getting an electric car. We haven't yet got it, we've got a little — I don't know whether I ought to mention it or not — a little German job. A [fossil-fuel powered] VW."
None of the current concerns about the planet occurred to him when he first crisscrossed the world in old BOAC jetliners — flying gas-guzzlers, complete with ashtrays in the armrests. "Yes, 40 years ago we didn't realise there was a problem of climate change. Forty years ago we were concerned about disappearing species and how we could save them. Arabian oryxes and so on, gorillas. Nobody said to me, and I didn't say to myself, you are wrecking the climate with the amount of carbon that jet airliners emit. You're complicit in that. It didn't occur to me."
His lifelong love affair with nature, creatures, unspoilt habitats and the wilderness began when his father gave him his first pet, an amphibian called a fire salamander, for his eighth birthday.
He beams as he recalls the occasion. "They're absolutely magical things. If you've never seen one before, it's jet black with sulphur spots on it. They are quite innocuous and they're quite slow moving so you can handle them no problem at all. I had an aquarium that I turned into a vivarium with moss and stones and so on, and a little pool at the bottom on one side."
His first foray into natural history collecting came a year later when he started supplying newts to the zoology department of Leicester University, where his father was principal, for thruppence each. Showing an early flair for enterprise, he didn't reveal that the newts were from a pond only yards from the department.
He joined the Television Service in 1952 after graduating from Cambridge, where he had studied geology and zoology. If you can't remember a time when there wasn't an Attenborough wildlife documentary on TV, it's because there wasn't one. In those days, the service was a fledgling arm of the BBC broadcasting to only a few thousand people. His brief as a producer included "politics, gardening, even knitting". Already married with an infant son, he had no plans to travel the world until a zoo keeper, who was to have presented a new programme about animal collecting, fell ill. In 1954 a 28-year-old Attenborough was dispatched with a cameraman to find a rare jungle bird.
"When I started making natural history films — I'm almost ashamed of it now, but there's no point in denying it — I was making a film about London Zoo, which was collecting animals. Rare animals? Oh good, let's go and scrag it and take it back to London. You wouldn't dream of doing that now. "
Zoo Quest was a success. More collecting programmes were commissioned. Colour television arrived. Film photography evolved to show animals in close-up, in slow motion, in high-definition, a spectacular window into the natural world of the African plains, the polar ice caps, rainforests, coral reefs, always with Attenborough as the guide.
On early trips he brought home animals to keep as pets — a practice he admits would be unthinkable today — including "lemurs, parrots and hummingbirds". The most unusual specimens were two lungfish, living relics of prehistoric times.
His favourites were a pair of bush babies that ran loose in the house and had a fondness for marking their territory with urine. He recalls that dinner guests would sniff the air as they entered the house, wondering whether their hosts were cooking strong-smelling soup.
These days he has firm views on which animals should be kept in zoos. "There are lots of things that live perfectly well in captivity and you can give them all they need. Equally there are things that should not, under any circumstances, be kept in captivity. You should not keep raptors, you shouldn't keep eagles in captivity. Dreadful. I don't think that you should keep lions in captivity, unless you can provide them with an enormous area. I wouldn't myself keep gorillas. I mean, that's a very difficult thing. They are highly intelligent animals. I suppose there are possibilities, but I wouldn't risk it."
He has been urinated on by bats, dive-bombed by gulls, and risked life and limb by swimming with hungry grey reef sharks. To capture that vital shot, he has put his head in the lion's mouth — for real. In 1961 he was filming a programme about Elsa the lioness. Sleeping in his Land Rover in the Kenyan bush, he was awoken "by a stench of bad breath and opened my eyes to find her jaw dripping saliva inches above my head".
For years he travelled with just a battered leather suitcase. His wife, Jane, would pack it for him and see him off at the airport, never knowing quite when he would return. Then, in 1997, when he was filming a series about bird life in New Zealand, Jane, then 70, suffered a brain haemorrhage. He flew to her bedside at a London hospital just in time for her to squeeze his hand before she died. They had been married for 47 years. Life is very different without her, he says, and he misses her terribly. Afterwards he threw himself deeper into his work.
Everyone has their favourite Attenborough anecdote or TV moment. If you watched Life on Earth in the 1970s, it may be the time he rolled around with silverback mountain gorillas in Rwanda. Or, more recently, on the BBC's Africa series, when he got down on all fours to chat to Nicky the baby rhinoceros. Or maybe the grimly compelling sight of the Galapagos racer snakes chasing and devouring hatchling marine iguanas, seen in Planet Earth II in 2016. His own favourite moments are not when the animals are reacting to him, but when he's observing.
"The most moving times, as far as I am concerned, are when the natural world is unaware of your presence. A swamp in northern Australia, for example. I can remember very well sitting in a hide in the darkness, waiting for the sun to come up. You can hear that there's a big community of water birds — and the sun comes up and you see egrets and there are crocodiles and you see a whole complex ecosystem just throbbing with life and beauty. You watch it for a bit, and you do something silly and alarm them, then the whole lot disappears. But you have that moment of revelation."
He is still making documentaries, writing books and presenting BBC Radio 4's Tweet of the Day (about birdsong, not Twitter). He still wears his trademark blue shirt and khaki chinos on screen, though he has shifted to satellite and streaming, making films for Sky and Netflix as well as the BBC — and drawing in bigger audiences than ever.
The one thing that may slow him down is if he runs out of film titles containing the word "planet". Attenborough's Our Planet was shown on Netflix last year, and his Seven Worlds One Planet on the BBC. He is working on a BBC series about plants, Green Planet. Previously he has made Planet Earth, Planet Earth II, Blue Planet and Blue Planet II, Frozen Planet and Our Fragile Planet.
These days he's less often behind the camera, more often in a recording studio providing the voiceover. He stresses that it's film crews who spend months capturing footage — and they, not he, should take the credit.
"People think I've shot the film and I get the credit. People say, what was it like when you got really close up with those narwhals, you know, underwater? I say, I wasn't there, and they say, what? I say, no [raising his voice for emphasis], I wasn't there!"
Looking back, he wishes he had spent more time with his son and daughter — Robert and Susan — as they were growing up. "If I do have regrets, it is that when my children were young, I was away for three months at a time," he has said. "If you have a child of 6 or 8 and you miss three months of his or her life, it's irreplaceable — you miss something."
He was there, however, to give Robert, now a Cambridge University anthropologist, a salamander on his eighth birthday, just as his father had done for him. "We unpacked this — it came in a box — I took it out and showed him. I said, 'Now there you are'. This thing just sat on his hand. I said, 'Put him in his new home'. He put him in his new home and it very slowly walked down to the water and there out from beneath its tail came a little one. My son looked at that with his eyes coming out of his head — as did I."
Money has never been his motivator, though he earned more than £1m ($2.02m) in 2017-18 from David Attenborough Productions, his private company. He still lives in the same Victorian townhouse near the station in Richmond, southwest London, that he shared with his wife. He was renowned for travelling economy class and never taking upgrades unless the whole crew was upgraded, until he reached 75, when the BBC insisted he travelled business class.
Despite his fame, he remains engagingly modest. For years, the joke in the Attenborough family was that he only got a knighthood because a palace official confused him with his older brother, Richard, the actor and director. And he's a paragon of honesty. He has never done an advert, he says, because "my job is telling the truth, and if I say margarine is butter, people will think, 'He'll say anything'."
So while we yawn when self-interested politicians warn about climate change, when Attenborough talks, we listen — even when his message is stark.
In the 60-plus years he has been making documentaries, he points out, the world's population has more than doubled: 7.8 billion people today, heading to 11 billion by the end of the century. Many of the habitats and species he filmed in those early days have vanished or are in retreat. If we don't mend our ways — rein in population growth and live less wastefully — we'll wipe out life as we know it, including ourselves.
So is he right to blame himself and his generation for the planet's problems? His 1961 film, Zoo Quest to Madagascar, was ahead of its time in many respects, including revealing the damage caused by climate change and deforestation. At one point in the historic documentary, Attenborough walks along the vast bed of a dried-up river in Madagascar, commenting that the lack of water is "a clear indication of the drastic changes in climate that have overtaken this part of Madagascar. It's likely that, only a few hundred years ago, when the gigantic birds [aepyornis] were alive, this was not a desert, but a great area of swamp".
Yes, climate change was already happening in 1961. Of course, the scale of our impact on nature has grown, as has the amount of money at stake. Climate change is now a global industry on which livelihoods, careers, reputations, marketing budgets and sales forecasts depend. It pays for academics, research groups, lobbyists, publishers and film-makers, among others, and generates profits for thousands of companies involved in green technologies. Tesla, the electric car-maker, has ballooned into the world's second-biggest car company by value. BlackRock, the world's biggest asset manager, is sinking a sizeable chunk of its $7 trillion funds into "sustainable" investments. British farmers' billions in subsidies will soon be calculated not just on food output but also on climate-change targets.
To sceptics, it sounds like opportunism. They take the view that there are always doomsayers warning of world disaster — holes in the ozone layer, acid rain, nuclear accidents — that there is always, as Tommy Lee Jones puts it in the film Men in Black, "an intergalactic plague that is about to wipe out all life on this miserable little planet".
Attenborough thinks this time it is genuinely different. The evidence is now too strong to resist the conclusion that we are heading for self-destruction. He cites a spate of extreme weather events such as the Australian bushfires (other experts have stopped short of making a direct link). Attenborough argues that the sceptics may never be convinced until it's too late.
"I think that proving it [the link between recent wildfires in Australia and California] to the degree that the sceptic will require is an impossible thing. But there have been people who have been warning that unless they change their ways these things are going to happen, and they've happened. We have to look at the realities. The reality is not very pleasant. It's not good — and there's no point in pretending it is."
Five years ago Attenborough met then-President Barack Obama, in the White House to address the crisis. Could he also win over the climate-change doubter-in-chief, President Donald Trump, who has described climate change as a "hoax" and a "money-making" industry?
"I, of course, would feel an obligation to try and persuade him that it's the case [that climate change poses a serious threat]," Attenborough says. "He's the most powerful man on Earth. Of course you would have the responsibility to try and persuade him that it is the case."
When I ran out of time to ask him questions, I wrote him an old-fashioned letter, not expecting that he would have time to reply. Did he have any pets? Did he have a smartphone? Did he write his books in longhand? A postcard — sold in aid of Kew Gardens — came back. He had no pets, he said ("I go away too much"). "No iPad, no iPhone, no email. I use the post & telephone." His one concession to modern technology, he added, was that in addition to longhand, he sometimes wrote on a computer.
For Attenborough, the message is simple. Be considerate. Live modestly. The future is at stake, he says, not for him but for the next generation, for his two granddaughters, at university in the UK.
"You know, we've overtaken the world. We are representatives of a very powerful, damaging species. So just be modest. Don't waste. Don't waste electricity. Don't waste food. Don't waste time."
His own time is running out, he says. "I'm 93. How long have I got? I haven't got 10 years, I don't think." Will he ever retire? "Well, when people want me to do things, I do things," he says. "If they don't want me to do it, I've retired.
"I have the greatest job in the world, you know. What a privileged time I've had. People provide me with wonderful pictures of things we've never seen before and ask me to write a sentence or two on it. Better than sitting in the corner knitting."
David Attenborough: A Life On Our Planet will be available to watch in cinemas and globally via Netflix later this year. For more information and to register for updates, visit www.attenborough.film #AttenboroughFilm