At 81, Ehrlich is still in the field, working on endangered species, the preservation of genetic resources and a deep understanding of natural butterfly populations. With his wife Anne, who is 79, he has been cranking out books about the environment, ecology and the heavy footprint of humanity for more than half a century.
His perspective has barely shifted in that time, though he does admit that he would not write his most famous book - The Population Bomb - the way it was put together back in the 60s. For a start, Anne's name would be on the cover as joint author. "They said you'd do better with a single author. I was young then."
He would do away, too, with three hair-raising scenarios which, though couched as possibilities and predictions set out, as the book declared, "the kind of disasters that will occur as mankind slips into the famine decades".
Flicking through a faded hardback edition of his ground-breaking book, dug out of the Auckland Public Library basement, Ehrlich quickly finds the never-to-be repeated scenarios at page 62 of the slim best-seller.
"There are a lot of things we wouldn't write today," he observes. "Show me a scientist who would write exactly the same thing he wrote 45 years ago."
He continues, with a broad smile: "If I could see into the future, Anne and I would be living on Bora Bora with a big wine cellar and beach boys for her" (at this point Anne tells him, 'Oh, stop it') "and young girls for me, because we would have bought low and sold high."
The Weekend Herald spent an hour with the Ehrlichs at Auckland Airport. They had come from Sydney and were heading down to Hamilton. Back in Australia, they left raging bushfires behind - a cue for Ehrlich to launch into the impact of climate change. He says despite the outlook becoming "grimmer and grimmer", he gets no sense of urgency from Prime Minister John Key or his Australian counterpart Tony Abbott to deal with global warming and rising sea-levels.
"Look around us," Ehrlich remarks from the relative discomfort of a plastic chair in a busy fast-food shop. "Auckland Airport is going to be under water one day."
As certain as that? "The timing is uncertain and I don't know the altitude of the airport. But we're here beside the sea and unless we build huge dykes to keep it out, then the waters are going to rise."
Besides threats to coastal areas, Ehrlich contends New Zealand is in line for a hit on its agriculture. Our farming systems emerged during a period of climate stability. But land-based enterprises added to greenhouse gas emissions, which in turn were connected to climate disruption. Food production was threatened by increasingly severe storms, droughts, heat waves and floods while the fossil fuel foundation on which agriculture was based for fertilisers, farm machinery and transport systems had to change if the worst impacts of climate upheaval were to be avoided. Ehrlich cautions that making political change is incredibly hard: "We've proved in the States that telling people what the science of climate change says does not alter behaviour."
He recalls an argument he once had with former Washington Post executive editor Ben Bradlee over "the media's view that the truth always lies in the middle and the habit of bringing one or two people with no credentials to counter what the best climate scientists in the world have to say.
"That continues to this day and no one knows what to do about it. As a scientist, I have to maintain credibility with other scientists. If get out there and start lying, I am cooked. But it doesn't matter if any number of experts appear in the Murdoch press denying the truth about climate change."
Ehrlich says he's had a hammering from critics over the years since The Population Bomb appeared. The book opened with the bald statement: "The battle to feed all humanity is over" and went on to predict hundreds of millions of deaths from starvation in the 1970s. Today, he says, of the planet's seven billion people, around a billion are hungry or malnourished.
Over four decades, somewhere in the order of 200 million to 400 million people have died from starvation or disease. He wasn't, he says, wrong about that.
But he did come famously unstuck with a bet he took with Julian Simon, a freemarket economist who argued that Earth could cope with more rather then fewer people. In 1980 they bet on the future price of a basket of metals. If the cost rose over a decade, reflecting scarcity in a crowded planet, Ehrlich would win. If it fell - indicating great strides in triumph of human ingenuity - Simon would come up trumps.
"Simon was running round saying the ecologist won't bet. Well, finally we thought we may lose the bet but what the hell, we'll shut him up for 10 years."
Ehrlich lost the bet and, he concedes, some credibility. He maintains that the commodities market was in a slump at decade's end, which tilted the odds towards Simon. "Another two years and we'd have won."
The memory seems to rankle with Ehrlich, who asserts that if he had published claims like Simon had made - the libertarian was an early sceptic on global warming - he would have been drummed out of the Royal Society and fired by Stanford.
Ehrlich is using a Royal Society paper he and Anne wrote last year on whether a global civilisation collapse can be avoided as the basis for his lecture tour. He contends that existing political structures do not lend themselves to making sacrifices for future generations, but somehow moulds have to be broken for "monumental" change to occur.
Ehrlich warns we don't have the luxury of time, and feels one of the hardest tasks will be persuading the rich countries - including New Zealand - to dial back rapidly on consumption while convincing the developing world that not everyone can be a wealthy American. What cannot wait, he insists, is a shift away from fossil fuels and lightening our carbon footprint.
"People seem to think if they can't get a new iPad every few weeks, then they're not really content. But there's no evidence that happiness increases with GDP." There is, though, plenty of evidence of mounting and potentially irreversible environmental and social costs to never-ending consumption.
In New Zealand's case, with its maritime history, it ought to be pushing for sail-powered ships to get its goods to far-off markets.
"There's a guy here - John Key - who talks about growing your way out of this or that ... you're growing your way into trouble, not out of it."
And he is dismissive of New Zealand's environmental credentials, saying "you're the record-breaker for destroying biodiversity".
To support his assertion, he points to imports of palm oil feed which have driven the dairy industry's rapid expansion. Supplies come from Southeast Asia, where plantations have sprung up after the removal of tropical rainforests.
Given the odds he quotes of the whole show going pear-shaped (10 per cent ), Ehrlich ponders the suggestion that, with all the evidence he marshalls in his collapse forecast, it seems a tough ask to avoid that outcome. He refers to Stephen Emmott's recent book, 10 Billion, which argues in frightening prose that Earth is hurtling towards that number of people this century.
Says Ehrlich, again with a chuckle, "His next-to-last line is: 'I think we're f*****'. I reckon it's a pretty clear summary. We don't have to be but we seemed to be aimed in that direction."
Who: Professor Paul Ehrlich, professor of biology, Stanford University
Where: Auckland Museum
When: Tuesday, October 29, 6.15pm
Tickets: allanwilsoncentre.ac.nz
