With half the Arctic summer sea ice gone, and climate change still just beginning, the fight has never been so urgent, says environmentalist Bill McKibben.
McKibben has been at the forefront of climate change action for 30 years, first as a journalist with the New York Times then an activist with 350.org.
He says climate change is the first ever time-limited test humanity has faced.
"If we don't solve it soon we won't solve it and there's no guarantee that we're going to - at the moment we're losing."
The oil and gas industry knows its time is up, he says, but is trying to squeeze every last dollar out of its business.
"These guys know in 30 years we'll run the world on sun and wind because it's free, but they don't want to surrender any sooner than they have to.
"They want to squeeze more cash out of this operation - but they're going to break the planet if they do."
McKibben welcomed the government's recent announcement that it will not grant new deep-sea oil and gas exploration permits.
"It's one of the signals that world needs to hear. Very few people have figured out we need to cut off the supply as well as demand … it's rare and encouraging to see a government that's figured out where the future lies."
Thirty years ago McKibben says climate change was an abstract concept - but no longer.
"Now it's clear what scientists warned about has come true, and come true much more quickly and with much more force than even the most dire predictions.
"Half the summer sea ice in the Arctic is gone and we're still near the beginning of climate change, which is why the fight has never been more urgent than it is now."
New Zealand has a "front row seat" to climate changes effects, he says
"It's your neighbours in the Pacific whose nations are disappearing, people are having to evacuate their homes.
"Because the tide means they can't live in places where humans have lived for thousands upon thousands of years.
"It's not their fault. Global warming manages to very efficiently injure most those who have done least to cause it - it's injustice on steroids."
That injustice has been fuelled by billions of dollars spent on disinformation, McKibben says.
"Thirty years ago the big fossil fuel guys - Exxon and the rest - knew everything there was to know about climate change. They had good scientists hard at work on it and they understood how fast the temperature was going to go up, and they believed their scientists. Exxon started building all its drilling rigs higher to compensate for the rise in sea level they knew was coming.
"What they didn't do, was tell anybody else."
McKibben says that campaign has recently paid rich dividends with a climate change denier now in the White House.
"We've gone from arguably one of the smartest leaders the US has ever had to a grotesque buffoon, and in his buffoonery threatening to drag down not only an important nation but also the whole planet."
But McKibben still sees reason for some hope.
"I'm confident that there's a movement in place around the planet that wasn't there a decade ago and that movement guarantees there'll be a fight - a serious fight."
He says the campaign to divest money from fossil fuels has gone much better than he expected. Since the campaign was launched six years ago $US6 trillion has been divested from fossil fuel companies.
It's an area where New Zealand needs to do more work, he says.
"The big banks here continue to pump money into the fossil fuel industry. Money is the oxygen on which global warming feeds."
Bill McKibben was in New Zealand last week as part of the Fossil Free Acceleration Tour.