Greenpeace is dismissing the terrifying results of a new study, which suggests we're decades too late to fight climate change.
Temperatures will continue to rise for a long time after we reach carbon-zero, European researchers say, because melting ice means less of the sun's energy will be reflected back into space.
If emissions peak in the 2030s and decline to zero by 2100, there will be a brief pause in global warming before it resumes again in the 2100s, their modelling showed. If we stopped emissions right now, it will take a bit longer for warming to resume, but their calculations suggest it's inevitable.
"All man-made emissions would have had to be cut to zero sometime between 1960 and 1970 - when global warming was still below 0.5C," they wrote in journal Scientific Reports.
Greenpeace NZ executive director and former Green Party co-leader Russel Norman disagreed, telling The AM Show it's not too late to save the planet from runaway climate change.
"It's using a much simpler climate model than the usual climate models used by the big international reports - like the Intergovernmental Panel on Climate Change report. When you look at the big climate models... they say there is still time to avoid out-of-control climate change."
Kiwi scientists appear to agree with Dr Norman.
"Earth system models typically contain hundreds of thousands of lines of code, and require a supercomputer to run on. Even then, a 100-year simulation may still take several months to run," said Laura Revell, environmental physicist at the University of Canterbury, noting the model used in the latest research was a simplified one that can spit out results in seconds.
"The results presented in this paper are very implausible and should not be seen as cause for alarm," added James Renwick of the Victoria University School of Geography, Environment and Earth Sciences.
The study's authors said to avoid runaway climate change, the world needs to start taking 33 gigatonnes of carbon out of the atmosphere every year - this would require 33,000 "big" carbon capture and storage plants to go online, a vast increase on the present 51.
Dr Norman says we can avoid the need for this if we decarbonise quickly - starting with a 50 percent drop in the next decade. But even supposedly clean-and-green New Zealand is nowhere near meeting its present, weaker targets.
"It gives you a sense of the scale of the challenge. We have to rapidly decarbonise transport, we have to really cut emissions out of agriculture. They're huge challenges - they're doable, but we really do need to get on with it... The next 10 years are going to be critical. We've got to halve emissions over the next decade. We still have time, but we've got to act quickly."