"He specialised in isotopic techniques, which he describes as like DNA tracing for gas particles.
Not all the CO2 in the atmosphere is from the burning of fossil fuels. For most of human history, the CO2 level has naturally fluctuated between 200 and 300ppm, which we know thanks to air samples trapped in glacier ice cores.
Those natural fluctuations are often cited by climate deniers to suggest that climate change is not man-made.
Naturally occurring carbon is made up of different isotopes. The most common types are called Carbon-12 and Carbon-13.
Carbon-12 is by far the most common type found in nature. Carbon-13 makes up about 1 per cent of the total.
But the exact amount can differ. There is slightly less Carbon-13 in fossil fuels like coal and oil compared to in atmospheric carbon.
Lowe and other international researchers found that while total CO2 in the air was increasing, the percentage of Carbon-13 isotopes compared to Carbon-12 was decreasing.
That proved that the additional CO2 in the atmosphere was coming from the burning of fossil fuels by humans, not anything else.
"That's the smoking gun. You can get every sceptic blue in the face but that's just open and shut evidence that this extra CO2 came from humans," he says.
"Unequivocal, no doubt."
Part of the problem was that the predicted temperature rise didn't show up for several years.
While CO2 was rising, the mercury was jumping up and down, with no consistency. But eventually, the signal separated from the noise and the heat started to climb. Once it did, it basically never stopped.
In hindsight, the conservative approach of the scientific community probably held progress back for a number of years, he says.
"As a scientists, we thought, 'No, you don't jump up and down and scream, we're not activists.' Losing our credibility was the big issue.
"It was a totally different time. If only I knew then what I know now ... Now it's different, many of us are out there doing stuff. We have to, this is an emergency."
