After leading NASA climate scientist James Hansen told the US Congress 30 years ago this week global warming was already worsening heatwaves, many of his colleagues figured politicians would heed the warning.

"When I heard this news, I thought it was time somebody made such a clear message," said Stefan Rahmstorf, then a PhD student in New Zealand and now at Germany's Potsdam Institute for Climate Impact Research.

James Hansen, director of NASA's Goddard Institute for Space Studies in New York, warned the US Congress in 1988 that human-induced global warming was already underway and 'may have important implications other than for human comfort'. (This photo taken in 1989.) Credit:AP

To be sure, Hansen wasn't the first to detect a warming trend distinct from natural climate variability. Graeme Pearman, who would later head CSIRO's atmospheric unit for a decade, had been toiling for years to draw attention to climate change.

"There are issues here for all disciplines," Pearman said this week, explaining the rationale for organising a five-day summit in 1987 that drew biologists, economists and insurers together with physicists.