91av

“THE world was warmer last year than at any time since records began,” led a story by Fred Pearce in the edition of 91av. It was also the warmest year in an already record-breaking decade, and the “greenhouse effect” was beginning to get public attention. But the extent of humanity’s contribution to this was still unclear. “Whether the current warming is due to the greenhouse effect from man-made pollution remains open,” we reported.

NASA scientist Jim Hansen (pictured) was sure that humans were to blame. In 1988, he caused an international stir, we reported, when he became the first climate scientist to publicly state: “the greenhouse effect is here”.

But much uncertainty remained, not least because untangling human effects from natural weather variations is far from easy. Hansen contended that a drought in the summer of 1988 was “a likely consequence of the greenhouse effect”, while the authors of a Science paper published in December of the same year believed an El Niño event to be the culprit.

The paper’s authors did acknowledge, however, that “the greenhouse effect may tilt the balance such that conditions for drought and heat waves are more likely”.

The world, of course, has continued to warm since those studies, with each passing decade bringing more record-breaking weather. At present, 2016 stands as the hottest year on record, but 35 heat records have already been set in 2019 (9 February, p 3).

We now also recognise that extreme weather is more likely in a warming climate. Thirty years ago, Alaskans experienced “their coldest winter in living memory”. A few weeks ago, the polar vortex brought record low temperatures to North America as there were record highs in Australia.

, the atmospheric carbon dioxide level was 353 parts per million. It is forecast to surpass the 410 ppm mark this year.