This month the world has been celebrating the 50th anniversary of Neil Armstrong setting foot on the Moon. But this week sees another scientific anniversary, perhaps just as important for the future of civilisation.
Forty years ago, a group of climate scientists sat down at Woods Hole Oceanographic Institution in Massachusetts for the first meeting of the “Ad Hoc Group on Carbon Dioxide and Climate”. It led to the preparation of what became known as the Charney Report – the first comprehensive assessment of global climate change due to carbon dioxide.
It doesn’t sound as impressive as landing on the Moon, and there certainly weren’t millions waiting with bated breath for the deliberations of the meeting.
But the Charney Report is an exemplar of good science, and the success of its predictions over the past 40 years has firmly established the science of global warming.
What is this ‘greenhouse gas’ you speak of?
Other scientists, starting in the 19th century, had already demonstrated that carbon dioxide was what we now call a “greenhouse gas”. By the 1950s, scientists were predicting warming of several degrees from the burning of fossil fuels. In 1972 John Sawyer, the head of research at the UK Meteorological Office, wrote a four-page paper published in Nature summarising what was known at the time, and predicting warming of about 0.6℃ by the end of the 20th century.
But these predictions were still controversial in the 1970s. The world had, if anything, cooled since the middle of the 20th century, and there was even some speculation in the media that perhaps we were headed for an ice age.
The meeting at Woods Hole gathered together about 10 distinguished climate scientists, who also sought advice from other scientists from across the world. The group was led by Jule Charney from the Massachusetts Institute of Technology, one of the most respected atmospheric scientists of the 20th century.
The Report lays out clearly what was known about the likely effects of increasing carbon dioxide on the climate, as well as the uncertainties. The main conclusion of the Report was direct:
We estimate the most probable warming for a doubling of CO₂ to be near 3℃ with a probable error of 1.5℃.
In the 40 years since their meeting, the annual average CO₂ concentration in the atmosphere, as measured at Mauna Loa in Hawaii, has increased by about 21%. Over the same period, global average surface temperature has increased by about 0.66℃, almost exactly what could have been expected if a doubling of CO₂ produces about 2.5℃ warming – just a bit below their best estimate. A remarkably prescient prediction.
Authors: Neville Nicholls, Professor emeritus, School of Earth, Atmosphere and Environment, Monash University