In August the United Nations Intergovernmental Panel on Climate Change released its sixth assessment report, described by secretary-general António Guterres as "code red for humanity".
Its stark assessment was that human activity, most notably greenhouse gas emissions from deforestation and burning fossil fuels, is causing drastic and potentially irreversible climate change. As if to drive home the report's message, this summer saw devastating floods kill more than 200 people in Germany and Belgium. Shortly afterward there were apocalyptic scenes as wildfires ravaged Greece.
The COP26 climate change conference is due to meet in Glasgow this November, and there will be significant pressure to agree a co-ordinated international reduction in greenhouse gas emissions. Previous agreements reached in Kyoto (1997) and Paris (2015) have had limited success, not least because of a lack of enthusiasm from the world's largest polluters.
In the United States climate change is highly politicised. Right-wing groups and the fossil fuel industry have for decades funded work casting doubt on the scientific consensus, taking their lead from the tobacco lobby. Similarly, Brazilian president Jair Bolsonaro has cast doubt on climate change and overseen the razing of 10,000 square miles of Amazon rainforest, roughly the size of Munster in just two years.
Glass cylinders
What is most frustrating for observers is that the science behind greenhouse gases has been understood for over 160 years. Indeed it is so straightforward that it was first demonstrated by an amateur without access to specialised equipment.
In 1856 the American Association for the Advancement of Science met in Albany, New York. One of the papers presented (although not read by its author) was by Eunice Foote, an inventor and women's rights campaigner.
Foote had placed regular air, water vapour, and carbon-dioxide in separate glass cylinders and compared their change in temperature when exposed to direct sunlight. The outcome was that the carbon-dioxide cylinder rose to greater temperatures than the others and also took much longer to cool. A larger amount of carbon-dioxide in the atmosphere, Foote argued, would inevitably lead to increased temperatures.
Despite its implications Foote's paper failed to make much impact. The physicist Joseph Henry, who read it out, failed to see its significance. Women were not always taken seriously in the rapidly professionalising world of science, and American scientific society was considered peripheral and underdeveloped in Europe.
But in 1859 the Irish physicist John Tyndall took up a similar line of inquiry. Tyndall had trained in Germany with some of the finest experimental scientists in the world, and held a prestigious professorship at the Royal Institution in London. This gave him access to the most advanced laboratory equipment available, and he was able to conduct more sophisticated experiments than Foote.
Using special apparatus Tyndall was able to replicate the effect of infrared radiation from the earth’s surface and more precisely measure its absorption and emission by various gasses. The results were conclusive: in the atmosphere some gasses such as carbon-dioxide and methane would act like the glass in a greenhouse, retaining surface heat and raising temperatures.
Ice ages
Foote had first theorised the link between carbon-dioxide and climate, and Tyndall had experimentally proved that link. It was a Swedish physicist, Svante Arrhenius, who in 1896 showed that at the end of historical ice ages an increase in atmospheric carbon-dioxide had contributed to warming the planet.
Using this discovery Arrhenius was able to demonstrate that burning fossil fuels could create carbon-dioxide emissions in large enough volumes to cause global warming and provided an equation to calculate its effect. He also coined a term for this process: the “hot-house effect”. There was now a proven link not just between carbon- dioxide and global warming, but between human activity and climate change.
In the 1850s an amateur woman in provincial America used basic equipment to demonstrate that carbon-dioxide could warm the planet. Successive generations of scientists have refined Foote’s work and linked it conclusively to fossil fuels. Thanks to their efforts the world leaders meeting in Glasgow this autumn understand how human activity creates climate change. Crucially, they also have the ability to do something about it. Let us hope that they do.
Dr Stuart Mathieson is is a postdoctoral fellow working in Dublin City University school of history and geography