At the opening of the United Nations climate change conference in Poland in December, UN Secretary-General António Guterres made a short speech with a long history. The twenty warmest years on record, he said, have occurred in the past twenty-two years, with the past four years the four warmest; the concentration of carbon dioxide in the atmosphere is the highest it has been in three million years; greenhouse gas emissions, after leveling off for the past three years, are once again on the rise, a trend led by China, the United States, and India. “We are in trouble. We are in deep trouble with climate change,” Guterres said. “Science demands a significantly more ambitious response.”
Such warnings have become so familiar that it is easy to lose sight not only of their significance, but also of the enormous effort behind each deceptively simple statement. In order to know that the planet has recently experienced the twenty warmest years on record, generations of scientists have had to measure temperatures precisely enough, frequently enough, and widely enough to distinguish a long-term global trend from the roar of short-term and local variations. In order to know that the concentration of atmospheric carbon dioxide is the highest it has been in three million years, scientists have analyzed the content of tiny air pockets trapped in ancient Antarctic ice and counted the number of microscopic stomata—portals for the intake of carbon dioxide—on the surface of fossilized leaves. In order to understand how humanity is changing the climate today and is likely to change it in the future, scientists have tracked interactions among phenomena at vastly different scales, from the molecular to the oceanic, and discerned how those interactions change over both time and space.
When the work of climate science began, in the seventeenth and eighteenth centuries, most Europeans accepted the Aristotelian model of a static global climate, a kind of spherical shell sectioned latitudinally into fixed temperature zones. The modern concept of climate as a dynamic system of air and ocean currents lay far in the future, as did the understanding that human activities could destabilize that system. The earliest climate scientists had no satellites to collect data and no computers to analyze them; they intuited that there was a story to be told about the atmosphere’s influences on Earth, and that this story could be found through the accumulation of careful measurements. As historian Deborah Coen recounts in her book Climate in Motion, this imaginative leap was a product of a particular time and place.
In 1526, when the Hungarian monarch Louis II was defeated and killed by the Ottoman forces of Suleiman the Magnificent at the Battle of Mohács, the crowns of Hungary…
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