Chris Mooney is a Pulitzer Prize-winning journalist and a CNN Climate contributor. He is currently a professor of practice in the Environmental Institute at the University of Virginia.Planet-warming pollution rates exploded after the end of World War II. James Watt’s steam engine launched the Industrial Revolution in 1769. Before that, for thousands of years, humans were clearing forested land for farming, releasing carbon from trees and plants into the atmosphere.The severity of global warming has long depended on your frame of reference — on what temperature you think was normal for the Earth before humans began changing it. But what year should mark that moment?AdvertisementAdvertisementAdvertisementAdvertisementThat’s what makes a groundbreaking new temperature dataset released by a group of scientists based in the United Kingdom so striking. The datasets used to diagnose the modern history of the planet’s climate — and to proclaim that the world is now very near to 1.5 degrees Celsius (2.7 degrees Fahrenheit) of warming — typically begin with the year 1850.The new one goes all the way back to 1781.This extended time frame matters because greenhouse gases in the atmosphere increased 2.5 percent between 1750 and 1850, enough to have caused some warming that the data hasn’t accounted for.Circa 1899: James Watt’s “Sun and Planet” steam engine, patented in 1781. The action of the beam engine, which operated cogs, meant that the steam engine could be applied to factory machinery. – Hulton Archive/Hulton Archive/Getty ImagesThe new temperature record, dubbed GloSAT, helps contribute to the growing sense among scientists that the Earth has warmed more than what calculations based on the 1850 starting year would suggest.AdvertisementAdvertisementAdvertisementAdvertisement“That 1850 start time is one that’s chosen for essentially practical considerations, given the information that’s available,” said Colin Morice, lead author of the new study and a scientist with the Met Office Hadley Centre in the UK. “For sure, 1850 is not the start of industrialization.”The new dataset, published in Earth System Science Data by 16 scientists, shows a significantly cooler Earth from the late 1700s through 1849 comp …
