With 2016 claiming the title of hottest year on record, models, statistics and timelapse photos are painting a pretty clear picture of who's to blame. Now scientists have updated one of the most comprehensive databases of the planet's temperature changes over time, taking into account records from a variety of sources and stretching back to the year 1 CE – and it's very damning evidence of human-induced climate change.
The Past Global Changes (PAGES) project was launched in 1991 as a way to study the planet's climatic past to help understand its present and future. In 2013, the PAGES 2k Consortium released an open-source database made up of 501 records, gathered and overseen by 98 scientists from 22 countries. Since then, the number of records has grown to more than 690.
These records come from a variety of sources, including tree ring measurements, corals, glacier ice, lake and seafloor sediment, mineral formations in caves, and even historical documents. While each of these might not be all that reliable on their own, cross-checking them against each other has shown they're all telling a very consistent tale, helping scientists build a detailed picture of the climate over the past 2,000 years.
That story is a grim one. The researchers found that until the middle of the 19th century, the Earth was going through a long-term cooling trend, but since 1880 the average global temperature has risen about 0.8° C (1.8° F). That uptick is so striking on a graph that scientists dubbed it the "hockey stick," and it's no coincidence that it began right around the time of the Industrial Revolution.
"It adds weight to the idea that the current rate of warming is unprecedented in the past 2,000 years, and, together with many other sources of evidence, further indicative of a human influence on climate," says Julien Emile-Geay, one of the scientists on the project. "It comes down to this: We know the human burning of fossil fuel is very rapidly warming the planet, and we know that the longer we wait, the harsher the consequences and the more costly it is to prevent them. What is the point of endlessly delaying action?"
The study was published in the journal Scientific Data.