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We're in uncharted territory - a new study says the warming we've seen in the past 100 years is unprecedented compared to the past 2,000 years.
From about year “zero” to the late 1800s, hot and cold spells would occur in different parts of the world at different times due to natural weather cycles, solar activity, and volcanic eruptions.
But since the late 1800s, when humans began burning fossil fuels for energy, the entire world has steadily warmed in a way that it did not for nearly all of the previous 2,000 years.
The study was published Wednesday in the British journal Nature.
"The warming of the climate system that we have seen in the last 100 years is fundamentally different than what we have seen in the previous 1,900 years," said study co-author Nathan Steiger, a climate scientist at Columbia University.
"The climatic times of the last 2,000 years, which have become popular with names like 'Little Ice Age' and 'Medieval Warm Period', were only phenomena on a regional or continental scale. These cold and warm decades can be explained by the climatic variability of nature.
"But it's only been since humans started burning fossil fuels that the entire Earth has warmed."
In fact, the study says that the rapid temperature increases towards the end of the 1900s and affected more than 98% of the Earth's surface.
He also said that modern climate change cannot be explained by random fluctuations, but by man-made emissions of carbon dioxide and other greenhouse gases.
To determine the Earth's temperature for the past 2,000 years, scientists searched more than 700 records of trees, ice, sediments, corals, cave deposits, documentary evidence, and other archives.
“It's true that during the Little Ice Age it was generally colder all over the world,” explained study co-author Raphael Neukom of the University of Bern, “but not everywhere at the same time. Peak periods of pre-industrial heat and cold periods occurred at different times in different locations. "