Skeptics of global warming sometimes claim that rising temperatures are just another natural change in the Earth's climate, such as the medieval warm period of the years 800 to 1200 or the Little Ice Age, a cooling period that extended from about 1300 to 1850.  However, a couple of studies published on Wednesday provide clear evidence that the increase in global temperatures over the past 150 years has been much faster and more widespread than any warming period in the last 2,000 years. It's not necessarily that Result of human activities.
"The well-known maxim that the climate is constantly changing is undoubtedly true," said Scott St. George, a physical geographer at the University of Minnesota in Minneapolis, in a written commentary on the studies. "But even if we look to the earliest days of the Roman Empire, we can not see any event that is somehow equivalent to warming in recent decades."
Since the beginning of the 20th century In the 20th century, the global average temperature on Earth has risen by about 2 degrees Celsius. Consensus among climatologists is mainly due to the burning of fossil fuels, which release carbon dioxide and other heat-binding greenhouse gases into the air. Without joint efforts to reduce greenhouse gas emissions, the global average temperature could increase by a further 5.4 to 9 degrees Celsius by 21
One of the studies published in the journal Nature shows that The Little Ice Age and other natural variations only affected limited areas of the planet, so that modern warming was the first and only warming-up period in the last two millennia , The other study, published in Nature Geoscience, shows that the pace of modern warming has far exceeded the changes that occurred before the rise of the industrial age of the Bern Geographical Institute in Switzerland analyzed climate data from 2000 years ago. In the absence of direct temperature information – thermometer measurements were scarce before the mid-19th century – the scientists studied data on growth rings of old trees, layers of glacial ice and remnants of coral whose layers vary depending on the chemical composition of the temperature of seawater.
The nature study recorded the temperature changes on the planet and found, for example, that the Little Ice Age did not affect the whole world at once. The scientists found that temperatures in the Pacific Ocean reached their low point around 1500. Europe and North America have not fully recovered for two centuries.
The same pattern was observed for the higher temperatures during the medieval warm period. The researchers found that less than half of the planet immediately felt the heat.
Research shows that more than 98 percent of the earth's surface was exposed to record temperatures during the current warming period. The finding shows how dramatically today's global temperature rise differs from previous periods of temperature change, the researchers said.
"We show that these periods are not globally coherent, as previously assumed," said Nathan Steiger, a climate scientist at Columbia University in New York City and co-author of the Nature Study. The current warming period is in stark contrast to today's warming, he added, calling it "a globally coherent warm period that is very different from that observed in the past."
For the Nature Geoscience study, the researchers reported compared a series of climate simulations to find out what might have triggered the changes. Neukom and his colleagues found that the fastest warming in the last two millennia took place in the second half of the 20th century.
The researchers also found that the main cause of temperature changes changed over time. Before 1850, fluctuations were mainly associated with volcanic eruptions that cooled the planet by throwing sunblocking ash into the stratosphere. After 1850, greenhouse gas emissions took over.
"It's exciting to see studies like these that combine rigorous statistics with huge databases to make clear conclusions about past climate change," said Gabriela Serrato Marks, a PhD student in paleoclimatology at The Massachusetts Institute of Technology, Cambridge , Massachusetts, was not involved in the new research.
Marks said some of the records used by the researchers may contain inaccuracies, adding that subsequent research could benefit from more robust data. "Future studies will be amplified by data from the Southern Hemisphere and higher-resolution data," she said.
Jennifer Hertzberg, paleoclimatologist at Old Dominion University of Norfolk, Virginia, was not involved in the research, citing the study as "very important" and praising the use of several statistical methods to reconstitute temperature change over time. She called on the public to take the results to heart.
"The global temperatures we are seeing now are higher than in the last 2,000 years," she said. "What we see now is new territory, it's time for everyone to wake up and make changes."
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