Saturday, June 09, 2018
We have a pretty good idea of what Earth's atmosphere has looked like for the past 800,000 years. Humans like us -- Homo sapiens -- only evolved about 200,000 years ago, but ice-core records reveal intricate details of our planet's history from long before humans existed. By drilling more than 3 kilometers deep into the ice sheets over Greenland and Antarctica, scientists can see how temperature and atmospheric carbon dioxide levels have changed from then until now.
For the 800,000 years we have records of, average global CO2 levels fluctuated between about 170 ppm and 280 ppm. Once humans started to burn fossil fuels in the industrial era, things changed rapidly.
Only in the industrial era has the number risen above 300 ppm. The concentration first crept above 400 ppm in 2013, and continues to climb.
Scientists debate the last time CO2 levels were this high. It might have happened during the Pliocene era, between 2 and 4.6 million years ago, when sea levels were at least 60 to 80 feet higher than today. It may have been in the Miocene, 10 to 14 million years ago, when seas were more than 100 feet higher than now.
In our 800,000-year record, it took about 1,000 years for CO2 levels to increase by 35 ppm. We're currently averaging an increase of more than 2 ppm per year, meaning that we could hit an average of 500 ppm within the next 45 years, if not sooner.
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