According to data from the Mauna Loa Observatory in Hawaii, the concentration of CO2 in the atmosphere is over 415 parts per million (ppm), far higher than any point in the last 800,000 years.
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That's the highest level since homo sapiens came onto the planet, meteorologist Eric Holthaus tweeted, and represents an increase of 15 ppm over just the past three years. "We don't know a planet like this," Holthaus said.
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CO2 emissions are largely caused by humans burning fossil fuels like coal, oil and natural gas.
They keep heat trapped on Earth that would normally disperse into space, making the planet warmer.
According to a recent report by the United Nations, climate change and human activity could result in the disappearance of over a million plant and animal species.