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99.9999% chance humans are causing global warming, and other science-based facts on climate change for Earth Day

The glaciers of Glacier National Park have been in retreat for many years, peaking in the 19th century at the end of a period called the Little Ice Age. Credit: Tim Rains, NPS

First among them, there's no longer any question that rising temperatures and increasingly chaotic weather are the work of humanity. There's a 99.9999% chance that humans are the cause of global warming, a February study reported. That means we've reached the "gold standard" for certainty, a statistical measure typically used in particle physics.

The mechanism is well understood and has been for decades. Humans burn fossil fuels such as oil, coal and gas, which release carbon dioxide (CO2), methane and other gases into the Earth's atmosphere and oceans. CO2 is the greenhouse gas that's most responsible for warming.

Study lead author Benjamin Santer of the Lawrence Livermore National Laboratory in Livermore, California, told Reuters that “the narrative out there that scientists don’t know the cause of climate change is wrong."