claim: Some experts think we’re on track to hit 550 ppm by the end of the century, which would cause average global temperatures to rise by 6 degrees Celsius
evidence: The average global temperature on Earth has increased by about 0.8° Celsius ( 1.4° Fahrenheit ) since 1880; Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20 °C per decade.