Letter: Humans broke climate, must be ones to fix it

For most of our Earth’s history, carbon dioxide (CO2) levels in the atmosphere have ranged between 180 and 280 parts per million. For the first time in the known history of Earth, CO2 reached 300 ppm in 1950. Today CO2 levels have reached 425 ppm. A 42% increase in just 75 years — an unheard-of rate of change to a level our world has likely never experienced.