Great Barrier Reef, Australia
On Oct. 24, more than 5,200 events took place in more than 180 countries for the 350 International Day of Climate Action. According to official estimates, MNN has learned that upwards of a million people participated in the worldwide events. The goal? To pressure world leaders to reduce carbon dioxide levels in our atmosphere down to 350 parts per million, the number scientists say is the safe limit for CO2.