evidence: While most GHGs are naturally occurring, human activities have also been leading to a problematic increase in the amount of GHG emitted and their concentration in the atmosphere. This increased concentration, in turn, can lead to adverse effects on climate. Effects include increases in the frequency and intensity of extreme weather events – including flooding, droughts, wildfires and hurricanes – that affect millions of people and cause trillions in economic losses. [...] Carbon dioxide (CO2), methane and nitrous oxide are the major GHGs. CO2 stays in the atmosphere for up to 1,000 years, methane for around a decade and nitrous oxide for approximately 120 years. Measured over a 20-year period, methane is 80 times more potent than CO2 in causing global warming, while nitrous oxide is 280 times more potent. [...] Since more energy enters than exits the planet, surface temperatures increase until a new balance is achieved. This temperature increase has long-term climate impacts and affects myriad natural systems.