Global warming is happening now. The planet's temperature is rising. The trend is clear and unmistakable. Every one of the past 40 years has been warmer than the 20th century average. 2016 was the hottest year on record. The 12 warmest years on record have all occurred since 1998. Globally, the average surface temperature has increased more than one degree Fahrenheit since the late 1800s. Most of that increase has occurred over just the past three decades. We are the cause. We are overloading our atmosphere with carbon dioxide, which traps heat and steadily drives up the planet’s temperature. Where does all this carbon come from? The fossil fuels we burn for energy—coal, natural gas, and oil—plus the loss of forests due to deforestation, especially in the tropics. The scientific evidence is clear. Within the scientific community, there is no debate. An overwhelming majority of climate scientists agree that global warming is happening and that human activity is the primary cause.