The Pentagon knows it. The world's largest insurers know it. Now, governments may be overthrown because of it. It is climate change, and it is real. According to the U.S. National Oceanic and Atmospheric Administration, last month was the hottest March on record for the United States since 1895, when records were first kept, with average temperatures of 8.6 degrees F above average. More than 15,000 March high-temperature records were broken nationally. Drought, wildfires, tornadoes and other extreme weather events are already plaguing the country.