Today, carbon dioxide (CO2) levels in our atmosphere are the highest they've been in 15 million years. It's the cumulative impact of an ever-expanding population―7 billion people and rising―and an ever-increasing thirst for energy, requiring 24/7 electricity, factories, cars, trucks, planes and more. CO2 and other gases, like methane and nitrous oxide, amplify what is called the greenhouse effect. Historically, this has been a good thing. These gases trap heat, making the atmosphere warm enough for the earth to sustain an enormous diversity of life, including people. But over the past 150 years since the industrial revolution, greenhouse gases have shot up by 30 percent, rapidly raising Earth's global temperature. This trend could spell disaster. Higher CO2 levels have altered the chemistry of the ocean―making it more acidic. The ocean plays a key role in regulating climate, absorbing more than a quarter of the carbon dioxide that humans put into the air. But the ocean is struggling to keep up with rising CO2 levels. And thousands of plant and animal species could go extinct without time to adapt to a warmer planet. Humans, too, could be forced to leave their homes from the multiple impacts of climate change.