Additional info from the Union of Concerned Scientists

Many circumstances require immediate action: Consider a full bladder or a red traffic light. We usually address such circumstances without delay, because the consequences of inaction — physical discomfort or legal troubles — are clear. When it comes to climate change, the urgency of the problem may not seem so obvious, since it doesn't sound an alarm or poke us in the eye. The consequences appear to be far away. And we find it hard to comprehend the significant risks posed by global warming, such as the rapid accumulation of carbon dioxide in our atmosphere or the impending rise in sea levels, because we can't, at the moment, see them with the naked eye. Yet if we fail to reduce heat-trapping emissions, we will cross a threshold, and the changes in our world will be irreversible.

Releasing carbon into the atmosphere is sort of like filling a water balloon from an outdoor faucet. If the water is merely trickling in, you can easily remove the balloon from the spout and have room to tie the knot. But if the spigot is gushing and the balloon is swollen with water, you have to act quickly and forcefully to remove it before it bursts.

Human activities, such as burning coal and oil in power plants and cars, have poured excessive amounts of carbon dioxide into the atmosphere, and the natural world just can't absorb it all. Like the swollen water balloon, the atmosphere is overloaded. The problem with adding more carbon dioxide, methane, and nitrous oxide gases to Earth's atmosphere is that they trap heat, causing global temperatures to rise. Even a rise of a degree or two makes a difference in many aspects of the world that people care about. Back in 1960, about 40 percent of a metric ton of emitted CO₂ would remain in the atmosphere and the ocean would absorb much of the rest. Now that has risen to 45 percent as the ocean has become saturated with carbon. This means that a ton of CO₂ emissions today traps more heat than it would have 50 years ago.

The evidence that global warming is happening now and that human activities are the primary cause is overwhelming. Indeed, recent research indicates that Earth's climate is changing more quickly than scientists had projected just a few years ago.

Climate change carries serious consequences both for humans and for ecosystems. This is a crisis that will affect our food, our national security, our water, our ability to live where we choose, and other basic human needs. Whether and how we address global warming isn’t just about science, it's about values.