The earth heating up a little? No, it’s unprecedented.

Can a small number underlie a big impact? We’re used to hearing about population sizes in the millions and budgets in the trillions. How can an overall global temperature rise of just 2 degrees C (3.6 degrees F), the target that governments — absent our own — have committed to avoid surpassing, be such a big deal? It sounds like such a small number: who could even say whether the outside temperature is 70 degrees F or 74 degrees F? Surely this must be scientific quackery, designed to instill fear or advance some nefarious purpose?

But the seeming insignificance of that tiny 2 degrees is misleading. First, understand that it’s a global average, obtained from incorporating thousands of individual readings over an entire year. Looked at this way, historical temperatures are extremely stable. In fact, average annual temperatures have stayed within about 1 degree C of each other over the past 1,000 years, and within about 2 degrees of each other over the past 14,000 years. The difference between civilization as we know it, and an ice age is only 5 degrees C. So if we warm 2 degrees C more than the historic average, we’re way beyond anything modern humans have experienced. Globally, we’ve already warmed about 0.85 degrees C since 1880, with most of that coming the past three decades. The last time the earth was this warm, sea levels were 20-30 feet higher than now. If you’re tempted to dismiss the importance of this small number, consider if you want your children living in a world with a climate unlike any in human history.