Hockey-stick identity

Okay kiddo, imagine you have a special tool that lets you measure how hot it is outside. Now, you use this tool every day for a whole year and write down the temperature. When you look at your notes, you notice that for the first few months, the temperature is pretty much the same, not too hot or too cold. But then, suddenly, it starts to get much hotter and keeps getting hotter and hotter as the year goes on.

This is kind of like something called the "hockey-stick identity." It's a way of looking at how something changes over time - just like measuring the temperature every day - but instead of temperature, we're looking at how much carbon dioxide is in the atmosphere.

Scientists have taken measurements of carbon dioxide levels going back hundreds of thousands of years and they noticed something interesting. For most of that time, the carbon dioxide levels were pretty steady, not too high or too low. But then, starting in the mid-1800s, when people started burning more and more fossil fuels like coal and oil, the carbon dioxide levels started to soar.

So, like the hockey stick tool, the graph of carbon dioxide levels over time looks pretty flat for a long time, then suddenly it shoots up and keeps going up. This is the "hockey-stick identity" - a way of describing how quickly these levels have risen in the past few centuries. And it's not a good thing, because high levels of carbon dioxide in the atmosphere are causing the planet to heat up, leading to climate change and all sorts of problems.