When we look back on 20th-century science a few decades from now, a few images that stand out above the rest. Earthrise may be the most famous. It was taken by Apollo 8 Astronaut Bill Anders 50 years ago last December. I’ve written before about how that single image changed the way we humans see our planet.

Here’s another image that also led to a dramatic change in how we see our planet:

That graph that would become known as the hockey stick. It was published in a paper by Dr. Michael Mann et. al on 15 March 1999 in the AGU Journal Geophysical Research Letters.

The stick was a powerful image showing how fast our planet’s temperature was rising compared to the stable climate of the past 1000 years. In 1999, there were a large number of people who insisted that the planet was not warming at all, and some even insisted that a new ice age was looming! The hockey stick showed clearly that we were indeed warming, and that something bad was happening to our stable climate.

Twenty years have passed, and the hockey stick has stood up against the firestorm of criticism it elicited. (Read this.) Most of that was from people with no background in science. Those who talk about any science quickly learn that when you show someone information that conflicts with their worldview, they will often dismiss it and or get angry, and accuse you of showing them fake data. This includes people who do not believe in vaccines and others who DO believe in chemtrails, UFO’s, or that pro-wrestling is real.

All of this happened to Dr. Mann after that paper was published, and all of it fell by the wayside as others did what science requires: replication.

If others cannot replicate your work, it will not be accepted as good science.

Other scientists did indeed replicate it, and improved upon it, with newly recovered data and observations. Dr. Mann improved his first graph with even better data as well. This week, a more recent version was posted on Twitter this week by Climatologist Stefan Rahmstorf. The stick is even sharper now and gets more so every year. It now shows how unusual the last 100 years have been.

In his book, Brian Fagan (the renowned archeologist) has called the stable climate of the Holocene, “The Long Summer“. All of human civilization developed in the stable climate of the last 6,000 years, but the data clearly shows that a real heat wave is headed for humanity and we are running out of time to deal with it.

It did not go unnoticed that on the very anniversary of the paper, thousands of students worldwide rallied to tell politicians that we must act on the climate threat. The impact of the hockey stick has indeed been profound, and a picture really is worth a thousand words. At times, it gets the entire world’s attention.

Dr. Mann received the premier award for environmental science this week, the Tyler Prize. After the firestorm that erupted over that paper in 1999, I asked him his feelings 20 years later. He said: “It’s certainly not what I signed up for. But informing the societal conversation about the greatest challenge we face is more important than ANY physics problem I might have solved.”

I think that sums it up perfectly.