I have not always believed that global warming was real, or of concern. For a period spanning my late elementary school days to the freshman year of college, I regarded the idea with a heavy dose of skepticism. In fact, I suspected it was false, and either a hoax or, more likely, an overreaction.

Before the fifth grade or so, I accepted global warming as true. But one day, as I read a children’s magazine, I saw the same article on the environment which they had published the previous year, making the same case about Earth’s temperature steadily rising, staring me in the face. Something seemed off to me. If this is really a big problem, I thought, why hasn’t someone already done something about it? I filed global warming away in the “unlikely” section of my brain.

Years later, in my freshman year of college, I learned the extent of my naïveté. Today, I’m still surprised at how many people—like I did before college—remain skeptical of the theory. Many are ignorant of the strength of the evidence for its reality, our role in the phenomenon, or the extent of the consensus of the scientific community on the subject. I dedicate this series of posts on global warming to those people who, like me, lacked proper information on this most important of matters. For global warming is real. We are, in fact, the primary cause of global warming. And if, as a species, we fail to act properly, it could mean the end of our civilization.

So, what, exactly, changed my mind about being a global warming skeptic to accepting the phenomenon as fact? In a word—evidence.

The graph above shows the average global temperature anomaly from the 1880’s to the early 2000’s. Temperature anomaly, in this case, refers to deviation from a chosen reference value. That these are average temperatures (or, in this case, the “mean” temperature) is important to remember. As we all know, the temperature of any two parts of the planet can vary drastically, from well below freezing in the Arctic to over a hundred degrees Fahrenheit in the Sahara (or on a typical summer day in Rapid City, South Dakota). Temperature varies from season to season, climate to climate, and to different extents in different locations. The average temperature, on the other hand, uses many measurements from different locations to estimate a midpoint to all those temperatures.

Because averaging global temperatures out a lot of random, local ups and downs, we can identify broader trends me mightn’t see through the noise. As this graph shows, the world is definitely warmer today than it was in 1880. Point of fact, it’s about .8 °C warmer than in 1880. After a .2 °C drop in the 1910’s, Earth’s temperature has increased quite steadily until the present day, with no clear sign of abating. So, over the century, the world has certainly been warming.

A change in temperature of .8 °C over more than a century may not come across as very alarming, but the story is different when you look a the long view. One of the graphs which persuaded me of the severity of global warming compared temperatures over the course of the past thousand years, demonstrating a severe uptick in the past century and a half. That graph became known as the “hockey stick.” Its accuracy has been the subject of controversy, given that we do not have thermometer readings of the world temperature before the 19^th century. Before that time, we have to take our estimates from secondary sources (such as historical documents) or the geological record. A lack of care in choosing one’s sources can result in skewed information, and that is exactly the accusation leveled at the creators of the “hockey stick.”

I started college in 2003. Luckily for you, it is 2013. Not only has the “hockey stick” stood up to scientific scrutiny—we also have better graphs:

This graph is from a study by Shaun A. Marcott and others. Their study reconstructs the mean global temperature anomaly for the past 11,300 years (as opposed to just 1,000). They compare 73 distinct sites, use geological markers to estimate the temperature, and use the most up-to-date radiometric standards to date their readings. This post at Open Mind has more detail on their methods, and their data is solid.

And the result? The world has been warmer before, but it has not gotten so warm so fast. Not for the past ten thousand years or more. In fact, starting from 7,000 years ago, the world’s climate had been cooling. Then, in the last century, the trend reversed. The world is about as hot as it was before the cooling trend began.

Why Nature’s sudden change of heart? There was none: the cause of this warming is us, and not Nature. In Part 2 of this series, I will explain how a race of naked apes could have such a large effect on the planet.