I realise that I am a bit odd. The fact is that I love graphs. Graphs make me happy, and sometimes sad. A good graph speaks to me like a Da Vinci painting or a Tolstoy novel. A good graph tells a story and there is no need for words. But I realise that graphs do not always speak to others. May be for many, graphs do not speak at all. I have often thought about how I could try to help others better understand graphs, even learn to love graphs. At work I introduced a Graphical Excellence Prize, that became known as the Florence Nightingale Prize because it was Florence Nightingale’s rose diagram that showed the power of graphs to change the World. Politics would be improved immensely, if debates were conducted in the light of a big graph projected on the wall with the relevant data such that politicians could no longer deceive us about the facts.
If I were to make a list of the most important graphs in the history of the World then right at the top of my list would be the Keeling curve. Back in the 1950s, Charles David Keeling started climbing thousands of metres to the top a volcano on Hawaii and filled a small bottle with air. By sending light through the air he measured the amount of carbon dioxide. After about ten years of making these measurements it became clear that the amount was steadily increasing. At first we could only speculate about where this extra carbon was coming from, but subsequent measurements on the change in the ratio of different isotopes of carbon, provided a smoking gun that the extra carbon dioxide was coming from burning fossil fuels.
I would like you to look at a version of the Keeling curve that I have included below.
All the data is in the public domain so you make your own plot if you prefer. We always encourage our students to make their own plots because while the data is the data, plotting it in different ways may lead to different conclusions.
For this plot I have overlaid each decade. The Keeling measurements of atomospheric carbon dioxide are shown as black dots and highlighted using a background in blue, green, yellow and red for the 1980s, 90s, 2000s, and 2010s, respectively. We can see two things. One is that there is quite a large yearly oscillation (which is well understood because of the difference between the Northern and Southern hemisphere) and the other is that the yearly average keeps on rising. Back in the 80s the amount of carbon dioxide was around 350 parts per million (ppm) whereas now it over 410 ppm. This is a big change and it is bad because we know that temperature is directly proportional to the amount of carbon dioxide in the atmosphere (the greenhouse effect). For the whole period of human evolution the amount was never more than 300 parts per million, so we are into uncharted waters, literally as the glaciers melt. The compaigning group 350.org would like us to get back to 350 ppm, i.e. back to the 80s level. This would help to reduce some of the amount of damage caused by rising sea levels. In the short term we just need to stop the amount increasing any further.
For me the big story in the Keeling curve is how we failed collectively to take it seriously. I was aware of it in the 80s and when I got the opportunity to vote, I voted Green, because they were the only ones talking about it. I thought that over time more and more people would become aware, vote Green and we would start to see a change in the trajectory of the curve. I am still waiting. I feel shame because waiting and voting was not enough. I failed because may be I could have done more to raise awareness. We all failed. The United Nations became involved in the 80s and the first Congress of Parties (COP) conference was held in 1995. This year we will have COP-26 in Glasgow. But the Keeling curve tells us that none of this – COP, green activism, more science, has made any different. The amount of carbon dioxide has gone on rising and rising in exactly the way that we could have predicted back in the 80s. There has been much talk, but no change in our trajectory. In fact, the only time that we saw a slight slowing in the rate of increase was in the early 90s due to the collapse of the Soviet Union. 
I partly understand why many people do not feel rising carbon dioxide and temperature are such a big deal. A 2 degree temperature rise does not sound that much. May be only now that we are seeing the increased frequency of extreme weather events resulting from the current 1 degree of warming, is it starting to sink in. The past year has been heartening in that we have seen an enormous increase in activism, especially from the young, and that has raised awareness much more widely. So the big question looking ahead is will the human race be able to change course, and when will be know whether we are making a different? For the answer to this second question, people like me will be looking at the Keeling curve. Our current trajectory, which is often called Business-As-Usual (BAU) is so well understood that we can project the Keeling curve into the future. This is the pink line in the plot. If the data (the black dots) come in above the pink line we are doing worse than business as usual, if they fall below the pink line then we are starting to do better.
What do you think is going to happen? I was going to suggest a bottle of wine for the person who is closest to the correct prediction for atmospheric carbon dioxide in 2030, but it seems rather flippant, and apparently half the world’s vineyards are going to be destroyed anyway. Until 2030, I suggest we step up our collective efforts both to cut our personal carbon footprints as much as possible, and use our votes and voices wisely to try and ensure a future for those that come after us.
 If you are interested here is another version of the Keeling curve that also shows the difference between the actual measurements and our expectations based on the Business-As-Usual prediction. Here we can clearly see the dip due to the collapse of the former Soviet Union in the early 90s. It shows that what happens on Earth – as long as it is dramatic enough – fairly quickly shows up in the data, so if we can shift our policy dramatically in the next decade we will see it in the data.