Climate Plots

The challenge of climate change can be explained with a small number of plots. I use them in my lectures and update them regularly. As a public service, I also make them available here. Please not that none of the plots below is based on modeling. These are observed and well documented changes to our planet.

The Keeling Curve

The atmospheric concentration of carbon dioxide (CO₂) has been measured since 1958 by the Scripps Institute of Oceanography. The data are available on the their webpage and is plotted below.

A number of important observations can be made:

• The concentration is currently above 410 ppm, which is higher than any time before during the last 3 million years. Our species has never experienced anything like this, and neither had any of our ancestors, since the genus Homo did not arrive until 2 million years ago. The Neanderthals would have been very surprised by what we have done to the planet in less than 200 years.
• The oscillations are due to the vegetation cycles of the Earth. They have an amplitude of roughly ±4 ppm, which is a useful number to know. There is a limit to the amount of biomass the Earth can produce.
• The CO₂-concentration is not only increasing but it is actually accelerating. It rose by roughly 0.8 ppm per year in the 60s and is increasing approximately three times as fast today.
• If we want to stay below 1.5 °C of global warming, we need to keep the concentration below 435 ppm. Unfortunately, we are going to cross this line in less than 10 years. Note also that it does not matter if we use 450 ppm as the limit. At the current rate of emissions, it would buy us less than seven more years.
• The carbon concentration can be fitted surprisingly well using a second-order polynomial. I have added the dates for the United Nations Framework Convention on Climate Change (1992), the Paris Agreement (2015), and the climate strikes initiated by Greta Thunberg in in 2018. During the last 30 years, we have not done anything to change this trend.

Carbon Emissions

Data for global CO₂-emissions can be obtained from the Global Carbon Project. Plotting these data against the annual rise in CO₂ concentration from the Keeling curve above, one obtains the following diagram.

The good news is that we know where the carbon dioxide in the atmosphere is coming from: the emission of 17 Gt of CO₂ increases the atmospheric concentration of CO₂ by roughly 1 ppm. If we want to stay below 435 ppm, we only have approximately 20 ppm left to go and therefore cannot emit more than

20 ppm × 17 Gt/ppm ≈ 340 Gt

This is the carbon budget. The only way to stop the CO₂-concentration from rising is to stop burning fossil fuel.

Global Average Temperature

The best source for the average temperature of the Earth is from NASA and the data are available on this webpage, which also provides the necessary references. I use the following dataset:

Combined Land-Surface Air and Sea-Surface Water Temperature Anomalies (Land-Ocean Temperature Index, LOTI)

The anomaly is calculated with respect to a reference period of 30 years. It is customary to use the period 1951-1980 but the planet had already seen some warming by then. I have therefore decided to use the years 1880-1909 as reference, which shifts the curves upward by 0.25 °C. After all, we want to compare with preindustrial temperatures.

The plot below shows annual and 11-year averages. It is obvious that the planet started heating up in the 80s and that the warming seems to be accelerating. We are very close to the 1.5°C target.

Currently, our planet is warming by slightly more than +0.2 °C per decade or +1.6°C-2.0°C during a human life span. Things do not look good for our children.

The Culpability of Big Oil

As reported elsewhere, Big Oil knew about the dangers of climate change already in the 70s. It is interesting to compare the predictions of their models with actual measurements. Apparently, even simple models are good enough to predict climate change, as thermodynamics cannot be fooled!

It is acually not surprising that the oil companies could predict the temperature. The biggest uncertainty in climate models is the amount of CO2 in the atmosphere. As the Big Oil controls this parameter, they effectly also control the climate of our planet.