Measuring $CO_2$ in Earth's atmosphere

How can we possibly know what $CO_2$ levels were before modern instrumentation?

Measuring atmospheric $CO_2$

If you want to get an idea of worldwide concentrations of $CO_2$ over long periods of time... is a city a good place to build a place to measure $CO_2$ concentrations in the atmosphere?

The Mauna Loa observatory is located on an extinct volcano on one of the Hawaian islands, in the middle of the Pacific Ocean.

Charles Keeling started making measurements of $CO_2$ in the 1950s.

Take a closer look at the recent data, and over the course of just last year.

  • During which months is $CO_2$ dropping?
  • Can you think of any annual processes on Earth that might be responsible?

Here is a world map (CIA)

The goal of environmental advocacy group 350.org is to get this graph down to 350 ppm once more. A key member of this coalition, Bill McKibben visited Goshen College in 2009.

Exxon used its fleet of tankers (travelling all over the world's oceans) to sample $CO_2$ worldwide (late 70s), and also concluded it was rising.

We now know that their in-house science-team did an excellent job of modelling climate impacts

Specifically, Exxon projected that fossil fuel emissions would lead to 0.20 degrees Celsius of global warming per decade, with a margin of error of 0.04 degrees — a trend that has been proven largely accurate.
Quick quiz!
  1. In 2015, 196 countries signed on to the "Paris Agreement" which had goal of limiting global temperature increase by the end of this century to less than ____ degrees C
  2. Pre-industrial levels of $CO_2$ in Earth's atmosphere? ____ ppm
  3. Today's approximate concentration of $CO_2$ in Earth's atmosphere? ____ ppm

How long has $CO_2$ been increasing?

How do we know atmosphere composition and temperature in the distant past? (Well, well before Mauna Loa...)

Each year, near the poles, snow falls, temperatures go up and down with the seasons, producing annual layers.

Elaine Hood, NSF; U.S. Antarctic Program photo library
Like tree rings, you can count backwards through the layers as you dig down into the snow.

Ice cores brought up from Antarctica preserve air samples back about 650,000 yr. (CO2 levels)

Temperatures from long ago?

Tree rings (thickness and density) depend on temperature and rainfall. We can go back ~11,000 yr. "dendrochronology"

Temperature also affects the ratio of O16 to O18. Oxygen isotope ratios in calcite (shells) ($\text{CaCO}_3$) can be used to deduce temperatures (Temperatures)

History of atmospheric carbon-dioxide

What happened around 1800?


(MacKay)

MacKay point out that the big increase is coincident with the industrial revolution.

Humans? One thing we did starting with the industrial revolution was to burn coal to power machines. Coal is almost pure carbon, so when we burn it, the chemical reaction is: $$C+O_2\to CO_2 + \text{heat}.$$

How long have we known about the Greenhouse effect?