1. Dr. Keeling's curve

Dr. Charles Keeling. Dr. Keeling, of the Scripps Insitute of Oceanography at UC San Diego, is best known for leading the measurement of atmospheric \(CO_{2}\) at an observatory at Mauna Loa, Hawaii. This record, which started in 1958 and continues to this date, showed the first significant evidence of rising atmospheric \(CO_{2}\) levels, from 320 parts per million to over 400 ppm today.

Keeling determined that although \(CO_{2}\) levels rise and fall on a regular basis due to natural plant activities, the significant systematic rise through the decades comes from humans burning fossil fuels, which releases \(CO_{2}\) into the atmosphere. – jsu


Why is it acceptable to say that \(CO_{2}\) levels at Mauna Loa, Hawaii are representative of \(CO_{2}\) levels around the world? – jsu


The atmosphere is is a well-mixed system. Measurements at distant sites may fluctuate with respect to each other, but the long term trend is the same.

Answer. I don't know, why?? – cvh

Answer. Tap the flash card above once, then tap "Show Answer" on the bottom of the screen to see.

(short answer: the atmosphere is well mixed). – jsu

A biography of Keeling's life and methods, documenting his persistent collection of accurate climate data in the face of variable funding and changing politics. – jsu

Measuring \(CO_{2}\) concentrations. As a postdoctoral fellow at Caltech, Dr. Keeling measured atmospheric \(CO_{2}\) concentrations using a device called a mannometer. In a simple mannometer, gas pressure is measured by placing the sample into the closed end of a U-shaped tube, and leaving the other end open to the atmosphere. Uneven pressures cause a column of mercury to move about.

By measuring the pressure of an air sample, removing the carbon dioxide by freezing, and measuring the pressure again, Keeling could determine \(CO_{2}\) levels with great accuracy. This was a laborious procedure, taking over 2 hours per sample. Thankfully, Keeling was patient and enjoyed the outdoors. – jsu

Later, as a staff scientist at Scripps, Keeling developed a faster way to measure \(CO_{2}\) concentrations, using a device called a non-dispersive infrared spectrometer. – jsu

Natural variations in \(CO_{2}\) levels. Prior to Keeling's research, scientists had assumed that atmospheric \(CO_{2}\) measurements were subject to large errors, since their readings displayed significant variations.

By taking regular measurements over hours, weeks, months, and years, Keeling discovered that these variations in fact followed a predictable pattern. \(CO_{2}\) levels drop during the day, as plants absorb the gas, then rise at night, as plants release it.

Seasonal variations occur as plants grow during the summer and die during the winter. Keeling studied isotope ratios to establish that these changes were due to the accumulation and loss of biomatter. – jsu

An interactive Keeling curve -- zoom in and out to explore the data on hourly, weekly, monthly, and yearly time scales, with data included all the way to the present day. – jsu

Question. Why does CO2 vary seasonally? – cvh

Question. Here's a map showing Mauna Loa's location. If CO2 were measured elsewhere (like the Southern Hemisphere, or on the mainland of N. America), how would the measurements be similar and how would they be different? – cvh

Seasonal variations are larger in the Northern Hemisphere because the Northern Hemisphere contains more plants. – jsu

A systematic rise upward. In the first few years Keeling collected his data, he noticed -- nearly overwhelmed by seasonal fluctuations -- a rise in \(CO_{2}\) concentrations of 1 ppm per year.

This rise might seem minute, but in the context of geologic time and Ice Age cycles, it is a sharp spike upward. By now, it is absolutely clear to scientists that this increase is a result of humans burning fossil fuels. – jsu

Combining the Keeling curve with historical data from ice cores, we see that the rise in \(CO_{2}\) levels is unlike anything the Earth has seen for hundreds of thousands of years. – jsu

Question. How about this longer view of recent CO2? – cvh

Question. Are there parts of this curve you want to know more about? – cvh

Accumulation of fossil fuel emissions. The rise in \(CO_{2}\) concentrations measured parallels the accumulation of emissions from fossil fuel burning. The chart above shows the expected rise, assuming 57% of emissions remain airborne.

This is a simplistic model -- more advanced climate models have made clear that the effect is human in origin. – jsu

Question. Add a card with your own sketch of a key portion of the global carbon cycle, indicating where human activity has an impact. – cvh

http://earthobservatory.nasa.gov/Features/CarbonCycle/ (Units in Gigatons and Gigatons Per Year) – cvh

Natural vs. Human-induced. The signals are distinct now.

(Stocker et al., Technical Summary, Climate Change 2013, Fifth Assessment Report of the IPCC) – cvh

What do the shaded blue and purple bars represent? – jsu

Error bars or estimated uncertainties in the climate models. We want to make sure differences we see are due to real effects, and not variability of models.

[1] http://www.youtube.com/watch?v=l8tPKj20GFo
[2] http://co2now.org/images/stories/pdfs/charles-keeling-and-measuring-atmospheric-co2-umn.pdf
[3] http://keelingcurve.ucsd.edu
[4] http://keelingcurve.ucsd.edu/why-are-seasonal-co2-fluctuations-strongest-in-northern-latitudes/

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