Week 4 of Protons for Breakfast is approaching in which we discuss Global Warming. I have just been updating the PowerPoint slides, and checking all the links and I came across the above video (from NOAA here) . It shows the whole story in 3 minutes and 15 seconds. I think it is wonderful, but I feel it needs some explanation to get the most out of it.
Update: I asked Andy Jacobsen from NOAA (who made the video) for his comments and I have included these in blue below. We disagreed over one point and I have included our exchange at the bottom of the page.
Start to 1 minute 42 seconds:
- This covers the period from 1980 to 2011 shows carbon dioxide concentration from at first a few, and then a few dozen, stations in the northern and southern hemisphere.
- Look at the map for the location of the stations
- One can see that the concentration in the southern hemisphere shows an inexorable rise, but the concentration in the northern hemisphere shows quite large annual oscillations. These are summarised in the graph on the right which shows data from the south pole in blue and data from Mauna Loa in red.
- Looking at the ‘clock’ in the middle of the picture one can see that the CO2 concentration in the northern hemisphere falls sharply in northern hemisphere summer – when growing things grab CO2 out of the air using photosynthesis. Its amazing to think of this subtle process changing CO2 concentrations globally!
- Notice the spikes in some of the data – presumably from monitoring sites positioned close to industrial centres.
- The “spikes” can also be due to natural processes, such as respiration by plants, animals, and microbes. This is why Keeling went to Mauna Loa and the South Pole–not only were previous measurement techniques unreliable, but the ambient variability of CO2 is generally quite strong. As the measurement network has expanded, we have begun taking measurements at sites with more local signals…hence the outliers.
1 minute 42 seconds to 2 minutes 2 seconds:
- Now we end the modern era measurements, and go backwards in time from 1980 to 1960 with the original data taken by Keeling at Mauna Loa.
2 minutes 2 seconds to 2 minutes 22 seconds:
- Now the data compresses and we go backwards in time quite quickly to show the first ice core measurements which are in fantastic detail – extending back two thousand years. At this point it becomes clear how amazingly rapid the rise in CO2 concentrations has been.
2 minutes 22 seconds to 2 minutes 2 seconds to 3 minutes 15 seconds:
- Now we reach the deep ice core results showing data that extends back first 400,000 years, and then 800,000 years.
- We see the CO2 concentrations rising and falling by around 100 ppm – correlating with the Earth descending into ice ages when the CO2 concentration is low (180 ppm) and experiencing interglacial warm periods when the CO2 concentration is high (280 ppm). Although the CO2 concentration is not thought to have directly driven these changes, it is thought to have reinforced the changes.
- Now we really see the context of the modern measurements. Since the period that human beings have existed as a distinct species (roughly 1 million years) we have never lived on a planet with CO2 concentrations this high.
- The rise of humanity has all occurred since the last glacial maximum, about 20,000 years ago.
- Concentrations now are more than 100 ppm higher than a ‘normal’ interglacial melt and will certainly rise by at least another 200 ppm in the coming decades – truly a massive change of geological significance. And although we don’t know the consequences of this for certain, they almost certainly imply a warmer and less icy world.
It would be good to know what happens next, but we have to work that out for ourselves. Sadly the BBC report today that the rate at which CO2 concentration is rising is accelerating. NOAA have the actual data which can be seen in the figure below.
Andy also wrote
I’m puzzled by your comment about CO2 not having a primary role in glacial-interglacial climate changes.
Paleoclimate researchers would all agree, I believe, that ice ages cannot be explained without invoking the radiative forcing impacts of 100ppm CO2 shifts. Perhaps the thinking has evolved since I last checked in on this issue, but my understanding is that CO2 is the most direct driver of glacial cycles. Of course, part of this is how you define drivers and feedbacks; water vapor is a classic example of this paradox. It has a big radiative impact, but is generally classified as part of a feedback loop due to its short atmospheric lifetime.
My comment about the role of CO2 is that (as I understand it) the interglacial changes are driven by orbital factors – Milankovitch cycles – and similar effects. These factors cause some warming and then this warming causes a rise in CO2 which then reinforces the warming. Similarly with glaciation – I thought the slow loss of CO2 reinforced a cooling climate trend, but did not trigger it. Obviously the situation is different now and clearly CO2 is now the trigger.