Temperature and CO2: A new figure for a new year

Last month, Science had a terrific review article on the threat that rising CO2 concentrations and rising temperatures pose to the world's coral reefs. Scientists, alas, are not great marketers. The plight of the world's coral reefs is a tough sell at a time when most North Americans are "holiday" shopping and powering all manner of coloured lights, inflatable Santas and animatronic reindeer (though the review did garner some front page and radio attention the week of publication).

In my mind, the most compelling feature of the paper was this one figure to the left (reprinted here without any particular permission, shhh). It is a simple inversion of the famous 420,000 year record of temperature and CO2 plots from the Vostok ice cores, shown in every climate change course, presentation and documentary. The very same data, plotted a different way: temperature vs. CO2, rather than temperature and CO2 over time.

I hope to see this figure used more often, whether in relation to coral reefs or not, because it clearly demonstrates three crucial points about the planet's current situation:

1. There is warming in the pipeline, like it or not. Today (pt. A) lies far outside the cluster of data points from the Vostok core. Those points represent a rough historical relationship between temperature presuming the climate is at equilibrium. Right now, we are experiencing what climate modelers call the transient response to CO2 forcing. If CO2 concentrations froze now, global temperatures would continue to rise until the climate reached equilibrium

2. That equilibrium point lies outside any experience the planet has had in the past 420,000 years, even without any future increase in greenhouse gas concentrations (as the current CO2 level is unprecedented). A further increase places the planet in an even farther outside the envelope of anything in the "recent" geological record, to use a geologists warped definition of the word recent.

3. Oceanic ecosystems - particularly coral reefs - that are sensitive to both the physical (temperature) conditions and the chemical (pCO2) conditions are already and will continue to experience a thermal and chemical environment not seen for hundreds of thousands of years. As I've said before, if you are a coral, pick your poison. This naturally raises the issue of what constitutes dangerous climate change, a key question tossed about a bit lately (see Climate Progress) that I will return to later.

Andrew Revkin, on his NY Times blog Dot Earth, has been asking what language, if any, can most effectively communicate the urgency of climate change, most recently using the idea of the "elevator speech" (Eli's is good). Is there one figure that tells the story best?

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