Climate Letter #1085

Atmospheric CO2 update—what happened in 2017?  For the best perspective use the link below, which opens with the interactive long-term chart.  Move the left cursor to expose everything from 2000 to the present.  Then focus on the blue line, which represents the running 12-month trend.  Get a straightedge and lay it along that line from mid-2003 through mid-1015, which would smooth out into a remarkably steady rise of almost exactly 2 ppm per year for twelve consecutive years.  In 2015-16 the major El Nino added an extra 2 ppm in about eight or nine months.  Since the spring of 2016 the path has reverted back to a rate that looks very much like the old 2 ppm per year.  Keep in mind that every possible kind of source or sink comes into play when determining this outcome, now around 407, not just fossil fuel emissions.  Those emissions on their own would actually measure out at almost 4 ppm per year, before the “normal” sinks come into play.  The reliability of those sinks, unfortunately, is open to question.  The blue line on the chart somehow has to flatten out completely within the next 20-30 years and then start working its way down again.  Some say 350 would be a safe target while others can make a case for going all the way back to below 300 if the goal is to maximize the margin of safety.
The IPCC is drafting an interim report with a focus on prospects for meeting the 1.5C target.  One key point is that the carbon budget for all human-activated greenhouse gas emissions will be used up in just 12 to 16 years at the current rate of output.  (That’s for only a 50% chance of holding within the target.)  Making reference to the chart in the above story, every year that continues on the 2 ppm trend takes away one full year from the allotted time that has been calculated.  In other words, when being on a limited budget, the magnitude of required effort, as high as it actually is, keeps getting higher every day.
New York City has announced plans for divestment and other actions against the oil and gas industry that are being praised as significantly helpful.  For one thing it sets an unusually powerful example.
–Bill McKibbin is one of those who are happy about this movement.  “New York and most of the world’s other great cities aren’t viable if the sea keeps rising: they will be destroyed. And New York, for one, isn’t taking it any more. It’s going to use its considerable power to try to hold the oil companies accountable.”
–Naomi Klein makes an equally eloquent statement to the same effect. By attacking the industry at its financial roots, “the politically impossible suddenly seems possible.”
How does the rise in atmospheric CO2 affect the acidity of freshwater systems (Scientific American)?  There is some effect but the whole situation is different from that of the oceans, and much more varied.  The conclusion: “Over time, lakes are experiencing quite variable CO2 concentrations, and all the biota that live in them are, too. Although still unknown, it may be that living in such complex water chemistry will ultimately help freshwater plants and animals adapt to the planet’s rising CO2 levels.”
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