Update: I asked climate scientist Bart Verheggen if he could shed some light on this issue–He did down below in the comments. His explanation makes perfect sense. If I can paraphrase Bart, even if emissions decrease, if the total emissions exceed the rate at which the natural sinks can remove our contributions, concentrations will increase–but see below for his full explanation. Thanks, Bart!
Over at my companion blog I posted on some surprising hiccups in the relationship between CO2 emissions and CO2 concentrations. After commenter pottereaton called my attention to an article Alexander Cockburn wrote, (where he noted that emissions declined but concentrations rose during the great depression), I took a quick look and noticed that the same thing happened in the early ’80s.
Of course it’s only in a fantasy world that they would move in lockstep, but it’s certainly curious that concentrations would rise 4 years in a row when emissions fell each of those four years. Well, here’s a look:
Base year 1979. Emissions in millions of metric tons of carbon (to convert to CO2, multiply by 3.667). Concentrations are in parts per million (volume). Emissions come from CDIAC. Concentrations come from NOAA.
The total fall in emissions is small–275 million metric tons in total. But the rise in concentrations is significant–6.25 ppm. The four previous years showed a rise of only 4.73 ppm, despite emissions increasing 505 metric tons. The four subsequent years were very much the same–concentrations increased 4.36 ppm while emissions increased 513 million metric tons.
In fact, in 9 years since 1959, emissions have decreased. In every one of those years, concentrations increased. The years that Alexander Cockburn looked at were 1929-1932. Emissions fell by 30%–but concentrations rose (slightly), from 306 to 307 ppm.
Look–I can understand that the response from our climate lags behind the things we do to it (and we do a lot…). But four years of declining emissions should have some sort of an effect on concentrations, shouldn’t it?
That is, if human emissions of CO2 are the driving force behind increased concentrations….
Last year I noted that one-third of all human emissions had occurred since the current (or perhaps recently expired) pause in temperature rises. I said then that it made at least a partial argument against high sensitivity to emissions. Looking at this I begin to wonder just how much of an effect our emissions are actually having.
I’d love a scientist to come and explain this to me. By which I don’t mean being patted on the head and told that natural variability explains it all. If it is natural variability then where else do we see it, and where do we see it going in the opposite direction? Where are the cases where concentrations fall for a couple of years despite increasing emissions?