CO2 in our atmosphere is still increasing. Last year the annual average amount has passed 400 ppmv (part per million by volume) for the first time in a long time — at least a million years.
The reason: we’re burning fossil fuels like oil, coal, natural gas. When we do, it turns that long-buied carbon into carbon dioxide, which ends up in the atmosphere. It’s as simple as that.
Lately, though, more and more are talking about reducing our emissions of CO2. So, how is planet earth doing? We haven’t stopped increasing atmospheric CO2, but is there any sign that at least we’ve slowed down?
Here’s CO2 concentration from the Mauna Loa atmospheric observatory:
Clearly there’s an annual cycle; we can see the planet “breathe” in and out each year. During spring and summer in the northern hemisphere (where most of the land is) plants grow, absorbing CO2 from the atmosphere. During fall and winter they decay, releasing CO2 back into the air.
So, the first thing I’ll do is remove the annual cycle to give a clearer picture of the changes which are not part of that annual cycle of plant growth and decay.
Then I’ll compute yearly averages of such “de-seasonalized” data. We get this:
Yes, it’s still going up. But how fast? I’ll estimate it in two ways. For one, I’ll fit a smooth curve, using a method which simultaneously estimates the rate of change. For an even simpler method, I’ll just take the difference in the amount from one year to the next. Both will give me estimates of how much CO2 is increasing each year, which we can examine for growth rate changes.
The two methods are in excellent agreement (black dots are the year-to-year changes, the red line is the smoothed estimate):
The rate of CO2 growth has been increasing (we knew that) so CO2 concentration has been accelerating. Unfortunately is hasn’t yet shown any sign that the acceleration has stopped.
We can also compute average CO2 over 5-year time spans, and smooth the data on a slower time scale, to get a more “ponderous” estimate of the growth rate. That gives this (again, the red line is the smoothed rate while the black dots are the rates estimated from 5-year averages):
There’s still no sign that we’ve stopped the acceleration of atmospheric CO2, let alone actually decreased the growth rate.
The world is finally waking up to the fact that to avoid climate disaster, we need to reduce CO2 emissions. But it seems not yet to have realized that what we really need to do is stop CO2 increase. The frightening truth is that not only have we failed to stop CO2 growth, we haven’t even slowed it down.
The more frightening truth is that as warming increases, we run the risk of triggering feedbacks in the carbon cycle. Perhaps the biosphere and/or ocean have already lost their capacity to absorb as much of our emissions as they have so far. We might trigger massive melt of the world’s permafrost, which could release massive amounts of carbon quite apart from what we’re digging out of the ground and burning.
If the warming we’ve already brought about, or that soon to come, releases yet more CO2 from sources other than fossil fuels …
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