By Lethbridge Herald Opinon on August 13, 2020.
Data has forced the conclusion about climate change
Marc R. Roussel
UNIVERSITY OF LETHBRIDGE
Imagine a game in which two players take turns, player one adding a cup of water to a bucket, and player two removing a cup. Averaged over time, the amount of water in the bucket stays the same. At some point, a third player enters the game. When player three’s turn comes around, he adds a tablespoon of water to the bucket. So every round, player one adds a cup, player two removes a cup, and player three adds a tablespoon. Slowly, the bucket fills.
This is a crude analogy to the carbon cycle. The anthropogenic contribution to atmospheric carbon dioxide is about the equivalent of a tablespoon to the cup that nature adds and removes from the atmosphere left to its own devices. It’s that extra tablespoon that is causing atmospheric CO2 levels to rise.
Let’s go back to our game: In one turn, player three doesn’t fill his spoon very carefully, and adds less than a tablespoon. Are we likely to notice the difference? If this behaviour is sustained over time, we will notice that the bucket fills more slowly. But after a single round? It would take a very careful measurement to notice the difference, and it would become almost impossible if the water in the bucket was sloshing around.
In a June 30 guest column, Cosmos Voutsinos argued that we should have seen a decrease in atmospheric CO2 during the COVID-19 lockdown, where he attributed the increase in atmospheric CO2 levels during the lockdown to natural sources.
On July 15, I pointed out that our decreased CO2 emissions during the lockdown (our partly filled tablespoon) still represented an excess over nature’s ability to remove CO2 from the atmosphere. In a July 31 guest column, Voutsinos adjusts his language, talking about a missing “reset signal.” I know just enough about signal analysis to know that detecting a temporary change in slope against a seasonally fluctuating signal is really hard. You certainly can’t see that sort of thing by eyeballing the data, and you need a number of points to either side of the slope change to have any hope of seeing it.
I could refute Mr. Voutsinos’ other points one by one, about peer-reviewed evidence (there are now several decades’ worth of such research), about the IPCC simply assuming that anthropogenic CO2 is the cause of rising atmospheric CO2 levels (there are decades of measurements of carbon fluxes, published in the peer-reviewed literature, that conclusively show this to be the case), about models reflecting the biases of the scientist (potentially true, which is why models go through extensive validation processes using historical data), but I would instead like to take this opportunity to pursue my bucket analogy a little further because there is an opportunity to understand something about our current situation that is under-appreciated by most of us.
At the point at which we left our players, the bucket was slowly filling up because player three had put the game out of balance. We might have started the game with half a bucket of water, but it relentlessly filled so that it is now three-quarters full. Then player three decides to quit the game. Players one and two continue their game. Here is the important part: now that the bucket is three-quarters full, it will stay three-quarters full as each player, in turn, adds and removes a cup of water.
Similarly, if we went to net zero tomorrow, atmospheric CO2 levels would not recover to pre-industrial levels quickly, if at all. This is an under-appreciated consequence of the industrial-era increase in atmospheric CO2 levels: the best we can hope for on the time scale of decades (the most relevant time scale to humans, who only live a few decades) is to stabilize atmospheric CO2 levels. The level at which CO2 levels stabilize will depend on when player three quits the game.
As Mr. Voutsinos points out, the carbon cycle is more complicated than my bucket analogy. And the climate response to CO2 is extraordinarily complex. Both have been the subject to intensive study over a lengthy period. Neither is perfectly understood, but that’s true of almost everything. That doesn’t mean that we don’t know what is going on at all. There is a strong consensus in the scientific community, in carefully peer-reviewed research, that humans are responsible for increases in atmospheric CO2 to levels well above any that this planet has experienced for hundreds of thousands of years, and that these high CO2 levels are driving climate change.
I will leave the readers of The Herald with one last thought: Nobody wants to believe in climate change. Scientists are people, too. They want to have their comfortable, modern life, enabled by cheap energy. The scientific community has come to the consensus that anthropogenic greenhouse-gas emissions are causing climate change because the data forced us to this conclusion.
If there had been strong evidence to the contrary, the scientific community would have embraced it so that we could go back to consuming resources guilt-free. The fact that scientists have come to such a strong consensus on anthropogenic climate change, despite the natural preference of humans for an easy life, tells you how strong the evidence is.
Marc R. Roussel is a professor in the Department of Chemistry and Biochemistry at the University of Lethbridge.