By: Dana Wagner on
Justin Trudeau, Prime Minister and MP for Papineau, in a press conference on November 30, 2015
It’s true. The atmosphere is pretty indifferent about the location of emissions. Almost identical amounts of carbon measured in different, remote parts of the world confirm this.FactsCan Score: True
At the global climate talks in Paris last week, Prime Minister Justin Trudeau sat down with the press.
He took a question on the impact of investing in emissions reductions in developing countries, a part of the Liberal government’s climate change plan.
Defending the spending strategy, Trudeau said, “the atmosphere doesn’t care where emissions get emitted … it only cares that they get emitted.”
Is this claim backed by science? FactsCan asked some experts. Without exception, they agreed with the Prime Minister.
Although the release of carbon around the world is uneven, the concentration of carbon in the atmosphere is relatively even.
There is evidence to support this. The Intergovernmental Panel on Climate Change tracked annual measures of carbon dioxide, or CO2, concentration in the atmosphere at two different sites, both in remote and rural areas. One is in Mauna Loa in Hawaii, the second is in the South Pole. Plotting the annual snapshots of carbon from each location shows, first, both lines trend upwards. And, interestingly, one line is a little higher than the other.
Source: IPCC, Climate Change 2013: The Physical Science Basis (p 12)
The higher line comes from Hawaii. That’s because of the two sites, Hawaii is closer to major emissions sources, explained Stewart Cohen, a climate change researcher with Environment Canada. However, the line from the South Pole site catches up, despite being farther away.
“What this tells us is that CO2 emissions are well distributed throughout the entire world’s atmosphere, even though a majority of emission sources are in the Northern Hemisphere,” Cohen said. “It also tells us that at current emission rates, these emissions accumulate over time, leading to higher concentrations worldwide.”
Luke Copland, the University of Ottawa research chair in glaciology, agreed with Trudeau too. “The atmosphere is generally well mixed, so it makes little difference as to where you emit CO2,” he said. Because emissions move around the world, “there’s no ‘good’ place to emit CO2 that wouldn’t be felt elsewhere.”
One nuance is that emissions locations do result in different concentrations at distances closer to Earth, but not significantly.
John Innes, the dean of forestry at the University of British Columbia, said that CO2 maps measured at certain altitudes show “a belt of higher concentrations” that correspond with the world’s industrial zones. But he said the difference between high and low concentrations is small.
Why does mixing happen?
Carbon is carried around by the jet stream and weather systems (see images that show this movement from the Jet Propulsion Lab).
Carbon mixes so well in the atmosphere for a complex-sounding reason: The residence time of CO2 in the atmosphere is greater than the atmosphere’s mixing time.
Think of a full bathtub, with water coming in from a tap, and flowing out from a drain. If bath oil is mixed in, the oil will mix in with the water faster than the time it takes for the water to drain. This is the analogy used by Maxime Boreux, a professor of geography at the University of Ottawa.
“The same is true for CO2,” Boreux said. “It stays in our atmosphere for about a century and it only takes the atmosphere a few months to mix it completely.”
The gas gets “vertically and horizontally mixed in the atmosphere at a much faster rate than uptake by forests and oceans,” pointed out Hind Al-Abadleh, an atmospheric chemistry professor at Wilfrid Laurier University.
Because mixing happens faster than the average time CO2 spends in the atmosphere, “it does not really matter where it is emitted on Earth,” Boreux said. “It would be very similar in our well mixed tub. Whether we add the oil on one side of the tub or the other, we will have a well-mixed perfumed bath in the end.”
He added, “this is why there needs to be global agreements of greenhouse gases emissions.”
Although carbon is mixed around, it’s interesting to note that it is not distributed perfectly evenly by circulations in the atmosphere. It’s “patchy,” said Jennifer Baltzer, the research chair in forests and global change at Wilfrid Laurier University. And scientists still don’t fully understand why atmospheric circulations behave the way they do (more answers are likely on their way, following the 2014 launch of a satellite designed to observe carbon). The patchiness doesn’t alter the verdict, however. Baltzer confirmed, “CO2 produced in one place will be carried elsewhere [and] ends up in lots of places that are very far from large emission sources.”
Trudeau’s claim that where emissions come from does not impact global carbon concentration is scientifically sound. The atmosphere really doesn’t care.