The Thin Blue Line
- Jesse Allen
- Sep 25, 2019
- 5 min read
When astronauts are asked how their trip to space has altered their view of the world, there always seems to be a common theme in their responses, that it's impossible to leave Earth and not come back an environmentalist. They often credit this mindset to the observation of the thin blue line that represents the glow of the Earth's atmosphere illuminated by a rising or setting sun. Here the thin blue line is imaged by the crew of the International Space Station, 400 km high, while the shuttle Atlantis was docked during mission STS-129 in 2009.
It's easy to understand how such an image could alter an astronauts perception of their home planet. We grow up viewing the Earth as an extremely resilient and stable system, with an enormous atmosphere stretching from horizon to horizon. There is no concern that we might run out of breathable air as our bodies consume from the almost limitless provision that has sustained countless generations of various organisms over billions of years. However, the perspective from the ground, or even from the air, doesn't allow one to appreciate the true scale of the atmosphere relative to the rest of the planet. Only by looking down from above can one squash these preconceptions of a robust atmospheric system surrounding the Earth and appreciate the true fragility and sparseness of the thin layer that shields us from the hostile environment of space.
So how thin is this atmosphere really? Well it turns out it's actually quite difficult to give a discrete figure for the size of the atmosphere, it doesn't really have a clear boundary and instead softly fades away with increasing altitude. Regulatory bodies have given the arbitrary definition of the Kármán line as the limit at 100 km (this point lays above 99.99% of the atmosphere). Comparing this figure to the diameter of the Earth (12 742 km) tells us that the atmosphere forms a blanket that is a mere 0.78 % as thick as the Earth itself. Compare this to the average ratio of thickness in a chickens eggshell to the rest of the egg, which is 0.83 % (shell thickness = 0.386 mm, mean diameter = 46.47 mm, link). In other words, an eggshell is by comparison to it's contents, thicker than the atmosphere is to the Earth, just consider that next time you're gently cracking an egg for your breakfast omelette.
Now lets zoom in and take a closer look to examine that thin eggshell-like atmosphere. The orange sliver closest to the Earth is the densest layer, the troposphere. Due to the strong pull of gravity, the troposphere contains about 75 % of the atmosphere's mass and is where almost all weather events occur. Of course, because this is where the majority of the atmosphere's mass is, this is also where the majority of our atmospheric pollution ends up, along that thin orange line. This orange sliver is on average 12 km thick (varies from pole to equator), or 0.09 % as thick as the Earth itself, that's roughly 1000 times smaller than the diameter of our planet.
Of course, however thin the blue line and that orange sliver may be, these images neither prove nor disprove that we humans are capable of causing climate change. That isn't something that one picture can solve; all these images do is to help put those claims in perspective. Is it so arrogant to think that we, a species capable of putting people on the Moon, are not capable of altering the properties of that thin blue line or that tiny orange sliver? Based on the current popular dialogue, these are clearly questions that require asking and it is likely that real action will not come without collectively altering our species perspective. One only needs to Google Image search "atmosphere" to be treated to a plethora of quite crappy examples of how our atmosphere is often portrayed in textbooks, as if it comprises of huge force-field like layers.
If this is the best material we can come up with for teaching about the layers of the atmosphere, then it's no wonder there is so much confusion out there about the state of it. I hear what you're saying, I'm being too harsh, give the diagrams some credit, at least the Earth is depicted as being round in all of them and the layers are named correctly after all. But depictions like this do more harm than good and might actually be contributing significantly to the public misunderstanding. Below I offer a new diagram that can be used by anyone that wants to, with the layers marked out correctly to scale. When I lectured on the chemistry of climate change to first year science students, the thin blue line, as well as this labelled version of it, were always the first things I showed to the students and you could see an immediate change in their perspective, the furrowing of brows as they leaned back in their seats and slowly began to nod as they came to an appreciation of the true scale of things.
As for the evidence supporting anthropogenic climate change, that will have to wait for another blog post, or perhaps even a series. For now just scroll back up and click on that thin blue line and appreciate it in all of it's high-res glory over at NASA's website and remember the next time your having a family BBQ and your uncle wants to engage you in a friendly debate over climate change, don't get sucked into a bitter rebuke of his poor science, just ask him if he's seen NASA's thin blue line and the orange sliver, then show him the picture, watch his brow and see if you catch it furrow, if even just a tiny bit.
COMMENTS IN DEFENCE OF CLIMATE CHANGE DENIAL
There is an abundance of passion and skepticism on both sides of the climate change debate. Skepticism, even of science, is healthy and should not be discouraged. However skepticism only works if it is applied equally to all sources; one cannot expect to find the truth by applying skepticism to all of the scientific information available without applying that same skepticism to alternative, usually politically motivated, points of view. While the current public mistrust of science is a tragedy, we should not be surprised that this is the state we are in; every past misdoing of science, and there has been a lot of them, has contributed to that erosion of trust. Science has no objective morality, it is just a tool and it's consequences depend heavily on the motivations of those that are using it. From intentional evil acts of wartime experimentation and clandestine government cover ups, to catastrophic blunders such as the Thalidomide birth defect crisis, the widespread use of toxic lead in fuels and the Chernobyl disaster; we who value what science has to offer cannot ignore these horrible acts if we wish to be taken seriously. There is a reason that the villainous mad scientist trope is a solid staple in popular culture and this is one of the demons we must slay in gaining back the public trust of science. If you wish to appeal to someone who mistrusts science, the first step is to acknowledge the legitimate reasons they have for doing so, before working to bridge that gap and challenging them to apply that same skepticism to their alternative sources of information.
Comments