Here’s a thought experiment. You start on the surface of the Earth, on a warm, sunny day. Beside you is a very tall tower, with a staircase around the outside. The tower goes all the way from ground level to outer space. (Don’t worry about the tower’s dimensions or why it exists.)
In this thought experiment, you’re a fitness nut, so you climb the tower. And you’re a geek, so you bring a thermometer to measure the air temperature as you climb. (You also bring an oxygen tank for some reason. Probably to add resistance.)
Each time you advance a thousand steps up the tower you stop for refreshments and to record the air temperature.
What do you predict the temperature looks like, as you ascend the super-high tower?
Most people know that as we climb the tower it will get colder outside. Much colder, eventually. Just imagine your typical mountain top, then picture that place being at the foot of a second mountain, somehow hovering in the air. How cold is it on the top of the second mountain?
Let’s talk ourselves into a model. The Sun warms the Earth’s surface, which then warms air. The warm air mixes in the atmosphere, so that it’s warmer at the surface and coldest at it’s outer limit.
The model looks like this when we plot it:
So, what does the actual profile look like? First of all, is there any reason to doubt that we can actually measure the temperature way up there? Stick a thermometer and an altimeter to a weather balloon, one would think, and it’s a fairly simple measurement. Temperature is not that hard to measure using a thermometer, although there are ways to do it wrong.
Anyways, this is what the profile actually looks like. (Here I have a cartoon; I first this in Ambaum’s Thermal Physics of the Atmosphere.) It’s beautifully featured! It’s nothing like the above prediction:
First it indeed gets colder as we walk, but only up until the edge of the first layer of the atmosphere, the one we live in. But then it gets substantially warmer again. And eventually, at much greater heights, it again begins getting colder. And at even greater heights – about 90 km high – the temperature again begins to increase, eventually surpassing the temperature on the surface.
This is nice climate science to talk about because we can definitely measure the temperature at different altitudes. And the results are counter-intuitive.
To explain why it stops getting colder, and starts getting warmer (the first time!), we have to understand a bit of atmospheric photochemistry. Basically, as soon as the Sun’s ultraviolet (UV) light runs into oxygen, it reacts with it to make ozone. So when the oxygen’s completely thinned out, that’s the boundary of where it’s easy to make ozone. And when light is absorbed by matter, the matter gets warmer, even if the matter is 30 km high.
So why am I talking about the ozone layer, which is thought to have a minimal impact on global warming?
The ozone layer, being made of oxygen, was not originally part of the atmosphere. Atmospheric oxygen is the consequence of early life’s unchecked mass-pollution (oxygen is a waste product of plant life, which preceeded animal life by about a billion years). This shows that climate change is a basic feature of Earth history, a feature that is impacted by living organisms.
Both proponents and critics of anthropogenic climate change ought to make reference to the same facts surrounding Earth history. These facts need to come from observations (measurements) because our intuition, and our cleverness, is not enough to uncover the truth about reality.
Ryan MB Hoffman has a B.Sc. in Biochemistry from Queen’s University in Kingston, Ontario, and a Ph.D. in Biochemistry from the University of Alberta in Edmonton, Alberta. He is mostly interested in how protein molecules fluctuate throughout their functional processes. During his doctoral work he studied troponin, which is a switch that regulates striated muscle contraction. He works as a post-doctoral scholar at the University of California, San Diego, at the Center for Theoretical Biological Physics. He is active with the Intrinsically Disordered Proteins subgroup of the Biophysical Society. Ryan likes to remind people that his contributions to TRN are performed entirely using his personal resources.