With our renewed understanding of the omnipresent force of gravity, and its profound effect on the heat distribution in planetary atmospheres via the pressure gradient it causes we can start to appreciate the numbers involved. If there was no gravity and we wanted to change the pressure of our atmosphere from its mid altitude value of 500Hpa to the near surface value of ~1000Hpa for the lowest kilometre, the force we would have to exert is vast. Our power stations churfing out enormous volumes of carbon dioxide 24/7 to power the compressors required would soon deplete all our fossil fuel reserves to hardly begin keeping up with the task.
Gravity does it for free. Effortlessly. Not a joule expended. It just ‘uses the force’, Jedi Knight style. We don’t know how it does its gravity thing, not even Sir Isaac Newton did, but we’re glad it does what it does to surface air density, because that’s what keeps the surface of the planet a lot warmer than it would otherwise be. Gravity. It’s big, and it’s strong. Equivalent to many millions of Megawatts over the surface of Earth. Teamed up with 1360W/m^2 of sunlight pouring into the dayside of the planet’s atmosphere, they’re a hot proposition, raising the grey-body temperature at the surface by more than 100K according to new figures calculated by our friends Ned Nikolov and Karl Zeller.
Compare and contrast with a trace gas in our atmosphere, carbon dioxide. Some people believe it acts to warm the surface of our planet, with the power of the longwave radiation it emits towards the ground. Others say it raises the effective height of emission of radiation to space to a cold place high in the sky, about 0.1km higher than it used to be before we emitted more of it over the last 60 years. They say the 90 parts per million increase is mostly responsible for the perhaps ~0.5K warming of the surface since 1950. It comprises 0.039% of the atmosphere, but can give the planet a fever. Reduce it by a mere 200 parts in a million they tell us, and we would face a big chill in ice age conditions.
I was tickled last week when I was browsing on the realclimate website and came across an exchange between our old friend Vukcevic and Gavin Schmidt, who pooh-poohed Vuk’s proposal for an effect on arctic circulation relating to changes in Earth’s magnetic field, another vastly powerful force. Gavin didn’t think the energy equivalent involved would be sufficient.
“Or do you have some magic mechanism?” he jibed “climate homeopathy perhaps?”
Et tu Gavin.