Global Warming of the Moon: Science Fiction

We have recently been bombarded by claims that there has been global warming on the Moon caused by the Apollo missions.  This is a quantitative claim, and can only be judged on the basis of numerical evidence.

Here’s the claim: footprints and rover tracks on the Moon have turned over some of the lunar soil, exposing deeper and darker layers of soil.  That darker soil of course absorbs more sunlight, which causes the Moon to get warmer.  The claim, based on data from the thermal probes left in drill holes at two Apollo landing sites, is that the “temperature of the Moon” rose by about 2 to 3 degrees Celsius.

But in fact it was only the temperature in a handful of areas of roughly 1 square meter that went up at all.  That’s a wildly different story, one that has universally been misrepresented by websites that claim to be good at interpreting science data for the general public.

So, let’s think about the Moon.  It is very dark (it looks “bright” at night because we see it in the night sky in comparison with the feeble light of distant stars and planets).  It has been established with high reliability that the (undisturbed) total moon absorbs 88% of the sunlight that strikes it, an albedo (reflectivity) of 1-0.88, or 0.12; only 12%.  The reflectivity of natural lunar soil is influenced by what has been called the “fairy castle” structure of lunar soil: the fluffy, very poorly compacted state produced by natural processes.  Where astronauts have walked on the lunar surface their weight has compressed the fluffy regolith, which of course turns it from an excellent insulator with very poor thermal conductivity into something with much better thermal contact between particles.  The same old solar radiation, hitting the boot-compressed surface layer, delivers slightly more heat to the thermal probes, raising their temperature by 2 to 3 degrees Celsius.  So several square meters of the lunar surface at the Apollo landing sites get slightly warmer than the rest of the Moon, and that is precisely where the thermal probes are located!

To say that the whole Moon is experiencing “global warming” is patently absurd.  The original scientific paper on the subject does not mention that phrase.  Any media source that delivers this message is clueless.  There is absolutely no evidence for global warming on the Moon.