Ice ice baby

I've just reached Planet Fenglewelt, where headlines recently appeared claiming that the inhabitants here may have already been accidentally geoengineering their planet without realising it.

The news broke at the 2015 American Geophysical Union Fall Meeting when NOAA scientist Charles Long announced that aeroplanes could be having a geoengineering effect.

Mr Long speculated that aerosols in contrails might be acting as nuclei on which water vapour condenses to form ice crystals high in the sky. Small ice crystals could be scattering sunlight on it's way through the atmosphere, thus stopping it from ever reaching and warming the planet surface.



Source: Wired.

The Smithsonian reported that the hypothesis originated when scientists noticed that the amount of sunlight reaching the planet surface had varied from the 1950s - 1980s, showing an initial "dimming" trend before "brightening" again. This subtle change couldn't apparently be accounted for by changes in the sun's actual output, so they started to look for possible explanations in the atmosphere - possible mechanisms that could be reducing the amount of solar radiation reaching the ground.

The hypothesis is still in early days and a lot more research needs to be done before it is confirmed. And in any event, aviation is estimated to account for up to 3.5% of total anthropogenic radiative forcing, so any conclusions that aeroplanes are cooling the planet would be premature to say the least!