Guest Post by Willis Eschenbach
From the Ministry of Settled Climate Science, I came across a most fascinating press report entitled Surprise Discovery Reveals a Whole New Source of Evaporation. Seems that scientists have noticed that light alone can evaporate water. I always figured they knew that, it only seemed logical to me. Light strikes a water molecule and has enough energy to knock it loose from the liquid surface. I even made a graphic of it somewhere in the past, but it’s lost in the mists of time.
Seems like it wasn’t known, though. Turns out there’s something called the “Thermal Limit of Liquid Water” which was believed to give the maximum evaporation rate for a given temperature and vapor pressure.
But if the water is exposed to light, the Thermal Limit can be exceeded. And not by a little. In one study they induced evaporation at 278% of the Thermal Limit.
White condensation on glass as green light evaporates a water-laden hydrogel. (Tu et al., PNAS, 2023)
There are a couple of big implications of this if the early experiments are verified. One is that it will make solar desalination much cheaper. Given the planet’s population and current water scarcity, this is huge news.
The other is that it’s going to mess with climate science. Consider the water droplets at the top of the clouds. Normally, when water evaporates, it cools the surroundings. But if some of it is evaporating without changing temperature … it’s gonna change the energy budget numbers.
I mean, before this you could say “X mass of surface water evaporated cools the surrounding by Y amount. When it condenses in the clouds it releases the latent heat and warms the cloud bases. And when the cloud evaporates, it cools the surroundings by Y amount”.
But with this new finding, both the first and last steps, the steps involving evaporation, are more complex. Now it seems that some of it evaporates without cooling the surroundings.
Not sure what to think about all that. My first question, unanswered in the press release, is:
Does the same hold true regarding longwave thermal radiation? My guess is no, but who knows?
My best to all,