This April 28, 2019 image from the ISS that shows what were first thought to be normal contrails from aircraft. Further study revealed they were “cloud tracks” left by ships. The emissions from a ship’s exhaust stack contain particles that readily combine with humid air near the ocean surface. It’s similar to what happens during cloud seeding. The process forms particularly large water droplets that are very effective at scattering light, hence their bright appearance in the image.
The impact of cloud tracks on global warming is an unanswered question and research is ongoing. Clouds can reflect incoming sunlight back into space, but they can also trap heat from escaping to space. The same can be said for contrails, which often cover huge areas of sky in busy flight corridors.
All of the climate models being run today on supercomputers suffer from a lack of accurate parameters for cloud cover. There’s just not enough data out there to predict the net effect. There’s a complex interplay of phenomena with clouds, some good for global warming, some bad for it:
Clouds reflect some incoming solar radiation (aka insolation), but they also trap heat radiation (aka infrared) from escaping into space at night. The actual amount reflected depends strongly on the size of water droplets in the clouds, and that size depends strongly on what the cloud condensation nuclei (CCN) are composed of. In clouds that form over the ocean, the CCNs are often sea salt from ocean spray, and salt is a hygroscopic substance that easily attracts water molecules. That leads to larger cloud droplets and increased reflectivity.
The heat balance is what’s crucial here. In equilibrium, the amount of heat gained by the Earth is balanced by the amount of heat lost. Temperatures remain stable. But ocean clouds have a lot to do with this heat balance and this is the largest unknown in climate models. Oceans cover 70% of the Earth’s surface so this is a huge factor in climate models. Research here will be invaluable.
It has been suggested by proponents of geoengineering, that perhaps we should try to increase marine clouds by artificial means so they would reflect more incoming sunlight and help lower global temperatures. There’s some pretty good science behind that argument, but as I’ve stated in other posts, there will likely be unintended consequences from geoengineering. Increasing marine clouds could also affect rainfall and drought patterns.
Rather, I would suggest investing further in renewable energy to reduce carbon emissions. The root cause of global warming is our continued use of fossil fuels. Best not to mess with Mother Nature unless we are forced into a corner. Geoengineering should be a last ditch solution.
Next Week in Sky Lights ⇒ Solar Canals