Geo-engineering

CO2 and other "greenhouse gases" trap heat from photons after they have entered the Earth's atmosphere. So, increasing the concentration of CO2, NOx, CH4 and other heat trapping gases makes the Earth become warmer.

On the other hand, there are chemicals that can increase the reflectivity of the atmosphere, either by themselves, or through nucleating the formation of water droplets that form reflective clouds at the right elevation. These chemicals can effectively increase the reflectivity of the Earth thereby deflecting photons back into space. For example, major volcanic eruptions eject vast amounts of sulfur dioxide into the upper atmosphere. This causes a short-term cooling as in the year without a summer following the eruption of Krakatoa.

The major geo-engineering solutions currently under discussion fall into two categories:

1. The proposal to seed the oceans with iron particles is a plan to remove net CO2 from the atmosphere by increasing the populations of algae in the deep ocean that consume CO2 in the process of photosynthesis.
   
2. Other proposals that are less well known would increase of reflectivity using either sulfur particles in the upper atmosphere (in place of sulfur dioxide) or by continuously seeding low clouds over the ocean with sea water.

This second approach could in theory be used as a last ditch intervention to recover from the loss of arctic sea ice by replacing the reflectivity of ice with clouds to prevent the arctic ocean from warming.

However, even if this worked we would still need a way to remove net CO2 from the atmosphere because the acidity of the ocean is already so high that we are beginning to risk killing the diatoms and other tiny organisms that form the basis of the food chain in the oceans.

So, either agricultural soil charcoal or seeding algae with iron or other means would be necessary in concert with increased reflectivity form seeding the upper atmosphere to avert ecological collapse of the oceans.

All of this suggests a brave new world of atmospheric geo-engineering, but one that suddenly appears less dangerous than letting the temperature spiral out of control.

A Proposal for increasing the total albedo of low clouds over oceans using sea water spray by Dr. John Latham, formerly Head of the Atmospheric Physics Research Group and Professor of Physics at the University of Manchester, UK (and now holding the honorary position of Senior Research Associate at the National Center for Atmospheric Research, Boulder, Colorado).