He said most of these cannot be made practical by 2050 or do not work at all. He noted the proposal to add iron to iron-deficient areas of the oceans to stimulate phytoplankton growth and remove carbon dioxide from the air. He said the latest research had determined that silicate was also a limiting nutrient and that the quantities required for human intervention could not be produced. Significant transport of dead phytoplankton biomass to the ocean bottom will also take hundreds of years, ruling out the use of this strategy in meeting the 2050 target date, irrespective of which nutrient is limiting.
Gaskill then described some of the options that involve reducing solar radiation, the energy source that powers the greenhouse effect. Proposals have been made to reflect sunlight from outside the atmosphere with thousands of square miles of mirrors or just inside the atmosphere with balloons, sulfate aerosols or aluminum oxide particles. If enough sunlight were reflected back into space, the heating from GHG emissions would be offset. The mirror strategy is not feasible and there are concerns the balloons won’t stay aloft long enough or stay spread out. Particle injection with sulfate aerosols may damage the ozone layer, while the residence time of aluminum oxide may not be long enough.
Gaskill said this leaves increasing the reflectivity or albedo of the surface of the Earth as the only practical alternative, even though only half the solar radiation that arrives at the top of the atmosphere reaches the surface. Both the downwelling solar and upwelling infrared radiation is measured in watts/meter2, a measure of the amount of energy impacting a surface area per unit time or flux. He showed some recent data from a NOAA surface radiation-monitoring site in NV to demonstrate the variation in these fluxes throughout the day. He said GHG emissions since 1700 have added about 2 watts/m2 to the IR flux in the atmosphere, about a 1% increase in total radiative forcing and that another 3-5 may be added in the 21st century.
He described several small-scale attempts to lower air temperatures by increasing surface reflectivity related to agriculture and the urban heat island effect. White and aluminized plastic mulches have been used to lower air and soil temperatures around vegetable plants and orchard trees by reflecting sunlight, allowing for better growth during hot weather and increasing the amount and uniformity of sunlight received by the plants. The use in orchards is said to provide for more uniform coloration of fruit. Whitening of shingles and pavements to reduce IR levels in urban areas has also been used.
Gaskill described several proposals to manipulate the global climate by increasing the surface reflectivity of the oceans with white floating plastic islands, white spheres or white foam and of land plants by spray coating them white. These were judged infeasible and/or too expensive.
He said the ideal candidates for surface albedo enhancement are the world’s deserts, citing their advantages of being largely uninhabited, sparsely vegetated, flat and stable with a high solar flux and low humidity (meaning less absorption of solar and IR by water vapor) and generally useless and noting their primary disadvantage of having the highest reflectivity of all surface areas except the ice caps.
He said that of the 7.5 million square miles of deserts, 75% are gravel plains, dry lakebeds and mountains with the Sahara, Arabian, Australian and Gobi accounting for 75% of all desert land. He showed examples of some of the flat, featureless terrain of the Sahara from Morocco to Egypt.
