More and more evidence is accumulating that global warming caused by man-made greenhouse gas emissions is occurring at an accelerating rate and that changes to the Earth's climate brought about by this warming are occurring much more rapidly than previously predicted. For example, the loss of permanent sea ice in the Arctic may now be on a trajectory to reduce the summer ice pack to zero by 2040, an outcome that only a few years ago wasn't supposed to happen before 2080. For a short explanation of the science behind the global warming greenhouse effect see Global Warming Science Basics

Along with the loss of habitat for polar bears and other Arctic wildlife that this wholesale melting of sea ice would bring comes the possibility of more rapid movement of glaciers held in check by the sea ice as well as climatic changes brought about by less reflection of sunlight and greater absorption of solar radiation by the exposed sea water.

At some point, the changes in the Arctic may lead to irreversible and unfavorable changes to the global climate such that even attempts at stabilizing or cooling the atmosphere may not be able to put Climate Humpty Dumpty back together again. For example, sea level rise due to a combination of thermal expansion of sea water and melting ice sheets may not be reversible in this century, leading to loss of coastal land and massive dislocation of coastal populations.

Global attempts to reign in man-made greenhouse gas emissions are not succeeding. Countries participating in the late starting and ill-planned Kyoto Protocol are finding it difficult to meet its modest emission reduction targets, while it is now clear that non-participating countries, like the U.S. have no real plans for reducing emissions.

There is also uncertainty as to the scope and requirements of any follow on treaty to Kyoto or whether any treaty or succession of treaties will achieve the desired reductions in emissions in time. Economic mechanisms like cap and trade emission programs have yet to be demonstrated to be effective in the short term for controlling greenhouse gas emissions in the absence of alternative technologies.

Technological changes that will be required to reduce emissions will take decades to implement, if not the rest of this century, due to a combination of lack of progress in developing new technologies and the installed and rapidly growing base of emission sources that run the gamut from 550MW coal fired power plants to rice paddies. Against this backdrop of melting ice, failed treaties, uncooperative governments and lack of replacement technologies, the nascent field of geoengineering has begun to receive attention from the media and policymakers.

Geoengineering or macro-engineering is the deliberate attempt by man to alter the global or regional climate by reducing the amount of solar radiation that is absorbed by the planet, the amount of carbon dioxide (the principal greenhouse gas) that is in the atmosphere or by manipulating ocean currents to redirect heat already in the ocean-atmosphere system.

While geoengineering technologies are often viewed as science fiction or simply not doable in time to stop global warming, some can probably be developed and applied soon enough to hold off the coming global climate catastrophe and within 5-10 years.

Although unilateral action on the part of the U.S. or other nations could be taken, due to logistical and geopolitical issues, it is more likely and desirable that an internationally sanctioned and supervised effort be carried out instead.

Indeed, no single geoengineering technology should be considered as "The Solution" and instead, a portfolio of these technologies should be developed, since any one might have negative side effects or other limitations that would make it unacceptable as a stand-alone treatment.

These technologies should only be considered for use as delaying tactics, to give us time to develop replacements for technologies that produce greenhouse gases. They shouldn't and cannot be considered as alternatives to reducing emissions, since most either have a limit as to how much warming they can offset or they can only address one facet of the problem.

For example, plans have been developed to reflect or scatter sunlight to reduce the amount of solar radiation that is re-radiated as infrared radiation. Some of these plans like those involving aerosols or space borne reflectors and lenses can theoretically be carried out on a scale to match all future emissions generated warming or even to roll back previous warming, while others like the plan to cover parts of the world's deserts can only address a finite amount of warming due to a limited supply of land.

However, these proposals do nothing to stop or reverse acidification of surface ocean waters by carbon dioxide or to remove the threat posed by the carbon dioxide in the atmosphere in absorbing infrared radiation should the sunlight reflection/scattering scheme(s) be stopped. Removal of climatologically significant quantities of carbon dioxide from ambient air either by biological or chemical means is not possible with current technologies.

Various geoengineering technologies are discussed and analyzed here including those that attempt to reduce the amount of incoming sunlight that is converted to infrared radiation. Comments are welcomed.