Can we slow or even reverse global warming?

Author: 
January 23, 2014

In principle, we can slow the rate of global warming by slowing the emission rates of heat-trapping gases—mainly carbon dioxide—and black carbon aerosol to the atmosphere. Some continued warming is inevitable. Stabilizing global temperature at its current level would be very difficult because it would require cutting the emission of heat-trapping gases all the way to zero. If and when zero emissions becomes possible, temperatures won't start to recover until heat-trapping gases are actually removed from the atmosphere. Such removal happens naturally on time scales ranging from less than a year (e.g., black carbon aerosol) to centuries (e.g., carbon dioxide). Additionally, technical means exist to remove some heat-trapping gases (including carbon dioxide) from the atmosphere.

Ultimately, global warming could be reversed by returning the abundance of heat-trapping gases in the atmosphere to pre-industrial levels (circa 1750). The challenge in slowing or reducing global warming is finding a way to make these changes on a global scale that is technically, economically, socially, and politically viable. Reducing our emission of carbon dioxide has the added benefit of slowing the rate at which humans are making the ocean's water more acidic, which is a threat to shell-forming organisms and the marine food chain.

In response to a request from the U.S. Congress, the U.S. National Academy of Sciences published a series of peer-reviewed reports, titled America's Climate Choices, to provide authoritative analyses to inform and guide responses to climate change across the nation. Relevant to this question, the NAS report titled Limiting the Magnitude of Future Climate Change explains policies that could be adopted to slow or even reverse global warming. The report says, "Meeting internationally discussed targets for limiting atmospheric greenhouse gas concentrations and associated increases in global average temperatures will require a major departure from business as usual in how the world uses and produces energy."

Alternative sources of energy

Transitioning to energy sources that do not emit greenhouse gases, such as solar, wind, biofuels, and nuclear, can slow the pace of climate change, though these energy sources face hurdles ranging from manufacturing capacity to debates about where to install some facilities. Images courtesy Energy.gov.

Alternative methods to slow or reduce global warming have been proposed that are, collectively, known as "climate engineering" or "geoengineering." Some geoengineering proposals involve cooling Earth's surface by injecting reflective particles into the upper atmosphere to scatter and reflect sunlight back to space. Other proposals involve seeding the oceans with iron to stimulate large-scale phytoplankton blooms, thereby drawing down carbon dioxide out of the atmosphere through photosynthesis. Such methods could work, in principle, but many climate scientists oppose undertaking geoengineering until we have a much better understanding of the possible side effects. Additionally, there are unresolved legal and ethical issues surrounding geoengineering.

Given these concerns, the American Meteorological Society published a position paper (readopted in January 2013) in which it said: "...research to date has not determined whether there are large-scale geoengineering approaches that would produce significant benefits, or whether those benefits would substantially outweigh the detriments. Indeed, geoengineering must be viewed with caution because manipulating the Earth system has considerable potential to trigger adverse and unpredictable consequences."