Catastrophic Climate Could Be Forestalled by Cutting Overlooked Gases [Slide Show]
Carbon dioxide gets all the attention, but there are a host of compounds responsible for global warming
![Catastrophic Climate Could Be Forestalled by Cutting Overlooked Gases [Slide Show]](https://www.scientificamerican.com/sciam/cache/file/D93D9F66-190B-4E20-A6F845DAE3CE84BC.jpg?w=590&h=393)
Catastrophic Climate Could Be Forestalled by Cutting Overlooked Gases [Slide Show]
- CARBON DIOXIDE: This colorless, odorless molecule is the primary greenhouse gas responsible for global warming. Concentrations of CO2 in the atmosphere are now at roughly 390 parts-per-million—up from roughly 280 ppm a few short centuries ago. As a result, CO2 is responsible for roughly 64 percent of the extra heat trapped by all greenhouse gases, which has resulted in warming global average temperatures by nearly one degree Celsius. Burning fossil fuels is the primary culprit, backed up by cutting down forests and clearing land for agriculture or urbanization. Changing those habits is hard, which is why the rate at which CO2 is added to the atmosphere continues to tick up—in 2010, atmospheric concentrations jumped by 2.3 ppm, compared with an average of roughly 2 ppm for the past decade and 1.5 ppm in the 1990s. Tom Raftery / Flickr
- BLACK CARBON: Although it's not technically a gas—more of an aerosol—soot, otherwise known as black carbon, can help warm the atmosphere during its residency of a few short weeks. And when it falls out of the atmosphere onto ice or snow, it helps melt it faster—a main reason such soot is helping speed warming in the Arctic. Such black carbon comes from one source: inefficient burning, whether dung fires or bad diesel engines. Eliminating those sources could begin to cool temperatures in weeks or months rather than the years required to see impacts from reducing CO2 emissions. Cutting down on smoky indoor air would also be a health boon. Courtesy of NASA
- SULFUR HEXAFLUORIDE: This colorless, odorless gas—SF6—is an insulator used in the circuit breakers of power equipment—and the most potent greenhouse gas known to science. Since the 1990s, its concentration in the atmosphere has doubled thanks to leaks from an ever-more sprawling global electric grid. That concentration is very likely to continue growing as the world gets increasingly wired for electricity. The gas persists in the atmosphere for millennia and contributes nearly 23,000 times as much warming per molecule as CO2 over the course of a century. Michael Pereckas / Flickr
- COOLING CHEMICALS: To help keep cool, a series of chemical refrigerants have been crafted in recent decades. Early refrigerants proved lethal to the planet's protective stratospheric ozone layer, as evidenced by the ozone hole pictured here. But their replacements—hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs)—are potent greenhouse gases: more than 11,000 times more effective at trapping heat over a century than a molecule of CO2. Growing demand means emissions of this set of gases are also growing as fast as 10 percent per year. The solution is to come up with yet more chemical alternatives—or cutting back on the need for refrigeration and air-conditioning. Given global warming, however, that may be a faint hope—and Brazil, China and India have explicitly blocked efforts to discuss phasing the chemicals out. Courtesy of NASA
- NITROUS OXIDE: Perhaps better known as laughing gas, N2O levels in the atmosphere have risen by 20 percent since 1750, reaching a concentration of 323 parts-per-billion in 2010, according to the World Meteorological Organization. That may not sound like much, but over 100 years laughing gas contributes roughly 300 times the warming of an equivalent amount of CO2—and a single molecule of N2O lasts roughly 120 years in the atmosphere. So where is all this extra laughing gas coming from? Fertilizers and manure, mostly. Given that the world's growing human population will require food, growth in emissions of this greenhouse gas are very likely to keep rising, but more judicious application of fertilizers—and better waste management for livestock—could help reduce levels of the gas in the atmosphere. Travis Isaacs / Flickr
- METHANE: More commonly known as natural gas, CH4 is also a fossil fuel. It is the second most common greenhouse gas after carbon dioxide, at 1.8 parts-per-million in the atmosphere. Concentrations have risen by 158 percent since 1750, according to the World Meteorological Organization. Rice paddies, livestock and manure lagoons as well as the gas released during coal and oil production dominate human sources, while decomposition in wetlands is the biggest natural source. The molecule lasts for roughly a decade in the atmosphere—but is 25 times more powerful at trapping heat than CO2 when compared over a century span. In other words, in the short period of time that it is in the atmosphere it traps 25 times more heat than a molecule of CO2 will over an entire century. And there are several methane "bombs" waiting to go off around the world—icy clathrates scattered across all seven seafloors that may thaw as oceans warm. Permafrost also stores roughly 1,000 gigatons of carbon around the world that microbes could transform into methane as polar regions warm. Already, atmospheric measurements have begun to detect a greater proportion of such permafrost methane in the atmosphere. Cutting human methane levels involves improving wastewater treatment, recovering methane released by oil production and coal mining, and capturing it as it wafts out of landfills. In addition to climate benefits, cutting back on methane would also cut down on smog, or ground-level ozone, which has turned once-blue skies milky, in addition to damaging crops and human health. © iStockphoto.com / Chrise Pole
