On June 2, U.S. President Barack Obama announced a sweeping plan to rein in carbon pollution from the nation's coal-fired power plants. It was the most significant step his administration has taken to address climate change. With the stroke of a pen, he has done more to tackle greenhouse gases (GHG) than any president in U.S. history.
To be sure, coal -- along with natural gas, and oil – is one of the main culprits causing climate change, but there are others you don't often hear about. (see chart from EPA).
Here are the top five contributors to greenhouse gas emissions from non-energy sources. Taken together, they account for about one-third of global emissions.
1. Deforestation. The degradation and destruction of the world's forests is one of the main sources of CO2, accounting for almost one-fifth of total GHG emissions worldwide. In Indonesia, vast swathes of tropical forest are cleared to plant palm oil, where it is used in everything from cooking oil, to ice cream, to lipstick, to biofuels. It is a highly versatile crop, but the demand for it is creating incentives to chop down Indonesia's forests. In Brazil, the main driver of deforestation is the clearing of land for cattle ranching. Deforestation in the Amazon specifically for cattle ranching alone accounts for 3.4 percent of global emissions.
2. Methane from livestock. The impact of cattle doesn't come just from chopping down trees. Cows are also a significant source of methane (CH4). The agricultural sector accounts for 14 to 18 percent of global GHG emissions and much of that comes in the form of methane, which is more than 20 times as potent a greenhouse gas as carbon dioxide. 80 percent of the agricultural methane comes from livestock – from cow manure, burps, and farts.
3. Soil carbon. The release of carbon dioxide from soil is a major source of global emissions that isn't often talked about. When farm land is plowed in order to plant crops, CO2 that was previously stored in the soil is released into the atmosphere. Modern agriculture involves intensive disruption of topsoil, and this alone is responsible 4.4 percent of global emissions
4. Landfills and wastewater. Another source of GHG emissions that flies below the radar is landfills. Waste discarded and left to rot can release huge volumes of methane when organic matter such as food decays. Also, wastewater treatment plants release methane as well as nitrous oxide (N2O), another short-lived but powerful greenhouse gas (about 100 times as potent as CO2). Taken together, waste and wastewater treatment make up about 3 percent of global GHG emissions.
5. Permafrost. Perhaps the most frightening sources of GHG emissions are the vast quantities of carbon dioxide and methane stored in permafrost, or permanently frozen soil. Permafrost is located mostly in the far northern hemisphere, and is frozen year round. But, as temperatures rise, some of areas may begin to thaw in summer months; by midcentury, the northern hemisphere could lose 20 to 35 percent of the permafrost area that currently exists. According to some scientists, this is the disaster scenario – as global temperatures rise, permafrost melts and releases methane, which contributes to more warming and further methane release. Current climate models do not incorporate such a catastrophic feedback loop, suggesting that even the most pessimistic projections could underestimate future warming. There is some evidence that the process is beginning, but the difficulty in measuring the release from permafrost means that data is inadequate.