Waste food in a landfill is a prolific producer of methane — a gas with 84 times the global warming potential of carbon dioxide.

Debates about the causes and effects of greenhouse gases are raging nationally at the moment. And with good cause: it’s clear that our planet is getting warmer and we need to act quickly if we are to correct our collision course with a global disaster. The foodservice industry can play a major role by changing its approach to the disposal of organic waste. Waste food is a major contributor to the creation of methane, a greenhouse gas with global warming potential that’s 84 times higher than carbon dioxide. Let’s take a look at the science behind this calculation to understand why waste food that goes into a landfill is such a big problem.

I live in California, a state recognized for its leadership in combatting pollution and encouraging its residents to participate in responsible waste disposal. Through landmark initiatives like the Integrated Waste Management Act and Beverage Container Recycling and Litter Reduction Act, California works toward a society that uses less, recycles more, and takes resource conservation to higher and higher levels. Our state leads the nation with roughly 65 percent diversion from landfill rate for all materials, and today recycling supports more than 140,000 green jobs in California.

But California still has a long way to go, especially with respect to disposal of organic waste. A 2008 study[1] found that approximately 30 million tons of waste ends up in California’s landfills each year, of which approximately 30 percent is compostable organic materials, 30 percent is construction and demolition debris, and nearly 20 percent is paper. It is the organic waste that represents a major problem, because greenhouse gas emissions resulting from the decomposition of organic wastes in landfills are a huge contributor to global warming.

To understand why it’s so important to divert organic waste away from the landfill, we need to understand the carbon cycle, the movement of carbon through the atmosphere, biosphere, geosphere, and oceans. After carbon is emitted, it ends up in reservoirs that include the atmosphere, ocean, rocks, soil, and vegetation. Carbon flows between these reservoirs, which ensure that not all of the emitted carbon stays in Earth’s atmosphere in gaseous form. The carbon cycle is therefore vital to keeping Earth’s temperature stable. The geological carbon cycle and biological carbon cycle are the two main parts of this biogeochemical cycle.

The geological carbon cycle is the movement of carbon from the atmosphere to the lithosphere (minerals on Earth’s surface). In the atmosphere, a combination of water and carbon forms a weak acid (carbonic acid) that falls down to the surface as rain. This type of acid will gradually dissolve the rocks on land through chemical weathering. As the rocks dissolve, ions such as calcium, magnesium, and potassium are released. These ions enter rivers and eventually end up in the ocean, where they evolve into a calcite sediment that form limestone rocks. Next, the movement of tectonic plates pushes the seafloor carbon deeper into Earth’s magma, where it eventually heats up and is released back into the atmosphere through volcanoes, vents, and CO₂-rich hot springs.

The biological carbon cycle, on the other hand, is the movement of carbon through the land, ocean, and atmosphere. Almost all life forms on Earth depend on sunlight and carbon dioxide to produce sugars they need for movement and growth. Plants use solar energy to turn carbon dioxide from the atmosphere into sugars through photosynthesis. Animals release carbon into the atmosphere through respiration, which releases energy contained in sugars. When plants and animals die, decomposers such as bacteria and fungi break down the dead tissue and release the carbon compounds stored in them.

The carbon cycle is equally important. Phytoplankton (microscopic marine plants that support the marine food chain) also photosynthesize carbon into oxygen, and some species transform carbon into tiny calcium carbonate plates on their exterior. When the phytoplankton dies, these shell-like plates settle on the ocean floor, along with other dead matter, and over time are compressed into limestone.

So, how does organic waste, particularly waste food, factor into this carbon cycle? When waste food ends up in a landfill it decomposes in a completely different manner compared to when it decomposes naturally in free air or in a composting facility. The reason is that organic material in a landfill is compressed and compacted beneath tons of non-organic material and, deprived of oxygen and natural pests, decomposes anaerobically. Decomposition in the absence of oxygen takes far longer than aerobic decomposition and, worse, releases biogas- a mix of methane (CH₄) and carbon dioxide (CO₂).

Methane is what we don’t want in the atmosphere. Methane’s lifetime in the atmosphere is much shorter than carbon dioxide, but CH₄ is more efficient at trapping radiation than CO₂. Pound for pound, the comparative impact of CH₄ is more than 84 times greater than CO₂ over a 20-year period.[2] How big a problem is landfill methane? In the USA, landfills are the third-largest source of methane- right behind agriculture. In 2017, methane accounted for about 10.2 percent of all U.S. greenhouse gas emissions from human activities.

There are two conclusions from all this. One, we need to ensure organic waste is not sent to the landfill. Two (and this is where restaurants come into the picture), we need to be more creative about where and how we dispose of waste food. How are you processing your waste food?

[1] https://www2.calrecycle.ca.gov/WasteCharacterization/Study/

[2] https://www.epa.gov/ghgemissions/overview-greenhouse-gases#methane