According to the United Nations, we currently use almost half of Earth’s ice free land area for growing food.  Agriculture in general demands approximately 70% of our freshwater use and accounts for roughly 25% of all of our greenhouse gas emissions.

Various foods differ in the resources they demand.  In fact, greater than 3/4 of all of our agricultural land is used for production of meat and dairy alone!

Choosing our foods with an eye toward sustainability can be a low hanging fruit for improving the state of the planet!

How can food choices help us achieve the Paris Climate Agreement targets?

To meet the Paris Climate Agreement targets, the U.S. needs to reduce its GHG emissions by 447 million metric tonnes per year relative to today’s levels, by 2020. That may sound like a lot, but if we divide that by the current US population, it comes out to 3,660 g CO2-eq/day. When you look at the carbon footprint of our daily activities, you’ll see that amount is actually achievable with modest voluntary changes!

For some people, dietary changes alone can achieve the entire per capita reduction. For example, just one bowl of beef chili has a carbon footprint of 3,020 g CO2-eq/day, while a bowl of lentil soup has a footprint of just 71 g CO2-eq/day. So switching the chili for the lentils saves 81% of the entire per capita reduction needed for that day!

The carbon footprints of our food choices throughout the day really add up. According to a study by Scarborough et al. (2014), a high meat diet has a carbon footprint of approximately 7.2 kg CO2-eq/day, while a low meat diet has a footprint of 4.7 kg CO2-eq/day, and a vegan diet has a footprint of approximately 2.9 kg CO2-eq/day.

Making changes in food choices, transportation, consumption, and conservation can all contribute toward our per capita target! For example, eliminating a 10 mile drive in a 40 mpg car saves 2,220 g CO2-eq/day, which is 62% of the way toward the per capita target.

Planetary boundaries concept

The idea of “Planetary Boundaries” was created by a group of scientists tasked with figuring out the key environmental processes we need to pay attention to (Rockstrom et al., Nature 2009).  This study is a classic, and has been cited and built on by many scientists.


This graph is incredibly useful, as it summaries in one picture all of the critical environmental issues we face!  Each slice of this graph shows a different way in which our actions can impact the Earth.  The green area in each slice of the pie represents a “safe operating space for humanity,” which is a level of disruption that we should not exceed in order to avoid abrupt changes in the biosphere. The red depicts how our current actions are impacting each process.

The Planetary Boundaries concept is one that can be used to inform policy.  For example the Paris Climate Accord is based on the prediction that exceeding a warming of 2 °C will have disastrous effects on human health, wildlife biodiversity, storm intensity, the water cycle, sea level rise and consequent migration of people, etc.

The graph shows that our current trajectory is not sustainable with respect to climate change, N cycling, and biodiversity loss.

All three of these most critical processes (climate change, N cycling, and biodiversity loss) are tightly linked to our food generation!

  • Climate change: We’ve seen how various types of foods have widely differing carbon footprints due to the resources required for production.
  • Nitrogen cycling: Nitrogen use in agriculture has magnified the amount of active nitrogen in ecosystems, which shifts ecological balances. Too much added nitrogen leads to large “dead zones” in the ocean (areas of the ocean where oxygen has been depleted due to excess algae), increased greenhouse warming due to nitrous oxide, increased smog, and elevated nitrate in groundwater.
  • Biodiversity loss: Conversion of natural habitat to agricultural land is a major driver of biodiversity loss.

Many of the other planetary boundaries are also strongly linked to food production!

  • Ocean acidification: This is caused by increased CO2 in the atmosphere that diffuses into the ocean. It’s sometimes called “the other carbon problem.”
  • Phosphorus cycling: Fertilizers used in agriculture are a major source of phosphorus.
  • Global freshwater use: Irrigation is the major use of water by humanity.
  • Land use change: Agriculture is the major driver of land use change.
  • Chemical pollution: Pesticide use in agriculture is an important cause of chemical pollution.

So, shifts in food choices have multiple environmental benefits, including reduced global warming potential, less nitrogen added to ecosystems, a healthier ocean, and more natural land for wildlife!   And, the many benefits of incorporating more plants in our diets are well-known.  And, shifts made for environmental reasons are generally better for your health as well!

Source: Rockstrom et al. (2009) “A safe operating space for humanity,” Nature 461:472-475.

More on climate change

These days there is no legitimate scientific debate about the reality of climate change or mankind’s role in creating this problem. The mechanism behind this is no mystery—the heat trapping effect of carbon dioxide and other greenhouse gases has long been known.  As we have been steadily and dramatically increasing the levels of these gases since the start of the industrial revolution, we have seen a concurrent rise in the Earth’s average temperature, as expected.   Regional variations in response to climate change are also expected and that is indeed what has been observed—some regions have gotten colder and some warmer.  These variations apply also to changes in the water cycle that have been occurring due to climate change.  Unfortunately, many areas that are already dry are projected to get even drier.

People are rightly concerned about the staggering human suffering and great economic burden that climate change presents.  We have seen a pattern of increasingly intense storms that batter our citizens and infrastructure. Rising sea levels already adversely impact coastal groundwater resources and will continue to do so.  Heat waves have cost lives among our most vulnerable populations.  Across the globe, storm surges that overwhelm protective structures will threaten greater numbers of people.  Animals and plants rely on indications from the climate for the timing of budding, mating, etc.—already climate change has disrupted healthy ecosystems in a multitude of ways.

How do we calculate the C footprints for this site?

Below is a table of some of the values used to calculate carbon footprint for this website.  They are from a recent paper by Heller and Keoleian (2014) that pulled together data from many other studies.  Table 1 allows you to compare the greenhouse gas emissions of various sources of protein.


What about beans and gas?

Many foods can cause gas in the intestine, including milk, wheat, various fruits and vegetables, beans, and high fructose corn syrup.

Will your intestines adapt to increased bean consumption? A 2011 study compared gas production over an eight-week period in groups given added beans compared to controls and found that during the first week, 35% of the bean-consuming participants reported increased gas, but this number steadily decreased throughout the duration of the study, reaching 5% by week 5, and 3% by week 8 (Winham and Hutchins, 2011).

What about the carbon footprint?  A study by Tomlin et al. (1991) analyzed gas production in healthy adults given an additional 200 g baked beans to their diets.  They produced on average 0.010 g/day methane, and 0.140 g per day of carbon dioxide.  If we assume methane is about 20 times more potent than CO2, that gives 0.340 g CO2-eq.  Compare that to the 1,995 g saved when switching from beef chili to beans (see Black Beans and Rice blog entry).

Some tips: If you are using canned beans, rinse before using.  If you are cooking them from dry, make sure to soak and cook them long enough, and discard the cooking water.

Sources on beans and gas:

Winham, D. M.; Hutchins, A. M. Perceptions of flatulence from bean consumption among adults in 3 feeding studies. Nutr. J. 2011, 10, 128.

J Tomlin, C Lowis, NW Read (1991) Investigation of normal flatus production in healthy volunteers. Gut, 32,665-669.