Tag Archives: Pescetarianism

Diet and Climate Change

In their 2009 study in Climatic Change, Stehfest et al. pointed out that “climate change mitigation policies tend to focus on the energy sector, while the livestock sector receives surprisingly little attention, despite the fact that it accounts for 18% of the greenhouse gas emissions and for 80% of total anthropogenic land use.” As many begin to realize the significance of agriculture-based emissions and contributions to climate change, researchers are increasingly studying this topic. Though this is definitely a very recent trend, I was able to find several studies from the last ten years which focus on the connection between dietary choices and future climate change. You can find these studies and more at the end of this post, if you want to read their abstracts and understand them more deeply. The basic idea behind all the studies is the same. They use measured demographic and agricultural trends (for example agricultural yields, dietary choices, population growth, wealth, etc.) to create a model which contains the many variables that together define our current food system. Researchers can then run different theoretical future scenarios through the model and find the resultant greenhouse gas (GHG) emissions of each scenario. Different scenarios assume certain changes to the current food system, such as reduced meat consumption or yield increases. See the figure below for an example of Stehfest et al.’s results.

Screen Shot 2015-02-02 at 3.20.43 PM

The above chart shows global GHG emissions in the year 2050, measured in gigatonnes CO2 equivalent. (A gas such as CH4 has a different Global Warming Potential (GWP) from CO2, based on its heat-trapping ability and lifetime in the atmosphere; the number graphed here is the estimated amount of CO2 equivalent to that of all GHGs emitted, based on GWP calculations for various gases such as CH4 and NO2.)

Each of the bars shown above represents a different future scenario. REF is the reference scenario in which all current trends continue. This could be thought of as the control. Scenario IP is based on widespread improvement in productivity. TM includes this productivity improvement as well as the adoption of specific emission mitigation technologies such as adding fat to cattle feed, which decreases the amount of CH4 cows emit during digestion. The CC, or Climate Carnivore scenario assumes that worldwide 75% of ruminant meat and dairy products are replaced by other animal products (in addition to the steps taken in IP and TM). Ruminant animal products (those derived from ruminants such as cattle, sheep, and goats) have inherently higher GHG emissions because these animals digest the cellulose in their food by way of fermentation, which produces the potent greenhouse gas CH4 as a byproduct. This explains the large reduction in emissions from the CC scenario. Finally, the FL or Flexitarian scenario assumes that 75% of animal products are replaced by plant-based sources (once again, in addition to IP and TM improvements).

As you can clearly see, the FL scenario, in which the least animal products are consumed, results in the lowest agriculture-based GHG emissions of all situations. As authors Hedenus et al. explain, “deep cuts in emissions from food and agriculture do not seem plausible without large changes in consumption towards less GHG intensive food, in particular less ruminant meat and dairy.” What I find fascinating here is the significance of the emissions reduction from simply decreasing consumption of ruminant products. I think this is encouraging for those who can see the value in eating fewer animal products, but are not able to change their diet drastically because of certain limiting factors. If we all made the effort to eat less beef and milk, the climate would be measurably better off.

In a similar study, authors Bajželj et al. asserted that “only when strategies include significant elements of demand reduction is it possible to prevent an increase in agricultural expansion and agriculture-related GHG emissions.” The emphasis here is on managing agriculture-based emissions from the demand side of the food chain rather than (or in addition to) the supply side, i.e. changing diets rather than changing agricultural methods. Agriscience research is focused almost completely on increasing yields and this effort is no doubt important, as the researchers acknowledge. However, there are “biophysical limits” on yields and we cannot continue to increase these forever. For this reason and many others, it is valuable and necessary to change the demand side of the food chain. This means changing our diet and eating less animal products. See below for a visualization of the findings of this study.


In the above chart, Bajželj et al. compare the emissions (in gigatonnes COequivalent per year) resulting from agriculture and land use change in six different scenarios. Every CT scenario assumes the continuation of Current Trends in yield increases. Every YG scenario is based on a worldwide closing of the Yield Gap, so that every region is producing at its maximum yield possible. Hence we can see that all YG scenarios involve less emissions, as food is produced more efficiently in these scenarios. Both number 1 scenarios (CT1 and YG1) include no dietary changes. Number 2 scenarios include 50% reduction in global food waste. Number 3 scenarios include this food waste reduction as well as adoption of a theoretical “healthy diet,” with decreased consumption of sugars, oils, and importantly a huge reduction in red meat and other animal products. In other words, CT1 represents a “business-as-usual” scenario while YG3 represents the optimal path for our food industry, and all other scenarios are combinations of different emission reduction strategies. The two horizontal lines in the graph represent benchmark emissions levels; the dotted black line shows the amount of CO2 produced by agriculture in 2009 and the red line shows the emissions level which would raise global temperatures by 2 ºC, a commonly used target.

The difference between CT1 and CT3 is clearly larger than that between CT1 and YG1. CT3 involves the adoption of dietary changes from CT1, whereas YG1 only involves improved yields from CT1. The larger emission reduction in CT3 means that food-demand changes can actually reduce emissions more than food-supply changes, at least as estimated by the model used here. Once again we can understand the importance of reducing consumption of animal products, as evidenced by the most recent scientific study.

Another 2014 study focused on the present consumption of animal products in UK rather than projecting into the future. In this study, Scarborough et al. surveyed more than 50,000 meat-eaters, fish-eaters, vegetarians, and vegans and calculated the GHG emissions of each of these diets based on “food frequency questionnaires” as well as existing estimates of the GHG emissions of 289 individual foods. Their findings were straightforward and telling: “after adjustment for sex and age, an average 2,000 [Calorie] high meat diet had 2.5 times as many GHG emissions than an average 2,000 [Calorie] vegan diet.” In this case, a “high meat diet” describes one which involves more than 100 grams of meat per day. 100 grams is about 3.5 oz, which is not a very large portion. Thus many meat eaters likely fall into this category.

Not surprisingly given what we know about animal agriculture, these studies clearly had similar findings about the relative emissions of different scenarios, namely the following: In order to reduce the contribution of agriculture to climate change, we absolutely need to eat less animal products. It should be noted that each study used different models, different assumptions, and different scenarios so that quantitative results varied widely. However, this doesn’t weaken the findings because different outputs can be expected from different methods. The relative differences between scenarios and the conclusions drawn by the researchers based on these differences were all remarkably similar, and this is the important part.

All these studies focused on determining the GHG emission reduction possibilities of dietary change, but they did not touch on how this drastic, widespread dietary change can actually come about. People in developing countries who grow their own food or spend much of their income on food likely rely so heavily on animal products in their diet that it would be impossible to eliminate them. They simply do not have other options available. However, many of us in developed countries are able to reduce our consumption of animal products to some degree. We generally spend less of our income on food and have many alternatives to animal-based protein available to us. We are some of the very few people in the world who have this opportunity to make this change, so I believe that it is our responsibility to do so. There is widespread scientific consensus (as evidenced in the numerous studies cited here) that reducing consumption of animal products is a positive step for the future health of our planet and climate. Those of us who understand the reality of climate change and are able to take actions against it should do so.

Studies mentioned in this post, and others:
Importance of Food Demand Management for Climate Mitigation (in Nature Climate Change, August 2014)

The Importance of Reduced Meat and Dairy Consumption for Meeting Stringent Climate Change Targets (in Climatic Change,  March 2014)

Climate Benefits of Changing Diet (in Climatic Change, February 2009)

Food Consumption, Diet Shifts, and Associated Non-CO2 Greenhouse Gases from Agricultural Production (in Global Environmental Change, August 2010)

Dietary Greenhouse Gas Emissions of Meat-eaters Fish-eaters, Vegetarians, and Vegans in the UK (in Climatic Change, June 2014)

Global Diets Link Environmental Sustainability and Human Health (in Nature, November 2014) 

Also, a Civil Eats article on the above study^

Thanks for reading,

Feel free to contact me with any questions or comments at eatfortheearth@gmail.com and check out my twitter, @Eat4theEarth, for interesting links and articles.