Food and Climate Change– How can we feed a growing world population without increasing global warming?i

I. Climate Change, Global Warming and Greenhouse Gases1. What is climate? Why is a trend to higher temperatures considered part of climate change?

Increased temperatures during the last century have caused other changes in climate. For example, increased temperatures have resulted in increased precipitation in many parts of the US.

In contrast, increased temperatures have caused changes in wind patterns that have resulted in decreased rainfall in the southwestern US.

This graph shows that, on average, global temperature increased during the last century. (The year-to-year variation in global temperature is caused by El Niño ocean currents, volcanic eruptions and other factors.) This graph also shows that the concentration of CO2 in the earth’s atmosphere increased.

2. Last winter, two weeks were unusually cold. Your friend complained that she was freezing and said that this was proof that there really isn’t any global warming. Do you agree or disagree? Explain why.

3. During the last century, both global temperatures and men’s average height have increased. Do these correlated trends mean that the increase in men’s height caused the increase in global temperature? yes ___ no ___ Explain why or why not.

The figure on the previous page shows that the increase in global temperatures was correlated with an increase in atmospheric CO2 concentrations. But correlation does not prove causation. Additional types of evidence are needed to test the hypothesis that the increase in atmospheric CO2 has been a major cause of the increase in global temperatures. Scientists have:

A. investigated whether there is a mechanism that can explain how more CO2 in the atmosphere could cause global warming

B. tested the ability of the hypothesis to predict future trendsC. evaluated whether other hypotheses could account for the observed trends.

4. As you read the evidence on this page and the next page, use the appropriate letter from the above list to label each type of evidence.

5. Laboratory experiments have shown that, when CO2 molecules absorb heat energy coming from one direction, the CO2 molecules then radiate heat energy in all directions. Based on this information, complete label c in this figure to describe what happens when the heat radiated by the earth is absorbed by molecules of CO2 in the earth’s atmosphere.

6a. Explain how more CO2 molecules in the earth’s atmosphere cause an increase in global temperature.

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6b. Why is CO2 called a greenhouse gas?

Nineteenth century scientists were able to predict future increases in global temperature, based on their understanding of the warming effects of CO2 in the atmosphere. As scientists have improved their models of climate change, their predictions of future trends have become increasingly accurate.

7a. Scientists have used scientific data and computer models to estimate the contributions of multiple factors to trends in global temperature. View the animated graph, “How Global Warming Stacks Up” (https://climate.nasa.gov/climate_resources/144/). For each factor in this table, summarize how this factor has affected global temperature change since 1880.

Possible Cause of Change in Global Temperature Effect on Global Temperature Trends

Changes in the earth’s orbit

Changes in the temperature of the sun

Volcanic eruptions

Forest replaced with types of land-use that reflect more light

Changes in ozone in the upper and lower atmosphere

Aerosol pollution

Increase in greenhouse gases

7b. What do you conclude about the main cause of the increase in global temperatures during the last century?

You may be wondering, “What’s all the fuss about a small increase in temperature (~1°C or ~2°F)?” Global warming and the resulting climate change have already caused harmful effects. For example, global warming has increased melting of glaciers, which has contributed to rising sea levels, which have increased the risk of coastal flooding in some areas. Climate change has also increased the risk of rivers flooding, due to more frequent periods of extremely heavy rainfall in central and eastern US, northern Europe, and Russia. In contrast, climate change has resulted in increased risk of drought in other regions (e.g. California and parts of Africa). These

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and other effects of climate change are expected to cause increasingly serious problems in the future as global warming continues.

II. CO2 and the Carbon Cycle In this section you will learn about processes that influence the concentration of CO2 in the atmosphere.

This figure shows a carbon cycle in nature. Carbon atoms cycle between CO2 in the air and organic molecules in living organisms and dead organic matter.

8a. After CO2 enters a plant (B arrow), how do the carbon atoms in CO2 become carbon atoms in organic molecules in the plant?

8b. Before CO2 is released into the air (A arrows), how do the carbon atoms in organic molecules become carbon atoms in CO2? How is this process useful for animals, plants and decomposers?

9. The giraffe weighs much less than the weight of all the food that the giraffe has ever eaten. What happened to all the weight of the food? Where did the atoms in the food molecules go?

10a. Carbon cycles in nature can be balanced, so the concentration of CO2 in the atmosphere stays relatively constant. However, if the total amount of trees and other plants increased worldwide, CO2 levels in the atmosphere would decrease. Explain why.

10b. Explain why the concentration of CO2 in the atmosphere increases when humans burn forests to clear land for agriculture.

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11. This figure shows a more complete carbon cycle. Use the information in this figure to explain how human activities have caused an increase in CO2 concentration in the atmosphere.

III. Food Production and Greenhouse Gases Some parts of agriculture are similar to a balanced carbon cycle in nature. Farm plants absorb CO2 during photosynthesis, and this roughly balances the CO2 produced by farm plants’ cellular respiration. In contrast, other parts of modern food production contribute to increased CO2 in the atmosphere.

12. Describe two ways that food production contributes to increased CO2 in the atmosphere. (Hint: Review your answers to questions 10b and 11.)

A.

B.

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CO2 is not the only greenhouse gas produced by agriculture. For example, nitrous oxide (N2O) is released by bacteria that metabolize nitrogen-containing molecules in fertilizer on agricultural land and in manure produced by farm animals. A molecule of N2O has about 300 times as much global warming effect as a molecule of CO2. Methane (CH4) is another greenhouse gas which is produced by some types of agriculture. A molecule of CH4 has about 30 times as much global warming effect as a molecule of CO2.

A lifecycle assessment estimates the total amount of greenhouse gases released during the entire process of producing a food, including everything from fertilizer production to cooking the food. This figure shows the results of lifecycle assessments for twenty different types of food. The amount of greenhouse gases is measured in CO2 equivalents (CO2e) per kilogram of food. CO2e gives greater weights to methane (CH4) and nitrous oxide (N2O) concentrations because of their greater contributions to global warming

13a. In general, which results in a greater amount of greenhouse gases released per kilogram of food consumed? animal foods ___ plant foods ___

13b. Explain the reasons for the difference between animal vs. plant foods in the amount of CO2 released per kilogram of food consumed. (Hint: Review the information you have learned, beginning with question 9.)

13c. Explain the reasons for the difference between animal vs. plant foods in the amount of nitrous oxide (N2O) released per kilogram of food consumed.

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The graph on the previous page shows that the amount of greenhouse gases released per kilogram of meat was almost four times higher for beef, compared to chicken. A second study used different methods, but found similar results. The amount of greenhouse gases (kilograms of CO2e) released per 1000 calories of food consumed was 9.6 for beef, compared to 1.7 for poultry.

One reason for this difference relates to special features of a cow’s digestive system, which allow cows to digest cellulose. Cellulose is the main component of plant cell walls and a very abundant molecule in grass and hay. Animals cannot make enzymes that digest cellulose, but cows have extra stomachs which contain microorganisms that can digest cellulose. Some of the microorganism in cow’s stomachs produce methane (CH4) as a waste product.

14. Explain why more greenhouse gases are released during the production of a serving of beef, compared to production of the same amount of chicken meat.

IV. How can we feed a growing world population without increasing global warming?

This figure shows that the world‘s population more than doubled from 1950 to 2015. The dashed line for future decades shows predicted increases in world population; the shaded area indicates uncertainty in the prediction of future trends.

If current methods of food production and current patterns of food consumption continue in the future, then increasing food production for the growing world population will result in increasing release of greenhouse gases. Also, as incomes increase for people in developing countries, they are likely to consume more meat (similar to the greater meat consumption of people in developed countries). This would cause additional increases in greenhouse gas release and global warming.

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15. How can we feed a growing world population without increasing greenhouse gas emissions and global warming? Propose several strategies to reduce the amount of greenhouse gases that will be released by future food production. (Hint: To get ideas for possible strategies, you may want to review the information on pages 5-7 and the list of Reliable Relevant Sources on pages 8-9.)

16. Suggest criteria that should be used to evaluate the advantages and disadvantages of each proposed strategy to reduce the amount that future food production will contribute to the release of greenhouse gases.

17. Prepare a brief report that evaluates a specific proposed strategy to reduce the amount that future food production will contribute to the release of greenhouse gases. Use the information from relevant sources in the list below to evaluate the advantages and disadvantages of your proposed strategy. Look for information in your sources to evaluate your proposal according to the criteria developed in question 16. If the information in your sources suggests improvements for your proposed strategy, you should include these improvements in your report.

Reliable Relevant Sources

Increased agricultural productivity can reduce the release of greenhouse gases.a. Intensive farming may ease climate change

(http://www.nature.com/news/2010/100615/full/465853a.html)b. Boosting milk-production efficiency can reduce cow methane-emission intensity

(https://news.psu.edu/story/383607/2015/12/07/campus-life/boosting-milk-production-efficiency-can-reduce-cow-methane)

c. Most new farmland comes from cutting tropical forest, says Stanford researcher (https://news.stanford.edu/news/2010/september/farmland-cutting-forests-090210.html)

More Efficient Use of Fertilizers to Reduce Nitrous Oxide Emissionsa. Fertilizer produces far more greenhouse gas than expected

(https://www.sciencenews.org/article/fertilizer-produces-far-more-greenhouse-gas-expected)

b. Management of Nitrogen Fertilizer to Reduce Nitrous Oxide Emissions from Field Crops (

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http://msue.anr.msu.edu/resources/management_of_nitrogen_fertilizer_to_reduce_nitrous_oxide_emissions_from_fi)

How much carbon can be stored in the soil by better farming techniques?a. Soil Power! The Dirty Way to a Green Planet

(https://www.nytimes.com/2017/12/02/opinion/sunday/soil-power-the-dirty-way-to-a-green-planet.html)

b. Soils cannot halt climate change (https://www.sciencedaily.com/releases/2018/02/180228134114.htm)

Reducing Waste to Reduce Greenhouse Gasesa. What’s Food Loss and Waste Got to Do with Climate Change? A Lot, Actually.

(http://www.wri.org/blog/2015/12/whats-food-loss-and-waste-got-do-climate-change-lot-actually)

b. UN launches campaign to cut 1.3 billion tons of global food waste (http://www.climatechangenews.com/2013/01/22/un-launches-campaign-to-cut-global-food-waste/)

c. Release: New research finds companies saved $14 for every $1 invested in reducing food waste (https://champions123.org/2017/03/06/release-new-research-finds-companies-saved-14-for-every-1-invested-in-reducing-food-waste/)

d. Improved Crop Storage Bags Can Improve Harvests and Incomes (https://foodtank.com/news/2016/02/improved-crop-storage-bags-can-improve-harvests-and-incomes1/)

Healthy eating can reduce greenhouse gas emissions.a. Healthy Diet May Reduce Gas; Greenhouse Gas, That Is

(http://www.climatecentral.org/news/diet-may-reduce-gas-greenhouse-gas-that-is-20160)b. Meat and Your Health (https://www.ewg.org/meateatersguide/a-meat-eaters-guide-to-

climate-change-health-what-you-eat-matters/meat-and-your-health/)c. Tax high carbon food, sugar for climate and health gains – study

(http://www.climatechangenews.com/2016/02/03/the-bitter-taste-of-taxing-your-steaks-carbon-footprint/)

d. How the Government Supports Your Junk Food Habit (https://well.blogs.nytimes.com/2016/07/19/how-the-government-supports-your-junk-food-habit/)

Shall we eat insects? a. Five reasons we should all be eating insects

(https://qz.com/84127/five-reasons-we-should-all-be-eating-insects/)b. Scientists still hoping to serve up insects as food source

(https://phys.org/news/2018-01-to scientists-insects-food-source.html)c. Exploiting a pest insect species Sphenarium purpurascens for food consumption: ecological,

social, and economic repercussions (Abstract available at http://www.wageningenacademic.com/doi/abs/10.3920/JIFF2014.0013?journalCode=jiff)

d. Optional more detailed and comprehensive source: Opportunities and hurdles of edible insects for food and feed (http://onlinelibrary.wiley.com/doi/10.1111/nbu.12291/epdf)

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i By Dr. Ingrid Waldron, Department of Biology, University of Pennsylvania. © 2019. Teachers are encouraged to copy this Student Handout for classroom use. The Student Handout and Teacher Notes with instructional suggestions and background information are available at https://serendipstudio.org/exchange/bioactivities/global-warming.