Lesson 2: What factors have caused a rise in global temperature over the past century? How has agriculture played a role?
MS-ESS3C: Human Impacts on Earth's Systems
MS-ESS3D: Global Climate Change
Science and Engineering Practices: Developing and Using Models (Carbon Cycle model)
Currently 97% or more of scientists agree that climate change over the past century is "extremely likely due to human activities." (https://climate.nasa.gov/scientific-consensus/)
Causes of rising temperature (via rise in greenhouse gases) include anthropogenic (originating in human activity) sources such as burning fossil fuels (coal, oil and gas) for electricity and transportation, cutting down trees, manufacturing/industrial activities, and agricultural practices such as tilling the soil.
The degradation of the world’s soils has released about 78 billion tonnes of carbon into the atmosphere (From 2017 FAO report on climate change)
Good carbon cycle diagram with text for context here.
Feedbacks from climatic changes such as melting permafrost, ice and glaciers drive additional climate change, as a decrease in reflective surfaces (i.e. snow and ice) causes an increase in absorption of incoming solar radiation, rather than reflecting the radiation back to space (also called the albedo effect).
Key greenhouse gases that cause rise in global temperature: carbon dioxide, water vapor, methane, and nitrous oxide (see https://climate.nasa.gov/causes/).
Methane is an incredibly potent greenhouse gas with a shorter atmospheric lifetime than CO2, but stronger climate forcing effects. It is a prime greenhouse gas emission from agricultural activities- mostly due to livestock production (methane is emitted from cow burps, farts, and manure).
View soil carbon videos in supplementary materials, including The Soil Story. (Some of this info will filter in to later lessons geared towards solutions, but is helpful to painting an overall picture of how ag might contribute to vs. solve the problems of climate change).
Do Now: Draw a picture of the carbon cycle (globally), and your school garden’s carbon cycle (locally). Do either individually or as whole class. Discuss where carbon is coming from and going to. Emphasize that right now more carbon is being released from human activities than ever before, so the cycle is out of balance. We want carbon to go from the atmosphere back into the soil, where it belongs and grows healthy plants! (hint: carbon dioxide is an essential ingredient in photosynthesis).
Mini Lesson: Sources of carbon emissions. Create a timeline or visual of carbon emissions starting with the Industrial Revolution and identifying modern sources of emissions (include transportation emissions, electricity generation, agriculture, industrial activities, and residential energy use).
Sources of carbon emissions from agriculture: tilling the soil (discuss what this is), cow farts and manure (methane), fertilizer and pesticide production (biggest source), transporting food over long distances, cutting down trees for agriculture (and other land use changes).
Agriculture can either be a source of or a sink for carbon emissions, depending on how it is practiced. FAO 2017 report: "Agriculture has been partly responsible for climate change, but is also part of the solution.”
U.S. terrestrial land carbon sink: estimated at 640-1,074 million tons CO2-equivalent, according to National Climate Assessment → lots more carbon can go back in the ground where it belongs!
Some estimates say increasing soil carbon storage just 0.4%/year globally could “halt the increase in the CO2 concentration in the atmosphere related to human activities.” https://www.4p1000.org/. This is a huge potential benefit, is cheaper than most other ways of reducing atmospheric CO2, and there are many other benefits to having more carbon in the soil besides fighting climate change.
Activity 1: Where do you see potential sources of GHG emissions in the farming or food system? How can we reduce these emissions? [Walk around the school and garden or do in-classroom brainstorm]. One key strategy: buy local or grow local organic food (without pesticides)!
Act it out: Carbon skit- students act out phases of the carbon cycle, with some students acting as certain carbon reservoirs (soil, trees, atmopshere, ocean), and others passing around token Carbon molecules depending on what activity is described. Full link to activity here (Credit: Janaki Jagannath).
Activity 2: [optional] How much does it cost when cows burp? ESJ4K jeopardy game
Shows carbon cost of beef production vs. wheat production
Introduces methane source (cows) as contributing factor to climate change.
Closing activity on carbon emissions- Play “Greenhouse Gas Freeze tag” (out in/near garden)- Play freeze tag to simulate greenhouse effect. Some players are greenhouse gases, most are rays of sunlight. Earth is at the middle, with “atmosphere” circle around it. Sun rays run in and touch Earth, then try to run out of circle boundary without being tagged by a GHG. When tagged, stay in “atmosphere” as GHG. Eventually, all students “tagged.” Debrief- what are sources of GHGs? How do we, in real life, get these out of the atmosphere? (Demo/example video below.)
Optional Assessment: see Materials below.