Lesson 3

Living With Environmental Change

 

Lesson Overview:

Lesson 3 discusses: 1) the impact of present and future environmental changes on human health; 2) environmentally wise living.

 

Content Standards Addressed:

Common Core State Standards 

 

Learning Objectives:

Students will:

  • Define the lesson's vocabulary words.
  • Recall facts about American environmental habits.
  • Describe environmental challenges that Earth's people currently face and could face in the near future.
  • Name simple steps that can conserve and protect land, air and water.
  • Explain the present and future benefits of safeguarding our natural resources.

 

Vocabulary:

Compost - organic matter that breaks down over time, under the right conditions.

Erosion - the wearing away of soil by wind or water.

E-waste - discarded computers, printers and related equipment, TVs and cell phones. Also known as electronic waste.

Radon - a naturally occurring, harmful gas that is released as the element radium decays.

Salinity - the percentage of salt present in water, including soil water.

Surface runoff - water flow beyond what can be absorbed by soil or other surface.

Volatile organic compound (VOC) - a harmful gas released by various liquids or solids.

Watershed - an area draining to a stream, lake, or ocean or other waterway.

 

Reproducible: How Much Do You Know? 

Students can take this quiz before starting the lesson. It will reveal what they already know about American environmental habits.

Make copies of the reproducible. The answers are provided here.  

What is the state of world health today? Consider that:

  • Each year, unsafe water sickens millions of people, often with fatal results.
  • Millions die of breathing-related diseases each year due to indoor and outdoor air pollution.
  • Land is deteriorating due to erosion and increasing salinity, with millions facing hardship as they struggle to relocate.
  • The rate of melanoma (a sometimes fatal type of skin cancer) is growing. So is the incidence of Alzheimer's disease, dementia and autism.
  • Insect-borne diseases like malaria and dengue fever are increasing.

All these issues can be connected to a weakened environment. The chances of developing health problems are greater for people who are already at risk: the very old and the very young, those who have long-term illnesses or are of limited means.

Whatever people's viewpoints are about present or future environmental change, most would agree that a "green," or environmentally friendly, lifestyle is beneficial. This lesson spotlights current environmental issues and offers suggestions for lifestyle changes that can reduce existing environmental damage while improving human health and well-being. Green living positively impacts our lives now, because it's a more healthful way to live. It can also positively impact our lives in the future by 1) ensuring we stay in good physical and mental health, so we can best prepare for an uncertain future; 2) reducing future impact on the environment; and 3) reversing existing environmental damage. This is important, because, while predictions indicate a few environmental changes may benefit humans, those that damage ecosystems will surely harm our health in the long run.​

Water:

While humans can survive for weeks without much food, water is absolutely essential to life. Without sufficient water, vital body functions cannot take place. Water helps us adjust to temperature changes. It moves oxygen to cells and nutrients to organs and tissues. It speeds the removal of waste and cushions joints and organs.

Most of Earth's fresh water is frozen at the polar ice caps, or in icebergs and glaciers; less than three percent of it can be accessed. Despite this, each human require a minimum of five gallons of fresh water every day for drinking and personal needs. Americans use far more than that - about 100 gallons a day! At present, as many as one-third of Earth's inhabitants face a crisis of water. It's estimated that, as the world's population grows to as many as 10.5 billion people in the next 50 years, the demand for clean water will rise by as much as 35 percent. Experts predict future water shortages will spark conflicts and even outright war between nations.

In addition to a water crisis, humans are presently at risk from unsafe water. Water becomes hazardous to health when contaminated by pesticides, fertilizers, medications and other chemicals, fuel and metals. Billions of people lack adequate sanitation, which also results in polluted water. Water pollution can result in serious or fatal illnesses like cholera, E. coli, giardiasis and norovirus infections.

Water can also become unsafe through surface runoff. Trees and other vegetation absorb excess water, so only about 10 percent of storm water runs off in natural areas. But paved areas like streets, driveways and parking lots can't absorb as much storm water. Runoff there can be as much as 55 percent. And runoff picks up everything from pesticides and road salts to pet waste as it flows into fresh water. It can also results in standing water, which provides a perfect breeding ground for mosquitoes and other insects that can carry fatal diseases like malaria and West Nile virus.   

 

Steps to Take:

The lack of sufficient, clean water threatens human health. Do you part to conserve water and keep it from contamination. Here are a few suggestions:

1. Go natural.

To conserve water and save money, replace large areas of grass that require watering and mowing with plants that are native to your area. Native plants don't require extra watering or water-contaminating fertilizers and pesticides, and they actually help prevent soil erosion by holding soil in place and serving as a windbreak.

Mow the remaining patches of grass with a push mower - and leave the lawn clippings afterword to feed the grass. A push mower provides a healthy physical workout, doesn't harm the environment (or human ears) and is less expensive to own and maintain. 

2. Water less.

Don't water grass. In dry weather, allow grass to go dormant and water only when absolutely necessary - about once a month. The grass won't be pretty and lush, but you'll save money on water, gasoline and electricity (to power the mower), and on fertilizer that can pollute land and water.

Established plants don't need to be watered except under drought conditions. Watering less often, but more deeply, is a secret to healthier plants. Several inches of mulch can eliminate much of the need for watering.

3. Don't dump.

Don't dump chemicals into local waters. This includes flushing medications and hosing oil, paint and other water pollutants down storm drains. Water filtration techniques cannot always completely remove these harmful substances from the water supply. Instead, mix them with kitty litter or other similar substance, place in a container with a lid and dispose in the trash. (This method also works well for motor oil and other oils and fats.) 

4. Mind your meter.

Check your water meter reading at an off time, when no one will be using the water for a couple of hours. Check it again two hours later. If it has changed, you may have a leak somewhere, wasting both water and money.

 

Further Research:

  • An area draining to a stream, lake, or ocean or other waterway is called a watershed. How's the health of your community's watershed? Students can find out by entering their ZIP code on the EPA Water News page, http://water.epa.gov.
  • Locate a U.S. map online that shows projected water demands in the next 50 years. Is your community at risk for water shortages now or in the future? If so, find out what steps are being taken by state or local governments (if any) to manage this risk.

 

Air:

Outdoor air pollution comes chiefly from burning fossil fuels like coal, and from natural and anthropogenic fires. Though outdoor air pollution often receives greater attention, the air pollution found inside living and working environments - which is usually invisible - is many times worse. The problems can be especially severe in newer, energy-efficient buildings, which keep heat - and air pollutants - inside.

The natural, but harmful, gas radon causes dangerously polluted air, and is the second-leading cause of lung cancer. The use of wood and other solid fuels for cooking and heating indoors affects an estimated three billion people and results in asthma, pneumonia, chronic respiratory disease and lung cancer. Air pollution can also cause cardiovascular disease and skin diseases.

Volatile organic compounds (VOCs), given off by household supplies, chemically-treated products, tobacco products and other goods, are also harmful. In addition to causing symptoms like headaches, irritation to the eyes, nose and throat, and dizziness, VOCs can actually damage the liver, kidney and central nervous system, and cause various cancers. Experts say indoor air pollution caused by VOCs can irritate and deteriorate the brain, and damage its blood vessels, resulting in diseases like Alzheimer's.

 

Steps to Take:

Indoor/outdoor air pollution threatens human health. Do your part to protect the air we all must breathe. Here are a few suggestions:

1. Reduce toxins in your home.

Switch from powerful, toxic household cleaners that release VOCs (volatile organic compounds) to eco-friendly cleaning products or, better yet, homemade cleaning solutions that use ingredients like baking soda, vinegar, lemon juice, olive oil and salt. Homemade products have the added benefit of saving money as they preserve the environment and protect human health. Listed below are some natural alternatives to commercial cleaners.

  • Mold and mildew cleaner: Full-strength lemon juice, white vinegar or hydrogen peroxide.
  • Scouring powder: Baking soda.
  • Window cleaner: 2 teaspoons of white vinegar in a quart of warm water.
  • All-purpose cleaner: 1 cup vinegar and 1/2 cup baking soda to a gallon of water.
  • Insect killer: Mix powdered sugar, yeast and baking soda. Sprinkle where insects have been seen.

A roaring fire in a fireplace stirs up cozy, warm feelings, but the smoke that results from wood fires can be a dangerous source of indoor air pollution. The health risks associated with burning wood are well-known. The air pollutants scar lung tissue and cause respiratory problems. Many eco-friendly alternatives to burning wood in traditional fireplaces are now available. Modern gas fireplaces burn clean fuels like bio-ethanol. And manufactured fire logs can burn 80-90 percent cleaner than wood, resulting in much lower levels of toxic gases and other pollutants.

A simple and eye-pleasing way to combat indoor air pollution is to grow plants inside. Indoor plants absorb toxins. Many of the best plants for this purpose also happen to be very easy to grow. They include:

  • Dracaena.
  • Palm.
  • Pathos.
  • Philodendron.
  • Snake plant.
  • Spider plant.

Radon is an odorless, tasteless gas found throughout the United States that is produced by the natural breakdown of uranium soil, rock and water. Breathing air containing radon is the second-leading cause of lung cancer. An inexpensive, short-term radon text kit is easy for you to use and the quickest way to test for radon in your home.

2. Shop locally.

Transportation activities in general produce 25-30 percent of U.S. greenhouse gas emissions. Transporting goods hundreds or even thousands of miles to their destinations contributes to the problem. Today, the average distance food travels before reaching the consumer's table is 1,500 miles! Buying foods that are in season from local growers is one small step we can take to help reduce air emissions. Local foods are usually fresher, less processed, do not contain preservatives, and are more nutritious and better-tasting. Buying locally grown food also supports community economies.

3. Beware of vampires.

The largest source of greenhouse gases is electricity generation. So conserve energy whenever you can. Appliances that remain plugged in when not in use still draw power and waste energy, not to mention money. This is known as "vampire power." Be sure to unplug all electrical devices, including TVs, computers and charges when not being used.

 

Further Research:

1. Divide the large group into three smaller ones. Have each group research one of the following. How do these innovations work? How do they help reduce the environmental impact of pollutants?

  • Low-emissions cook stoves.
  • Inexpensive water filtration systems.
  • No or low VOC paint and other household products.

2. Explore the proposed relationship between VOCs ad dementia, Alzheimer's disease and autism. What do the latest medical studies reveal?

3. Appoint a team to monitor your community's outdoor air quality for one week, including pollen, carbon monoxide and ozone levels. If the air quality is unhealthy, ask them to post a warning in a common area of the building where your group meets (or in your classroom). Poor air quality can produce fatigue and reduce performance, as well as cause symptoms like coughing and wheezing.

 

Activity:

If possible, take a short walking tour of the building where your group meets. Have students bring along a pencil and notebook to take notes. Ask them to imagine they're architects hired to "green up" the building. If money were no object, what improvements would they suggest to 1) create a healthier indoor environment, 2) reduce energy consumption and 3) save money? Suggestions may include:

  • Installing solar panels to help heat the building.
  • Replacing traditional bulbs with energy-efficient ones.
  • Planting mature trees and shrubs to shade the building from the summer heat, provide a windbreak in winter and absorb carbon that ordinarily would enter the atmosphere.
  • Adding windows or skylights to windowless rooms. Providing natural light may eliminate the need for artificial lighting at certain times of day, which reduces energy costs.
  • Replacing hazardous chemical cleaners that poison air with more natural, safe cleaners.

 

Land:

Millions of acres of forests, wetlands and other natural settings are transformed each year into farmland, housing developments, roadways, etc. These "improvements" to the land often require later enhancements like chemical fertilizers and water diversions, both of which compromise land and water. Scientists believe the earth's ability to sustain human life in the future may be compromised by the degrading of the environment now.

Since chemical fertilizers and pesticides pollute water and land, natural alternatives are being explored in order to boost crop yield. These include 1) encouraging pollination by attracting bees, butterflies, ants and other insects and 2) supporting bird and fish populations, since they eat insect pests. Planting native flowering plants, reducing (or eliminating altogether) the use of pesticides and increasing green space are all important first steps toward attracting pollinators. Insect-eating birds can be attracted by providing birdbaths, a variety of seeds and nuts that appeal to those bird varieties, and birdhouses, nesting boxes and roosts.

 

Discussion:

With the world population growing steadily, it's estimated the demand for safely grown food will rise by as much as 80 percent by the mid-21st century. Each human will need adequate living space and a sustainable lifestyle. Some sources estimate people today enjoy an average 430 square feet of living space, though researchers claim we actually need only about 120 square feet. (If possible, measure this dimension within your room.) As a comparison, traditional American Indian dwellings afforded each person about 20-60 square feet of living space. (Measure this dimension as well, if possible.)

Use a search engine to research "tiny houses." Discuss:

  • What might be the advantage(s) of living in an area this size?
  • What might be the disadvantage(s)?
  • If more Americans lived in smaller living spaces, would it help the environment? Why or why not? (Answers vary, but could include: fewer construction materials used, much less energy required for heating and cooling a small area, etc.)
  • Would you agree to live in a very small living space? Why or why not?

Humans consume food and use materials for shelter and other needs in order to survive. Our ability to produce these through technology and natural resources is beneficial, but also results in lots of garbage where those products are manufactured, packaged, used and, eventually thrown away. A century ago, "garbage" was mostly food waste, and wood and coal ashes that eventually decomposed and returned to the soil. Today, one-third of what we throw away is nonrecyclable.

Land is polluted by household waste as well as:

  • Animal wastes.
  • Lead and other metals.
  • Hazardous chemicals.
  • Improper disposal of construction, industrial and other waste.

 Land pollution is known to cause human health problems like birth defects, skin inflammations, high blood pressure, neurological disorders, mental retardation, organ abnormalities and respiratory problems.

 

Reproducibles: Consumption Part 1 and Consumption Part 2

The average American generates more than 4 1/2 pounds of garbage each day. How do your students compare? Make copies of the reproducibles. Give Consumption, Part 1 to each student along with a large, unused trash bag (if funds permit). Tell them they are to record all the products they use in the next 24 hours on the worksheet, and fill the bag with the waste - packaging, etc. - from what they've consumed. (They should place messy waste like banana peels and yogurt containers in separate bags to keep the rest from becoming soiled.)

When the group reassembles, students should have their completed worksheets and trash bags. Give each student a copy of Consumption, Part 2

After students weigh their nonrecyclables, ask:

  • Would recycling what you can really make a significant difference in your environmental "footprint" (the impact they have on the environment) this day?
  • Brainstorm ways the rest of their waste could be used productively. Answers include composting fruit and vegetable waste and reusing packaging (for example, using clean bread wrappers to store leftovers or saving greeting card fronts for art projects).

Have the students list their nonrecyclables and rank them by their decomposition time. Then share the following information.

Scientists have provided estimates of how long it will take certain types of trash to decompose. Under the right conditions, microorganisms will break down organic materials. Some synthetic materials may break down if exposed to ideal quantities of sunlight, water, and air.   

Fruit/vegetable waste...................................................................

Paper products.............................................................................

Milk Carton.....................................................................................

Products made from wool or cotton.............................................

Lumber..........................................................................................

Nylon fabric...................................................................................

Leather products..........................................................................

Rubber products...........................................................................

Aluminum or tin cans.....................................................................

Plastic bags & disposable diapers................................................

Styrofoam and plastic containers.................................................

Glass.............................................................................................

3-4 weeks or more

1 month or more

3 months or more

1 year or more

15 years or more

40 years or more

50 years or more

80 years or more

100 years or more

500 years or more

?

?

Invite students to share the changes they've decided to make in their consumption. For example, in the future they may decide to buy products that more easily decompose, like paper cups instead of foam cups. Or they may decide that they'll no longer buy bottled water, but will instead refill a nontoxic plastic or stainless steel water bottle. After one week, remind group members of their commitments. In a month's time, as them to write a half-page summary of their experience.

  • How successful were they in changing their consumption habits?
  • Were the changes difficult to make?
  • Did their actions motivate others to change? Who?
  • What other pledges, if any, have they made along the way?

 

Alternate Activity:

If the previous activity seems impractical, consider doing the activity as a group. Obtain permission for students to sort school cafeteria waste after lunch one day. Complete the worksheet as a group. Do ask students to make individual commitments, then follow up as previously described.

 

Steps to Take:

We can attack land pollution by changing the amount we consume and throw away.

Reduce.

  • Use the 30-Day Rule. Wait 30 days after first considering a purchase before buying. This keeps you from impulse buying.
  • Buy only high-quality items that will last and use up completely what you buy.
  • An average 9 percent of a product's cost goes toward its packaging. So save money - and pollute less - by buying products with less packaging.
  • Borrow books, newspapers, magazines and movies from the library instead of buying them.
  • Instead of buying gifts:

- Spend time with someone.

- Bake some goodies.

- Share plant cuttings or flowers from your home or garden.

- Create a gift from recycled materials.

- Suggest a "white elephant exchange" of regifted items.

Reuse.

  • Give things away instead of throwing them away. Take items to a second-hand store or consignment shop. Donate them to a library, school, shelter or clothing drive.
  • No time to sort, bag and haul out unneeded stuff? Hire a junk removal service that will take it away, then donate, recycle or dispose of it for you.
  • Save money by eliminating disposable items from your shopping list. For example, use rags instead of paper towels and cloth napkins instead of paper.
  • Reuse your school supplies from one year to the next. (Why do you need a new backpack, binder or lunchbox if the old ones are still in good shape?) 

Recycle.

  • Be aware of community recycling rules. Using the Internet, locate nearby facilities that accept e-waste, hazardous waste and other types of waste your local recycler will not.
  • Take advantage of e-waste take-back programs that local businesses like appliance and hardware stores offer.
  • Use a search engine to locate national companies that sponsor recycling programs for unusual products like athletic shoes, cosmetic containers and packing peanuts.
  • When shopping, make it a point to choose products that come in recyclable containers.

Rebuy.

  • Try to buy products made from recycled materials, like notebook paper and bathroom tissue. 
  • Buy used items from thrift stores, garage sales, online marketplaces and home improvement resale shops are often in great shape and are a good value. An added bonus: profits from your purchases may go to fund projects benefiting your community.

 

Composting:

Composting is an easy, productive way to recycle household food scraps and yard waste. Compost is simply organic matter that breaks down over time, under the right conditions. Composting involves layering waste materials with soil and fertilizer. These layers consist of:

  • Layer 1: Coarse garden materials, like shrub trimmings and twigs
  • Layer 2: Animal manure or other fertilizer
  • Layer 3: Soil
  • Layer 4: Leaves, grass clippings, vegetable/fruit scraps, egg shells and coffee grounds - even soiled paper, as long as it's not coated.
  • Layer 5: Fertilizer
  • Layer 6: Soil
  • Layer 7: Repeat the layering process until the compost container is full.

After creating the compost pile, the homeowner should turn it every month or so, which adds air and mixes any additions with the already decomposing materials. Water can be added at that time, just enough to make the pile damp. If properly cared for, the compost should be ready to use to fertilize plants or enhance garden soil in about three to four months. 

Composting can help keep 20-30 percent of all household waste out of landfills. If the waste decomposes anyway in a landfill, why is it important to compost? The truth is that waste doesn't decompose well in landfills. Tightly packed and buried under many feet of soil, this waste isn't exposed to air, so it takes much, much longer to break down - decades or even centuries. In the process, methane and carbon dioxide gases can be used in a positive way to produce energy, composting household waste adds nutrients to garden soils to make them healthier. And it prevents the need for polluting chemical fertilizers, saving money, so it makes better sense for the homeowner - and for our planet.

 

E-waste: A Growing Problem

It's estimated that in the near future the amount of e-waste - discarded computers, printers and related equipment, TVs and cell phones - will be enough to fill dump trucks circling the earth twice! On average, consumers only recycle about a fourth of their e-waste. Many indicate recycling e-waste is just too much trouble. Or they don't know how to recycle it or where to take it. The majority is simply thrown out, leading to pollution from lead, mercury and other chemicals and other toxic substances. Many manufacturers and retailers will accept e-waste, and may actually buy it back from the consumer. Locate these environmentally responsible companies easily online by using a search engine.

 

Activities:

1. Invite crafty students to design and make useful, artistic items from nonrecyclables. Display their creations at an open house or other school event.

2. Ask interested students to research eco-friendly clothing of natural fibers like cotton, bamboo, silk, wool and hemp.

  • How does this type of clothing compare in price with clothing made from polyester, rayon, nylon and other synthetic fabrics?
  • Are there advantages to wearing natural fibers? Synthetic fibers?
  • Where can eco-friendly clothing be purchased in your area?

3. Divide the larger group. Invite each small group to create a scavenger hunt of 10 items of waste for another group to find. When each group has located the items on their list, ask:

  • Which of these items can be recycled?
  • Can the nonrecyclables be reused? If not, what eco-friendly alternatives (if any) can be substituted by the school (or organization) in the future?

4. Assign groups of students to explore and share their findings about the following topics using the U.S. EPA (Environmental Protection Agency) website,  

  • Food waste management.
  • Your EPA region's and/or state's current efforts in food waste recovery, composting.
  • Waste reduction success stories.

5. Your students can calculate their environmental "footprints." Simply go to www.epa.gov and type "personal emissions calculator" into the search bar.

6. If possible, take a tour of a local landfill or recycling facility. Ask the group to set goals for their field trip. What would they like to find out? What do they hope to see while there? Have each student prepare three questions to ask personnel while visiting.

 

Healthy Environment = Happy Humans

Every year, 3 million people worldwide die unnecessarily from being overweight or obese. A healthy lifestyle includes eating a balance of basic foods in moderate serving sizes, as well as adequate physical activity. Environmentally friendly living naturally leads to increased physical activity because human power is often used. Since greenhouse gas emissions come partly from household transportation needs, human-powered transportation like cycling or walking helps the planet while improving overall health.

The possibility of being healthier may not be enough to motivate someone to do his or her part of keeping our air, water and land in good condition. Perhaps the possibility of being happier might. Studies show people who spend time in and around nature are more content. Living near nature and spending time outdoors (even doing outside chores) apparently improves our moods.

Why is that? Researchers have found a link between low levels of vitamin D and depression. Greater exposure to natural sunlight increased the level of vitamin D in the body, which has been shown to decrease anxiety and aggression, improve energy and enjoyment of life. Experts say being outside for a short time on a sunny day without UVB ray blocking sunscreen - just 10 minutes at noon - is enough to produce a healthy daily dose of vitamin D.

 

Independent Research: SAD (Seasonal Affective Disorder)

Anyone living north of Atlanta's latitude won't get enough vitamin D from sunlight during the winter because the sun's UVB rays don't penetrate Earth's atmosphere during that season.  Take an informal poll: Have group members noticed mood changes during different seasons? Have interested students research seasonal affective disorder (SAD) and share their findings with the large group: What are the symptoms? What treatment(s) are used? If you do live in a cold-weather climate, invite students to draw up a plan for warding off the effects of SAD. 

 

Reproducible: Mood Tracker

Does being indoors or outside affect your students' moods? Make copies of the reproducible. Ask them to track mood shifts over a week's time (or another length of time you determine). Then have them compare their moods with where they've been. Does there seem to be a connection between the two?

What about those who don't get outside much during the day, if at all? Studies have shown prison inmates are healthier, hospital patients recover more quickly, and nursing home patients enjoy more natural sleep patterns when they live in buildings that provide natural lighting. "Daylighting" techniques also help employees and students have better attendance, improved study habits and better performance of simple tasks. Exposure to daylight helps people feel better and it also conserves energy, so it can help them save money as well.

Many people like to "unwind" by watching TV. Researchers say watching TV is actually a great way to become more stressed out. Human brains need rest. When we do outdoor activities like walking, hiking and biking, surrounded by nature, our brains de-stress as our thoughts wander and we wonder things. As a result, we feel more at peace and less burdened by our problems and issues. The connection between humans and nature is so strong that just listening to natural sounds, like a babbling brook, ocean waves or birds chirping, petting an animal or looking at a landscape painting relaxes people, reduces their stress levels and aids their healing.

Keeping our air, water and land healthy so we can enjoy the unpolluted beauty of our natural surroundings will help protect our future physical, mental and emotional health. We must commit to preserving our land, air and water, if only for selfish reasons; the sake of our own happiness and sense of well-being. Lesson 4 will address actions students can take in their own communities to:

1. Promote good stewardship of the earth.

2. Influence others to take a stand for the environment as well. 

 

Reproducible: Environmental Crossword

Your students will review Lesson 3 as they do this crossword.  The answers are here.

 

Special Note:

Wrap up this lesson by distributing a Climate Change Wheel chart to each student. This chart is based on the U.S. Environmental Protection Agency's (EPA's) "Global Warming Wheel Card." This handy, easy-to-use tool estimates carbon dioxide emissions from everyday activities and offers suggestions on reducing them.

Your students may well wonder what "pounds of carbon dioxide" means, practically speaking. Boost their understanding by having them enter their total emissions output (or savings) into the EPA's Greenhouse Gas Equivalencies Calculator at its website. The calculator translates emission totals into more understandable analogies like emissions from railcars of coal or tanker trucks of gasoline, or savings from planting tree seedlings or preserving acres of forest.