Energy and Global Warming
How does one take a classroom of students who think that the greenhouse effect has something only to do with growing tomatoes to a group of students who know how the greenhouse effect works and what role they play in contributing to global warming? Combining the goal to guide students to think critically about the positive and negative impacts of human technology with the objective that students understand the concept of our sun's energy and how the Earth's global climate works will be a challenge. Therefore, the unit will begin with a very structured framework before students can move to individual research.
We will begin by developing some basic definitions and creating a useful glossary of important terms and concepts. The students' understanding of this 'vocabulary' should be reflected in their final performance task by their using the words in the reports -- students also will encounter many of the terms in the course of their research and so a glossary will be helpful. More terms can be added as questions arise or as students discover other essential words or phrases. The teacher resource list contains books and websites (some interactive) that explain many of the basic terms in great detail and in varying degrees of complexity. The class will create a word wall of the terms and their definitions that will be accessible throughout the unit. Some of the key terms to be used in the unit are energy, heat, light, global warming and the greenhouse effect.
Energy is defined as the ability to do work. The kinds of energy include heat (thermal), light (radiant), mechanical, electrical, chemical, and nuclear energy. There is stored or potential energy (chemical or gravitational, e.g.) or working energy (mechanical and kinetic) energy. The sources of energy are renewable (solar, wind, hydropower) and non renewable (fossil fuels and nuclear). The class will discuss these ideas and come up with practical examples to demonstrate their understanding. We will relate the idea of fuel and energy to their eating of a good breakfast and the energy they have (or do not have) to do work throughout the day. We will talk about the furnaces in their homes and apartments and the kinds of cars their families drive -- what fuels are they using and where do they come from? Heat is energy that is transferred by a difference in temperature, specifically from a hotter object to a cooler object; thermodynamics is the study of heat and how it changes into different forms of energy. There are laws that describe how transfer takes place and for this unit we will look at the first and second laws of thermodynamics. Light and heat are considered electromagnetic radiation that is categorized by wavelength and frequency. Radiation with higher frequency has shorter wavelength and that with lower frequency has longer wavelength.
Global warming is a term usually used to describe the effects of decades of pollution on long-term weather patterns. Today, the idea of global warming is well known, if not well understood. It is not unusual to hear someone complaining about a hot day or a freak storm and blame it on global warming, even though it may not be true. Additionally with blockbuster movies like "The Day After Tomorrow" people are growing more and more aware of what this term means. The greenhouse effect is a complicated phenomenon which involves the earth absorbing energy at all wavelengths and emitting them as heat, which is then trapped by gases in our atmosphere. When people talk about the global warming on Earth, they are usually referring to this somewhat more complicated process called the greenhouse effect. However, the greenhouse effect is not a bad thing by itself -- it is what allows Earth to stay warm enough for life to survive.
Weather and Climate
Weather is local and short-term. If it snows in the town where you live next Tuesday, that is weather. Climate is long-term and does not usually relate to one small location. Changes in climate sometimes take tens of thousands of years. That means if you happen to have a winter that is not as cold as usual, with not very much snow -- or even two or three such winters in a row -- that is not a change in climate. It is also important to understand that even small changes in climate can have major effects. When scientists talk about "the Ice Age," you probably envision the world frozen, covered with snow and suffering from frigid temperatures, but actually during the last ice age the earth's average temperature was only 5 Celsius degrees cooler than modern temperature averages (earthobservatory.nasa.gov). In specific terms, an increase of 1 or more Celsius degrees in a period of one hundred to two hundred years would be considered global warming. Over the course of a single century, an increase of even 0.4 degrees Celsius would be significant. It is also important to realize that in global warming the extremes are affected the most.
The Greenhouse Effect
Global warming is believed to be caused by an increase in the greenhouse effect. The greenhouse effect is not a bad thing by itself -- it is what allows Earth to stay warm enough for life to survive. You can think of the Earth like your car sitting out in a parking lot on a sunny day. Your car is always much hotter inside than the outside temperature if it's been sitting there for a while. The sun's rays enter through your car's windows. Some of the heat from the sun is absorbed by interior of the car. When those objects release this heat, it does not all get out through the windows. Some is reflected back in -- the heat radiated by the seats is a different wavelength than the light of the sun that made it through the windows in the first place. So a certain amount of energy is going in, and less energy is going out. The result is a gradual increase in the temperature inside your car.
When the sun's rays hit the Earth's atmosphere and the surface of the Earth, approximately 70 percent of the energy stays on the planet, absorbed by land, oceans, plants and atmospheric gases. The other 30 percent is reflected into space by clouds, snow fields and other reflective surfaces (earthobservatory.nasa.gov). Even the 70 percent that gets through does not stay on earth forever, rather things around the planet, like bodies of water, land formations, or people and plants absorb the sun's heat then eventually radiate that heat back out. Some of it makes it into space, and the rest of it ends up getting reflected back down to earth where it hits certain gases in the atmosphere, such as carbon dioxide, methane gas and water vapor. This heat that is trapped by the Earth's atmosphere keeps the planet warmer than it would be without an atmosphere, because more energy is coming in through the atmosphere than is going out. This is all part of the greenhouse effect that keeps the Earth warm. If there were no greenhouse effect, Earth would look a lot like . Mars does not have a thick enough atmosphere to reflect enough heat back to the planet, so it gets very cold there.
The greenhouse effect happens because of certain naturally occurring substances in the atmosphere. Unfortunately, since the Industrial Revolution, humans have been pouring huge amounts of those substances into the air, including carbon dioxide (CO2), nitrous oxide (NO2), methane gas (CH4) and water vapor.
Carbon dioxide (CO2) is a colorless gas that is a by-product of the combustion of organic matter. It makes up less than 0.04 percent of Earth's atmosphere, most of which was put there by volcanic activity very early in the planet's life. Today, human activities are pumping huge amounts of CO2 into the atmosphere, resulting in an overall increase in carbon dioxide concentrations.(3) These increased concentrations are considered the primary factor in global warming, because carbon dioxide absorbs infrared radiation. Increased CO2 means more energy absorption and an overall increase in the planet's temperature.
The Institute reports that carbon emissions worldwide have increased from about 1 billion tons in 1900 to about 7 billion tons in 1995. The Institute also notes that the average surface temperature of Earth has gone from 14.5 degrees C in 1860 to 15.3 degrees C in 1980.(4)
Nitrous oxide (NO2) is another important greenhouse gas. Although the amounts being released by human activities are not as great as the amounts of CO2, nitrous oxide absorbs much more energy than CO2 (about 270 times as much). The use of large amounts of nitrogen fertilizer on crops releases nitrous oxide in great quantities, and it is also a by-product of combustion.
Methane is a combustible gas, and it is the main component of natural gas. Methane occurs naturally through the decomposition of organic material and is often encountered in the form of "swamp gas." The following human-made processes produce methane:
1) By extracting it from coal
2) From large herds of livestock (i.e., digestive gases)
3) From the bacteria in rice paddies
4) Decomposition of garbage in
Methane acts much like carbon dioxide in the atmosphere, absorbing infrared energy and keeping heat energy on Earth. There is also evidence that a large-scale introduction of methane into the atmosphere (such as from the release of huge chunks of methane ice locked under the oceans) could have created brief periods of intense global warming that led to some of the mass extinctions in the planet's distant past(5).
Water vapor is the most abundant greenhouse gas, but it is, more often than not, a result of climate changes rather than of man-made emissions. Water or moisture on the Earth's surface absorbs heat from the sun and the surroundings. When enough heat has been absorbed, some of the liquid's molecules may have enough energy to escape from the liquid and begin to rise into the atmosphere as a vapor. As the vapor rises higher and higher, the temperature of the surrounding air becomes lower and lower because temperature decreases with height. Eventually, the vapor loses enough heat to the surrounding air and it condenses back into a liquid. Earth's gravitational pull then causes the liquid to "fall" back down to the earth, thereby completing the cycle. This cycle is also called a "positive feedback loop" which is when an action causes a reaction that then prompts the original action to reoccur, resulting in a cycle between the two. A "negative feedback loop' is when the action causes a reaction that then decreases the occurrence of the original reaction. Water vapor is more difficult to measure than the other greenhouse gases and scientists are uncertain as to the exact part that it plays in global warming. But, the NOAA does have this to say:
As water vapor increases in the atmosphere, more of it will eventually also condense into clouds, which are more able to reflect incoming solar radiation (thus allowing less energy to reach the Earth's surface and heat it up).(6)
Effects of Global Warming
We have seen that an average drop of just 5 degrees Celsius over thousands of years can cause an ice age; so what will happen if the Earth's average temperature increases a few degrees in just a few hundred years? There is no clear answer because even short-term weather predictions are never perfectly accurate because weather is a complex phenomenon. To make climate predictions we can only make educated guesses based on our knowledge of climate patterns through history.
Glaciers and ice shelves around the world could begin to melt. In fact, this is already happening (http://www.guardian.co.uk/climatechange/). The loss of large areas of ice on the surface could accelerate global warming because less of the sun's energy would be reflected away from Earth to begin. An immediate result of melting glaciers would be a rise in sea levels. Initially, this would only be an inch or two. Sea levels would also rise because ocean waters would grow warmer, causing the water to expand. Even a modest rise in sea levels could cause flooding problems for low-lying coastal areas. With a rise in the overall temperature of the ocean, ocean-borne storms such as tropical storms and , which get their fierce and destructive energy from the warm waters they pass over, would increase in number and force. Additionally, changes in sea level could alter the Atlantic current that keeps the northern hemisphere a temperate region.
Less abrupt changes would occur around the world as average temperatures increased. In temperate areas with four seasons, the growing season would be longer with more precipitation. This could be beneficial in many ways for these areas. However, less temperate parts of the world would likely see an increase in temperature and a sharp decrease in precipitation, causing long droughts and potentially creating deserts.
The most devastating effects, and also the hardest to predict, would be the effects on the world's living ecosystems. Many ecosystems are very delicate, and the slightest change can kill off several species as well as any other species that depend on them. Most ecosystems are interconnected, so the chain reaction of effects could be immeasurable. The results could be something like a forest gradually dying off and turning to grassland or entire coral reefs dying. Many species of plants and animals would adapt or move to deal with the shift in climate, but many would become extinct. The effect on the biodiversity of the Earth could be devastating.
The human cost of global warming is hard to quantify. Thousands of lives per year could be lost as the elderly or ill suffer from and other heat-related trauma. Poor people and underdeveloped nations would suffer the worst effects, since they would not have the financial resources to deal with the problems that come with an increase in temperature. Huge numbers of people could die from starvation if a decrease in precipitation limits crop growth and from disease if coastal flooding leads to widespread water-borne illness.
Is Global Warming a Problem?
There is agreement that global warming is happening, but scientists disagree as to the severity of the problem and to what extent people should worry about its effect. Their arguments have to do with interpretation of data. For instance, the data show a measurable upward trend in global temperatures. Some scientists argue that this is either because we do not have enough long-term historical climate data or because the data we do have is not clear enough. Some also argue that the data is being interpreted incorrectly by people who are already worried about global warming. That is, these people are looking at the statistics with biases in mind, instead of looking at the evidence objectively and trying to figure out what it means. Finally some argue that any increase in global temperatures we are seeing could be a natural climate shift, or it could be due to other factors than greenhouse gases, such as changes in solar activity. These scientists say that the Earth is more resistant to climate changes on this scale than we think. Plants and animals will adapt to subtle shifts in weather patterns, and it is unlikely anything catastrophic will happen as a result of global warming. Slightly longer growing seasons, changes in precipitation levels and stronger hurricanes, in their opinion, are hardly disastrous. They also argue that the economic damage caused by cutting down on the emission of greenhouse gases will be far more damaging to humans than any of the effects of global warming.
Most scientists, however, recognize that global warming is something to be worried about. They will tell you that global warming is real and that it is likely to do some kind of harm. The effects are sill being studied and debated, and political agendas have certainly had an influence.
What can we do to slow global warming?
There are a few things we can do to slow global warming. It all boils down to reducing the activities that create greenhouse gases. As individuals we can help by using less energy. The electricity that operates many of the devices in our homes comes from a , and most power plants burn fossil fuels to generate that power. Turn off lights when they're not in use. Take shorter showers to use less hot water. Use a fan instead of an air conditioner on a warm day, or keep the air conditioner set to a higher temperature and then use a fan to circulate the air. Take public transportation or drive more fuel-efficient cars. Walk or ride your bike if possible or car pool on your way to work. Driving your car generates more greenhouse gases than almost anything else you do. Other specific ways you can help decrease greenhouse-gas emissions are: to make sure your car is properly tuned up and the tires are inflated properly. This allows it to run more efficiently and generated fewer harmful gases. Turn lights and other appliances off when you are not using them. Even though a light bulb does not generate greenhouse gas, the power plant that generates the electricity used by the light bulb probably does. You should recycle. Garbage that does not get recycled ends up in a , generating methane; plus, recycled goods require less energy to produce than products made from scratch. It is good to plant trees and other plant life where you can. Plants take carbon dioxide out of the air and release oxygen. One should never burn garbage. This releases carbon dioxide and hydrocarbons into the atmosphere.
To really reduce the emission of greenhouse gases, we need to develop non-fossil fuel energy sources. Hydroelectric power, solar power, hydrogen engines and fuel cells could all create big cuts in greenhouse gases if they were to become more common.
At the international level, the was written to reduce CO2 and other greenhouse gas emissions worldwide. Thirty-five industrialized nations have committed to reducing their output of those gases to varying degrees. Unfortunately, the United States, the world's primary producer of greenhouse gases, did not sign the treaty.