decreased levels of vitamin A
possible increase in levels of vitamin D produced by the skin
reduced abundance of UV-sensitive nitrogen-fixing bacteria
loss of crops dependent on these bacteria
disruption of nitrogen cycles
loss of plankton (supported by a supernova-related extinction event 2 million years ago)
disruption of ocean food chains
Most of these effects are based on the ability of UV radiation to alter DNA sequences. It is this potential which has made the Ozone Layer such a gift to life ever since photosynthesis provided the oxygen to fuel its production. Its total loss would undoubtedly be devastating to nearly all life.
In 1987, 43 nations agreed in the Montreal Protocol to freeze and gradually reduce production and use of CFCs. In 1990, the protocol was strengthened to seek elimination of CFCs for all but a few essential uses. Today, Hydrochlorofluorocarbons (HCFCs – similar compounds which replace one chlorine with a hydrogen) have replaced CFCs, with only 10% of their ozone-depleting activity levels. Unfortunately, HCFCs are greenhouse gases (see next lesson), so their role as alternatives is a mixed blessing. HFCs (hydrofluorocarbons) are another substitute; because these contain no chlorine, they have no ozone-depleting activity, and their greenhouse effect is less than HCFCs (though still significant). One HFC is currently used in automobile air conditioners in the U.S.
If ozone-depleting substances have been virtually eliminated, is ozone depletion no longer a problem?
Unfortunately, we have not yet reached that point. Levels of CFCs in the atmosphere are beginning to decline, and ozone levels appear to be stabilizing (Figures above and 14) for years after 2000). Scientists predict that ozone levels could recover by the second half of this century; the delay is due to the long half-life of CFCs in the stratosphere. However, recovery could be limited or delayed by two unknowns:
Developing countries outside the Montreal Protocol could increase their use of CFCs.
According to scientists, global warming would cool the stratosphere and increase ozone depletion because cooler temperatures favor ozone decomposition.
Preventing Air Pollution
Throughout this lesson, we have discussed solutions to specific problems for our atmosphere. A quick recap of ways to maintain our atmosphere and its ecosystem services from this chapter includes:
Reducing use of fossil fuels
Switching to cleaner fuels, such as nuclear power
Switching to renewable energy sources
Increasing fuel efficiencies
Supporting legislation for fuel efficiencies
Supporting national and international agreements to limit emissions
Utilizing pollution control technologies: e.g., scrubbers on smokestacks and catalytic converters for motor vehicles
Creating and supporting urban planning strategies
As always, costs are high and tradeoffs must be considered. The classic example is nuclear power, whose effects on the atmosphere are less than those of fossil fuels. Unfortunately, it has high potential for health damage and high costs – both economic and environmental – for storage and transport of nuclear waste.
Because fossil fuel use is the cause of so many atmospheric as well as water and soil pollutants, the solutions mentioned in the last two lessons apply here, as well. The final lesson on Climate Change relates directly to both fossil fuel combustion and atmospheric change, so more pollution solutions, specific to climate change, will be presented. You should also review the individual responses at the end of the lesson on biodiversity, because that list focuses on ways you can change your own life to help protect the environment.
Lesson Summary
Earth’s atmosphere, as we understand it today, provides ideal conditions and essential raw materials for life.
Throughout Earth’s history, the atmosphere has changed dramatically, and life caused some of the changes.
Within human history, the atmosphere had been in a dynamic equilibrium: balancing photosynthesis, respiration, evaporation, and precipitation.
Primary pollutants are directly added to the atmosphere by processes such as fires or combustion of fossil fuels. Secondary pollutants are formed when primary pollutants interact with sunlight, air, or each other.
The majority of air pollutants can be traced to the burning of fossil fuels for heat, electricity, industry, transportation, and waste disposal.
Worldwide, air pollution causes as many as 2.4 million deaths each year.
Aerosols (particulates and liquid droplets) cab cause global dimming, or reduction in sunlight reaching the Earth.
Light pollution can interfere with bird migrations, sea turtle reproduction, nocturnal animal behavior, and human activity.
Rain, snow, fog, dew, and even dry particles which have an unusually low pH are commonly considered together as Acid Rain.
Normal rain has a pH of about 5, due in part to formation of a weak (carbonic) acid from CO2.
Burning fossil fuels adds NOx and SOx gases to the atmosphere; these form strong acids (nitric and sulfuric) and change the pH of rain to as low as 2.4.
Acid rain leaches nutrients and toxins from soils, weakening forests and killing aquatic animals.
Limestone in bedrock or watersheds buffers the effects of acid rain for certain lakes.
The development of taller smokestacks only sent pollution elsewhere, but scrubbers in smokestacks and catalytic converters in motor vehicles help to reduce emissions.
The Ozone Layer in the stratosphere – formed from O2 – protects Earth’s life from mutagenic UV radiation.
Ground-level ozone – formed from automobile exhaust and industry – is a component of smog, which irritates eyes and respiratory membranes.
Ozone depletion is a global reduction in the thickness of the ozone layer, caused by chlorine and bromine atoms which reach the stratosphere.
The ozone hole is a seasonal thinning of ozone above the Antarctic.
CFCs in aerosol sprays, refrigerants (Freon), cleaning solvents, and fire extinguishers are the primary ozone-depleting substances (ODSs).
The 1987 Montreal Protocol has reduced the use of CFCs and ozone depletion.
Chemical substitutes, though less harmful, still cause damage, and countries outside the Protocol may still add ODS to the atmosphere.
Global warming would cool the stratosphere and increase ozone depletion, because cooler temperatures favor ozone decomposition.
Because fossil fuels are the source of many air pollutants, reducing their use is the key to solving air pollution problems.
Technology can help by developing alternative energy sources, increasing fuel efficiencies, and improving pollution control.
Governments can help by legislating fuel efficiencies and pollution control, urban planning, and forging agreements with other governments.
Review Questions
Summarize the importance of the gaseous “life support system” which Earth’s atmosphere provides, and the dynamic equilibrium which characterizes the natural atmosphere.
Describe the ecosystem services provided by Earth’s atmosphere.
Distinguish between primary and secondary pollutants, and give an example of each.
Define acid rain and trace the steps in its formation.
Why is rain with a pH of 5 not considered acid rain?
Analyze the effects of acid rain on soils, water resources, vegetation, animals, and humans.
Define ozone depletion and explain its causes.
Explain the consequences of ozone depletion.
Chart the air pollution problems discussed in this chapter together with a primary cause and an important prevention practice for each.
Problem Major Cause Major Prevention Practice
Global Dimming Dust from erosion Contour plowing, conservation tillage, cover crops
Light Pollution Urbanization, artificial lights Alteration of spectra and design of lights
&
nbsp; Smog Automobile exhaust Catalytic converters, emissions control
Acid Rain Generation of electricity from coal Reduce use, scrubbers
Ozone Depletion CFC emission Eliminate use, find substitutes
Why are international treaties, such as the Montreal Protocol and the Kyoto Treaty, so important in solving air pollution problems?
Further Reading / Supplemental Links
US Environmental Protection Agency, Effects of Acid Rain - Surface Waters and Aquatic Animals, ACID RAIN, US EPA website, last updated 8 June 2007. Available online at:
http://www.epa.gov/acidrain/effects/surface_water.html
http://www.epa.gov/highschool/air.htm
http://www.anr.state.vt.us/site/html/reflect/April5.htm
http://www.epa.gov/acidrain/
http://www.atm.ch.cam.ac.uk/tour/
http://www.epa.gov/ozone/
http://www.pbs.org/wgbh/nova/sun/
http://www.documentary-film.net/search/sample.php
http://www.skyandtelescope.com/resources/darksky
http://www.wellesley.edu/Biology/Faculty/Mmoore/Content/Moore_2000.pdf
http://en.wikipedia.org
Vocabulary
acid rain
Precipitation in any form which has an unusually low pH.
aerosols
Airborne solid particles or liquid droplets.
air pollution
Alteration of the Earth’s atmosphere by chemical, particulate, or biological materials.
algal bloom
A rapid increase in the growth of algae, often due to a similar increase in nutrients.
anthropogenic sources
Sources of pollution related to human activities.
biodiversity
Variation in life – at all levels of organization: genes, species, and ecosystems.
ecosystem
A functional unit comprised of living things interacting with their nonliving environment.
eutrophication
An increase in nutrient levels in a body of water, often followed by an increase in plant or algae production.
global dimming
A reduction in the amount of radiation reaching the Earth’s surface.
global warming
The recent increase in the Earth’s average near-surface and ocean temperatures.
greenhouse effect
The trapping by the atmosphere of heat energy radiated from the Earth’s surface.
light pollution
Production of light by humans in amounts which are annoying, wasteful, or harmful.
nonpoint source pollution
Runoff of nutrients, toxins, or wastes from agricultural, mining, construction, or developed lands.
ozone depletion
Reduction in the stratospheric concentration of ozone molecules, which shield life from damaging ultraviolet radiation.
ozone hole
A seasonal reduction in ozone levels over Antarctica.
ozone layer
A concentration of ozone molecules located between 15 and 35 kilometers above Earth’s surface in the stratosphere.
point source pollution
Single site sources of nutrients, toxins, or waste, such as industrial or municipal effluent or sewer overflow.
pollution
Release into the environment of chemicals, noise, heat or even light beyond the capacity of the environment to absorb them without harmful effects on life.
primary pollutants
Substances released directly into the air by processes such as fire or combustion of fossil fuel.
secondary pollutants
Substances formed when primary pollutants interact with sunlight, air, or each other.
sustainable use
Use of resources at a rate which meets the needs of the present without impairing the ability of future generations to meet their needs.
Points to Consider
What are the major ecosystem services provided by our atmosphere?
Could you now explain to a friend or family member the difference between the “hole in the ozone” and “global warming"?
In what ways have we already begun to add the costs of atmospheric changes to our economic system?
Can you think of additional ways in which we could build in these costs?
How can we gain support for adding environmental costs to economic costs?
Lesson 18.4: Climate Change
Lesson Objectives
Explain the mechanism of the greenhouse effect.
Recognize that the greenhouse effect maintains an equilibrium.
Compare greenhouse conditions on Earth to those on Mars and Venus.
Explain the extent of current increases in the Earth’s temperature.
Review past changes in the Earth’s temperatures.
Summarize the evidence and support for greenhouse gases as the cause of recent global warming.
Discuss the significance of global warming for Earth’s ecosystems.
Relate global warming to current global stability.
List the atmospheric gases that absorb the Earth’s thermal radiation, and their sources.
Evaluate possible solutions to the problem of global climate change.
Recognize the tradeoffs required by nuclear power plants: reduced emissions vs. radioactive fuels and waste
Introduction
On December 10, 2007, the Intergovernmental Panel on Climate Change (IPCC) and former US Vice President Al Gore received the Nobel Peace Prize “for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change.” The Peace Prize is designated “to the person who shall have done the most or the best work for fraternity between the nations, for the abolition or reduction of standing armies and for the holding and promotion of peace congresses." A high honor, the award also announced to the world that climate change (Figure below) is a critical issues for the future of the Earth and its people. What is climate change? What are its causes? How do its effects relate to world peace? What are “the foundations for the measures that are needed to counteract such change”? Can individuals like us help? These are the questions we will explore in this last lesson about human ecology.
Figure 18.49
Temperature variations from 1940-1980 averages show that most of the Earth warmed significantly in just a single decade. The average temperature change across the entire globe for this period is 0.42C (0.76 F). Over the past 100 years, surface air temperatures have risen 0.74 0.18 C (1.33 0.32 F).
What is the Greenhouse Effect?
The Greenhouse Effect is a natural feature of Earth’s atmosphere – yet another ecosystem service. Without the Greenhouse Effect, Earth’s surface temperature would average -18oC (0oF) – a temperature far too cold to support life as we know it. With the Greenhouse Effect, Earth’s surface temperature averages 15oC (59oF), and it is this temperature range to which today’s diversity of life has adapted.
How does this ecosystem service work? The Greenhouse Effect is summarized in Figure below. Of the solar radiation which reaches the Earth’s surface, as much as 30% is reflected back into space. About 70% is absorbed as heat, warming the land, waters, and atmosphere (you may recall that only about 1% is converted to chemical energy by photosynthesis). If there were no atmosphere, most of the heat would radiate back out into space as infrared radiation. Earth’s atmosphere, however, contains molecules of water (H2O), carbon dioxide (CO2), methane (CH4), and ozone (O3), which absorb some of the infrared radiation. Some of this absorbed radiation further warms the atmosphere, and some is emitted, radiating back down to the Earth’s surface or out into space. A balance between the heat which is absorbed and the heat which is radiated out into space results in an equilibrium which maintains a constant average temperature for the Earth and its life.
Figure 18.50
Without greenhouse gases, most of the suns energy (transfor
med to heat) would be radiated back out into space. Greenhouse gases in the atmosphere absorb and reflect back to the surface much of the heat which would otherwise be radiated.
If we compare Earth’s atmosphere to the atmospheres which surround Mars and Venus (Figure below), we can better understand the precision and value of Earth’s thermal equilibrium. Mars’ atmosphere is very thin, exerting less than 1% of the surface pressure of our own. As you might expect, the thin atmosphere cannot hold heat from the sun, and the average surface temperature is -55oC (-67oF) – even though that atmosphere is 95% CO2 and contains a great deal of dust. Daily variations in temperature are extreme, because the atmosphere cannot hold heat.
Figure 18.51
The thickness of a planets atmosphere strongly influences its temperature through the Greenhouse Effect. Mars (left) has an extremely thin atmosphere, and an average temperature near -55C. Venus (right) has a far more dense atmosphere than Earth, and surface temperatures reach 500C.
In contrast, Venus’ atmosphere is much thicker than Earth’s, exerting 92 times the surface pressure of our own. Moreover, 96% of the atmosphere is CO2, so a strong Greenhouse Effect heats the surface temperature of Venus as high as 500oC, hottest of any planet in our solar system. The thick atmosphere prevents heat from escaping at night, so daily variations are minimal. Venus’ atmosphere has many layers which vary in composition, and scientists have identified a layer about 50 km from the surface which could harbor liquid water and perhaps even life; some scientists propose that this would be a reasonable location for a space station. Near this altitude, pressure is similar to the Earth’s sea level pressure, and temperatures range from 20oC to 37oC. Nitrogen, though only 3.5% of Venus’ atmosphere, is present in the same overall amounts as on Earth (because the density on Venus is so much greater); oxygen, however, is absent, and sulfuric acid would present challenges.
CK-12 Biology I - Honors Page 88
