INTRODUCTION TO ENVIRONMENTAL SCIENCES

LECTURE NOTES

 

Global Warming and Ozone Loss

 

 

Climate is the long-term (30+ years) physical properties of the troposphere (or the time-averaged weather) for a given area. Cannot be determined by observing the day-to-day weather over the short term. Temperature and precipitation are the two most important climate factors.

 

Global climate controlled by numerous naturally occurring factors, including solar output, Earthıs axial wobble (precession of the equinoxes; 22,000-year cycle), Earthıs axial tilt (44,000-year cycle), shape of the Earth's orbit (eccentricity; 100,000- and 400,000-year cycles), atmospheric levels of CO2 and other greenhouse gases (thousands-millions of years cycles), position of the continents (millions of years cycle), rates of plate motions (same), and intensity of volcanism (same).

 

 

I. Greenhouse Effect

 

A number of gases in the earth's atmosphere trap heat. These include water vapor, CO2, ozone, methane, N2O, and CFC. All act like the glass of a greenhouse.

 

Gases allow solar UV energy to strike the earth's surface and warm it. This heat then radiated back as infrared energy, which is absorbed by greenhouse gases, warming the lower atmosphere. The higher the concentration of greenhouse gases, the more heat that gets trapped, and the warmer the troposphere becomes.

 

Our planet is as warm as it is (average temperature of 60 F rather than 0 F) because of these greenhouse gases. Makes our ecosystems and biological diversity possible.

 

 

A. Human Impact

 

Due to human activities, atmospheric levels of many greenhouse gases have risen substantially in the last century. Many are more efficient heat trappers than CO2, but the much larger increase in CO2 concentration makes it the gas of greatest concern.

 

Increasing levels of CO2 and other greenhouse gases due largely to burning of fossil fuels, agriculture, deforestation, and use of CFCs. CO2 levels now 30+% higher than the mid 1800s (highest CO2 levels in the last 150,000+ years). CO2 concentrations may double from pre-industrial levels by 2050.

 

Based upon studies of past climates and atmospheric gases, there is a direct correlation between global mean temperature and amount of atmospheric CO2. However, there is still a question of cause and effect (chicken or the egg) between the two.

 

Globally, the 15 warmest years on record have all occurred since 1979. Is this due to natural or anthropogenic causes?

 

 

B. Computer Models

 

Utilizing complex computer models of our atmosphere, climatologists now predict a rise in average global temperature of between 3-10 degrees F by the end of this century. There is still some uncertainty in the predictions of these models.

 

Climate predictions are only as good as the models and data used to make them. Now use general circulation models coupled with models of the earth's oceans (large reservoirs of heat and CO2) and atmospheric aerosols (can reduce solar input). Also need to incorporate the effects of clouds (reflect sunlight) and deforestation.

 

Models are imperfect, but are getting better. Short-term predictions have been verified by observation and models have reproduced past conditions fairly accurately.

 

All models agree that the earth will warm up as the result of increased CO2. The question now is exactly how much.

 

 

II. Possible (Probable?) Effects of Global Warming

 

Earthıs average climate will be warmer than it has been it the past 10,000 (150,000?) years.

 

Northern hemisphere (more land) will warm more than southern hemisphere (more oceans). Poles will warm more than tropics. Arctic has already warmed by as much as 10 F (Antarctic Peninsula by 4 F). Antarctic ice shelves are beginning to break up at an accelerated rate, arctic summer sea ice has been reduced by 15%, and Greenlandıs ice sheet is thinning.

 

Warmer atmosphere causes greater water evaporation causing greater average precipitation and stronger and more numerous storms (hurricanes, thunderstorms, tornadoes). Results in more frequent and severe floods and wind damage. This may have a profound impact on the world's insurance industry and premium rates.

 

Sea level will rise due to expansion of warmer water and melting of grounded glacial ice (floating sea ice has no impact). Sea level has risen about one foot since 1900. Estimates are between 2 and 5 feet more by 2100. May be even greater (as much as 20 feet!) if Antarctic ice shelves melt, but this should take hundreds of years.

 

Even at the lower limit of predicted sea level rise, large areas of world's coasts will flood more severely and frequently. Some low-lying islands will all but disappear (i.e. Maldives). Coastlines will recede by as much as 1000 feet horizontally for every one- foot rise of sea level.

 

Climate belts will shift away from the equator towards the poles by about 100 miles for every 1 F rise in global average temperature. Average shift will be about 350 miles by 2100. Means New Jersey will have the climate now found in North Carolina. Deserts in the southwest and Mexico will expand into the U.S. heartland, the world's most important food producing region. Droughts may become more frequent and severe, leading to the return of Dust Bowl conditions.

 

Food producing regions will migrate north into Canada and Russia where soils are much thinner and less fertile. World agricultural production may drop by 50% or more. Climate belts also will shift to higher altitudes (500 feet for every 1 F) again reducing the size of agricultural areas. This shift may also lead to loss of habitats and less biodiversity (more extinctions) in mountain environments.

 

More irrigation will be needed to supply enough water in a warmer climate. Water supplies may not be able to keep up with demand.

 

Tree ranges will shift greatly, altering the location of specific ecosystems. Many species may not be able to adapt or migrate fast enough and become extinct. May already be seeing this in the recent worldwide dying (bleaching) of coral.

 

Tropical diseases, such as malaria and yellow fever will spread to new areas. The range of tropical pests (killer bees) will expand.

 

Somewhat paradoxically, certain regions of the globe will cool, largely due to changes in ocean currents. The issue of greatest concern is the slowing, if not cessation, of the Gulf Stream due to an influx of low density, fresh melt water from the arctic and Greenland. This may cause the warm, high salinity Gulf Stream waters from sinking to the bottom of the Atlantic near Iceland, bringing the current to a stop. Less heat will be transferred to northern Europe and eastern North America, causing the climate to cool dramatically in those regions.

 

Not all regions of the planet will respond similarly in a globally warmer world. Regardless of the details, a warmer greenhouse world will be different and we, and every other species, will have to adapt (or become extinct). Because of our technology, we can adapt. Other species do not have that option.

 

 

III. Solving the Problem of Global Warming

 

Is there even a problem? A few scientists say no, but the data is getting harder and harder to ignore. Others believe we still do not have enough data to act and justify the expense of reducing CO2 emissions. A third group of scientists believe we cannot afford not to act even with the uncertainty as to the seriousness of the situation. Would you pump your house with a potentially harmful gas without being sure of the outcome? Thatıs the experiment weıre running now on our planet.

 

There also is the issue of a time delay between acting to lower CO2 emissions and the impact that reduction will have on a warming climate. What we do today will not be felt until around 2050.

 

Reducing global warming by increasing worldwide energy efficiency also has other benefits, including less air pollution, less loss of biodiversity, fewer imports of foreign fuels, and better health. Shouldnıt we do this even if global warming was not a concern?

 

 

A. Ways to Reduce Global Warming

 

Would need to lower present CO2 emissions by around 75% in order to stabilize atmospheric levels at present values. Can do this by increasing energy efficiency, use less coal and more natural gas, switch to renewable forms of energy, reduce deforestation, slow population growth, and remove CO2 from present emissions more efficiently.

 

These things are not being done at present. As a result, it is predicted that CO2 emissions will increase by 50% in the next 20 years. Even a 50% reduction will leave atmospheric levels at around 450 ppm (up 50% from pre-industrial levels). Elvis has already left the building!

 

B. International Agreements

 

The 1992 Earth Summit in Rio de Janeiro only committed countries to reducing emissions back to 1990 levels. Most of these were developed countries and only half of them will actually meet their goal.

 

Developing countries increasing their emissions by 5% per year (14 year doubling time). By around 2025 China will emit more CO2 than any other country, although the U.S will still have the highest per capita emissions.

 

1997 Kyoto Treaty requires developed countries to reduce CO2 by an average of 5.2% (U.S. 7%) below 1990 levels by 2012. U.S. emissions predicted to be 30% higher by then! Developing countries (even China and India) do not have to reduce emissions, although emission credits could be traded.

 

Although the Kyoto Treaty was a start, it still fell well short of the 60% reduction below 1990 levels needed to stabilize atmospheric levels of CO2. U.S. and a few other industrialized nations have pulled out of the treaty, largely due to economic reasons and the claim that the treaty is unfair. Given this, we need to prepare for a warmer world now.

 

 

IV. Ozone Depletion: Is It a Threat?

 

Stratospheric ozone (O3) blocks 95-99% of UV radiation from reaching earth's surface. Allows life to exist on the land. Since the 1960s, ozone levels have fallen by 10-50%, depending on latitude. More UV striking earth's surface, causing long-term health problems for humans, and threatening the existence of some plants and animals.

 

 

A. Causes of Ozone Depletion

 

Problem stems from the use of a wide variety of chlorofluorocarbons (CFC) used as propellants, coolants, solvents, sterilants, fumigants, and in foam bubbles. Widely used because they are stable, insoluble in water, non-corrosive, nontoxic, and inflammable. They seemed like the perfect molecules.

 

However, once emitted into the atmosphere, CFC molecules rise to the stratosphere and remain there for decades. They react with UV radiation, losing a chlorine atom. Chlorine then reacts with ozone, converting it to an O2 molecule and O ion. Each CFC molecule does this to tens of thousands of ozone molecules so that ozone is destroyed faster than it can be created.

 

Other chlorine and bromine bearing molecules used in industry can do the same thing. Natural sources of chlorine and bromine (volcanic gases and sea spray) are typically soluble in water and are quickly washed out of the atmosphere.

 

Ozone depletion is greatest over the poles (50+%), particularly Antarctica. This is due to the buildup of Cl2O2 on ice crystals (also act as a catalyst for ozone depleting reactions) during the frigid winters. When sunlight returns in the spring, the Cl2O2 is rapidly destroyed releasing a burst of chlorine and causing a rapid reduction in ozone. Eventually, by the end of the polar summer, ozone levels rebound.

 

Each spring large amounts of ozone-depleted air is released from the poles and spreads over the higher southern (Australia, New Zealand, South Africa, Argentina, Chile) and northern (Europe, North America, Asia) latitudes. UV levels rise by as much as 15% in these regions.

 

 

B. Effects of Ozone Depletion

 

For humans, the most important health impacts from lower ozone and higher UV levels are more cataracts, premature aging of the skin, more severe sunburns, and more skin cancers.

 

Present loss of ozone estimated to produce over 300,000 additional skin cancers worldwide each year. Three types: squamous cell, basal cell, and malignant melanoma. The first two are very curable if caught early, whereas the latter is often fatal. Present ozone loss also estimated to produce 1.5 million additional cataracts.

 

Estimated that in the U.S., 12 million additional skin cancers will occur with about 200,000 deaths occurring over the next 50 years.

 

Other human health impacts include suppression of the immune system and the increase in tropospheric ozone, which will increase respiratory diseases.

 

Increased UV also will lower crop yields ($2.5 billion/year in U.S.), decrease forest and phytoplankton productivity (increasing global warming and destroying ecosystems), and increase the degradation and destruction of many materials, including plastics (become brittle) and paints (fade).

 

Humans might have to limit their time outdoors and wear protective clothing and sunscreens. Already beginning to see this. Unfortunately, animals can't do these things. They need to evolve increased natural resistance to elevated UV levels. There may not be enough time for this to happen, increasing extinction rates.

 

 

C. Ways to Reduce Ozone Loss

 

Best way is to stop producing all ozone-depleting chemicals. Still will take decades to return to normal levels (prior to 1950).

 

A number of substitute compounds already exist to replace CFCs, including HCFC, HFC, HC, ammonia, H2O, terpenes, and helium. Some deplete ozone at a greatly reduced rate and some also are greenhouse gases. There is no single answer.

 

Recent agreements have led to the international phasing out of CFCs. Worldwide production is down over 80% since 1988. This should result in a stabilization of ozone levels 10-30% lower than present by 2080 in the northern hemisphere.

 

Unfortunately, China and India have not signed these agreements, other countries are not meeting their obligations, and there is a black market for CFCs in the U.S. where they are now illegal. May prolong ozone depletion into the 22nd century.