Ask A Scientist© Environmental Science Archive

Author:     pam
Text:       What causes global warming and the hole in the ozone layer?

Response #: 1 of 11
Author:     Eric Dallman
Text:       Pam, such a seemingly simple questions require unfortunately 
elaborate answers. Since you have asked two questions, I will split my answer 
into two sections: *** What is causing global warming and what can we do to 
stop it? Well, first of all, it is not exactly clear if there is indeed global 
warming at all. The phenomenon of global warming was discovered when data from 
various weather stations was compared from year to year. There seemed to be a 
trend of increasing temperatures at most of the data collection points. This 
indicated that the planet was warming at an alarming rate. If you think about 
it, a rise in temperature of a few degrees or so at 50 or 100 points on the 
earth does not mean that the earth is getting hotter. It means that the data 
points are getting hotter. Most of the original data was collected in the 
forties and fifties at locations in or adjacent to urban areas. As time went 
on the areas of data collection became more urbanized. Logically, more people 
and buildings produce more heat. Data collection at remote sites that did not 
become urbanized did not indicate any warming at all. However, when all the 
data was averaged, a very frightening picture emerged. The planet seemed 
doomed. Because of the uncertainty of the original data (due to changes in 
population at the data collection points), many new weather stations were set 
up and an international committee was established to study global warming.



Unfortunately, it takes many years of data collection before a trend can be 
established. The last reports I have read have disproved the very existence of 
global warming, showing instead that URBAN warming (an increase in temperature 
in areas of increasing population) does occur. If you think about it, a 
weather station set up outside Chicago at an airport by some corn fields over 
40 years ago cannot compare to the same station at what is now O'Hare airport. 
Most weather stations set up in remote areas that still remain in remote areas 
show no significant increase in average annual temperature. Well, theories 
abounded about global warming, yet the fact remained that the data did indeed 
show a trend of temperature increase, hence the formation of various 
investigative groups. Now that I have given more than enough information 
biased toward the lack of global warming, I will address your question. Global 
warming is thought to occur by the green house effect. Light radiates from the 
in many different wavelengths or colors. Light of very short wavelength (i.e., 
ultraviolet) passes through the earth's atmosphere, stopped only partially by 
the ozone layer, and is reflected back into space. As it is reflected, the 
light loses some of its energy (imagine light waves as a ball bouncing with 
less force than you threw it after it hits the ground) and does not return 
with as much energy as when it came in. Gases within the earth's atmosphere 
(most notably carbon dioxide or C02) trap the reflected light (now having less 
energy) and does not it escape into space. The low energy waves are reflected 
back toward earth, becoming heat. A simple experiment to demonstrate this is 
to leave your car parked in the sun on a summer day. Light enters the windows 
and is reflected off the seats, etc. The light waves lose some of their energy 
as they are reflected and cannot escape past the same glass widows they came 
in through. Do not leave your dog in the car if you try this, it can get very 
hot inside the car. Not all ultraviolet light gets to the earth. A large 
portion is stopped by the ozone layer before it has a chance to reach us at 
all. A hole in the ozone layer would let more ultraviolet light through, 
causing more energy (energy) to reach the earth's surface. This may contribute 
to global warming as the ultraviolet energy reaching the earth is ultimately 
converted to heat after it is reflected. Ozone layer holes (depletion) are 
addressed in the answer to your second question. Increasing the amount of C02 
in the atmosphere will increase the amount of reflected energy capture and 
lead to a temperature increase. Where does the C02 come from? Two things 
really: Industry and destruction of trees (in rain forests, for example). 
Industries typically burn things which produce C02 directly. Trees use up C02. 
Cutting them down reduces the amount of C02 "sucked up" from the atmosphere 
and leads to an overall increase. If global warming is indeed a fact (and 
though it has not been proven, it also cannot be shown not to occur), it could 
pos. possibly be prevented by reducing the amount of C02 put into the 
atmosphere from burning hydrocarbons and by stopping the destruction of the 
rain forests. *** What is causing the hole in the ozone layer? Your second 
question is, once again, based somewhat on speculation. You see, the first 
time anyone actually looked at the structure of the ozone layer they 
discovered a hole. If that hole had always been there is a matter of debate. 
Some people believe that the ozone layer has always had a hole in it and that 
the hole was only recently observed because studies of the ozone layer 
structure were not given high priority. Without giving you the same lengthy 
explanation I gave the first question, the ozone layer hole is being caused 
(theoretically) by the release of chlorinated fluorocarbons into the 
atmosphere. Chlorinated Fluorocarbons (CFCs, from now on) are chemicals 
typically used in air conditioners, refrigerators, and as propellants in 
aerosol cans. These compounds rise into the atmosphere and, when stuck by high 
energy Light waves (such as ultraviolet light), form highly reactive compounds 
which destroy ozone. You will remember from the last question that ozone 
reflects harmful ultraviolet rays back into space before they reach earth. If 
more ultraviolet light reaches the earth (say from a loss of ozone) the earth 
stands a greater chance of warming up. The USA and several other countries 
have recently taken a very strong stance against ozone depleting agents such
as CFCs (there are other ozone depleting substances, CFCs are the most widely 
used). The biggest contributor of ozone depleting CFCs, however, remains car 
air conditioning units. These things leak by nature and most cars made within 
the last 10 years have them. To give fair time to the other side of the story, 
it cannot be proven if the hole in the ozone layer was always there or if it 
always there but only recently discovered. Also, the supposed "hole" is at the 
polar regions of the earth where it would be expected that the ozone would be 
thin (due to such things as the earth's rotation). If industrial chemicals 
(i.e., CFCs) which are not found in nature really contributed to an ozone 
layer hole, would not the hole be found over the areas where such chemicals 
are released? Though hypothetically CFCs get into the upper atmosphere and 
destroy ozone, there is not a clear cut model that can show how or why they 
only reach the polar regions. ******* CONCLUSION ******** The crux of the 
matter is that in the case of both your questions, much more research is 
needed before a definitive answer is had. Given the magnitude of the situation 
of either global warming or an ozone layer depletion, the possibilities of 
neither should be dismissed.

Response #: 2 of 11
Author:     Mark Fernau
Text:       Hi! I am an atmospheric scientist. I think that Eric Dallman's 
explanations for the ozone hole and global warming are good as a start, but I 
think he is overly skeptical as to his assessment of their importance. It is 
true that the ozone has only been measured since the mid-70's so we do not 
know historical conditions but the British who first discovered it showed a 
steady increase in the hole with it first showing up only after several years 
of measurement. Also, this year's hole was the largest since measurements 
began. The reason it is found only at the pole and not at the source region 
(some measurements have shown decreases at lower latitudes) is that the unique 
weather conditions necessary to trigger ozone loss are only found at the pole, 
namely extreme cold and a closed wind pattern that prevents the hole from 
breaking up. Further, whether it is real or not is a moot point, since the 
world, through the Montreal Protocol and later revisions, has agreed to stop 
emitting CFCs and is switching to substitutes. Eric Dallman is correct to say 
that measurements cannot prove that global warming is already occurring. On 
the other hand, they cannot prove that it is not occurring. The world may have 
warmed about 1 degree F, sea level has risen a little, and all over the world, 
glaciers are retreating. This combined with the scientific certainty that the 
greenhouse gases do trap heat (proved in lab) and that the greenhouse gases 
are increasing in the atmosphere (from human sources) mean that even if the 
gun is not smoking, it is loaded and cocked, to use a metaphor. The question 
of interest is not whether the increase in greenhouse gases will change 
climate, but by how much and how quickly, and will any other natural phenomena 
counteract the warming? Unfortunately, scientists can not answer those 
questions with any accuracy yet, at least on the regional scale that is of use 
to government decision makers. So, while atmospheric and other scientists try 
to reduce uncertainty as to climate change and its effects on plants, rivers, 
oceans, forests, etc. and economists try to figure out how much it will cost 
to fight climate change, the policy maker (Congress) must either do nothing at 
the risk of making it harder and more expensive (and maybe impossible) to stop 
climate change, or make a value judgment as to how much insurance he wants to 
purchase against the chance of catastrophic global warming. This is a very 
complicated issue, both the science and the policy, and I cannot do it justice 
here, but send me a message if you are interested in further discussion.



Response #: 3 of 11
Author:     Don Libby
Text:       Eric Dallman and Mark Fernau gave thorough replies so I will be 
brief. We know that carbon dioxide in the atmosphere is accumulating, and we 
know that global temperatures are rising, but we are not sure how the two may 
be related. It is estimated that humans contribute about 10 percent of the 
annual C02 emission, the rest coming from natural sources. There is not much 
we can do to stop global warming, we will simply have to learn to live with 
it. However, there is plenty we can do to stop air pollution, and air 
pollution is a more immediate threat to human health. Please read "50 Simple 
Things You Can Do To Save The Earth" by the earth works group, published by 
the Earth Works Press of Berkeley, CA. Personally, I do not worry about global 
warming because the climate has been changing constantly since long before 
humans arrived - this is just more of the same.

Response #: 4 of 11
Author:     Mark Fernau
Text:       Reply to Don Libby. It may be true that only 10~ of the annual 
carbon emissions come from humans, but if one looks at the amount by which the 
atmospheric carbon loading is INCREASING every year, people who study the 
carbon cycle feel that this increase is almost entirely due to humans. Your 
que sera attitude toward global warming is certainly a valid response but I am 
not sure people who live in Bangladesh or the Pacific Islands who are in 
danger of being inundated or the corn farmers or sugar maple producers whose 
livelihood could migrate north or become extinct would share your lack of 
concern. Finally, ground-level air and water pollution are certainly a more 
immediate threat to human health and certainly take priority in most policy-
maker's minds. For that matter, at this time just trying to improve the 
economy or provide food, shelter, and health services are taking the front 
seat over any environmental concerns for eastern Europe, Africa, South 
America, etc. Our biggest challenge as developed countries is to get these 
other countries over this hump in a way that does not repeat our mistakes and 
allows them the LUXURY to worry about the environmental effects of their 
actions to better themselves.

Response #: 5 of 11
Author:     Mark Fernau
Text:       Note to students from Mark Fernau. After reading Eric Dallman's 
explanation of the greenhouse effect more closely, I believe he has made a 
common error. He talks about ultraviolet radiation being reflected by the 
Earth's surface and then trapped, leading to heating. What actually happens is 
that the W light is ABSORBED by the Earth's surface, and then RADIATED back to 
space as INFRARED radiation by the Earth. It is IR and not W because the 
Earth's surface is much cooler than the sun. Some of the IR radiation that is 
headed to space is trapped by the greenhouse gases, leading to a warmer Earth. 
This is the greenhouse effect. What we are worried about today is the increase 
in this greenhouse effect caused by human emissions of greenhouse gases, not 
the greenhouse effect itself. If there were no greenhouse effect at all, the 
average temperature of the Earth would be 0 degrees Fahrenheit and life as we 
know it might not exist at all! Note: W radiation is the kind that comes from 
a "blacklight". IR radiation is the kind that you feel as heat from a warming 
light at McDonald's or around a campfire.



Response #: 6 of 11
Author:     Mark Fernau
Text:       I just realized that the second part of Pam's question about 
global warming was what can we do about it...Don Libby' book sounds like a 
start (50 things...). Basically, the answer is that all the things that are 
good to save energy and reduce air pollution and stop acid rain are also good 
for the greenhouse effect. These are conservation measures such as driving 
less and slower, keeping the house cooler/warmer, recycling, insulating your 
house, using renewable energy, etc. Philosophically, this means altering our 
western consumer-oriented life style, something that is not easy to do, even 
if you are idealistically interested in "saving the environment." Beyond that, 
the average person can write letters to politicians and industries or practice 
boycotts/selective purchasing and then letting the companies know about and 
why you did it. The real problem that makes global warming such a tough 
question is that we could stop every auto and turn off every factory and power 
plant in America and it will have a relatively minor effect on the amount of 
climate change predicted by scientific climate computer models. As long as 
China and other developing countries choose to use their abundant coal and 
wood resources to better themselves, just like we did in the past, then our 
actions can not solve the problem. As I said in my previous note, the trick is 
to help these countries to avoid our mistakes, through technology sharing or 
financial assistance.

Response #: 7 of 11
Author:     Robert Topper
Text:       I would like to point out that there seems to be evidence for some 
very interesting chemistry occurring in the polar regions which may account 
for the low concentrations of ozone there.

Response #: 8 of 11
Author:     Don Libby
Text:       Mark Fernau, I am sure folks in Bangladesh do worry about floods, 
as they have been living with them for centuries. I am sure farmers are 
worried about droughts, as they have been living with them for centuries. So 
what if climate change redraws the political boundaries and redistributes 
wealth? Is it really better if political change is forced by deliberate social 
action rather than by nature or by the non-deliberate side effects of the 
"development" that you covet? Do we really need the threat of global 
environmental catastrophe in order to redistribute the benefits of development 
more equitably to all the peoples of earth? Could not we just do it to be nice 
for a change?

Response #: 9 of 11
Author:     Mark Fernau
Text:       Don Libby, I do not believe I said that I "covet" development, if 
you please. I must admit that I enjoy my dishwasher and second car even as I 
know I may be changing climate, polluting the atmosphere, and depleting the 
resources of future generations . . . seriously, though, I find your reply 
confusing. You denigrate development at the same time that you want to 
redistribute it equitably . . I do not think it is too much to ask to have a 
refrigerator, reliable water supply, space heating, and a reliable food 
supply. The trick is to acquire these things without the "mistakes" that the 
developed countries have made re the environment. Also, I just do not agree 
with your cavalier attitude toward climate change and its effects on 
individual humans. Yes, society will adapt but that does not mean there will 
not be a lot of microscale suffering. If a citizen of Bangladesh chances of 
drowning can be changed from 1 in 5 say, to 1 in 100 or less by society's 
acts, is that worthwhile as a goal? I think so.



Response #: 10 of 11
Author:      Don Libby
Text:        Dear Mark Fernau, I did not mean to take this discussion in the 
direction of an ugly emotionally charged squabble, and I apologize for my 
misleading step in that direction when I said you "covet" development. What I 
meant was that we often take the ideas of "development," "progress," and 
"economic growth" for granted, as articles of faith rather than as problematic 
goals to which we aspire. I am for development, although I prefer a variety 
called "sustainable development", which emphasizes the importance of a 
continuing, long term relationship between economic systems and the 
environment. Gifford Pinchot, founder of the Forest Services once said that to 
the utilitarian maxim that "the greatest good for the greatest number shall be 
the measure of right and wrong", he would add the phrase "the greatest good 
for the greatest number for the longest time", since a good that accumulates 
over time is greater than one that does not. Let me make my position on 
climate change clear. First, because of uncertainty in the direction, 
magnitude, and rate of change in the global climate, and because of 
uncertainty in the role of anthropogenic gases in the global climate, and 
because of the small proportion of total emissions contributed by human 
activity, it is not rational to believe we can control the climate. Therefore 
we are forced to consider how social systems can be made more adaptable and 
resilient IF the climate changes or if sea levels rise. To me, that is the 
central question raised by climate change, and one that is seldom addressed. I 
think that opening global markets to move capital and labor more efficiently 
would be a big help in this regard. Anything that improves international trust 
and trade will help if big change is coming.

Response #: 11 of 11
Author:     Mark Fernau
Subject:    Global Warming/Ozone Layer
Text:       OK, I see your point, Don Libby. But I still disagree with one 
point that you make. I agree that humans may have difficulty with "controlling 
the climate" because of the uncertainties that you list and also because I 
just do not think the world will agree on any course of action any time soon, 
BUT you are missing the mark when you say that human activity only contributes 
a small portion of the emissions of greenhouse gases. We contribute just about 
the ENTIRE portion of those emissions that are making the "baseline" 
concentration increase, as Keeling's data and others clearly show is 
happening. It is this increase in the ~airborne fraction" of emissions that 
has got everyone in an uproar. I also think Gro Bruntland's sustainable 
development is laudable approach. I just hope the world can figure out how to 
make it a reality.