Kenneth Green, resident scholar at the American Enterprise Institute and author of the book Global Warming, Understanding the Debate, provided the following answers to global warming questions posed by a middle school student.
1. Do you believe that global warming is due to human activity? Why or why not?
I do believe that some of the warming observed in the twentieth century was due to humanity’s emissions of greenhouse gases into the atmosphere as a result of burning fossil fuels, industrial chemicals, and intensive livestock cultivation. The reason I believe this is that there is a good scientific theory that suggests certain kinds of gases (called greenhouse gases) will trap heat in the atmosphere, leading to predictable changes in the temperature patterns on Earth.
The theory of the “greenhouse effect” suggests that putting additional greenhouse gases into the air would result in additional heat being trapped in the atmosphere mostly in areas where the air holds little water vapor to obscure the “greenhouse signal.” Other sources of warming, like increased sunshine or more heat coming from the center of the Earth or being brought to the surface by slow-moving ocean currents, would not necessarily be expected to show that pattern of warming.
When scientists look at the data that are available, the pattern of warming they find for the last 50 years agrees better with the greenhouse theory than with a non-greenhouse theory. That is, what has been observed is an increase in temperatures over parts of the Earth where the air holds little water vapor.
Exactly how much of the observed warming is due to the greenhouse gases themselves is unclear because nature is complicated and there are other climate factors that could amplify or cancel out the impact of adding greenhouse gases to the atmosphere. And all of our observations take place against a background of a chaotic climate and very limited data, so a warming could be hidden by a cooling of non-human origins, or it could be made to seem worse by a coincidental warming of non-human origin.
It’s even possible that there could be some climate cycle we know nothing about that is fooling everyone, and the tools of science are just not good enough to have ruled that out. But in my personal opinion as a person who studied environmental science, it’s more likely we’ve seen some global warming due to human activity, and aren’t being fooled by mysterious forces.
2. What is your opinion on the theory that the Earth goes through warming and cooling periods and that we are just in a warming period right now?
Well, that’s not only a theory, that’s something humanity has a long historical record of. The Earth has long-term climate cycles that result from our irregular orbit around the sun (called Milankovich cycles), as well as from cycles of greater and lesser solar activity.
Based on what scientists understand of those cycles, we are indeed in a warming period right now, having been in a “little ice age” until the early 1800s. But that’s not to say you couldn’t have both a natural warming period and added greenhouse warming.
3. Do you believe in the greenhouse effect? Why or why not?
I believe in the greenhouse effect because it is based on plausible, testable theories that have, in fact, been tested in laboratories as well as through observations of the Earth and other planets. It is well-understood that without heat-trapping greenhouse gases in our atmosphere, the Earth would be much colder–probably too cold for life as we know it to exist.
But again, the greenhouse effect is only one “layer” in the way people think about the climate. Other things that happen both on the Earth and in space can increase or decrease the greenhouse effect.
Here’s an analogy for you: In your bathroom, you have heat from your home heating, from your light bulbs, and from your blow-dryer if it’s running. You also have cooling from cold water running through the pipes and carrying heat away, not to mention evaporation from standing sources of water, and maybe a draft from your window.
The overall temperature of the room is a combination of all those things, including the heat put out by your own body, and it would change as the seasons changed outside the house. The Earth is a bit like that, there are many things going on at once, including the greenhouse effect, all of which add up to create the thing we experience as weather and discuss in long-term blocks as “the climate.”
4. What is your opinion on the theory of sunspots causing temperature change on Earth?
As I’m not an astrophysicist, I will admit that I have not studied the detailed physics of how sunspot activity affects the amount of radiation that is taken in by the Earth from space (either directly or by way of the Sun’s impact on cosmic rays, which are another source of energy that reaches the Earth from space). So if you want more information on this, you should talk to someone who’s spent more time studying the sun.
But as I do know that sunspots indicate areas of more intense solar energy output, I would think this theory is probably true also.
Of course, the fact that we have multiple sources of potential heating and cooling does not really mean that any one of them is right or wrong. You could have any combination of heating and cooling forces going on at any given time on the Earth, as I mentioned above.
Thank you for taking the time to read this email. I look forward to hearing your response.
I wrote a book on this for middle-school students that you might find in your library, Kevin. The name of the book is Global Warming, Understanding the Debate. It was published in 2002 and is a little out of date now, but the basic science has changed very little in six years, and most people tell me they still find it useful.
Good luck with your studies!
Kenneth P. Green, D.Env.
Kenneth Green, D.Env. can be reached at [email protected].