Questions from readers

As part of this series, The N&O has asked Dr. Douglas J. Crawford-Brown of the University of North Carolina at Chapel Hill to answer your questions. Crawford-Brown is director of UNC's Institute for the Environment and a professor in the departments of environmental sciences and engineering, and public policy.

If you have more questions, you can send them to globalwarming@newsobserver.com. Please provide your name, the town or city where you live and a phone number.

Q: We own property at South Topsail Island and in Elizabeth City. What impact will sea level rise have on these locations in the future?

Jonathan Smith

A: I doubt you will see any dramatic changes over the next 10 years unless storm frequency and intensity increase (and that is another prediction of climate change). It is more likely that any significant sea level rise causing you to abandon a site would be in the latter half of this century. But we just don't know how rapidly sea level will rise, because it depends on how quickly Antarctic ice shelves, Greenland, etc., begin to break up. If they do break up in our lifetime, the coastal towns are in for some serious changes, including loss of the barrier islands.

Q: Has the Earth ever warmed up before?

Robert M. Upton

A: The Earth has gone through many cycles of warming and cooling over millions (and even billions) of years. Our orbit gets closer to and then farther from the sun. Energy emitted from the sun gets more intense and then less intense. There also are periods when there are more greenhouse gases in the atmosphere, due to things like volcanoes that can release gases from inside the Earth. So any current climate change sits on top of these natural cycles. It is not that humans are creating a new KIND of warming, it is that we are speeding up this natural process at precisely a time when we have a much larger population of people to be affected.

Q: How much carbon does an automobile that averages 23 mpg emit during a round-trip commute of 20 miles?

Marvin Woll

A: Your 20-mile trip at 23 mpg would consume about a gallon of gas (actually, 87 percent of a gallon). One gallon of gas releases about 20 pounds of carbon dioxide (since the carbon in the gas joins with oxygen to make the carbon dioxide). So your trip of 20 miles will release about 17 pounds of carbon dioxide each day.

Q: Can you please tell me the effect that the Milankovich Cycles have on global warming?

Chip Atchison

Raleigh

A: The Milankovich Cycles describe how the earth moves, and tilts, during its orbit around the sun. This motion causes more or less sunlight to reach the earth, over about a 100,000 year cycle. It is what causes the earth to go into ice ages periodically. It also causes us to go into warmer periods when we are closer to the sun and have the right tilt. So it is part of a natural cycle of warming and cooling, with our own greenhouse gases adding to the warming part of that cycle.

Q: Mini Global Warming: I read there was already a warming in the Middle Ages tucked in the middle of a couple cold ages. Why is that not talked about in Gore's video and included in the whole picture?

Duane Hansen

Cary

A: It is discussed at length in the scientific literature. It led to the growth of the population of Europe because crops were much easier to grow and harvest. So warming is not always a bad thing! The difference here is that the degree of warming during that period (which was in the early Middle Ages) was significantly smaller than the warming we are expecting from the current greenhouse gas warming. My answer to such questions like this (and it is a good question) is that the earth always has and always will go through cycles of hot and cold. What we are doing as a society is changing when those cycles hit and the intensity of the changes.