The Greenhouse Effect. A little greenhouse effect is a good thing. Millions of years before humans arrived on the scene, carbon dioxide and other gases in the atmostphere started the natural greenhouse effect. It works like this: Solar energy that isn’t absorbed in the stratosphere or reflected back into space by clouds gets absorbed by the surface of the Earth, then radiated back out as infrared radiation—heat. But this heat doesn’t escape back out to space. Instead, it’s trapped by the water vapor, carbon dioxide, methane and other naturally occurring gases in the atmosphere. That’s why the Earth is such a cozy place to live. Without the natural greenhouse effect, says Dr. Fred Mackenzie, UH professor of oceanography and author of the global climate change textbook Our Changing Planet, the Earth would be a ball of ice with surface temperatures of minus 20 degrees Celsius.
So if the greenhouse effect is natural and good, what’s the problem? The problem, as Mackenzie explains it, is an enhanced greenhouse effect. Enhanced, that is, by human-produced greenhouse gases, namely the 6 billion tons of carbon dioxide dumped into the atmosphere every year as a by-product of burning fossil fuels, followed closely by CFCs, then methane and nitrous oxide, which are byproducts of agriculture. This enhanced greenhouse effect is what causes the global warming that everyone is talking about—warming above and beyond what the natural greenhouse effect produces. The argument is simple: If naturally occurring amounts of these gases trap just enough heat to keep us comfortable, billions more tons of these gases will trap even more heat. Maybe more than we can stand.
The question of the day, as Honoluluans break into sweat on even shortest walks outdoors, is, Are we seeing enhanced global warming already? For most scientists, the answer is a qualified Yes. Mackenzie is a contributor to the Intergovernmental Panel on Climate Change, a group of scientists and policymakers from 120 different nations dedicated to studying climate change. In December 1995, the IPCC announced that “the balance of evidence… suggests a discernible human influence on global climate.”
Coming from any other group of people, such a statement would sound like waffling. Coming from scientists, it’s nearly a shout. “Scientists are very conservative,” says Mackenzie. “We don’t like to alarm people. What the IPCC is saying is that there have been climate changes over the past 200 years that cannot be explained entirely by natural processes.”
In fact, the evidence seems irrefutable that man is warming up the planet. The concentration of CO2 in the atmosphere is now higher that it’s been in more that 160,000 years, and is 20 percent higher than it was just 200 years ago. One of the climate changes observed, and attributed to the added greenhouse gases, is that the mean global surface temperature has increased by 0.3 to 0.6 degrees Celsius since the late 1800s and half of this increase has occurred in just the past 40 years.
If population and energy use continue to grow as they have in the past, we will double the amount of carbon dioxide we produce by the year 2050, from 6 to 12 billion tons per year. Not surprisingly the IPCC projects that the Earth will get hotter—1.5 degrees to 4.5 degrees Celsius hotter over the next century in this scenario—and that we have ushered in an age of climate instability likely to cause “widespread economic, social and environmental dislocation over the next century.” This warming could have some serious consequences for Hawaii over the next 100 years:
Atlantis Submarines to replace The Bus? Sea levels could rise as much as 3 feet by the year 2100. That’s not enough to flood the streets of downtown Honolulu, but all our beaches as we know them, and beachfront roads and property, would all be affected. It might become harder to sell Hawaiian vacations if we have to erect sea walls where all the sand used to be. “Sea-level rise can have a number of negative impacts on tourism, ports and harbors, human settlements, and natural freshwater systems in coastal areas,” as one IPCC document puts it, in a nicely understated, scientific way.
The projected sea-level rise is not caused entirely by melting polar ice caps, as many people assume. Seawater itself actually expands when it warms. There is also a slight chance that the West Antarctic Ice Sheet could disintegrate in a warmer world, which would also significantly raise sea levels. Exactly what circumstances could bring this about aren’t known, but in a disturbing development, a 1,000-square-mile iceberg did break loose from the Larsen Ice Shelf a year ago—10 years earlier than predicted—while sections of three other ice shelves disintegrated into smaller pieces.