The planet could warm more than 20 degrees Fahrenheit by 2100, sea levels might be nine inches higher and summer sea ice in the Arctic would disappear.
The 2013 report of Intergovernmental Panel on Climate Change (IPCC) projects these results for a “worst-case” emissions scenario.
Forecasts like this are frightening. Many environmental organizations believe they are grounds to stop burning fossil fuels. Some go further. Greenpeace suggests on their website that “oil, gas and coal company directors who mislead the public by funding climate denialism and stopping action on climate change” should be personally liable for damages. This sounds like a crisis.
Before you join a survivalist colony, consider the operative word in the prediction: “could.” Different IPCC models project a 5.4 degree Fahrenheit rise by 2100, with sea levels a modest 2.6 inches higher than today—for the same emissions scenario. That is less scary, but scientists do not know which is right. Forecasting is an uncertain business.
It is possible to check the IPCC forecasts by comparing predictions from 1990, 1995, 2001 and 2007 with actual temperatures over the last decade or so. All four predicted a small global temperature rise—anywhere between one-tenth and one-quarter of a degree Celsius. This was the verdict of the best scientific minds, using state of the art computer modeling informed by space age data—but the actual trend has been practically flat since 1998.
Conservative groups like the Heartland Institute point to this hiatus to assert, “global warming…is not a crisis” and call for people to “oppose global warming alarmism.” They believe the models are untrustworthy. Certainly, model predictions are not as reliable as scientists may wish.
The models missed the hiatus because of “internal variability, with possible contributions from forcing error,” according to the 2013 IPCC report. Internal variability means short-term natural cooling possibly canceled the expected warming to produce a temporary flat trend. The models were not sophisticated enough to follow decade-scale fluctuations. This interpretation means long-term predictions like the one for 2100 would still be reliable.
In contrast, “forcing error”means the models could be wrong about some climate variables. For example, rising temperature means more evaporation, which could produce cloudy skies. Clouds cool the planet by reflecting sunlight, but warm the planet by trapping heat below them, so the net effect might go either way. If models are wrong about such effects, their long-term predictions are less reliable.
Deciding how dangerous global warming is and how far people should go in trying to stop it is not an absolute science question, but it should be informed by science. The greenhouse effect is well established in physics and dictates that if CO2 keeps increasing the temperature will rise. However, the specifics of when and how much are too complex for perfect prediction. Too often, each side of the debate cites a few suggestive facts and trumpets an opinion. As college students, we are educated people who should go beyond the partisan argument, examine the facts and make our own judgment.
Climate change column: part 2 click here
Scientists from the Intergovernmental Panel on Climate Change predict a wide range of possible future temperatures. In the worst-case emissions scenario (red line and shading), the planet could warm more than 20 degrees Fahrenheit by 2100.
