For years debate has raged over the reality of global warming. On one side are most scientists (and a lot of politicians) who make predictions that global warming will cause the earth's mean annual temperature to rise by 2-3° C and sea level to rise by about a meter in response to rising levels of CO2 in the earth's atmosphere. These predictions are based on principles of physics and atmospheric chemistry. On the other side are a minority of scientists (and a lot of politicians) who question global warming science and doubt the predictions that the earth will warm by 2-3° C and sea level will rise by a meter over the next 80 years.
But there is a third side to this argument that is rarely heard but brings an important perspective to the debate. There are a small number of scientists who not only support the idea of global warming, but believe that the earth will become far hotter then is generally believed. How much hotter??---some scientists predict the mean annual temperature of the earth will be as much as 16°C (29° F) hotter then present by the year 2100.
Since the earth has already warmed by about 1° C since 1850 in response to CO2 emissions, lets just stipulate that global warming is happening and go on to the next logical step which is to review the widely varying predictions of how much global warming we will be seeing because of CO2 emissions. Why do some scientists believe global warming in the 21st century will be about 10 times greater then the conventional estimates of 2-3°C?
There are two ways to make predictions in Earth Science. One way is to develop extremely complex numerical models that try to capture all of the relevant chemical and physical processes involved, and then use the numerical model to evaluate what happens as various parameters are changed. For global warming, computer models designed to predict the weather patterns of the Earth are tweaked and run to simulate the earth's climate with higher levels of CO2 in the atmosphere. These very complex models typically predict warming of 2-3°C. Unfortuntely, the earth's climate system is so complex that even the largest computer model must make innumerable assumptions and simplifications so no computer model actually captures all the details of how earth's climate actually works.
The other way to make predictions in the earth sciences is by using numerical regressions. This kind of modeling involves making repeat measurements of a process and the result and then extrapolating to predict what will happen if the process becomes more intense. For instance, if you measure wind speed and ocean wave heights over a range of wind speeds you can develop a regression equation that will predict the wave height for any wind speed, even including greater windspeeds then you have actually observed. Using paleoclimate data, regression curves have been developed that show how hot the earth was in the past at varying levels of atmospheric CO2. The last time the earth had CO2 levels of ca. 1000 ppm comparable to those we will attain by the year 2100 was 30-100 million years ago, when tropical conditions reached all the way to the poles and the earth was about 16° C (29°F warmer then now).
Both the numerical models and the regression climate models have obvious flaws. The numerical models can never accurately model every aspects of the earth's climate system decades into the future, while regression models are so oversimplified that they don't include factors other then CO2 levels that may've amplified prehistoric temperatures to much higher levels then we may actually see by the year 2100. But both kinds of models have some kind of inherent validity, and the extreme discordance between the these two kinds of modeling should be ringing alarm bells that global warming may turn out to be significantly more intense then most scientists now believe.
So far there has been too much heat and not enough light from the debate over the global climate problem. In the future there will be too much heat....period.
No comments:
Post a Comment