A Skeptic's Guide to Global Warming

What makes the climate change?

Climate includes a forced part that is directly related to "external" factors like how much sunlight there is. If we know the change in forcing - such as the seasonal change from winter to summer or an ongoing increase in atmospheric CO2 - in principle we can predict the climate change.

Climate also includes an internal part that changes spontaneously. This is the same kind of process that generates turbulence in the wake of a car, creates the weather, and makes ocean currents meander and eddy (figure). There are theoretical limits to how far in advance internal changes can be predicted. Phenomena with such names as El Nino-Southern Oscillation and Atlantic Multidecadal Variability produce climate variations, but how large an effect they have on multi-year trends in global mean surface temperature is a subject of current research.

Sea surface temperature (colors) showing relatively warm water of the Gulf Stream off flowing offshore of the eastern US.

Strangely enough, it can be easier to predict things further in the future than closer. On January 1, we would have trouble predicting the change in temperature in Boston from January 1 to the 10th, because the answer will depend on unpredictable weather. However, we can make a more accurate 6 month prediction of the change from January average to July average because the change will be dominated by the large known change in local sunshine from winter to summer. Similarly, if we know that atmospheric composition will change a certain amount each year, we may be better at predicting the increase in 10-year average temperature from 100 years of accumulating chemical changes than in predicting the internally-driven ups and downs of temperature over the next 10 years.

Next: Is global warming caused by humans or nature?
Return to front page.

Last modified: 21 July 2018