Predictions

Having established that there has been an increase in mean global temperature over the last century, and that this increase has been correlated with enhanched emissions of greenhouse gases, the question now is: can we predict whether the increase of concentration of greenhouse gases will bring about global climatic changes?

Because of the inherent complexity of the problem, powerful computers need to be used to run programs modeling the atmosphere-ocean system. In a typical model, the globe is divided in cubes, or cells, 500 Km on the side and several hundred meters in height. Each cell communicates with its neighbors; it can exchange radiative energy, wind, water, etc. Equations relating the interactions of these elements are solved at a particular moment in time, and the process is repeated to give projections of climate at future times. Because these programs are very complex and slow to run, the grid is ratehr coarse and simplifications in the description of the interactions are introduced.

To check that the particular model chosen is a sound one, scientists use historic data on temperatures, gas composition, etc. to predict the climate at present time. If the prediction is off mark, changes in the models are made.

Predictions vary depending on the sophistication of the model and on certain assumptions which are made.

  • Once begun, the warming, and its consequences, will last for a long time (hundred(s) of years), since the greenhouse gases have a long lifetime in the atmosphere.
  • Models predict a warming between 1.5 and 3 C by the ned of the next century.
  • Higher temperatures will be over land than over the oceans.
  • Greater variablility in the local whether is expected (more frequent droughts, floods, etc.).
  • Sea levels will rise due to melting of glaciers by 15 to 95 cm.

    • The greatest uncertainties in these predictions come from:

  • Insufficient data.
  • Limited understanding of role of clouds and the oceans
  • Limited knowledge of coupling of atmosphere/ocean.
    • This page was produced by Gianfranco Vidali