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20. What about storms and other extreme weather events?

The factors governing tropical storms are different from those governing mid-latitude storms and need to be considered separately.

One of the conditions for formation of typhoons or hurricanes today is a sea surface temperature of 26°C (79°F) or greater. With higher global average surface temperature, the area of sea with this temperature should be larger. Thus the number of hurricanes could increase. However, air pressure, humidity, and a number of other conditions also govern the creation and propagation of tropical cyclones. The critical temperature for their creation may increase as climate changes these other factors. There is no consistent indication whether tropical storms will increase in number or intensity as climate changes. Nor is there any evidence of change over the past several decades.

Mid-latitude storms are driven by equator-to-pole temperature contrast. In a warmer world, this contrast will probably weaken since surface temperatures in high latitudes are projected to increase more than at the equator (at least in the northern hemisphere). Higher in the atmosphere, however, the temperature contrast strengthens. Increased atmospheric water vapor could also supply extra energy to storm development. We do not currently know which of these factors would be more important and how mid-latitude storms would change in frequency, intensity, or location.

21. Can projections be improved?

Better computers alone will not solve the problems associated with positive and negative feedbacks. Better understanding of atmospheric physics and chemistry and better mathematical descriptions of relevant mechanisms in the models are also needed, as are data to validate models and their subcomponents. Significant improvements may require decades.

22. Is it possible to avoid the projected warming?

It is possible only at great expense or by incurring risks not now understood, unless the earth is itself self-correcting. Continued increases in atmospheric concentrations of greenhouse gases would probably result in additional global warming. Avoiding all future warming either would be very costly (if we significantly reduce atmospheric concentrations of greenhouse gases) or potentially very risk (if we use climate engineering). However, a comprehensive action program could slow or reduce the onset of greenhouse warming.