Research Results
Storms in the Future: Changes in Intensity, Cloudiness, Rainfall and Economic Costs
Title | Introduction | Methods | Results 1 | Results 2 | Results 3 | Discussion
Results, Part 1
Team 1: Can warm and cold years of the past be used as proxies for future climate change?
The average storm frequency distribution of five "coolest" years was subtracted from that of the five "warmest" years. The resulting difference appears in Figure 1. The red areas indicate where storms are more likely to occur in the warmer years, while the blue areas show where storms are less likely to occur in the warmer years. Examining these differences reveals a reduction in the number of storms over the central and eastern United States regions during the "warmer" years. There is also a northward shift in the frequency of storm tracks off the eastern coast of North America and in the northern Atlantic Ocean and extending into Europe during the "warm" years. We may expect a decrease in the frequency of storms over the central United States in the future as well as a northward shift of the storm tracks. This could in part be due to a northward shift of the jet stream and a decrease in its intensity. The same contrast for the most extreme years generated a comparable prevalence for the northward shift and regional decreases (Figure 2).
Figure 1: Difference in Storm Frequencies for the Five Warmest Winters - the Five Coolest Winters
Figure 2: Difference in Storm Frequencies for the Warmest - the Coolest Winter.
A similar operation was done with the storm frequencies of the control and CO2 doubled runs of the GISS GCM. Subtracting the frequencies of the control run from those of the CO2 doubled run resulted in identical trends as to the regional changes in storm activity, with a much less pronounced suggestion of decreases over the continental United States (Figure 3). A comparison of similarly made differences for the average intensity and maximum intensity produced noisy, inconclusive results for all cases.
Figure 3: Difference in Storm Frequencies in the GCM, CO2 Doubled Conditions - Control
To further examine this northward shift and maintain objectivity, trends in the number of mid-latitudinal storms and high-latitudinal storms were observed. These plots show a decrease in the number of mid-latitudinal storms and an increase in the number of high-latitudinal storms, furthering evidence that the tracks of the storms will move northward if global warming continues (Figures 4 & 5).
Figure 4:Total Number of Northern Hemisphere Midlatitude Storms, January 1961 - 1998
Figure 5: Total Number of Northern Hemisphere High-latitude Storms, January 1961 - 1998.
Given this repeated trend, correlations were calculated for the North Atlantic Oscillation (NAO) Index and storm frequency and storm intensity. The only significant relationship is, again, found between frequency and the NAO (Figure 6). This correlation is contrary to the usual implications of the NAO. The positive phase of the NAO is usually connected with an increase in storms over the North Atlantic, while Figure 6 shows an increase in the number of storms over the midlatitudes with the negative phase of the NAO.
Figure 6: Number of Midlatitude Storms vs. NAO Index, January 1961 - 1998. Correlation Coefficient = -0.52 (>99% Significance)
Title | Introduction | Methods | Results 1 | Results 2 | Results 3 | Discussion
