Climate change is expected to affect Mobile and surrounding region by increasing average, seasonal, and extreme temperatures, as well as shifting precipitation patterns between seasons and over time.
Over the past 50 years, no significant and consistent trend in annual average temperature was observed across all five weather stations. Significant cooling trends in minimum temperature in April, September, and the fall season, and increases in the number of consecutive days over 95 and 100oF per year, was observed at four out of the five weather stations.
In the future, annual average temperatures are expected to warm by approximately the same amount as warm temperature extremes, whereas cold temperature extremes are projected to warm to a slightly lesser degree. In other words, the magnitude of changes in cold temperatures, including the average temperature for winter and fall months, is expected to be slightly smaller than changes in average temperatures, while the magnitude of changes in hot temperatures, including the average temperatures of warmer summer months, may be slightly greater than the change in average temperatures. Relatively large increases are expected in the number of days per year over a given high temperature threshold (e.g., 95 or 100oF), as well as in the number of consecutive days over these thresholds.
For all temperature-related indices, there is a significant difference between the changes expected under higher as compared to lower emissions by end-of-century. For many but not all of these indices, there is also a difference by mid-century. Inter-scenario differences are most pronounced for projected changes in warm and hot temperatures, and less pronounced for changes in cold temperatures.
No historical changes were observed in average annual precipitation over the last 50 years, and little change is expected in the future. There is some indication that seasonal precipitation may increase during winter and fall, particularly over the near-term to mid-century. This is balanced by consistent projections of little change to decreases in summer precipitation. However, all seasonal changes are on the order of no more than 10% relative to climatological precipitation during the period 1980-2009.
The most consistent and significant trends observed in the historical data are increases in the exceedence thresholds for accumulated precipitation. In the future, additional slight increases are projected in the amount of rainfall occurring in 24h, 48h, and 96h, as well as in maximum 3-day precipitation accumulations. However, these changes are not significantly different between scenarios, nor even across different time periods, suggesting that whatever mechanism may be driving these changes may not be overly sensitive to the magnitude of future global change.
There is some indication of a greater trend towards drying under higher as compared to lower emission scenarios, consistent with projected changes for the greater Southeast region. In general, however, inter-scenario differences tend to be insignificant or well within the range of uncertainty for most precipitation-related indicators.
Analysis of the bias in simulated maximum and minimum temperatures and precipitation do not reveal any particular global climate model, or sub-set of models, that consistently perform better than others in simulating observed climate over this region. Hence, using the complete multi-model mean coupled with the range continues to be the most reliable way to incorporate model or scientific uncertainty into any impact analyses.
The projections described here underline the value in preparing to adapt to the changes that cannot be avoided. Due to complex interactions between temperature and the different factors that affect precipitation in the Gulf Coast region, there is not a clear correlation between future greenhouse gas emissions and precipitation change. The effects documented in this report suggest that reducing emissions would reduce the magnitude of temperature changes, but it is not clear what would be the impact (if any) of reducing emissions on precipitation-related effects.