Richard Pollman, a meteorologist for the National Weather Service in Detroit/Pontiac, gave us a talk on climate change and gardening. His specialty is providing forecasts and warnings for the protection of life and property. “Weather” is our daily precipitation/sunshine/temperature. Climate is the long-term trends, long-term averages. The greenhouse effect is a natural phenomenon which makes earth habitable, but humans have enhanced the amount of CO2 in the air which traps more heat. In 1960 there were 310 ppm of CO2 in the air: there are now 420 ppm. The average global temperature has increased 1 degree since 1900. The land and sea are both warming, and the sea ice is decreasing. Hot days are more common, and cold days are less so. There are more really wet days with fewer days of light rain. The poles are showing the majority of the changes.
Our weather patterns stay stationary for longer: thus the hurricane stayed over Houston for days and dropped 52” of rain in some places. Oppositely, droughts are prolonged. There are more record highs than record lows. The lakes moderate Michigan’s climate with warmer overnight lows. The frost-free growing season in the Midwest grew longer by 9 days between 1900 and 2000.
The climate is wetter in the north, especially in winter and spring, and dryer in the south. There are 37% more heavy rain events and 10% more rain.
Richard emphasized that the key messages are the following: climate change is real; it’s us; experts agree; it’s more bad than good; we can still fix it. Agricultural yields will decrease on average.
In Michigan our average temperature has increased 2 degrees, and extreme heat will become more common. Flooding will be more frequent due to increased precipitation in winter and spring. The effect on the water level in the Great Lakes is unclear: increased precipitation and evaporation may cancel each other out.
There are very clear criteria for severe thunderstorm warnings – winds over 58 mph and/or hail 1” or more in diameter, but Richard emphasized that every thunderstorm is dangerous due to lightning. The weather service sends out tornado warnings when there is turbulent vertical motion due to strong winds, and severe weather is imminent in a small area for 30-60 minutes. Tornado watches are declared when conditions are favorable for a large area for several hours. Weather.gov/Detroit is the local NWS website.
Every family should have a preparedness plan: under a stairwell in the basement or under heavy furniture with as many walls between you and the outside. A bike helmet is a useful head protection. Mobile home dwellers should seek shelter in nearby buildings or get in a ditch as a last resort. If you are trapped in a vehicle you should buckle up and stay away from windows as much as possible.
If there is lightning, don’t wait for the rain. Get out of the water and move away from others. The highest object will be the target, so don’t take shelter under a tree. A hard-topped vehicle is a suitable shelter. If the road is flooded, turn around because it is impossible to estimate how deep the water is. Unplug your major appliances, don’t take a shower and don’t use corded phones during a thunderstorm.
Citizens can help the weather service by taking a class on tornadoes and becoming a spotter or by reporting precipitation each day through CoCoRaHS. I have done the latter for several years now and find that my accurate rain records make me a better gardener.