Contributed by Bill Krasean
If computer models of changing climate are accurate — and they get better all the time — Michigan’s weather in less than a century may be similar to Oklahoma’s today.
With little question summers will be hotter and there will be far fewer — if any — bitter cold spells in winter. Although predictions about precipitation are less reliable, there may be longer periods of drought and short, intense periods of heavy rain and snow.
That according to Dr. Perry Samson, professor of Atmospheric, Oceanic and Space Sciences at the University of Michigan and noted tornado chaser. Samson, who co-founded the Internet site wunderground.com, spoke July 10, 2012 at the Kellogg Biological Station symposium “Translating Science/Telling Stories: Agriculture, Water Quality & Changing the Climate Conservation.”
His talk was on “Buckeyes Growing in Ann Arbor and Other Potential Climate Disasters.”
In his talk to journalists and fellow scientists Samson said there are few scientists who still question human influence on climate, although there is not yet certainty on the degree that the burning of fossil fuels and other human activities are influencing global warming.
“There are natural fluctuations in global climate,” he said. “But we know for certain that human activities are a contributing factor.”
Samson said there is a clear distinction between weather and climate. Weather is what you encounter when you step outside. Climate is the accumulation of temperature, precipitation, storms, droughts and other atmospheric conditions over long periods of time. “It’s dangerous to say that the heat we had the last two weeks was evidence of climate change,” he said. “Next summer could be cooler and people could say that the climate is cooling.”
Two decades ago, when climate science was in its infancy, scientists were noting that the first signs of a global warming trend would first show up in polar regions. In the years since, summer ice cover in the Arctic has been shrinking, permafrost has been melting and other changes are confirming that prediction. Samson said that Arctic ice in summer could be gone within the lifetimes of many at the talk.
He said that the modest 3º C rise in average global temperatures in recent decades is trumped by a 12º C rise in polar temperatures.
Decreasing polar ice is one of several components of feedback mechanisms at work to raise global average temperatures, he said. As ice melts, less solar energy is reflected back into space and more absorbed by the dark water and land. Additionally, as heat-trapping levels of carbon dioxide continue to rise, ocean temperatures rise as does the amount of moisture in the atmosphere.
Oceans, which cover about three-fourths of the globe, are carbon sinks, meaning that a significant portion of the human-generated carbon dioxide is absorbed by the ocean and kept out of the atmosphere where it traps solar energy. But, Samson said, warmer ocean water is less efficient in absorbing carbon dioxide and more of the heat-trapping gas enters the atmosphere.
He noted one potential mitigating factor: More atmospheric moisture means more clouds. It’s not yet clear, however, if cloud cover will help slow the rise in global temperatures. “If they are thin clouds, such as cirrus, the impact will be less than if clouds are thicker,” he said. “We don’t yet know what kinds of clouds will form,” but regardless of the thickness, clouds are probably a less important factor in climate change than other feedback mechanisms.
Climate models used to predict long-term trends are the same ones used to predict weather over the next week or two, he said, and most people know how unreliable short-term predictions can be. Still, all the long-term climate models predict rising temperatures and it’s very likely “that our grandchildren will live in a wildly different world,” he said.
That wildly different world means more intense heat and a profound impact on health.
Samson said that on his first day of a class he teaches at UM, he asks his students how they are most likely to die from weather — freezing, tornados or heat? He justifies the gruesome nature of the question by noting: “I have tenure.”
The answer is heat, he said. More than half of all weather-related deaths now are from extreme heat.
One thing the models are predicting over the next century sounds somewhat ironic: More drought and more rainfall. “What that means,” he said, “is that there will be longer periods of drought and less frequent, but more intense rainfall, causing flooding.” And as temperatures rise and there is more moisture in the atmosphere, there likely will be more hurricanes, some of which threaten major cities along the southern U.S. coast, as well as major changes in global rainfall patterns.
His big fears are hurricanes in the South and a loss of the monsoon season in Southeast Asia, disrupting decreasing food supply. Miami is due to be hit by a Katrina-like hurricane, he said, and yet people keep building along the coast.
Samson said that even if all human carbon dioxide emissions ended today it would be 100 years before atmospheric conditions returned to what they are at present. The half-life of carbon dioxide in the atmosphere is 120 years and oceans are slower at responding to global temperature changes.
“If that’s the case, you may ask why bother to change our lifestyle,” he said. “But there is value in making adjustments now for long-term benefits.”