For some, the evidence of global warming is hard to accept, especially when it has been difficult to draw the link between individual storms and an increase in atmospheric greenhouse gasses.
Now a new study by a climate scientist at Pennsylvania State University has done just that.
By studying the pattern of the jet stream, Professor Michael Mann and a team of other scientists showed that warmer ocean temperatures are making the jet stream more erratic pulling more warm, tropical air into northern reaches of the U.S., for example, increasing the frequencies of summer hurricanes in New England, more tornadoes in Iowa, as well as bringing more persistent droughts.
Mann and his colleagues' study links more frequent, severe, and long-lasting storms with the more erratic jet stream flow, according to a report in the Washington Post.
A primary driver, Mann's report says, is the fact that the Arctic is warming faster than mid-latitude regions.
The jet stream is channeled between colder air to the north and warmer air to the south. Because Arctic air is no longer reliably as cold, the jet stream has become more erratic, meandering back and forth like a stratospheric river.
When it plunges to the south, it pulls cold air down over warm land and water and sets up big storms. When it pulls north, the jet stream traps heat to its south, locking places like the southern U.S. in drought.
This weak division between warm and cold air also slows down the jet stream, allowing these disruptive weather patterns to linger, Mann and his colleagues note.
The study calls the more frequent jet stream meanderings "quasi-resonant amplification," and says that if world leaders can't get greenhouse emissions under control, that people should expect more of the same.
The good news, the study says, is that if greenhouse gas emissions are reduced—and vehicles are a significant portion of that—the pattern is reversible.
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