Winter storms in the United States and in the United Kingdom may have been made worse by global warming. This conclusion has been reached before, most recently in an essay by a British climate scientist. Tim Palmer, a climate scientist and a professor at Oxford University, published a “Perspectives” essay in Science where he theorized that thunderstorms in the tropical region of the western Pacific may have shifted part of the jet stream, causing the polar vortex that caused such severe winter weather over Canada and the northern United States last winter. Ocean temperatures in that critical region of the Pacific are some of the warmest in the world, and global warming has just pushed the temperature higher, Palmer said. Those warm temperatures produced ripples in the jet stream, and those ripples caused the cold weather over Canada and much of the United States.
The first four months of 2014 were cold and snowy in northern North America, so people might have missed the connection with global warming that Palmer thinks exists. The connection is there even if global temperatures have not been rising lately. Palmer further suggests that the warming phenomenon could be worsened by increasing carbon dioxide emissions linked to human activity. The western Pacific is acting as a heat sink, trapping heat energy and heading off a rise in global temperatures, Palmer wrote. The heat sink, made hotter by global warming, may have made the winter worse in much of the northern hemisphere.
In addition, the trapped heat generated thunderstorms, which released heat energy. That heat energy drove typhoons and disturbed the atmosphere enough to move part of the jet stream. The Pacific warming also contributed to Australia’s heat wave this year and to Haiyan, the storm that killed 6,000 people in the Philippines.
Meteorologists agree that the southward-moving jet stream caused the stretch of unusually cold weather. Areas north of the jet stream generally feature arctic temperatures in winter, which moved south with the shifting air currents. The same jet stream movements touched off storms in the Atlantic. Those storms moved into northern Europe and, among other problems, caused flooding in the UK.
In spite of what happened last winter, Palmer’s theory does not predict that future winters will just as cold. The conditions were a one-time event. This year, a recurring band of warm Pacific water that runs up the coast of South America, El Nino, is due to return. The return of El Nino would release a huge amount of heat energy, producing a warmer winter.
Palmer’s latest work builds on research he began almost 30 years ago on weather patterns and climate trends in the eastern United States.
Palmer’s theory uses a mechanism similar to that in another theory proposed earlier this year by Rutgers University scientist Jennifer Francis. She believes that melting artic ice is reflecting less sunlight, allowing less heat to be reflected into the atmosphere. That mechanism thins the jet stream and makes it unstable. Another theory suggests that the harsh winter was just one of those climate variations that happen sometimes. Although researchers are at odds as to the existence of global warming, research by Palmer and Francis suggest that weather is part of a complex system that can be disturbed in unexpected ways.
By Chester Davis