The record-breaking cold weather in the eastern U.S. is likely caused by global warming. How does this happen?
While the temperatures in the Arctic are still cold, they have warmed almost twice as much as the rest of the Earth. In order to understand what is going on, an analogy that may be helpful is to think of a giant mound of cold air centered on the North Pole. The colder the air the taller and steeper the mound. As the Arctic has warmed the mound has flattened somewhat. Now think of the jet stream (which shows up on most weather maps) as a closed river circling around the Earth with the North Pole as its usual center. The jet stream acts as a guide for highs and lows.
The jet stream always ripples as it moves around the Earth. As the Arctic warms, the more flattened mound of cold air allows the jet stream to more easily meander, like rivers in flat areas. Also like rivers in flat areas the jet stream slows down. As the meanders get bigger they can extend further south and north, allowing very warm or cold air into places they rarely go. Since the jet stream now is slower and meanders more it can sometimes develop a “block” that can be stable for weeks, guiding highs and lows on the same paths over and over.
Since these “blocks” can be very stable for extended periods, this can allow the cold or heat to build up in places where such conditions rarely exist. The center of the U.S. is now experiencing such an extended “block” as the jet stream extends almost to the Gulf of Mexico.
Such “blocks” have become more common as the slowing jet stream meanders more. With a warming Arctic, larger meanders in the jet stream, and the occasional “block,” we will get weather patterns that are more extreme and that will tend to last longer.
David Hart, Torrey
