In Part 1 of this series, I discussed the dramatic drop in Arctic sea ice. In this second part, I focus on exactly how that dramatic drop is affecting your weather.
But how can the disappearance of Arctic sea ice affect your weather? As it turns out, the answer is actually quite simple. I'll explain it in just three steps.
First, we need just a little background. Jet streams (rapidly-moving 'rivers' of air, miles above the surface of the planet) have a substantial effect on our weather throughout the year. The northern polar jet stream is particularly important in the U.S.
In the summer, it's position allows warm air to move up from the equator, and in the winter, it's position allows cold air to move down from the Arctic. Notice the 'waves', or ridges, in the polar jet stream - they'll be important later:
Every bit as meaningful, the polar jet stream moves weather systems from west to east in the Northern Hemisphere. And it's this vital characteristic of the polar jet stream that's impacting your changing weather right now, because the disappearance of Arctic sea ice is directly affecting the ability of the polar jet stream to 'move' your weather.
Let's get started with those three steps. The warming trend in the Arctic is almost twice as large as the global average in recent decades - mostly due to the disappearance of sea ice.
Step 1: 'Bright' Arctic sea ice reflects sunlight, but ice-free 'dark' ocean water absorbs it.
The dark water warms in ice-free summers, and by fall we can see unusually high temperatures (anomalies) like this:
A temperature anomaly of 6C, or nearly 11F, is jaw-dropping BTW.
Step 2: In the fall, the warm ocean water releases that excess heat.
Step 3: Because the polar region has absorbed more heat (and is therefore warmer), the temperature difference between the equator and the pole is reduced. And this reduction in temperature difference means two things:
One - the polar jet stream itself slows down. In North America, winds have slowed by about 14% since 1980. You can clearly see the relationship between September sea ice area, and zonal winds (which drive the jet streams), below:
Two - the 'waves' in the polar jet stream that I mentioned above (Rossby waves, to be precise) get 'bigger' - and bigger waves not only bring in more extreme temperatures, they also move more slowly.
Each phenomenon on it's own would reduce the ability of the polar jet stream to 'push' weather systems along. But when combined, the end result is that we're actually getting a double whammy from this change.
We can already see that some weather systems move from west to east more slowly now, and that extreme temperatures/precipitation events are far more common. Simply put, no matter what your current weather is, there really can be too much of it. Too many sunny days result in a prolonged drought. When badly-needed rains finally show up, too many rainy days bring floods and heavy soil erosion. Long cold snaps bring harsh (and sometimes deadly) conditions - just as extended heatwaves do.
In the U.S., we've seen a rapidly-increasing number of instances where 'stuck' weather patterns result in extreme weather events. The disappearance of Arctic sea ice is already having a measurable effect on your weather - and the effect isn't good.
For those of you who want to understand this phenomenon in more detail - below: Dr. Jennifer Francis explains this research in a 16-minute video presentation.
Jennifer Francis, Rutgers University, 25 January 2012. The "Arctic Paradox" was coined during recent winters when speculations arose that the dramatic changes in the Arctic may be linked to severe snowstorms and cold temperatures in mid-latitudes, particularly along the U.S. east coast and in Europe. Recent studies have illuminated these linkages. Evidence is presented for a physical mechanism connecting Arctic Amplification -- the enhanced warming in high northern latitudes relative to the northern hemisphere -- with the frequency and intensity of several types of extreme weather events in mid-latitudes, such as droughts, floods, heat waves, and cold spells.
Evidence Linking Arctic Amplification to Extreme Weather in Mid-Latitudes (Francis, Vavrus, 2012)
Weather and Climate Summit - Day 5, Jennifer Francis (full 1:24 presentation)