The days have been getting longer in the northern hemisphere since December 21, 2017, but the coldest days are normally in January. In North America the cold started early this year. And let’s not forget the snow. But one area of the globe has temperatures well above normal.
Erie’s Christmas Present
On December 25 and 26, 2017, Erie, Pennsylvania broke its one- and two-day snowfall records with over four and five FEET of snow, respectively.
Erie had never gotten that much snow in a week. The snow-lover’s bonanza was compliments of a low pressure system over Canada, which brought persistent winds off the lake that shares the city’s name. As we discussed in last month’s Climate Change Checkup, long-lasting weather events like this and the record rain of Hurricane Harvey, which stalled over Texas, are becoming more common.
The weather pattern which produces Lake Effect snow also brings cold air into the eastern US. The snow and cold are forecast to continue, as a large fold in the jet stream has stopped the normal west to east progression of weather systems.
Fortunately for Erians, a feedback will put a crimp in the atmosphere’s ability to bury the city in snow: Once the lake is partly or mostly frozen, the Lake Effect will be slowed or shut off.
Arctic Temperatures Assume Typical Winter Above-Average Values
The last decade has seen a prominent change in arctic temperatures. While summer temperatures hover near freezing every year, winter temperatures have departed by up to 10 C (18 F) above the average of 1980-2000. In 2017, according to data compiled by the Danish Meteorological Institute, outside of the four warmest months (May through August), the arctic temperature was not below average one single day.
The extreme warming near the north pole is due to what meteorologists call arctic amplification: Two feedback effects produce a warming three times the global average.
What Are The Feedbacks?
The earth reflects some of the sun’s electromagnetic radiation. The percentage that is reflected, expressed as a decimal between zero and one, where zero means no sunlight is reflected and one means all of it is reflected, is called the albedo. Most of what is reflected is lost to space.
The albedo of ice is 0.6 and snow-covered ice is 0.9. The albedo of open ocean is 0.1. An ice-covered arctic reflects most of the incoming solar radiation, while an ocean-covered arctic would absorb most of it.
Waves on the open ocean are bigger than on small patches of open sea. Waves impact the ice when they reach it and break it up. The broken ice melts faster than a single sheet because more edges are exposed.
Why Does All The Warming Occur In The Winter?
The latent heat of ice/water is very high, meaning it requires a lot of heat to melt ice. It takes 330 kilojoules of heat to melt a kilogram of ice at its freezing point.
When the air temperature over sea ice is below freezing, heat added raises the temperature of the air; when the air temperature reaches freezing, any additional heat is used up melting ice, so the air temperature remains about steady just above freezing.
A Likely Feedback Of The Future
The high latent heat of water/ice has given humanity some breathing room with respect to the warming of the arctic and its possible effects on global weather. It’s taking a long tome for the arctic to become ice-free. But once the ice is gone, the water will heat up rapidly, because the specific heat of water (the amount of heat needed to raise the temperature) is very small relative to the latent heat of water/ice.
Remember that kilogram of ice that we melted with 330 kilojoules of heat? If we apply the same 330 kilojoules to a kilogram of water at its freezing point (zero degrees Celsius), the temperature will rise to 80 degrees Celsius.
The conclusion is obvious: Once the arctic is ice-free, the temperature of the water will rise — not to 80°, because much of the added heat will be distributed in the oceans. But with the water warming, ocean currents are virtually certain to change, and the effects of the changes on climate are unknown.
Another Astronomical Event
On December 21, 2017, the sun, which had been meandering southward, turned around and headed north. Well, not exactly, but that’s what it looked like to a casual observer. Actually, the earth reached its maximum tilt of 23-1/2 degrees away from the sun in the northern hemisphere.
But another astronomical event is approaching. On January 4, 2018, at 9:17 a.m. Eastern Standard Time to be precise, the earth will be 91.4 million miles from the sun — 3.1 million miles closer than it will be on July 3. How can that be? Is the earth getting flung out of the solar system? Luckily, no.
The earth’s path around the sun is not a circle; it is an ellipse. The earth’s closest approach to the sun is called perihelion and the farthest distance is called aphelion. Winter temperatures in the northern hemisphere would be several degrees colder if the dates were reversed.
The next Weather Around The World will be published on February 6, 2018, and the next Climate Change Checkup will be published in mid-January, 2018, after NOAA’s release of the December and full-year 2017 land and sea temperatures.