Many of you may have learned in high school earth science — and forgotten since — Earth is farther from the sun in the summer than it is in the winter. In fact, this year’s aphelion (point farthest from the sun) in Earth’s orbit was July 4, as illustrated in Dr. Marshall Shepherd’s article in Forbes.
The perihelion (point closest) occurs in the winter. Earth’s orbit is not truly circular and is actually elliptical at times. Some of those numerical values we learned in our youth were median numbers. Earth is not always 93 million miles from the sun, and the moon is not always 240,000 miles from Earth. Right now, Earth is 94.5 million miles from the sun, as Shepherd pointed out.
On Jan. 5 next year, Earth will be 91.4 million miles from the sun, in the dead of winter. Earth’s orbit has eccentricities — irregularities — brought on by various gravitational forces including that of the moon. These irregularities are calculated by precision mathematics and astrophysics. Even the tilt of our axis, which we’ve all read is 23.5 degrees is only an approximation because of fluctuations. There are also other irregularities in our orbit related to what are called Milankovitch Cycles, one of which has a 100,000 year period.
We know these cyclical variations in our orbit and distance from the sun have been directly related to past glaciations and warmings. When lay climate change skeptics ask, “How come we had big warmups way before humans were around?” the Milankovitch Cycles are a big part of the proven answer.
We also know the current stage of these cycles dictate the Earth would be cooling now rather than warming, were it not for human activity outweighing the Milankovitch impacts. These cycles are very complex for the scope of this article. If you’d like to learn more about these fascinating elements, here is a well-done explainer, courtesy of Indiana University.
Getting back to summer heat and axial angles, we are hotter in the summer simply because of the tilt of the axis bringing solar input at a more direct angle to the Northern Hemisphere. In the winter, that angle affords us a more diffuse distribution of solar energy, much like tilting a flashlight so its light spreads out and becomes weaker at any given point when spread out. This NOAA image featured in Forbes lays the angle issue out.
We’ll segue here back to this summer, and arctic warmth. The high latitudes have been experiencing near record and record warmth frequently since this past winter, as well as during the previous winter. The current round of incredible warmth is tied, once again, to a blocking pattern like those which have become more common since the acceleration of peak warming in the Arctic and the weakened jet stream which frequently results. (That, of course, is directly tied to the warming caused by human activity which was accurately predicted by climate models four decades ago.) On July 4, NWS Anchorage tweeted out an extraordinary record high.
The #4thofjuly2019 was one for the books. Several ALL-TIME high temperature records were set at official observation sites throughout Southern #Alaska. But that's not all...there were more daily temperature records set too! #AKwx #ItsHotInAlaska pic.twitter.com/GxcdUaD9ld
— NWS Anchorage (@NWSAnchorage) July 5, 2019
Anchorage hit 90 degrees, breaking the old record by 5 degrees. There have been numerous readings in the upper 80s to near 90 in Alaska and parts of arctic Russia. There appears to be a relationship between a record low Arctic Sea ice maximum back in early April and record low-for-early summer ice levels which have followed, from the National Snow and Ice Data Center.
As I’ve written about several times, the reduced coverage of highly reflective sea ice being replaced for longer parts of the season with highly absorptive dark sea waters changes the solar energy balance regionally with hemispheric effects. Again, this feedback mechanism may lead to improved summer ship navigation in the Arctic regions but, other than that, it’s mainly bad news. With arctic warming comes more polar jet stream weakening and more blocking episodes. Those episodes include winter polar vortex weakenings allowing the jet stream to buckle southward more frequently, leading to more frequent regional arctic outbreaks. In the warm weather months, blocking episodes in the Northern Hemisphere can lead to more deadly heat waves, such as the deadly heat wave last week in much of Europe, and the current heat over much of the Arctic. Blocking also led to the inland stalling of devastating Hurricanes Harvey and Florence.
The warming then lends itself to record ice minima in September, a shorter freeze season for the Arctic Ocean, thinner ice as a result, and more ready melting of that thinner ice the following warm season. That’s why it’s called a feedback mechanism.
I’ll finish with a non sequitur note of optimism for our local weather in the near term. If you are as weary of this very warm and oppressively humid air mass as I am, you’ll be happy to know a bubble of relief is still en route by Sunday. Clouds will part with more sunshine by afternoon, and LESS HUMIDITY. This model depiction and its little wind barbs are all coming from the northeast, and the numbers represent much lower dewpoints.
Temps will be in the upper 70s Sunday afternoon. We will warm back into the 80s next week, and humidity will edge up by Wednesday. At this point, however, the dew points should be staying well shy of 70-plus. Warm and moderately humid beats oppressive every time. If you disagree with that, talk to the hand.