This is the week of the fall equinox. To be precise, Thursday will be the day when our Sun crosses Earth's equatorial waistline and days will grow shorter and cooler in the Northern hemisphere.
The September equinox also marks what is usually the annual minimum of sea ice in the Arctic Ocean - that ice having spent the summer melting further and further away.
Scientists have said they expect this year's remaining ice to be declared the second smallest summer minimum on record - despite a cloudy (and therefore cooler) summer at the top of the world. So even with less of the sun's glare over the summer, the ice melted away faster and earlier than usual from an already record low maximum ice buildup during the winter of 2015.
It's an ugly cycle that now is feeding on itself. As more ice melts, more ocean becomes exposed, and open water absorbs more heat than ice because ice reflects the sun's rays. This causes Arctic temperatures to rise, feeding a loop that causes still greater amounts of ice to melt.
Since 2002, every September ice retreat has exceeded the long-term average (1981-2010), and the last 10 record lows have all occurred since 2005, according to scientists.
So what? So can you say climate change, and mounting evidence for it?
Ninety-nine percent of the planet's freshwater ice is locked up in the Antarctic and Greenland ice caps, and some studies indicate sea levels could rise by six feet this century, and still more in the next, putting many of the world's populated coastal areas under water.
Now scientists also are monitoring a key current in the North Atlantic to see if rising sea temperatures and increased freshwater from melting ice are altering the "ocean conveyor belt," an enormous oceanic stream that plays a major role in the global climate system, according to Environment 360, a publication of the Yale School of Forestry & Environmental Studies.
An oceanographic team this year is hauling up dozens of moored instruments that track currents far beneath the North Atlantic Ocean's surface. The data team members retrieve will be the first complete set documenting how North Atlantic waters are shifting and whether there is a long-term slowdown in ocean circulation. A similar string of moorings across the middle of the Atlantic already has detected a disturbing drop in this ocean's circulation pattern.
Scientists say that since those monitors were installed in 2004, they have recorded the Atlantic current wobble and weaken by as much as 30 percent, "turning down the dial on a dramatic heat pump that transports warmth toward northern Europe," states the Yale report. "Turn that dial down too much and Europe will go into a deep chill."
If you think this sounds like the movie "The Day After Tomorrow" when an ocean current shutdown threw much of the northern hemisphere into a deep freeze, you're not far off. The disaster at the heart of the film was based in some reality, according to Environment 360.
So looking at this new data will be interesting. Hopefully it will serve only to help scientists better understand the effects of our ocean currents, and not to spell movie-like drama.
In the meantime, down here in Chattanooga, we're having anything but a cool-down. For September-to-date alone, we're averaging 5.9 degrees above normal with a rainfall that is more than an inch below normal for the month and more than 13 inches below normal for the year. Our daily forecasts through Sunday include beaming sun and temperatures in the 90s. So much for the Autumn equinox and its promise of shortening and therefore cooler days.
Here's an interesting statistic for you: According the National Weather Service's weather data for Chattanooga, in the 137 years of weather record-keeping, we've had 43 years that saw annual maximum high temperatures of 100 degrees or more. Seven of those 100-and-up years (including this one) occurred in the past 10 years, and 18 of them - bordering on half - have occurred since 1970.
Feeling that our days are hotter is not just your imagination. Nor is it a hoax.
The world - population 9 billion and growing - is warming, and Arctic sea ice is shrinking - more than it has in nearly two centuries.