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Global warming could cause cooling — yes, cooling — in some parts of the world

Don Paul

Of the world’s oceans, the North Atlantic has been the saltiest. Salty water has greater density than fresh water, and that density leads to sinking, which drives some of the world’s great conveyor currents. Those currents, in turn, drive much of the earth’s climate regionally and globally.

These conveyor currents are what is known as the thermohaline circulation. Watch the video above to see an illustration of the currents or, courtesy of Climate Central, click here to view a basic diagram of what this circulation looks like in the Atlantic.

The cold, salty waters of the North Atlantic sink from their own density and weight, travel southward along the bottom of the ocean bed and eventually begin to rise as they absorb heat again near the tropics. This warming current, part of which is known as the Gulf Stream, makes all the difference in the climate of much of northern and western Europe, and eastern North America.

Examine the path of the Gulf Stream and its reach northeastward to European latitudes north of Labrador. You may notice that New York City’s latitude is closer to that of central Portugal and Spain and that the Carolinas line up with northwestern Africa. In other words, much of Europe is farther north than many Americans realize. Without that warm current, you can begin to imagine what the climate would be at such northern latitudes. Great Britain’s temperatures would match up with those closer to those of coastal northeastern Canada. The Gulf Stream’s proximity to the U.S. East Coast also clearly makes a large contribution to our climate as well in the east.

There has been an ongoing dilution of North Atlantic salinity since early in this century, and it is tied to freshwater ice melt. That melt, of course, is directly linked to our mean warming climate. In addition to glacial ice melt, one of the two largest sources of meltwater is Greenland:

Greenland alone has been averaging an ice mass loss of 280 gigatons, close to 310 billion tons, per year between 2002 and 2016. All of that melting ice is freshwater. (One large Greenland glacier has greatly slowed its melt rate in the last two to three years due to cold water from the seabed farther out in the Atlantic upwelling to where the ice meets the sea. That has been allowing that one glacier to grow, temporarily. Even so, the mean ice loss on Greenland continues as noted.)

This massive infusion of freshwater into the North Atlantic is the primary reason salinity is going down. It may be the underlying cause of a developed persistent cold spot in the North Atlantic during the last few years.

There are many unanswered questions, some of them troubling. Paleoclimatological evidence exists that past virtual shutdowns of the Gulf Steam current have occurred related to warming-linked dilution of salinity. During those past shutdowns, rapid climate change occurred in western and northern Europe, as well as in portions of eastern North America. As you might guess by now, those changes involved regional sharp cooling, not warming.

The emphasis is on regional. A slowing, weakening or virtual stopping of the Gulf Stream would have drastic effects, but those effects would be regional, not global. With the tremendous increase in the greenhouse gas load that has occurred and that is ongoing, we don’t yet have good modeling on how much of such regional cooling would be mitigated by the mean warming climate. The last time such changes occurred in the Gulf Steam, atmospheric carbon dioxide and methane levels were lower than they are now, yet warming occurred due to the earth’s orbital eccentricities being largely responsible for past glacial advances and retreats, prior to human influence.

As of now, Dr. Michael Mann of Penn State reports in a Yale Climate Connections interview: “We are 50 to a hundred years ahead of schedule with the slowdown of this ocean circulation pattern, relative to the models,” according to Mann. “The more observations we get, the more sophisticated our models become, the more we’re learning that things can happen faster, and with a greater magnitude, than we predicted just years ago.”

Regardless of any such regional cooling, should it develop, the earth’s mean temperatures would continue to rise on a global basis. The evidence is not yet conclusive that this lessening of salinity is fated to go on and reach such critical levels, but it is quite suggestive.

Coming up in the forecast: Halloween and beyond

Here’s what appears to be setting up for Halloween weather and what follows at the start of November.

Widespread rain will develop on Halloween, probably becoming a soaking rain by the trick-or-treat hours. Daytime temps will seasonably mild, in the upper 50s, slowly falling into the 40s during the evening.

Friday will probably pose greater problems with strong to possibly high winds and damaging gusts. A deep storm system will be passing to our north, and these winds are likely to cause Lake Erie shoreline flooding. If this trend in the models continues, some trees could be at risk, with wet soils and still some limited foliage on the branches Friday.

Yes, it may get just cold enough for some wet snowflakes to arrive at higher elevations Friday and Friday evening. As of now, this doesn’t look like a setup for significant snow even in the hills. But as I used to say on tv, “I’ll keep you updated.” If there are any real changes, I’ll adjust the forecast in the comments section.

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