Friday, April 20, 2018

An Ominous Omen For Earth Day 2018

Image result for thermohaline circulation

Earth Day is this Sunday, April 22nd, and the really bad news for climate deniers - as well as the rest of us   -  has arrived. We've now learned the Atlantic Ocean circulation that carries warmth into the Northern Hemisphere’s high latitudes is slowing down because of climate change. This was announced by a team of scientists last Wednesday, indicating one of the most feared consequences of global warming is already coming to pass.

Of course, this was first highlighted in the science fiction film, The Day After Tomorrow, though to be sure the events depicted in that movie were extreme and radically compressed in temporal sequence.  After the film came out, and we watched it at the local cinema, Janice asked my opinion. I basically dismissed it as "pseudo-scientific nonsense."  That was before I investigated the origin of the theory, basically tied to disruption or cessation of the thermohaline circulation - for example, governing  the currents which ensure warmer water (such as in the Gulf of Mexico) is transported to the northern hemisphere.  Hence, it's actually a part of the greater scale ocean circulation.

The  theory tracks back to Dr. Wallace Broeker - a geo-scientist at Columbia University-  who originally conjectured that global warming would increase rainfall and river discharge into the North Atlantic. That combination would then lower surface water density (fresh water being less dense than salt water) and the lower density surface water would not sink. 

This would disrupt the thermohaline current (circulation) so that warmer water could no longer be pulled from lower latitudes toward Europe. In the paradoxical result, global warming would plunge Europe into another ice age. To be sure, Dr. Broeker assumed a 50 percent increase in precipitation and increased wetness in Central Asia and North America. (By contrast the IPCC has projected only a 5-10 increase in precipitation).

At the time I perused these results, while I gave Broeker's  hypothesis more credibility, I still didn't believe any major disruption of the THC was plausible. That was before the recent announcement that the Atlantic meridional overturning circulation (AMOC)  has declined in strength by 15 percent since the mid-20th century to a “new record low.”  This was the conclusion of the scientists in a peer-reviewed study published in the journal Nature.

That percentage difference represents a decrease of 3 million cubic meters of water per second, the equivalent of nearly 15 Amazon rivers.

Some of the AMOC’s disruption may be driven by the melting ice sheet of Greenland, and indeed, other new research last week showed that Greenland’s massive ice cap is melting at the fastest rate for at least 450 years. This influx will continue to weaken the Amoc into the future until human-caused climate change is halted.
For an insight into the Thermohaline circulation:

We now have been alerted, based on the research (and in a nod to Broeker) that serious disruption to the ocean current crucial in controlling global climate must be avoided “at all costs”.   THAT is the new message for this Earth Day. The alert follows the revelation last week that the system is at its weakest ever recorded

For those inclined to dismiss these findings as  more climate change "blurtations"  or hype, they ought  to  process that past collapses of the giant network have seen some of the most extreme impacts in climate history, e.g. western Europe particularly vulnerable to a descent into freezing winters. A significantly weakened system is also likely to cause more severe storms in Europe, faster sea level rise on the east coast of the US and increasing drought in the Sahel in Africa.  

This new research  clearly worries  climate scientists because of the huge impact global warming has already had on the currents and the unpredictability of a future “tipping point”.  The currents that bring warm Atlantic water northwards towards the pole, where they cool, sink and return southwards, is the most significant control on northern hemisphere climate outside the atmosphere.

Professor Stefan Rahmstorf,  one of the world's leading oceanographers at the Potsdam Institute for Climate Impact Research, has stated:  

From the study of past climate, we know changes in the Amoc have been some of the most abrupt and impactful events in the history of climate,”

Oceanographer Peter Spooner, at University College London, shares the concern noting: “The extent of the changes we have discovered comes as a surprise to many, including myself, and points to significant changes in the future.”  

He isn't exaggerating. A collapse in the AMOC would mean far less heat reaching western Europe and plunge the region into very severe winters, the kind of scenario depicted (in extreme fashion) in the movie The Day After Tomorrow. A widespread collapse of deep-sea ecosystems has also been seen in the past. 

Another byproduct is that as the AMOC weakens, it might actually increase summer heatwaves. That is because it takes time for the cooling of the northern waters to also cause cooling over the adjacent lands. However, the cooler waters affect the atmosphere in a way that helps warm air to flood into Europe from the south, a situation already seen in 2015

A primary message for this Earth Day is to spread the word about this latest research, to educate citizens worldwide. Because it will impact all of them.

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