Global warming is now slowing down the circulation of the oceans — with potentially dire consequences

[AvantHiatus]

Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2554.html

 

 

 

 

Why the U.S. suffers from a Gulf Stream system slowdown

One thing that will not happen from a shutdown of the circulation is a sudden, dramatic freezing of Europe. It will certainly cool, relative to a world in which the circulation remains robust — but that will be offset by rising average temperatures due to global warming, says Rahmstorf. The “Day After Tomorrow” scenario will not come to pass.

However, there are many other effects, ranging from dramatic impacts on fisheries to, perhaps most troubling of all, the potential for extra sea level rise in the North Atlantic region.

That may sound surprising, but here’s how it works. We’re starting out from a situation in which sea level is “anomalously low” off the U.S. east coast due to the motion of the Gulf Stream. This is for at least two reasons. First, explains Rahmstorf’s co-author Michael Mann of Penn State University, there’s the matter of temperature contrast: Waters to the right or east of the Gulf Stream, in the direction of Europe, are warmer than those on its left or west. Warm water expands and takes up more area than denser cold water, so sea level is also higher to the right side of the current, and lower off our coast.

“So if you weaken the ‘Gulf Stream’ and weaken that temperature contrast…sea level off the U.S. east coast will actually rise!” explains Mann by e-mail.

But there’s another factor, too, involving what is called the “geostrophic balance of forces” in the ocean. This gets wonky, but the bottom line result is that “sea surface slope perpendicular to any current flow, like the Gulf Stream, has a higher sea level on its right hand side, and the lower sea level on the left hand slide,” says Rahmstorf. (This would only be true in the northern hemisphere; in the southern it would be the opposite.)

We’re on the left hand side of the Gulf Stream. So weaken the flow, and you also raise the sea level. (For further explanation, see here and here.)

Indeed, researchers recently found a sudden, 4-inch sea level rise of the U.S. East Coast in 2009 and 2010, which they attributed to a slowdown of the Atlantic overturning circulation. Rahmstorf says that “for a big breakdown of the circulation, [sea level rise] could amount to one meter, in addition to the global sea level rise that we’re expecting from global warming.”

Shutting down the circulation would also almost certainly have effects on global weather — changing around major planetary heat transport processes tends to do that — though scientists don’t know yet what those would look like.

So in sum: It appears that we’ve just seen yet another surprise from the climate system — and yet another process, like the melting of Antarctica, that seems to be happening faster than previously expected. And indeed, much like with that  melting, the upshot if the trend continues is an especially bad sea level rise for the United States — the country more responsible than any other on Earth for the global warming that we’re currently experiencing.

http://www.washingtonpost.com/news/energy-environment/wp/2015/03/23/global-warming-is-now-slowing-down-the-circulation-of-the-oceans-with-potentially-dire-consequences/

[blizzard1024]

So if the AMOC slows down due to global warming, then there will be less oceanic heat transport into the Arctic Ocean which would allow the  Arctic sea ice to recover which would help cool the NH.  Additionally, there would be less heat transport to higher latitudes in general which would spread across the mid and high latitudes countering warming. If this effect is strong enough it could reverse the warming which would speed up the AMOC again which then would lead to an oscillation. This likely has occurred in the past during glacial times when there was more land ice that melted and more disruption of the AMOC.

[AvantHiatus]

Sorry but that is not how it works. The North Atlantic cooling is regional, perhaps helped along by the +NAO. That is all, nothing more, nothing less. There are are downstream effects for sure. A sudden shutdown is not expected, which is what is required to begin cooling the Northern Hemisphere in a substantial way.

 

You need to read some of Hansen's exponential melt papers. The anomalous CO2 forcing signal is bypassing the oscillation and glacial melt timescales that have traditionally governed previous AMOC shutdowns. This is why Europe just had their warmest year on record during a time when the AMOC is collapsing rapidly.

 

http://www.columbia.edu/~jeh1/mailings/2012/20121226_GreenlandIceSheetUpdate.pdf

 

 

Iceberg cooling effect. Exponential change cannot continue indefinitely. The negative feedback terminating exponential growth of ice loss is probably regional cooling due to the thermal and fresh-water effects of melting icebergs. Temporary cooling occurs as icebergs and cold fresh glacial melt-water are added to the Southern Ocean and the North Atlantic Ocean. As a concrete example, Fig. 9 shows the global temperature change in simulations with GISS modelE (Schmidt et al., 2006; Hansen et al., 2007c) with and without the melting iceberg effect. GHGs follow the A1B scenario, an intermediate business-as-usual scenario (IPCC, 2001, 2007; see also Figs. 2 and 3 of Hansen et al., 2007b). Ice melt rate is such that it contributes 1mm/year to sea level in 2010, increasing with a 10-year doubling time; this melt rate constitutes 0.034 Sv (1 Sverdrup = 1 million m3 per second) in 2065 and 0.1 Sv in 2080. Half of this melt-water is added in the North Atlantic and half in the Southern Ocean. By 2065, when the sea level rise (from ice melt) is 60 cm relative to 2010, the cold fresh-water reduces global mean warming (relative to 1880) from 1.86°C to 1.47°C. By 2080, when sea level rise is 1.4 m, global warming is reduced from 2.19°C to 0.89°C. These experiments are described in a paper in preparation (Hansen, Ruedy and Sato, 2011), which includes other GHG scenarios, cases with ice melt in one hemisphere but not the other, and investigation of the individual effects of freshening and cooling by icebergs (the freshening is more responsible for the reduction of global warming). Note that the magnitude of the regional cooling is comparable to that in 'Heinrich' events in the paleoclimate record (Bond et al., 1992), these events involving massive iceberg discharge at a rate comparable to that in our simulations. Given that the possibility of sea level rise of the order of a meter is now widely accepted, it is important that simulations of climate for the 21st century and beyond include the iceberg cooling effect. Detailed consideration of the climate effects of freshwater from ice sheet disintegration, which has a rich history (Broecker et al., 1990; Rahmstorf, 1996; Manabe and Stouffer, 1997), is beyond the scope of our present paper. However, we note that the temporary reduction of global warming provided by icebergs is not likely to be a blessing. Stronger storms driven by increased latitudinal temperature gradients, combined with sea level rise, likely will produce global havoc. It was the prospect of increased ferocity of continental-scale frontal storms, with hurricane-strength winds powered by the contrast between air masses cooled by ice melt and tropical air that is warmer and moister than today, which gave rise to the book title "Storms of My Grandchildren" (Hansen, 2009).

 

At the end of the day, you end up with substantial global warming coupled with prolific storms caused by the temperature contrast between deep moderated AGW tropics (which are building up OHC and thermal inertia even faster due to the collapse of AMOC) and the growing Delta T with the polar regions.

 

Frontal systems from the polar and mid laditudes colliding with these tropical airmasses generates the so called 'storms of my grandchildren'.

 

Having the AMOC shut down will make things worse in terms of weather damages and disrupting ocean ecosystems, even if it might prevent the Earth from torching in the short-term. (2.5C vs 5C by 2100).

 

Interestingly, Hansen has temperatures peaking in 2035-2050 before dropping and giving away to chaotic climate fluctuations and and hellish weather as the system readjusts to meltwater cooling.

 

Additionally, in order to generate sufficient meltwater to cause this scenario, immense Sea Level Rise will have occured. The moral of the story is that AMOC shutdown will not 'reverse' global warming. The arctic sea ice stabilization is not related to the AMOC, just natural variability interplay.

[AvantHiatus]

[StudentOfClimatology]

This is debatable, but there's also plenty of literature that disagrees with the conclusions drawn here. Personally, I don't see the system pulling another Younger Dryas anytime soon.

[blizzard1024]

Sorry but that is not how it works. The North Atlantic cooling is regional, perhaps helped along by the +NAO. That is all, nothing more, nothing less. There are are downstream effects for sure. A sudden shutdown is not expected, which is what is required to begin cooling the Northern Hemisphere in a substantial way.

 

You need to read some of Hansen's exponential melt papers. The anomalous CO2 forcing signal is bypassing the oscillation and glacial melt timescales that have traditionally governed previous AMOC shutdowns. This is why Europe just had their warmest year on record during a time when the AMOC is collapsing rapidly.

 

http://www.columbia.edu/~jeh1/mailings/2012/20121226_GreenlandIceSheetUpdate.pdf

 

 

At the end of the day, you end up with substantial global warming coupled with prolific storms caused by the temperature contrast between deep moderated AGW tropics (which are building up OHC and thermal inertia even faster due to the collapse of AMOC) and the growing Delta T with the polar regions.

 

Frontal systems from the polar and mid laditudes colliding with these tropical airmasses generates the so called 'storms of my grandchildren'.

 

Having the AMOC shut down will make things worse in terms of weather damages and disrupting ocean ecosystems, even if it might prevent the Earth from torching in the short-term. (2.5C vs 5C by 2100).

 

Interestingly, Hansen has temperatures peaking in 2035-2050 before dropping and giving away to chaotic climate fluctuations and and hellish weather as the system readjusts to meltwater cooling.

 

Additionally, in order to generate sufficient meltwater to cause this scenario, immense Sea Level Rise will have occured. The moral of the story is that AMOC shutdown will not 'reverse' global warming. The arctic sea ice stabilization is not related to the AMOC, just natural variability interplay.

 

Basically the effect of this is to slow global warming down so maybe saying reverse was a little extreme. I don't think you can say with any certainty how this would affect the severity of storms either. With global warming the land heats up more than the oceans which in effect can reduce baroclinicity too especially in the winter. The system is very chaotic and difficult to discern at such a small time and space scales of projected storminess 50 years from now.

[Sophisticated Skeptic]

Interesting.  Could of influenced the nearly absent Atlantic tropical seasons the last few years. 

[AvantHiatus]

Interesting.  Could of influenced the nearly absent Atlantic tropical seasons the last few years. 

Some study (I forget), found a correltation between AMOC slowdown and 2010's enhanced activity. I think the Atlantic thing is just noise or cyclical. The MDR has been hostile and ruled by subsidence. This leaves the sub-tropical Atlantic and GOM responsible for taking up the slack.

 

You would think a cold North Atlantic would enhance TC activity by giving the tropics greater impetus for heat exchange. On the other hand, the +NAO is very effective at sweeping the MDR with dry air and strong winds.

[csnavywx]

This is debatable, but there's also plenty of literature that disagrees with the conclusions drawn here. Personally, I don't see the system pulling another Younger Dryas anytime soon.

I don't think anybody was suggesting a YD event, here or otherwise. Mike Mann actually did a video interview with Peter Sinclair this week and helped dispel that suggestion with a wider audience.

 

I think it IS fair to say that there is conflicting literature on the cause of changes in the AMOC. The real difference with this paper is the long-term reconstruction of the strength of the AMOC. If this paper stands up to further research and scrutiny, then it's potentially a landmark paper.

 

There's real and serious consequences to a significant slowdown or shutdown of the AMOC and if we're behind the curve on significant changes to it (as this paper suggests), then it warrants significant further attention.

 

Anyways, here's the full paper.

[AvantHiatus]

https://robertscribbler.wordpress.com/2015/03/23/world-ocean-heartbeat-fading-nasty-signs-north-atlantic-thermohaline-circulation-is-weakening/

World Ocean Heartbeat Fading? ‘Nasty’ Signs North Atlantic Thermohaline Circulation is Weakening

 

 

In a warming world, two things happen to throw a monkey wrench into the conveyor belt. First, melting ice, mostly from Greenland, dilutes the surface waters where the Gulf Stream reaches its northernmost extent. Since fresh water is less dense than salty water, the water has a more difficult time sinking to begin its journey southward. Second, the surface water is warmer than it used to be, and since warm water is less dense than cold water, this just adds to the problem.

Put the two together and you start to jam up the works, with the result that the whole conveyor belt slows down. And the water along the Atlantic coast of the U.S. begins to rise at an accelerating rate. While scientists expect sea level to rise by about 3 feet over the next 90 years or so, in places like New York City and Norfolk, Va., it could be significantly more. New York, where sea level is already a foot higher than it was in 1900, was just reminded of what happens when higher seas are pushed ashore by a major event like Superstorm Sandy.

 

[Typhoon Tip]

As a hypothesis ... it's almost like GW has a vestige of sinusoidal oscillatory behavior along the longer term course of that rise.

 

Or perhaps that apparent periodicity merely mimics a sinusoidal curve.  Either way, the thermohaline mass/density balance offseting what GW would otherwise mean for middle and high latitudes around the Atlantic, has been written and refereed for decades actually. It's an interesting subject matter.

 

It is as though the mean atmosphere warms dramatically (inside of 500 years is but a geological instant!), floods low saline land/glacial melt ... slowing/stoppage of the oceanic conveyor allows cooling to re-introduce, because of less warm oceanic conveyor delivery to higher latitude ...etc etc.  

 

But then as C02, and increased WV associated with heating, land and ocean floor methane locking is released...all tallied, then over come that interim cooling, then the real hot house Earth is a half Millennium or so down the road. 

[AvantHiatus]

As a hypothesis ... it's almost like GW has a vestige of sinusoidal oscillatory behavior along the longer term course of that rise.

 

Or perhaps that apparent periodicity merely mimics a sinusoidal curve.  Either way, the thermohaline mass/density balance offseting what GW would otherwise mean for middle and high latitudes around the Atlantic, has been written and refereed for decades actually. It's an interesting subject matter.

 

It is as though the mean atmosphere warms dramatically (inside of 500 years is but a geological instant!), floods low saline land/glacial melt ... slowing/stoppage of the oceanic conveyor allows cooling to re-introduce, because of less warm oceanic conveyor delivery to higher latitude ...etc etc.  

 

But then as C02, and increased WV associated with heating, land and ocean floor methane locking is released...all tallied, then over come that interim cooling, then the real hot house Earth is a half Millennium or so down the road. 

For me, this topic is the canary in the coal mine and should be enough to convince everyone that AGW is a real threat. Hysteresis points are lurking around the corner across the board. Some of them conflicting in opposite directions leading to a truely chaotic planet.

[Sophisticated Skeptic]

yea, but the sad thing is...our ADHD society only cares about issues when their immediate and affecting them.

 

and polititians only care about the price tag.

 

Just like with our crumbling roads / bridges and infrastructure. If it costs too much, we just use duct tape for a temporary fix....until another major bridge fails...then they talk about it in congress again.