Model vs Model: Is the North Atlantic Current Collapsing?

Essay by Eric Worrall

h/t Dr. Willie Soon; 12,900 years ago the North Atlantic Current failed, likely due to the emptying of an enormous glacial lake. This catastrophic lake failure is believed to have disrupted ocean currents, which led to an abrupt return to ice age conditions which lasted for over a thousand years.

The glacial lake which caused this calamity no longer exists, but the remote possibility global warming could trigger a new ice age is a favourite scenario of climate alarmists.

Article Published: 

Interbasin and interhemispheric impacts of a collapsed Atlantic Overturning Circulation

Bryam Orihuela-PintoMatthew H. England & Andréa S. Taschetto 

Nature Climate Change (2022) Cite this article

Abstract

Climate projections suggest a weakening or collapse of the Atlantic Meridional Overturning Circulation (AMOC) under global warming, with evidence that a slowdown is already underway. This could have significant ramifications for Atlantic Ocean heat transport, Arctic sea ice extent and regional North Atlantic climate. However, the potential for far-reaching effects, such as teleconnections to adjacent basins and into the Southern Hemisphere, remains unclear. Here, using a global climate model we show that AMOC collapse can accelerate the Pacific trade winds and Walker circulation by leaving an excess of heat in the tropical South Atlantic. This tropical warming drives anomalous atmospheric convection, resulting in enhanced subsidence over the east Pacific and a strengthened Walker circulation and trade winds. Further teleconnections include weakening of the Indian and South Atlantic subtropical highs and deepening of the Amundsen Sea Low. These findings have important implications for understanding the global climate response to ongoing greenhouse gas increases.

Read more: https://www.nature.com/articles/s41558-022-01380-y

Of course, all these problems go away if what is actually happening is cyclical natural variation.

The evolution of the North Atlantic Meridional Overturning Circulation since 1980

March 2022

Nature Reviews Earth & Environment 3(4)

DOI:10.1038/s43017-022-00263-2

Authors: , Laura Jackson, Arne Biastoch, Martha W. Buckley, Damien Desbruyères, Eleanor Frajka-Williams, Ben I. Moat, Jon Robson

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the climate through its transport of heat in the North Atlantic Ocean. Decadal changes in the AMOC, whether through internal variability or anthropogenically forced weakening, therefore have wide-ranging impacts. In this Review, we synthesize the understanding of contemporary decadal variability in the AMOC, bringing together evidence from observations, ocean reanalyses, forced models and AMOC proxies. Since 1980, there is evidence for periods of strengthening and weakening, although the magnitudes of change (5–25%) are uncertain. In the subpolar North Atlantic, the AMOC strengthened until the mid-1990s and then weakened until the early 2010s, with some evidence of a strengthening thereafter; these changes are probably linked to buoyancy forcing related to the North Atlantic Oscillation. In the subtropics, there is some evidence of the AMOC strengthening from 2001 to 2005 and strong evidence of a weakening from 2005 to 2014. Such large interannual and decadal variability complicates the detection of ongoing long-term trends, but does not preclude a weakening associated with anthropogenic warming. Research priorities include developing robust and sustainable solutions for the long-term monitoring of the AMOC, observation–modelling collaborations to improve the representation of processes in the North Atlantic and better ways to distinguish anthropogenic weakening from internal variability. The Atlantic Meridional Overturning Circulation (AMOC) has a key role in the climate system. This Review documents AMOC variability since 1980, revealing periods of decadal-scale weakening and strengthening that differ between the subpolar and subtropical regions.

Read more: https://www.researchgate.net/publication/358935843_The_evolution_of_the_North_Atlantic_Meridional_Overturning_Circulation_since_1980

Laura has been writing about cyclical variation for quite a while.

Recent slowing of Atlantic overturning circulation as a recovery from earlier strengthening

May 2016
Nature Geoscience 9(7)
DOI:10.1038/ngeo2715
Authors: Laura Jackson, Kenneth Andrew Peterson, Christopher David Roberts, , Richard A. Wood

Abstract

The Atlantic meridional overturning circulation (AMOC) has weakened substantially over the past decade. Some weakening may already have occurred over the past century, and global climate models project further weakening in response to anthropogenic climate change. Such a weakening could have significant impacts on the surface climate. However, ocean model simulations based on historical conditions have often found an increase in overturning up to the mid-1990s, followed by a decrease. It is therefore not clear whether the observed weakening over the past decade is part of decadal variability or a persistent weakening. Here we examine a state-of-the-art global-ocean reanalysis product, GloSea5, which covers the years 1989 to 2015 and closely matches observations of the AMOC at 26.5° N, capturing the interannual variability and decadal trend with unprecedented accuracy. The reanalysis data place the ten years of observations-April 2004 to February 2014-into a longer-term context and suggest that the observed decrease in the overturning circulation is consistent with a recovery following a previous increase. We find that density anomalies that propagate southwards from the Labrador Sea are the most likely cause of these variations. We conclude that decadal variability probably played a key role in the decline of the AMOC observed over the past decade.

Read more: https://www.researchgate.net/publication/303502652_Recent_slowing_of_Atlantic_overturning_circulation_as_a_recovery_from_earlier_strengthening

The reason I don’t lose any sleep over the North Atlantic scenario is the scale of the disturbance likely required to trigger such a collapse. The last collapse, 12,900 years ago, was believed to have occurred when the ice wall holding Lake Agassiz broke.

Lake Agassiz was gigantic, 170,000 square miles of fresh water which covered much of North America, much larger than any modern lake. When the ice wall gave way, a deluge of fresh water suddenly dumped into the ocean, triggering large scale ocean current changes.

Right now, in today’s world, there doesn’t seem to be any comparable trigger. There are no vast bodies of fresh water like Lake Agassiz, whose abrupt collapse could cause an ocean current disturbance of a magnitude comparable to what happened 12,900 years ago.

Of course, the apparent lack of plausible causation doesn’t stop climate alarmists from playing with their models, and publishing scary global warming causes ice age scenarios.

via Watts Up With That?

https://ift.tt/7bUpejE

June 7, 2022 at 08:49PM

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