Archives par mot-clé : North Atlantic

Apparent Atlantic warming cycle likely an artifact of climate forcing

by A.E. Messer & S. Lajeunesse, March 25, 2021 inPennStateNews

This map of the Earth shows the spacial pattern of temperature variance by percentage. The most variance is seen in the tropics with less at the poles. IMAGE: DANIEL J. BROUILLETTE. PENN STATE

UNIVERSITY PARK, Pa. — Volcanic eruptions, not natural variability, were the cause of an apparent “Atlantic Multidecadal Oscillation,” a purported cycle of warming thought to have occurred on a timescale of 40 to 60 years during the pre-industrial era, according to a team of climate scientists who looked at a large array of climate modeling experiments.

The result complements the team’s previous finding that what had looked like an “AMO” occurring during the period since industrialization is instead the result of a competition between steady human-caused warming from greenhouse gases and cooling from more time-variable industrial sulphur pollution.

“It is somewhat ironic, I suppose,” said Michael E. Mann, distinguished professor of atmospheric science and director, Earth System Science Center, Penn State. “Two decades ago, we brought the AMO into the conversation, arguing that there was a long-term natural, internal climate oscillation centered in the North Atlantic based on the limited observations and simulations that were available then, and coining the term ‘AMO.’ Many other scientists ran with the concept, but now we’ve come full circle. My co-authors and I have shown that the AMO is very likely an artifact of climate change driven by human forcing in the modern era and natural forcing in pre-industrial times.”

The researchers previously showed that the apparent AMO cycle in the modern era was an artifact of industrialization-driven climate change, specifically the competition between warming over the past century from carbon pollution and an offsetting cooling factor, industrial sulphur pollution, that was strongest from the 1950s through the passage of the Clean Air Acts in the 1970s and 1980s. But they then asked, why do we still see it in pre-industrial records?

New Northern North Atlantic Study Finds The Coldest Period With The Most Sea Ice Of The Last ~85 Years…Is Today

by K. Richard, August 24, 2020 in NoTricksZone

Ecological conditions for 3 temperature- and sea ice-sensitive species show the sub-Arctic North Atlantic has been cooling and gaining ice since 1940.

In recent months, several scientific publications have documented a dramatic cooling trend in the subpolar North Atlantic, with temperatures plummeting 2°C since 2008 (Bryden et al., 2020) or -0.78°C per decade since 2004 (Fröb et al., 2019). Maroon et al. (2020) even point out 2015 was the coldest of the last 100 years.


Decadal predictability of North Atlantic blocking and the NAO

by Athanasiadis et al., June 3, 2020 in Nature (Open Access)


Can multi-annual variations in the frequency of North Atlantic atmospheric blocking and mid-latitude circulation regimes be skilfully predicted? Recent advances in seasonal forecasting have shown that mid-latitude climate variability does exhibit significant predictability. However, atmospheric predictability has generally been found to be quite limited on multi-annual timescales. New decadal prediction experiments from NCAR are found to exhibit remarkable skill in reproducing the observed multi-annual variations of wintertime blocking frequency over the North Atlantic and of the North Atlantic Oscillation (NAO) itself. This is partly due to the large ensemble size that allows the predictable component of the atmospheric variability to emerge from the background chaotic component. The predictable atmospheric anomalies represent a forced response to oceanic low-frequency variability that strongly resembles the Atlantic Multi-decadal Variability (AMV), correctly reproduced in the decadal hindcasts thanks to realistic ocean initialization and ocean dynamics. The occurrence of blocking in certain areas of the Euro-Atlantic domain determines the concurrent circulation regime and the phase of known teleconnections, such as the NAO, consequently affecting the stormtrack and the frequency and intensity of extreme weather events. Therefore, skilfully predicting the decadal fluctuations of blocking frequency and the NAO may be used in statistical predictions of near-term climate anomalies, and it provides a strong indication that impactful climate anomalies may also be predictable with improved dynamical models.

Causes of the Rapid Warming of the North Atlantic Ocean in the Mid-1990s

by P. Homewood, April 9, 2020 in NotaLotofpeopleKnowThat

Most of us are probably familiar with the pattern of Arctic sea ice decline between 1979 and 2007, followed by a period of relative stability. Most of the decline took place after the mid 1990s.

The decline is nearly always explained away as the result of global warming, but a couple of old studies show this not to be the case.

In 2011, Robson & Sutton found that the sub polar gyre underwent remarkable and rapid warming in the mid 1990s, and that this was linked to changes in the North Atlantic Oscillation:

New Study: A Massive Cooling Of 2°C In 8 Years (2008-2016) Has Jolted Large Regions Of The North Atlantic

by K. Richard, February 14, 2020 in NoTricksZone

From 2008 to 2016 a widespread cooling ranging from 0.6°C to more than 2.0°C has chilled effectively the entire oceanic region from E. Canada to N. Iceland to S. Europe. The cooling persists year-round and extends from the surface down to depths of 800 m.


Image Source: Bryden et al., 2020

A year ago scientists revealed a large swath of the North Atlantic surface had cooled at a rate of -0.78°C per decade between 2004 and 2017 (Fröb et al., 2019).

North Atlantic Sea Levels Have Been Falling At A Rate Of 7.1 mm/yr Since 2004…In Tandem With 2°C Cooling

by K. Richard/Chafik et al. 2019, January 20, 2020 in NoTricksZone

Rapid cooling in the North Atlantic has reversed regional sea level changes and has apparently spread to the Greenland ice sheet

Image Source: Chafik et al. (2019)

Despite stressing global sea level rise is worrisome and due to anthropogenic warming, Chafik et al. (2019) report a distinct cooling trend in the North Atlantic that coincides with a transition to falling regional sea levels since 2004.

Deep-water circulation changes lead North Atlantic climate during deglaciation

by F. Muschitiello et al., March 20, 2019 in Nature


Constraining the response time of the climate system to changes in North Atlantic Deep Water (NADW) formation is fundamental to improving climate and Atlantic Meridional Overturning Circulation predictability. Here we report a new synchronization of terrestrial, marine, and ice-core records, which allows the first quantitative determination of the response time of North Atlantic climate to changes in high-latitude NADW formation rate during the last deglaciation. Using a continuous record of deep water ventilation from the Nordic Seas, we identify a 400-year lead of changes in high-latitude NADW formation ahead of abrupt climate changes recorded in Greenland ice cores at the onset and end of the Younger Dryas stadial, which likely occurred in response to gradual changes in temperature- and wind-driven freshwater transport. We suggest that variations in Nordic Seas deep-water circulation are precursors to abrupt climate changes and that future model studies should address this phasing.