by Blackport P. & Fyfe, J.C., Nov 11, 2022 in ScienceAdvances
Projections of wintertime surface climate over Europe depend on reliable simulations of the North Atlantic atmospheric circulation from climate models. However, it is unclear whether these models capture the long-term observed trends in the North Atlantic circulation. Here, we show that over the period from 1951 to 2020, the wintertime North Atlantic jet has strengthened, while model trends are, on average, only very weakly positive. The observed strengthening is greater than in any one of the 303 simulations from 44 climate models considered in our study. This divergence between models and observations is now much more apparent because of a very strong jet observed over the past decade. The models similarly have difficulty capturing the observed precipitation trends over Europe. Our results suggest that projections of winter atmospheric circulation and associated precipitation over Europe may be unreliable because they fail to capture the response to human emissions or underestimate the magnitude of multidecadal-to-centennial time scale internal variability.
by P. Gosselin, Apr 30, 2022 in NoTricksZone
New studies on the Atlantic current system assess the threshold between natural fluctuations and a climate change-driven evolution
25 April, 2022/Kiel, Germany. With a new publication in the scientific journal Nature Climate Change, researchers from Kiel once again contribute to the understanding of changes in the Atlantic Meridional Overturning Circulation (AMOC) – also known as the “Gulf Stream System”. It is important both for the global climate as well as for climate events in Europe. The authors focus on the question whether human-induced climate change is already slowing down this oceanic circulation. According to the new study, natural variations are still dominant. Improved observation systems could help detect human influences on the current system at an early stage.
Is the Atlantic Meridional Overturning Circulation (AMOC) slowing down? Is this system of ocean currents, which is so important for our climate, likely to come to a halt in the future? Are the observed variations a natural phenomenon or are they already caused by human-induced climate change? Researchers from various scientific disciplines use a wide range of methods to better understand the gigantic oceanic circulation.
“The AMOC provides Europe with a mild climate and determines seasonal rainfall patterns in many countries around the Atlantic. If it weakens over the long term, this will also affect our weather and climate. Other consequences could be a faster rise in sea levels at some coasts or a reduction in the ocean’s ability to take up carbon dioxide and mitigate climate change”, Professor Dr. Mojib Latif, Head of the Research Unit: Marine Meteorology at GEOMAR Helmholtz Centre for Ocean Research Kiel, explains. “We depend on the AMOC in many ways – but so far, we can only guess how it will develop, and whether and how strongly we humans ourselves will push it towards a tipping point where an unstoppable collapse will take its course.”
Using observational data, statistical analyses and model calculations, a team led by Professor Latif has therefore examined changes in the current system over the past one hundred years in greater detail. The results have now been published in the scientific journal Nature Climate Change. According to the researchers, part of the North Atlantic is cooling – a striking contrast to the majority of ocean regions. All evaluations indicate that since the beginning of the 20th century, natural fluctuations have been the primary reason for this cooling. Nonetheless, the studies indicate that the AMOC has started to slow down in recent decades.
by P. Homewood, June 13, 2021 in NotaLotofPeopleKnowThat
It’s not new, but it’s worth going over it again.
We have seen how Greenland temperatures rose sharply in the 1920s, and remained at levels similar to the last decade until the 1960s, when they fell equally sharply. This change in climate is closely interlinked with the Atlantic Multidecadal Oscillation (AMO), which switches from cold to warm phase, and back again, roughly every 50 to 60 years:
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?
by G. Müller-Plath, Nov 29, 2020 in WUWT
The present paper contributes a critical commentary on the recent finding by Mann, M. E., Steinman, B. A. and Miller, S. K (2020). Absence of internal multidecadal and interdecadal oscillations in climate model simulations. Nat. Commun. 11, 1–9.
Climate oscillations are recurring large-scale fluctuations in the surface temperatures of the oceans in connection with the atmosphere. This commentary focuses on the Pacific Decadal Oscillation (PDO, interdecadal timescale) and the Atlantic Multidecadal Oscillation (AMO, multidecadal timescale), which have been regarded as intrinsic climate drivers on the adjacent continents in numerous studies based on observations and paleoclimate reconstructions (Henley, 2017; O’Reilly et al., 2017). In a recent paper, Michael E. Mann and colleagues (Mann et al., 2020, hereafter M20) fail to find a PDO signal in global measured and modeled temperatures that is statistically different from noise. They further propose that the significant AMO-like signal is mainly due to anthropogenic aerosols in the 20th century, and to statistical artifacts before. Therefore they doubt the intrinsic nature of the two oscillations. The present paper shows that M20’s results are largely artifacts themselves with issues ranging from using inadequate data and referencing improper literature on anthropogenic aerosols with regards to the AMO to inappropriately interpreting the results with regards to the PDO.
by K. Richard, Oct 22, 2020 in NoTricksZone
European winter temperature variability is “dominated” by the North Atlantic Oscillation (NAO), which is, in turn, modulated by solar activity.
Even proponents of anthropogenic global warming (AGW) agree natural processes (AMO, NAO, ENSO, solar forcing, volcanism) drive temperature variability. But they insist the rising temperature trend is human-caused.
So if we don’t have a regional upward trend, is the non-warming natural or anthropogenic?
Lüdecke et al., 2020 find temperatures across Europe have been oscillating, not rising in linear fashion, for the last century. The timings of the temperature undulations correspond quite closely to natural ocean cycles (the NAO and AMO). The authors detail a non-linear and indirect solar activity impact on these ocean cycles, and ultimately to the European climate.
by P. Homewood, April 5, 2020 in NotaLotofPeopleKnowThat
Just following up on Joe Bastardi’s article yesterday about El Ninos and Arctic warming, it is worth looking at longer term trends.
Below is the chart of the MEI, with red indicating El Ninos and blue La Ninas.:
Extended Multivariate ENSO Index
As we can see, the period 1925 to 1945 was dominated by powerful El Ninos. This of course was also the time of great warming in the Arctic, known as “The Warming in The North”, when temperatures across much of the Arctic were as high as they are now.
During the 1950s, a much colder climate took over in the Arctic, until it became warmer again in the 90s. This was also a period when La Ninas dominated.
The climate in the Arctic is also very well correlated with the Atlantic Multidecadal Oscillation (AMO):
Continuer la lecture de El Nino & Arctic Warming In the 1930s →
by P. Gosselin, December 11, 2019 in NoTricksZone
Not CO2 related
A little later in the report we also find a flow diagram for the Victoria Falls:
Figure: Water flow rate-volume at the Victoria Falls an den 1907-2006. Source: Beilfuss 2012 (immediately pdf)
We see a strong variability from year to year. On a scale of several decades, the period 1940-1980 is characterized by particularly high flow rates. The early 20th century was rather dry. A coupling to the 60-year-old ocean cycle offers itself. The Pacific is far away, but the wet Zambezi phase fits quite well into the negative PDO:
igure: The Pacific Decadal Oscillation (PDO). Source: By Giorgiogp2 – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=13297650
by P. Gosselin, July 7, 2019 in NoTricksZone
By Die kalte Sonne
(German text translated by P Gosselin)
Seven years ago, in our book “The Forgotten Sun”, we proposed using ocean cycles for medium-term forecasts. At the time, the climate establishment was strictly opposed to this. Today fortunately times have changed.
On March 15, 2019, a team led by George Krokos analyzed the temperature development of the Red Sea in Geophysical Research Letters, which has become noticeably warmer in recent decades. The researchers put this into a long-term context and found a strong correlation with the 70-year ocean cycle of the AMO (Atlantic Multidecade Oscillation).
Now that AMO has reached its peak, Krokos and colleagues expect the Red Sea to cool in the next three decades.
Natural Climate Oscillations may Counteract Red Sea Warming Over the Coming Decades
Recent reports of warming trends in the Red Sea raise concerns about the response of the basin’s fragile ecosystem under an increasingly warming climate. Using a variety of available Sea Surface Temperature (SST) data sets, we investigate the evolution of Red Sea SST in relation to natural climate variability. Analysis of long‐term SST data sets reveals a sequence of alternating positive and negative trends, with similar amplitudes and a periodicity of nearly 70 years associated with the Atlantic Multidecadal Oscillation. High warming rates reported recently appear to be a combined effect of global warming and a positive phase of natural SST oscillations. Over the next decades, the SST trend in the Red Sea purely related to global warming is expected to be counteracted by the cooling Atlantic Multidecadal Oscillation phase. Regardless of the current positive trends, projections incorporating long‐term natural oscillations suggest a possible decreasing effect on SST in the near future.