October 2024 – Page 9 – Iowa Climate Science Education

, Dr. Kevin E. Trenberth, a distinguished scholar at the National Center for Atmospheric Research, commented on this movie: “I don’t recall a lot except that the whole science was incredibly wrong,”, “one does not get an ice age out of global warming.”

Likely you’ve heard the recent and previous warnings from Mann and friends about the ocean conveyor belt (including the Gulf Stream) slowing down and freezing us all. With the COP gathering next month, something scary must be proclaimed, and Global Freezing is it, replacing Global Boiling earlier this year. The declaration signed by Mann and 23 other scientists was Open Letter by Climate Scientists
to the Nordic Council of Ministers, Reykjavik, October 2024. Preface:

“We, the undersigned, are scientists working in the field of climate research and feel it is
urgent to draw the attention of the Nordic Council of Ministers to the serious risk of a
major ocean circulation change in the Atlantic. A string of scientific studies in the past few
years suggests that this risk has so far been greatly underestimated. Such an ocean
circulation change would have devastating and irreversible impacts especially for Nordic
countries, but also for other parts of the world.”

“Given the increasing evidence for a higher risk of an AMOC collapse, we believe it is of critical importance that Arctic tipping point risks, in particular the AMOC risk, are taken seriously in governance and policy. Even with a medium likelihood of occurrence, given that the outcome would be catastrophic and impacting the entire world for centuries to come, we believe more needs to be done to minimize this risk.”

The Warning is based on Fear, not Facts

1. The AMOC has been stable for the last four decades.

Florida Current transport observations reveal four decades of steady state Volkov et al 2024

Abstract

The potential weakening of the Atlantic Meridional Overturning Circulation (AMOC) in response to anthropogenic forcing, suggested by climate models, is at the forefront of scientific debate. A key AMOC component, the Florida Current (FC), has been measured using submarine cables between Florida and the Bahamas at 27°N nearly continuously since 1982. A decrease in the FC strength could be indicative of the AMOC weakening. Here, we reassess motion-induced voltages measured on a submarine cable and reevaluate the overall trend in the inferred FC transport. We find that the cable record beginning in 2000 requires a correction for the secular change in the geomagnetic field. This correction removes a spurious trend in the record, revealing that the FC has remained remarkably stable. The recomputed AMOC estimates at ~26.5°N result in a significantly weaker negative trend than that which is apparent in the AMOC time series obtained with the uncorrected FC transports.

Fig. 1: The Western Boundary Time Series
observing network in the Straits of Florida.

The network consists of the submarine telecommunications cable between West Palm Beach and Grand Bahama Island (cyan curve), ship sections across the Florida Current (FC) at 27°N with in situ measurements at nine stations (white circles), two bottom pressure gauges on both sides of the FC at 27°N (yellow stars), and along-track satellite altimetry measurements (magenta dotted line). CTD Conductivity-Temperature-Depth, LADCP Lowered Acoustic Doppler Current Profiler, XBT expendable bathythermograph.

Fig. 6: Florida Current (FC) volume transports corrected for
the secular change in the Earth’s Magnetic Field (EMF).

a The time series of the daily FC volume transport: (blue) not corrected for the secular change in the EMF, (red) corrected for the secular change in the EMF. The linear trends of the FC transport not corrected and corrected for the EMF are shown by the blue and red lines, respectively. b The differences between the cable and ship section transport for the cable data (blue squares) not corrected for the EMF and (red circles) corrected for the EMF. The linear trends of the differences (ΔT) not corrected and corrected for the EMF are shown by the blue and red lines, respectively.

Fig. 2: The Florida Current volume transport.

Daily transport estimates from the cable record (black; prior to corrections applied in this study); estimates from the Pegasus (orange diamonds) and Pegasus in dropsonde mode (Pegasus-DM; light blue circles) sections; estimates from the dropsonde sections (blue circles); and estimates from the Lowered Acoustic Doppler Current Profiler (LADCP) sections (red circles). The linear trends for 1982–2023, 1982–1998, and 2000–2023 periods are shown by the orange, cyan, and magenta lines, respectively.

2. Paleo records show past AMOC changes due to seafloor shifts not climate change.

Controlling factors for the global meridional overturning circulation: A lesson from the Paleozoic, Yuan et al. 2024.

Abstract

The global meridional overturning circulation (GMOC) is important for redistributing heat and, thus, determining global climate, but what determines its strength over Earth’s history remains unclear. On the basis of two sets of climate simulations for the Paleozoic characterized by a stable GMOC direction, our research reveals that GMOC strength primarily depends on continental configuration while climate variations have a minor impact. In the mid- to high latitudes, the volume of continents largely dictates the speed of westerly winds, which in turn controls upwelling and the strength of the GMOC. At low latitudes, open seaways also play an important role in the strength of the GMOC. An open seaway in one hemisphere allows stronger westward ocean currents, which support higher sea surface heights (SSH) in this hemisphere than that in the other. The meridional SSH gradient drives a stronger cross-equatorial flow in the upper ocean, resulting in a stronger GMOC. This latter finding enriches the current theory for GMOC.

On the basis of a series of simulations for the Paleozoic, we find that the GMOC is primarily controlled by:

freshwater input into ocean;
wind-driven Ekman pumping in the midlatitudes, and
SH anomaly in low latitudes.

The latter two factors are especially important for the strength of the GMOC and are highly related to continental configuration. Our major conclusions find validation through Paleozoic climate simulations using the HadCM3 model by Valdes et al. (53, 67) and a non-IPCC class model, FOAM, by Pohl et al. (52) (figs. S17 and S18). This last study by Pohl et al. (52) also pointed out the unfortunate absence of proxy data for validating the direction and magnitude of the Paleozoic GMOC.

Controlling factors for the global
meridional overturning circulation

Fig. 5. Schematic of controlling factors for the GMOC during the Paleozoic. The schematic is based on the situation for 400 Ma. Three main factors are shown, the less net precipitation in the south SH; the strong westerlies, ocean surface current, and Ekman upwelling in the midlatitude region in NH; the SSH anomaly and associated pressure anomaly in the low-latitude region.

Although there has been tremendous interest in understanding the mechanisms that govern the MOC, surface topography in the westerlies region and the presence of an open seaway in the low-latitude region were previously largely overlooked. Our study thus draws attention to how the evolution of continents in these two regions affects the strength of MOC. Our study indicates that the traditional theory for MOC misses an important element, that is, the influence of a low-latitude seaway. Previous studies either did not have such a seaway (1, 34, 43) or had a partial seaway that connected the present-day Atlantic Ocean and Pacific Ocean only (32–34). Their focus was mostly on the strength of the AMOC and mechanism invoked generally involved freshwater and salinity only (32, 33, 68), while as demonstrated above, a fully open low-latitude seaway affects the MOC in a fundamentally different way.

3. AMOC alarm presupposes Arctic “Amplification” of Global Warming

Activist scientists claim the Arctic is warming up to five times faster than lower latitudes. This is based on models projecting scarce temperature records great distances over the Arctic ocean drift sea ice. There are three flaws in the arctic warming claim (from Arctic “Amplification” Not What You Think)

a, Arctic Amplification is an artifact of Temperature Anomalies

Clive Best provides this animation of recent monthly temperature anomalies which demonstrates how most variability in anomalies occur over northern continents.

b. Arctic Surface Stations Records Show Ordinary Warming

Locations of 118 arctic stations examined in this study and compared to observations at 50 European stations whose records averaged 200 years and in a few cases extend to the early 1700s.

The paper is: Arctic temperature trends from the early nineteenth century to the present W. A. van Wijngaarden, Theoretical & Applied Climatology (2015). My synopsis: Arctic Warming Unalarming

c. Arctic Warmth Comes from Meridional Heat Transport, not CO2

4. Hypothesis that rising CO2 will collapse the AMOC is flawed.

The “AMOC is collapsing” narrative goes like this:

Ocean circulation is driven by density differences, which depend on the salinity and the temperature of the water. Cold, salty water is heavier than warm, fresh water. When flowing water reaches Greenland, it becomes very cold and salty, causing it to sink and flow south, where the water warms and rises closer to the surface again. Some compares the process to a conveyor belt going around and around.

This graphic shows a highly simplified schematic of the Atlantic Meridional Overturning Circulation (AMOC) against a backdrop of the sea surface temperature trend since 1993 from the Copernicus Climate Change Service (https://climate.copernicus.eu/). Image credit: Ruijian Gou. > High res figure.

Changing the salinity of the water messes up the way the water flows. That’s why the melting of the Greenland ice sheets is a big problem: It’s injecting a ton of freshwater into the ocean far north, where the water is usually very salty. The more freshwater, the weaker the circulation—not to mention that atmospheric temperatures are also increasing, which also makes water lighter. The new study shows that if the density dynamics change enough, the conveyor belt will eventually stop moving, aka “collapse.” That means it won’t transport any water, saline, or heat across the globe.

So the scenario is that supposed amplified Arctic warming will cause iceberg calving and glacial melting, and the freshwater will slow and eventually stop the AMOC. Firstly, the above study shows seafloor configuration has greater impact than salinity changing. Secondly, the spread of freshwater is not so simple.

Role of the Labrador Current in the Atlantic Meridional Overturning Circulation response to greenhouse warming, Shan et al. 2024

Abstract

Anthropogenic warming is projected to enhance Arctic freshwater exportation into the Labrador Sea. This extra freshwater may weaken deep convection and contribute to the Atlantic Meridional Overturning Circulation (AMOC) decline. Here, by analyzing an unprecedented high-resolution climate model simulation for the 21st century, we show that the Labrador Current strongly restricts the lateral spread of freshwater from the Arctic Ocean into the open ocean such that the freshwater input has a limited role in weakening the overturning circulation. In contrast, in the absence of a strong Labrador Current in a climate model with lower resolution, the extra freshwater is allowed to spread into the interior region and eventually shut down deep convection in the Labrador Sea. Given that the Labrador Sea overturning makes a significant contribution to the AMOC in many climate models, our results suggest that the AMOC decline during the 21st century could be overestimated in these models due to the poorly resolved Labrador Current.

5. The “Tipping Point” scare is unscientific.

Uncertainties too large to predict tipping times of major Earth system components from historical data, Ben-Yami et al. 2024

Abstract

One way to warn of forthcoming critical transitions in Earth system components is using observations to detect declining system stability. It has also been suggested to extrapolate such stability changes into the future and predict tipping times. Here, we argue that the involved uncertainties are too high to robustly predict tipping times. We raise concerns regarding

(i) the modeling assumptions underlying any extrapolation of historical results into the future,

(ii) the representativeness of individual Earth system component time series, and

(iii) the impact of uncertainties and preprocessing of used observational datasets, with focus on nonstationary observational coverage and gap filling.

We explore these uncertainties in general and specifically for the example of the Atlantic Meridional Overturning Circulation. We argue that even under the assumption that a given Earth system component has an approaching tipping point, the uncertainties are too large to reliably estimate tipping times by extrapolating historical information.

“The conclusions of this study are certainly in line with my understanding of the current state of the art,” says Gavin Schmidt, a climate scientist and professor at Columbia University and the director of NASA’s Goddard Institute for Space Studies (GISS). Schmidt was not involved in the new work, but has extensively researched climate variability and systems like AMOC.

“I have not been impressed by previous or recent efforts to predict upcoming tipping points in either AMOC or ice sheets — there is more going on than just patterns in time series and we still don’t have sufficiently complex and calibrated models to have a robust idea of what will happen,” says Gavin Schmidt, director of NASA’s GISS.

Footnote

In researching for this post I discovered an informative website Ocean to Climate Science news & articles on topics related to ocean and climate by oceanographer Sang-Ki Lee. Some additional examples of studies for further reading on this issue are below.

Gulf Stream’s fate to be decided by climate ‘tug-of-war’

A stable Atlantic Meridional Overturning Circulation in a changing North Atlantic Ocean since the 1990s

Detectability of an AMOC Decline in Current and Projected Climate Changes

Global surface warming enhanced by weak Atlantic overturning circulation

Nonstationarity of the Atlantic Meridional Overturning Circulation’s Fingerprint on Sea Surface Temperature