Methane Hydrates Tipping Point threatens to get crossed

The July 2020 ocean temperature anomaly on the Northern Hemisphere was 1.11°C or 2°F above the 20th century average, the highest July anomaly on record. The yellow circles onthe image below are July data and red circles are data for other months.

The July 2020 ocean temperature anomaly on the Northern Hemisphere was well above the latent heat tipping point of 1°C above the 20th century average, threatening to soon reach the methane hydrates tipping point of 1.35°C above the 20th century average.

These are only two of ten tipping points that are hitting the Arctic, as described in a earlier post, while additionally there are further tipping points that do not specifically hinge on what happens in the Arctic, e.g. the ozone layer is very vulnerable, as described in an earlier post.

The latent heat tipping point

An earlier analysis indicates that the latent heat tipping point gets crossed when ocean temperature anomalies on the Northern Hemisphere get higher than 1°C above the 20th century average. As above image indicates, the tipping point did get crossed temporarily on several occasions in recent years, but this year it looks to have been crossed irreversibly, as indicated by the trend.

[ Record low volume? ]

As the image on the right indicates, there still is sea ice present at the surface of the Arctic Ocean, so there still is sea ice in terms of volume. However, there now is virtually no ice left underneath the surface of the Arctic Ocean to act as a buffer.

In other words, the sea ice has virtually lost its capacity to act as a buffer to consume further heat entering the Arctic Ocean.

Once the latent heat tipping point is crossed, further incoming heat will have to get absorbed by the Arctic Ocean, instead of getting consumed by the melting of sea ice, as was previously the case.

As long as there is sea ice in the water, this sea ice will keep absorbing heat as it melts, so the temperature will not rise at the sea surface and remain at zero°C. The amount of energy that is consumed in the process of melting the ice is as much as it takes to heat an equivalent mass of water from zero°C to 80°C.

Ocean Heat

Meanwhile, global heating continues and more than 90% of global heating is going into oceans.

Arctic sea ice is getting very thin and, at this time of year, it is melting rapidly, due to heat entering the Arctic Ocean from above, from the Atlantic Ocean and the Pacific Ocean, and from rivers that end in the Arctic Ocean.

The two images below shows the difference in sea surface temperatures of the Arctic Ocean, between August 4, 2020, 12 GMT and a forecast for August 22, 2020, 12 GMT. The important difference between the two images is the shrinking of the pale blue area in the Arctic Ocean, where the sea surface temperature is below 0°C, and the increase in areas with other tints of blue where the sea surface temperature is above 0°C.

The image below, from a recent post, shows ocean surface temperatures on August 10, 2020, with very high anomalies showing up where the sea ice has disappeared. The image also shows that the Arctic Ocean in many places is very shallow (right panel).

[ from earlier post ]

The dramatic decline of the sea ice becomes more clear when looking at Arctic sea ice volume. The image below, by Nico Sun, shows volume up to August 31, 2020.

The dramatic decline of the sea ice is even more evident when looking at Arctic sea ice thickness. The image below, by Nico Sun, shows thickness up to August 31, 2020.

Below is a Universität Bremen image showing Arctic sea ice thickness on August 29, 2020.

The navy.mil animation below was run on September 15, 2020, and shows Arctic sea ice thickness over 30 days (last 8 frames are forecasts for September 16 - September 23, 2020).

The image below shows a forecast for September 15, run September 14, 2020. 

The image below shows that, on August 30, 2020, the mean air temperature in the Arctic (80°N to 90°N) was still above the freshwater freezing point (0°C or 32°F or 273.15°K), well above the mean temperature for 1958-2002 and also above the year 2012 which had exceptionally high temperatures in September.

As long as the air temperature remains above the freshwater freezing point, the sea ice will keep melting from above, on top of the melting that occurs from below as a result of ocean heat entering the Arctic Ocean from the Atlantic Ocean and the Pacific Ocean.

Above ads.nipr.ac.jp image shows sea ice in 2020 (red line) still shrinking in extent. Arctic sea ice on September 13, 2020, was 3.55 million km², i.e. well below extent for that date in any other year except for 2012, when extent was as low as 3.18 million km² (on September 15 and 16, 2012). 

According to NSIDC, sea ice extent on September 15, 2020, was 3.737 million km², while extent on September 17, 2012, was 3.387 million km².

The image below, updated by the University of Bremen September 10, 2020, shows Arctic sea ice extent perilously close to 2012 extent. Note that the University of Bremen has meanwhile "reprocessed the data".

On the Northern Hemisphere, ocean temperatures are very high at the moment. The image below illustrates that, showing sea surface temperatures as high as 33.8°C on August 26, 2020. For some time to come, water flowing into the Arctic Ocean from the Atlantic Ocean and the Pacific Ocean will therefore remain higher than it used to be.

River water flowing into the Arctic Ocean also contributes to rising temperatures of the water of the Arctic Ocean.

Furthermore, there are numerous feedbacks, e.g. when black carbon from forest fires settles on sea ice, this causes albedo changes in a self-reinforcing feedback loop, i.e. as less sunlicht gets reflected back up into the sky, more sunlight will be absorbed by the sea ice, speeding up its decline.

As confirmed by a recent study, dramatic abrupt climate change is taking place in the Arctic, and another dangerous feedback of the rising heat is stronger storms, as also discussed in an earlier post.

Stronger storms can bring more moisture into the Arctic. Above image shows a forecast for August 29, 2020, 1200Z, with two cyclones hitting the Arctic Ocean and with 100% relative humidity at the North Pole, at 1000 hPa.

Above image shows a cyclone, forecast for August 25, 2020, with wind north of Greenland as fast as 67 km/h or 41 mph.

Above image shows that rain is forecast to fall over the North Pole on August 26, 202, 12Z.

The image on the right is a forecast for August 26, 2020, 21Z. The image shows strong wind over the North Atlantic, while another cyclone is showing up north of Greenland.

Sea ice is very thin at the moment, so it is vulnerable to get broken up into small small pieces, thus speeding up its melting, as warm water can more easily reach the broken-up pieces from all sides.

Such storms can batter the sea ice, and they can come with rain, further devastating the sea ice by speeding up melting and creating melt-pools on top of the ice with a low albedo.

The image on the right shows a forecast for August 29, 2020. Rain is showing up north of Greenland, as another cyclone is forecast to hit the area. The cyclone is forecast to have strong winds spinning counter-clockwise, thus threatening to speed up the drift of the sea ice north of Greenland toward Fram Strait.

A sequence of cyclones could in a short time push much of the thickest of the remaining sea ice out of the Arctic Ocean through Fram Strait.

The methane hydrates tipping point

As discussed in earlier posts such as this one, the rising temperature of the Arctic Ocean threatens to destabilize methane hydrates contained in sediments at the seafloor of the Arctic Ocean.

As the top image shows, the methane hydrates tipping point could be crossed soon, as the Arctic Ocean is heating up dramatically, which is in part the result of the latent heat tipping point getting crossed, which makes that the temperature of the Arctic Ocean can rise very rapidly.

The methane hydrates tipping point threatens to get crossed as ocean temperature anomalies on the Northern Hemisphere become higher than 1.35°C above the 20th century average, which threatens to occur early next year.

Because the Arctic Ocean in many places is very shallow, heat can quickly reach sediments at the seafloor, which threatens to destabilize methane hydrates. The water of the Arctic Ocean is particularly shallow over the East Siberian Arctic Shelf (ESAS), making that the water there can warm up very quickly during summer heat peaks with heat reaching the seafloor and penetrating cracks in frozen sediments at the seafloor, which can lead to abrupt destabilization of methane hydrates contained in these sediments.

As discussed in an earlier post, the loss of subsurface sea ice is only one of ten tipping points hitting the Arctic. As the temperature of the oceans keeps rising, more heat will reach sediments at the seafloor of the Arctic Ocean that contain vast amounts of methane, as discussed in this page and this post.

Large abrupt methane releases in one spot will quickly deplete the oxygen in shallow waters, making it harder for microbes to break down the methane there, while methane that is rising through waters that are only shallow will also be able to enter the atmosphere very quickly, leaving little time for microbes to break down the methane.

As illustrated by the 2012 image on the right, a large abrupt release of methane from hydrates in the Arctic can have more warming impact than all carbon dioxide emitted by burning of fossil fuel in a year. This is due to the high global warming potential (GWP) of methane following its release.

As this heating is concentrated in the Arctic, it will contribute to further methane releases from hydrates in the Arctic, in another self-reinforcing feedback loop.

The situation is extremely dangerous, given the vast amounts of methane present in sediments in the ESAS and given that there is very little hydroxyl in the air over the Arctic to break down the methane.

[ from earlier post ]

Ominously, the MetOp-1 satellite recorded a peak methane level of 2945 parts per billion (ppb), at 586 mb on the afternoon of August 18, 2020.

Two days later, the MetOp-1 satellite recorded a peak methane level of 2778 ppb, at 469 mb on the afternoon of August 20, 2020, while mean methane levels reached 1907 ppb.

That afternoon, on August 20, 2020, the MetOp-1 satellite recorded an even higher methane level, of 1923 ppb, at 293 mb, i.e. higher up in the atmosphere.

The danger is further illustrated by the image below, posted in February 2019 and showing a potential rise of 18°C or 32.4°F from 1750 by the year 2026.

Indeed, a rise of 18°C could eventuate by 2026, as illustrated by the image below and as discussed in an earlier post.

The situation is dire and calls for immediate, comprehensive and effective action, as described in the Climate Plan.


Links

• NOAA Global Climate Report - July 2020
https://www.ncdc.noaa.gov/sotc/global/202007

• Danish Meteorological Institute - 5 Day Ocean Forecast - Universal (Greenwich) Time
http://ocean.dmi.dk/anim/index.uk.php

• Danish Meteorological Institute - sea ice thickness and volume
http://polarportal.dk/en/sea-ice-and-icebergs/sea-ice-thickness-and-volume

• Danish Meteorological Institute - Arctic temperature
http://ocean.dmi.dk/arctic/meant80n.uk.php

• Danish Meteorological Institute - Arctic sea ice extent
http://ocean.dmi.dk/arctic/icecover.uk.php

• NOAA ocean heat content
https://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/index.html

• MetOp satellite - methane
https://www.ospo.noaa.gov/Products/atmosphere/soundings/iasi

• Arctic sea ice - thickness - navy.mil
https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/arctic.html

• Arctic sea ice - thickness - Universität Bremen
https://seaice.uni-bremen.de/databrowser

• Climate reanalyzer - precipitation, wind and pressure forecasts
https://climatereanalyzer.org/wx/fcst/?mdl_id=gfs&dm_id=world-ced&wm_id=prcp-mslp-gph500

• New release: Arctic warming satisfies criteria for abrupt climate change https://www.bjerknes.uib.no/en/article/news/arctic-warming-satisfies-criteria-abrupt-climate-change

• Past perspectives on the present era of abrupt Arctic climate change - by Eystein Jansen et al. https://www.nature.com/articles/s41558-020-0860-7

• Copernicus Atmosphere Monitoring Service
https://atmosphere.copernicus.eu/charts/cams

• Arctic sea ice extent - NSIDC
http://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph

• Arctic sea ice extent - Vishop, Arctic Data archive System, National Institute of Polar Research, Japan
https://ads.nipr.ac.jp/vishop/#/extent

• Arctic sea ice extent - University of Bremen 

https://seaice.uni-bremen.de/data/amsr2/today/extent_n_running_mean_amsr2_previous.png

• North Hole 2020?
https://arctic-news.blogspot.com/2020/08/north-hole-2020.html

• Arctic Hit By Ten Tipping Points
https://arctic-news.blogspot.com/2020/04/arctic-hit-by-ten-tipping-points.html

• Why stronger winds over the North Atlantic are so dangerous
https://arctic-news.blogspot.com/2020/02/why-stronger-winds-over-north-atlantic-are-so-dangerous.html

• Very High Greenhouse Gas Levels
https://arctic-news.blogspot.com/2020/05/very-high-greenhouse-gas-levels.html

• Critical Tipping Point Crossed In July 2019
https://arctic-news.blogspot.com/2019/09/critical-tipping-point-crossed-in-july-2019.html

• Fast Path to Extinction
https://arctic-news.blogspot.com/2020/06/fast-path-to-extinction.html

• Crossing the Paris Agreement thresholds
https://arctic-news.blogspot.com/p/crossing.html

• 2°C crossed
https://arctic-news.blogspot.com/2020/03/2c-crossed.html

• Why America should lead on climate
https://arctic-news.blogspot.com/2016/01/why-america-should-lead-on-climate.html

• Methane's Role in Arctic Warming
https://arctic-news.blogspot.com/2016/02/methanes-role-in-arctic-warming.html

• The Threat
https://arctic-news.blogspot.com/p/threat.html

• When will we die?
https://arctic-news.blogspot.com/2019/06/when-will-we-die.html

• A rise of 18°C or 32.4°F by 2026?
https://arctic-news.blogspot.com/2019/02/a-rise-of-18c-or-324f-by-2026.html

• Most Important Message Ever
https://arctic-news.blogspot.com/2019/07/most-important-message-ever.html

• Climate Plan
https://arctic-news.blogspot.com/p/climateplan.html

North Hole 2020?

Will there be open water at the North Pole in August 2020?

Above images show, on the left, sea surface temperatures on August 4, 2020, with a forecast on the right for August 9, 2020.

On the image at the left, the center of the Arctic Basin (pale-blue) still has a sea surface temperature below 0°C (or 32°F).

Around that pale-blue area is a blue area where sea surface temperatures are 0 to 2°C (or 32 to 35.6°F).

Seawater will freeze and stay frozen at about −2 °C (28 °F). The sea surface of the Arctic Ocean contains less salt, so the sea ice will stay frozen longer, even as temperatures rise, but it will melt at 0°C (or 32°F).

As the images show, the blue area where sea surface temperatures are at or above 0°C (or 32°F), is encroaching upon the pale-blue area at the center of the Arctic Basin, and appears to reach the North Pole at August 9, 2020.

Hat-tip to Albert Kallio for pointing at this.

Above combination image shows the running twelve-month averages of global-mean (top) and European-mean (bottom) surface air temperature anomalies relative to 1981-2010, based on monthly values from January 1979 to July 2020.

The shape of current anomalies is very similar to the peak reached around 2016. This in itself is alarming and it is even more alarming since the peak around 2016 was reached under El Niño conditions, whereas the July 2020 temperature was reached under ENSO-neutral conditions, as the image below illustrates.

The image below shows surface temperatures as high as 6.1°C or 42.9°F north of Greenland for August 7, 2020, with wind coming from the south-east.

The image below shows sea surface temperatures as high as 2.2°C or 36°F north of Greenland on August 7, 2020.

The image below shows Arctic sea ice volume, with the black line showing volume in 2020, up to August 12, 2020.

The dramatic decline of the sea ice becomes even more evident when looking at the fall in thickness. The navy.mil animation below was run on August 11, 2020, and shows sea ice thickness over 30 days (last 8 frames are forecasts for August 12 - August 19, 2020).

16°C (or 60.8°F) at northern tip of Greenland

The temperature was 16°C (or 60.8°F) on August 7, 2020, 10:00 am, at Kap Morris Jesup, at the northern tip of Greenland. The lowest temperature at Kap Morris Jesup over the past few days (i.e. from July 27 Jul 1:00 am — August 11, 1:00 am) was 0°C, i.e. on August 6, 2020, 7:00 pm. The average temperature at Kap Morris Jesup over this period was 8°C (or 46.4°F).

Remember that above 0°C, ice will melt. The water temperature of the Arctic Ocean underneath the sea ice is warmer, and this has been melting the sea ice from below. There still is a (rapidly thinning and shrinking) layer of sea ice at the surface of the Arctic Ocean, because until recently, air temperatures had remained low enough to maintain it, while it also takes time for the ice to melt. As long as there is ice, the heat will be consumed by the process of melting - once the ice is gone, temperatures will rise even more rapidly.

Relative humidity over this period was 69%, which means there was quite a bit of rain as well, further speeding up the melting.

The image below shows the ice at the northern tip of Greenland on August 6, 2020.

The image below shows ocean surface temperatures, with very high anomalies showing up where the sea ice has disappeared.

Above image also shows that the Arctic Ocean in many places is very shallow, which means that heat can quickly reach sediments at the seafloor, threatening to destabilize methane hydrates.

Methane levels are very high at the moment, the MetOp-1 sattelite recorded a mean methane level of 1917 ppb at 293 mb on August 4, 2020 pm, with high methane levels visible over the East Siberian Arctic Shelf (ESAS).

High methane levels were recorded over the Arctic Ocean by the MetOp-1 satellite on the morning of August 8, 2020, at 469 mb.

The situation is dire and calls for immediate, comprehensive and effective action, as described in the Climate Plan.


Links

• Danish Meteorological Institute - 5 Day Ocean Forecast - Universal (Greenwich) Time
http://ocean.dmi.dk/anim/index.uk.php

• Danish Meteorological Institute - sea ice thickness and volume
http://polarportal.dk/en/sea-ice-and-icebergs/sea-ice-thickness-and-volume

• Copernicus - Surface air temperature for July 2020
https://climate.copernicus.eu/surface-air-temperature-july-2020

• NOAA - ENSO: Recent Evolution, Current Status and Predictions - August 3, 2020
https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

• Temperature at Kap Morris Jesup, the northern tip of Greenland
https://www.timeanddate.com/weather/@3421844/historic

• NASA Worldview image of northern tip of Greenland, August 6, 2020

https://worldview.earthdata.nasa.gov

• Climate Plan
https://arctic-news.blogspot.com/p/climateplan.html

Arctic sea ice could disappear completely within two months' time

Arctic sea ice fell by 3.239 million km² in extent in 25 days (i.e. from July 1 to 25, 2020). Melting will likely continue for another two months. If it continues on its current trajectory, the remaining 6.333 million km² of Arctic sea ice could disappear completely within two months' time.

The fall in extent over the next two months' time may not remain as as steep as it was in July, yet the sea ice still could disappear completely. One reason for this is that, over the years, sea ice thickness has been declining even faster than extent. The rapid decline in sea ice thickness is illustrated by the sequence of images below.

The image on the right further illustrates that sea ice is getting very thin, which threatens the latent heat tipping point to get crossed. 

Sea currents and the Coriolis force will make that the influx of warm, salty water into the Arctic Ocean will continue. With no buffer of sea ice left underneath the surface of the sea ice to absorb incoming ocean heat, more heat will accumulate in the Arctic Ocean, threatening that the methane hydrates tipping point will get crossed.

The navy.mil animation below was run on August 3, 2020, and shows sea ice thickness over 30 days (last 8 frames are forecasts for August 4 - August 11, 2020). 

Here's another indication that the buffer is disappearing fast. North of Greenland and of the Canadian Arctic Archipelago, less than 700 km from the North Pole, the sea ice is disappearing, precisely where the thickest sea ice used to be located. 

High greenhouse gas levels are causing high temperatures over the Arctic and high ocean temperatures. 

On July 25, 2020, sea surface temperatures in the Arctic Ocean were as high as 20.8°C or 69.4°F (at the green circle on above image).

At that same location, on July 22, 2020, sea surface temperatures in the Arctic Ocean were as much as 17°C or 30.5°F higher than the daily average during the years 1981-2011. 

This location is where the Pechora River flows into the Barents Sea (the green circle pointed at by the white arrow on above image).

Distortion of the jet stream is causing more extreme weather, resulting in the recent lengthy heatwave over Siberia that has heated up the water of rivers flowing into the Arctic Ocean.

A cyclone was visible over the Arctic Ocean on July 28, 2020, as illustrated by the image on the right. 

Underneath on the right is a forecast for August 7, 2020, showing rain over the North Pole. 

In summary, Arctic sea ice may disappear completely over the next two months, and there are at least six reasons why this could occur:

• Low Arctic sea ice extent;
• Low Arctic sea ice thickness;
• High ocean temperature;
• High greenhouse gas levels;
• High temperatures over the Arctic;
• Distorted jet stream causing extreme weather such as storms that can break up the sea ice. 

As the image below shows, sea surface temperatures in the Arctic Ocean on August 1, 2020, were as much as 11.5°C or 20.7°F higher than 1981-2011 (at green circle, off the coast of Siberia, opposite Greenland). 

Ominously, the MetOp-1 satellite recorded peak methane levels of 2933 ppb, at 469 mb, on the afternoon of July 30, 2020.

The situation is dire and calls for immediate, comprehensive and effective action, as described in the Climate Plan.


Links

• NSIDC Arctic sea ice
http://nsidc.org/arcticseaicenews

• Polar Portal - sea ice volume
http://polarportal.dk/en/sea-ice-and-icebergs/sea-ice-thickness-and-volume

• NASA Worldview
https://worldview.earthdata.nasa.gov

• Arctic Hit By Ten Tipping Points
https://arctic-news.blogspot.com/2020/04/arctic-hit-by-ten-tipping-points.html

• Fast Path to Extinction
https://arctic-news.blogspot.com/2020/06/fast-path-to-extinction.html

• 2020 Siberian Heatwave continues
https://arctic-news.blogspot.com/2020/06/2020-siberian-heatwave-continues.html

• Climate Plan
https://arctic-news.blogspot.com/p/climateplan.html

Global warming and ice sheet melting: Portents of a Younger dryas-like stadial event

Global warming and ice sheet melting:

Portents of a Younger dryas-like stadial event

by Andrew Glikson

Linear climate projections by the IPCC are difficult to reconcile with the paleoclimate evidence of stadial cooling events which closely succeeded warming peaks, including the Younger dryas (12.9–11.6 kyr ago), Laurentian melt (~8.3 kyr) and earlier interglacial stadials. Each of these events followed peak interglacial temperatures, leading to extensive melting of the ice sheets and transient stadial cooling events. Current global temperature rises in the range of ~ +1.19 ± 0.13 °C (Northern Hemisphere) and higher in the Arctic are consistent with this pattern, leading to the build-up of ice melt pools south of Greenland and around Antarctica. The growth of these pools is likely to progress toward large-scale to a global stadial, inducing differential warming and cooling effects leading to major weather disruptions and storminess, possibly analogous to the Younger dryas and Laurentian melt events.

Linear temperature rise projections by the IPCC are unlikely in view of (1) amplifying feedbacks of greenhouse gases and global warming on land and ocean, and (2) stadial cooling effects due to the flow of ice melt water from the large ice sheets into the North Atlantic Ocean and the circum-Antarctic ocean (Figure 1). Apart from the absolute GHG level (~500 ppm CO₂-equivalent), the high rise rate of ~2-3 ppm CO₂/year and thereby temperature is driving dangerous weather events. The extreme rise in greenhouse gases in the atmosphere is evident from a comparison with past climate events (Figure 6). Linear temperature projections and thereby environment change are complicated by storminess due to collisions between air masses of contrasted temperatures. As the Arctic jet stream weakens, warm air currents from the south and freezing air masses from the north cross the boundary, a pattern already manifested by Arctic heat waves and fires and by penetration of freezing air masses into mid-latitudes, i.e. the “Beast from the East” snow storms. The increasing extent of cold ice melt pools around Greenland and Antarctica (Figure 1) suggest such a process is already in progress, signifying an onset of an interglacial stadial, as modelled by Hansen et al. 2016 and Bronselaer et al. (2016).

Figure 1 A. The cold ocean region south of Greenland visible on the NASA's 2015 global mean
temperatures (NASA/NOAA; 20 January 2016), the warmest year on record since 1880;
B. Circum-Antarctic summer surface temperatures, showing the large Weddell Sea and other
cold Sub-Antarctic ocean anomalies related to the flow of ice melt water into the ocean, and a seasonal
warming anomaly in the Ross Sea due to upwelling of warm salty water from the circum-Antarctic current.

Stadial events

Late Pleistocene climate cycles were controlled by orbital parameters of the Milankovitch cycles including eccentricity (~100,000 years), obliquity to the ecliptic plane (~41,000 years) and precession/wobble of the Earth’s axis (~19,000 and ~23,000 years). The Younger dryas of 12,900 to 11,600 years ago following the Allerod BÖlling warm peak and marked by cooling of near -20°C in Greenland and (Figure 2A, B), has major implications for climate change projections for the 21-23rd centuries.

The Younger dryas is the longest of three late Pleistocene stadials (Figure 2A) associated with abrupt climatic changes that took place over the last 16,000 years. According to Steffensen et al. 2008 based on deuterium isotopes in ice cores the abrupt onset of the Younger dryas in Greenland occurred over less than 1 year and ended over less than 3 years (Figure 2B), or about 50 years based on stable water isotopes representing the air temperature record. Evidence for the effects of the Younger dryas stadial has also been identified in tropical and subtropical regions (Shakun and Carlson, 2010) (Figure 3). The underlying factors for the Younger dryas and Laurentian (Figure 4) stadial events are the deglaciation of Northernmost America, flow of cold ice melt water into the North Atlantic Ocean and into North American lakes (Lake Agassiz), and the retreat southward of the North Atlantic Thermohaline Current.

Suggestions of a comet impact origin of the Younger dryas are inconsistent with (1) the recurrence of stadial events following peak interglacial temperatures over the last 420,000 years (Figure 5) and (2) the paucity of clear evidence for a large extraterrestrial impact contemporaneous with the Younger dryas, including the little known age of the radar-detected crater below the Hiawatha Glacier In northwest Greenland.

Figure 2A Air temperatures at the Last glacial maximum (20-16 kyr), BÖlling-Allerod warm peak,
Younger dryas (12,900 to 11,600 years ago) and 8.2 kyr Laurentian stadial event. This image
shows temperature changes, determined as proxy temperatures, taken from the central region
of Greenland's ice sheet during the Late Pleistocene and beginning of the Holocene.

Figure 2B. deuterium evidence for onset cooling temperature and terminal
warming of the Younger dryas stadial event (14,740-11,660) (Steffensen et al. 2008).

Figure 3. Magnitude of late Holocene glacial-interglacial temperature changes
in relation to latitude. Black squares are the Northern Hemisphere (NH),
gray circles the Southern Hemisphere (SH) (Shakun and Carlson, 2010).

The youngest recorded stadial, the Laurentian melt, between ~8,500 and ~8.000 years ago (Figure 4), is indicated by distinctive temperature–CO₂ correlation with global CO₂ decline of ≈25 ppm by volume over ≈300 years, consistent with the lowering of North Atlantic sea-surface temperatures and weakening of the AMOC (Atlantic Meridional Ocean Circulation).

Figure 4 A. The ~8.2 kyr Laurentian stadial event in a coupled climate model (Wiersma et al. 2011);
B. Reconstructed CO₂ concentrations for the interval between ~8,700 and ~6,800 BP, based on
CO 2 extracted from air in Antarctic ice of Taylor Dome (Wagner et al. 2002).

The Younger dryas and the Laurentian stadials are not unique, as peak temperatures in every interglacial event over the last 420,000 years were followed by sharp cooling events (Figure 5). Apart from the absolute level of greenhouse gases (GHG) in the atmosphere the high rate at which GHG concentrations are rising, as shown by comparisons with previous extreme warming events (Figure 6), enhances extreme weather events, as well as retards the ability of fauna and flora to adapt to the new conditions.

Figure 5 (a) Evolution of sea surface temperatures in five glacial-interglacial transitions recorded in
ODP 1089 at the sub-Antarctic Atlantic Ocean (Cortese et al. 2007). Grey lines – δ 18 O measured on
Cibicidoides plankton; Black lines – sea surface temperature. Marine isotope stage numbers are 
indicated on top of diagrams. Note the stadial following interglacial peak temperatures; (b) the last 
glacial maximum and the last glacial termination. Olds- Oldest dryas; Old – Older dryas; Yd – Younger dryas.

Figure 6 (A) Reconstructed atmospheric CO₂ variations during the Late Cretaceous–early Tertiary
derived from the Stomata indices of fossil leaf cuticles calibrated by using inverse regression
and stomatal ratios (Beerling et al. 2002);
(B) Simulated atmospheric CO₂ at and after the Palaeocene-Eocene boundary (after Zeebe et al. (2009).
Compare the CO₂ ppm/year values with the current rise of 2 to 3 ppm/year;
(C) Global CO₂ and temperature during the last glacial termination (After Shakun et al., 2012)
(LGM - Last Glacial Maximum; OD – Older dryas; BA - Bølling–Allerød; YD - Younger dryas);

The average global land and ocean surface temperature for March 2020 was 1.16°C above the 20th century average global level of 12.7°C. Current CO₂ rise and warming rates exceed that of the Last Glacial Termination (LGT) (21–8 kyr) (Figure 6C), the Paleocene-Eocene Thermal Maximum (PETM) (55.9 Ma) (Figure 6B) and the Cretaceous-Tertiary boundary (K-T) (64.98 Ma) impact event (Figure 6A). The relations between warming rates and the migration of climate zones toward the poles (Figure 7), including changes in the atmosphere and ocean current systems, are in the root of the major environmental changes in these zones.

Figure 7. Expansion of the tropical African climate zone (vertical red lines) into subtropical and Mediterranean
climate zones to the north and south (Migration, Environment and Climate Change, International Organization
for Migration, Geneva, Switzerland (Regional Maps on Migration, Environment and Climate Change.

Future Stadial events

IPCC climate change projections for 2100-2300 portray linear to curved temperature progressions (SPM-5). However, amplifying feedbacks and transient cooling events (Stadials) ensuing from the flow of ice melt water into the oceans during peak interglacial warming events, impose abrupt temperature variations (Figure 5). The current flow of ice melt water from Greenland and Antarctica (Figures 8, 9) is leading to regional ocean cooling in the North Atlantic and around Antarctica (Rahmstorf et al, 2015; Hansen et al. (2016); Bronselaer et al. 2018; Purkey et al. 2018; Vernet et al. 2019) (Figures 1, 8). Under high greenhouse gas and temperature rise trajectories (RCP8.5) this implies future stadial events as modelled by Hansen et al. (2016) (Figure 10) and Bronselaer et al. (2018) (Figure 11).

Depending on different greenhouse emission scenarios (IPCC 2019; van Vuren et. al. (2011), including the CO₂ forcing-equivalents of methane (CH4) and nitrous oxide (N2O), the total CO₂–equivalent rise has reached 496 ppm (NOAA, 2019). As the oceans heat contents is rising, upwelling of warm sublayers is melting the leading edges of continental glaciers (Figure 8). This factor and the flow of ice meltwater from leading glacier fronts and grounding lines lead to stratification of the sub-Antarctic ocean and an incipient onset of a southern ocean stadial (Figure 8).

Figure 8. The transition from grounded ice sheet to floating ice shelf and icebergs

Figure 9. Greenland and Antarctic ice mass change. GRACE data are extension of Velicogna et al. (2014)
gravity data. MBM (mass budget method) data are from Rignot et al. (2011). Red curves are gravity data
for Greenland and Antarctica only; small Arctic ice caps and ice shelf melt add to freshwater input.

Satellite and mass balance measurements of the large ice sheets indicate their rapid reduction (Figure 9). Variations in ice thickness, ice drainage and ice velocity data in 176 Antarctic basins between 1979 and 2017 indicate a total mass loss rise from 40 ± 9 Gt/year in 1979–1990 to 50 ± 14 Gt/year in 1989–2000, 166 ± 18 Gt/year in 1999–2009, and 252 ± 26 Gt/year in 2009–2017 (Figure 9). This amounts to an increased melting by more than 6-fold in about 40 years, contributing an average sea level rise of 3.6 ± 0.5 mm per decade, with a cumulative 14.0 ± 2.0 mm since 1979 (Rignot et al. 2019). The mass loss concentrated in areas closest to warm, salty, subsurface, circumpolar deep water (CDW), consistent with enhanced polar westerlies pushing CDW toward Antarctica.

The Greenland ice sheet contains approximately 2,900,000 GtI of ice. During the exceptionally warm Arctic summer of 2019, Greenland lost 600 GtI of ice. Under global GHG and temperature rise this rate is likely to be exceeded. The Greenland ice sheet may not last much longer than a Century. The Antarctic ice sheet weighs approximately 26,500 Gigaton. For a loss greater than ~250 GtI/year it could last for 105 years or less. For accelerated ice melt rates under rising GHG concentrations it could last for significantly shorter time, except for possible negative feedbacks associated with stadial cooling?

Hansen et al. (2016) suggest that, depending on ice melt rates of the polar ice sheets, transient cooling events (stadials) can be expected to develop over periods dependent on the rates of ice melt (Fig. 10). Stadial cooling of about -2°C lasting for several decades (Figure 10) may affect temperatures in Europe and North America. The model is consistent with a slowdown of the Atlantic Meridional Ocean Circulation (AMOC) (Weaver et al. 2012) and the exceptional growth of a cold water region southeast of Greenland, (Rahmstorf et al, 2015).

Figure 10. A. Model surface air temperature (◦C) change in 2096;
B. Surface air temperature (◦C) relative to 1880–1920 for several ice melt scenarios.

According to Bronselaer et al. (2018) temporal evolution of the global-mean surface-air temperature (SAT) shows meltwater-induced cooling translates to a reduced rate of global warming (Fig. 11), with a maximum divergence between standard models and models which include the effects of meltwater-induced cooling of 0.38 ± 0.02°C in 2055. As stated by the authors “We demonstrate that the inclusion in the model of ice-sheet meltwater reduces global atmospheric warming, shifts rainfall northwards, and increases sea-ice area”, and “Antarctic meltwater is therefore an important agent of climate change with global impact, and should be taken into account in future climate simulations and climate policy.”

Figure 11. The 2080–2100 meltwater-induced sea-air temperature anomaly relative to the standard
RCP8.5 ensemble. Hatching indicates where the anomalies are not significant at the 95% level.

Conclusions

Based on the paleoclimate record, global warming, penetration of cold and warm air masses across weakened polar boundaries, increased ice melting rates, sea level rise and near-surface cooling of large ocean tracts (Figures 10, 11), collisions between warm and cold air and water masses and thereby storminess are likely to determine the future climate of large parts of Earth. With rising greenhouse gas levels and their amplifying feedbacks from land and oceans these developments are likely to persist in the long term. The continuing migration of climate zones toward the poles is likely to be disrupted by developing stadial effects and differential warming and cooling effects, leading to major weather disruptions and storminess. Continuing release of greenhouse gases and their amplifying feedbacks could lead to tropical Miocene-like conditions about 4 to 5 degrees Celsius warmer than late Holocene climate conditions which allowed agriculture and thereby civilization to emerge.

Andrew Glikson

Dr Andrew Glikson
Earth and Paleo-climate scientist
ANU Climate Science Institute
ANU Planetary Science Institute
Canberra, Australia


Books:
The Asteroid Impact Connection of Planetary Evolution
http://www.springer.com/gp/book/9789400763272
The Archaean: Geological and Geochemical Windows into the Early Earth
http://www.springer.com/gp/book/9783319079073
Climate, Fire and Human Evolution: The Deep Time Dimensions of the Anthropocene
http://www.springer.com/gp/book/9783319225111
The Plutocene: Blueprints for a Post-Anthropocene Greenhouse Earth
http://www.springer.com/gp/book/9783319572369
Evolution of the Atmosphere, Fire and the Anthropocene Climate Event Horizon
http://www.springer.com/gp/book/9789400773318
From Stars to Brains: Milestones in the Planetary Evolution of Life and Intelligence
https://www.springer.com/us/book/9783030106027
Asteroids Impacts, Crustal Evolution and Related Mineral Systems with Special Reference to Australia
http://www.springer.com/us/book/9783319745442