Tuesday, May 19, 2020

An uncharted 21-23rd centuries’ climate territory

by Andrew Glikson

Precis

21–23ʳᵈ centuries’ transient ocean cooling events (stadials), triggered by ice melt flow from the Greenland and Antarctic ice sheets into the adjacent oceans, herald conditions analogous in part to those of the Younger Dryas stadial (12.9–11.7 kyr) which succeeded the pre-Holocene Bölling-Allerod thermal maximum. The subsequent Younger Dryas cooling event was associated with penetration of polar air masses and ocean currents, leading to storminess, analogous to recent breaching of the weakened polar jet stream boundary, ensuing in major snow storms in North America and Europe and cooling of parts of the North Atlantic Ocean and parts of the circum-Antarctic ocean triggered by the flow of ice melt water from melting glaciers.

21–23ʳᵈ Centuries’ Stadial freeze events

IPCC climate change projections for 2100-2300 portray linear to curved temperature progressions (SPM-5). By contrast, examination of transient cooling events (stadials) which ensued from the flow of ice melt water into the oceans during peak interglacial warming events portray abrupt temperature variations (Fig. 1). The current flow of ice melt water from Greenland and Antarctica ensuing from Anthropogenic global warming is leading to regional ocean cooling in the North Atlantic near Greenland and around Antarctica (Rahmstorf et al, 2015; Hansen et al. (2016); Bronselaer et al. 2018; Purkey et al. 2018; Vernet et al. 2019) (Fig. 2). The incipient developments of ice melt-derived cold water pools in ocean regions adjacent to the large ice sheets imply portents of future stadial events such as, inexplicably, are not indicated by the predominantly linear IPCC climate projections for the 21–23ʳᵈ centuries (IPCC AR5). By contrast, as modelled by Hansen et al. (2016) and Bronselaer et al. (2018), under high greenhouse gas and temperature rise trajectories (RCP8.5), the ice meltwater flow into the oceans from the Antarctic and Greenland ice sheets would lead to cooling of large regions of the ocean, with major consequences for future climate projections. This would include the build-up of large cool ocean pools in the North Atlantic south of Greenland (Rahmstorf et al, 2015) (Fig. 2A) and around Antarctica (Fig. 2B).

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 amounts to 496 ppm (NOAA, 2019), close to transcending the melting points of large parts of the Greenland and Antarctica ice sheets. Given the extreme rise in temperature since the mid-20th Century, where the oceans heat contents is rising, an incipient cooling of near-surface sub-Greenland and sub-Antarctic ocean regions raises the question whether incipient stadial events, perhaps analogous to the Younger Dryas stadial (Johnsen et al. 1972; Severinghaus et al. 1998), may be developing?

Interglacials, late Pleistocene and early Holocene stadial events

Stadial effects in the late Pleistocene record follow peak interglacial temperatures (Cortese et al., 2007) (Fig. 1). During the last glacial termination (LGT) stadial effects included the Oldest Dryas at ~16 kyr, the Older Dryas at ~14 kyr and the Younger Dryas at 12.9 - 11.7 kyr (Fig. 3), the latter with sharp transitions as short as 1 to 3 years (Steffensen et al., 2008), signifying a return to glacial conditions. A yet younger stadial event is represented at ~8.4 - 8.2 kyr when large-scale melting of the Laurentian ice sheet ensued in the discharge of cold water via Lake Agasiz (Matero et al. 2017; Lewis et al., 2012) into the North Atlantic Ocean. The Laurentian cooling involved temperature and CO₂ decline of ~25 ppm over ~300 years (Fig. 3B and C) and a decline of the North Atlantic Thermohaline circulation.

Figure 1. (a) Evolution of sea surface temperatures in 5 glacial-interglacial transitions recorded in
ODP 1089 at the sub-Antarctic Atlantic Ocean. Grey lines – δ¹⁸O 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 (Cortese et al. 2007).
 (b) The last glacial maximum and the last glacial termination.
Olds  Oldest Dryas; Old – Older Dryas; Yd – Younger Dryas.

Greenland and Antarctica ice melt events

Oxygen isotopes (¹⁸O/¹⁹O), argon isotopes (⁴⁰Ar/³⁹Ar) and nitrogen isotopes (¹⁵N/¹⁴N) studies of Greenland ice cores (Johnsen et al. 1972; Severinghaus et al. 1998) indicate a rise in temperature to -36°C, followed by a sharp fall to -50°C (Table 1; Fig. 3A). At lower latitudes the mean temperatures drop about -2°C and 6°C (Table 1). In the southern hemisphere temperatures dropped by about -2°C in lower latitudes and about -8°C at high latitudes and (Fig. 4; Table 1) Shakun and Carlson, 2010).

Figure 2. A. The cold ocean region south of Greenland visible on NASA's 2015 global mean temperatures, the warmest year on record since 1880. Colors indicate temperature anomalies (NASA/NOAA; 20 January 2016);
B. Circum-Antarctic summer surface temperatures, showing the large Weddell Sea cold anomaly
and a seasonal warming anomaly in the Ross Sea due to upwelling of warm salty water.


Table 1.

Cooling intervals (stadial events) during late Pleistocene and early Holocene interglacial phases.
Isotopic Stage 
Agemax kyr
Agemin kyr
∆tkyr
TmaxoC SST
TminoC SST
∆ToC 
Stadial MIS 11-12 Ref. A
434 kyr
424 kyr
10 kyr
19.3oC SST
13.4oC SST
-5.9oC
Stadial MIS 9-10  Ref. B
346 kyr
331 kyr
5 kyr
19oC SST
13oC SST
-6oC
Stadial MIS 7-8   Ref. C
243.5 kyr
241.5 kyr
2.0 kyr
18oC SST
15.5oC SST 
-2.5oC
Stadial MIS 5-6 Ref. D
136 kyr
130 kyr
6.0 kyr
19oC SST
15.2oC SST
-3.8oC
Younger Dryas stadial ice core In Greenland
MIS 1-2-3  Ref. E
12.86 kyr
11.64 kyr
1.22 kyr
Greenland ice core
-50oC Greenland ice core
-14±3oC
Greenland ice core
Younger Dryas at lower and mid-latitudes of the NH (Fig. 4) Ref. F
12.86 kyr
11.64 kyr
1.22 kyr


-2 to -6oC
8.3 kyr Stadial  Ref. G
8.45 kyr
8.1 kyr
0.35 kyr
-28oC
CO₂=310 ppm
-30oC
CO₂=275 ppm
-2.0oC
Figure 3. A. Temperature variations during the late Pleistocene to the beginning of the Younger Dryas stadial
and the onset of the Holocene, determined as proxy temperatures from ice cores of the central Greenland ice sheet;
B. The ~8.2 kyr stadial event in a coupled climate model (Wiersma et al. 2011);
C. Reconstructed CO₂ concentrations for the interval between ~8,700 and ~6,800 B.P. 

based on CO₂ extracted from air in Antarctic ice of Taylor Dome (Wagner et al. 2002).
Figure 4. 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)

Antarctic ice melt dynamics


Circum-Antarctic surface air temperatures, precipitation and sea-ice cover (Bronselaer et al. (2018), including testing the effects of ice-shelf melting, identifies penetration of relatively warm circumpolar deep water below 400 m into the grounding line underlying the ice shelf (Figs 5, 6A). The flow of ice melt water into the adjacent ocean forms an upper cold water layer away from ice shelf areas (Figure 6B). These authors indicate the flow of ice-sheet meltwater results in a decrease of global atmospheric warming, shifts rainfall northwards, and increases sea-ice area and offshore subsurface Antarctic Ocean temperatures.

Figure 5. Schematic circulation and water masses in the Antarctic continental shelf (Purkey et al., 2018) displaying layering of the sub-Antarctic into a cold ice melt-derived upper layer (-2.1°C) overlying a warmer water zone (-1.0°C) which acts as a source of modified warm water penetrating the grounding zone of the glacial ice shelf.

Figure 6. A. The grounding zone where the bedrock-grounded ice sheet transits to a freely floating ice shelf over several km. The floating ice shelf changes in elevation in response to tides, atmospheric air pressure and oceanic processes. B. The Helium (∆He% - Temperature proxy) profile in the Amundsen Sea. The black dots indicate the sampling depth, and the grey dotted lines indicate the isopycnal (density) lines. The shelf break is located at about ∼280 km).

In turn warmer salty water from the circum-polar deep water (CDW) from the circum-Antarctic current can penetrate below the cold off-shelf layer, as is the case in the Weddell Sea Gyre (Figures 5, 6 and 7).

Figure 7. Penetration of relatively warm and salty water from the circum-Antarctic current below the cold off-shelf surface layer of the Weddell Sea Gyre.

Global stadial cooling events


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 at times dependent on the rates of ice melt (Fig. 8). 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). These authors suggest stadial cooling of about -2°C lasting for several decades (Fig. 8B), depending on ice melt rates, can affect temperatures in Europe and North America.

Figure 8. A. Model surface air temperature (°C) change in 2055–2060 relative to 1880–1920 for modified forcings.
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. 9), 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. The SAT response shows the effect of ice meltwater becomes weaker as the ocean becomes more stratified as a result of both moderate to deep level warming and cooling/freshening at the surface (Fig. 6B). 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 9. A. 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.
B. Time series of the global-mean sea-air temperature (SAT) anomaly relative to the 1950–1970 mean.
Orange shows the standard ensemble and blue shows the meltwater-included ensemble. Solid lines show ensemble means, the dark shading shows the 95% uncertainty in the mean and the light shading shows the full ensemble spread of 20-year means. The green bar indicates the period when the standard and meltwater ensembles diverge.

Based on the paleoclimate record, global warming and rates of melting and surface cooling around parts of Antarctica and the North Atlantic (Fig. 2) would determine the future climate of large parts of Earth. Transient stadial cooling events, inherently associated with meters-scale sea level rise, would result in increased temperature polarities between subpolar and tropical latitudes, leading to storminess where polar-derived and tropical-derived air masses and ocean currents collide. Regional to global stadial cooing would, in principle, last as long as ice sheets remain. Once the large ice sheets are exhausted a transition takes place toward tropical Miocene-like and even Eocene-like conditions about 4 to 5 degrees Celsius warmer than 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


Friday, May 15, 2020

April 2020 temperatures very high

Temperatures in April 2020 were very high. The image below shows very high temperature anomalies over the Arctic.


The image below shows that the April ocean temperature anomaly in the Gulf of Mexico in 2020 was 1.71°C or 3.08°F higher than the 1910-2000 average, and the highest on record.


Temperatures in the Gulf of Mexico were already very high in March 2020, as illustrated by the image on the right, from an earlier post.

There are three reasons why this is very worrying:

1. The Gulf Stream carries ever hotter water along the path of the Gulf Stream toward the Arctic Ocean, thus speeding up the temperature rise of the Arctic Ocean.

2. As the Gulf Stream slows down, due to increased meltwater, more heat is accumulating along the path toward the Arctic Ocean, threatening to invade the Arctic Ocean in abrupt strong bursts, powered by stronger winds over the North Atlantic, as discussed in earlier posts such as this one.

3. There's also the danger that a freshwater lid is extending at the surface of the North Atlantic that threatens to cause more ocean heat to move underneath the sea surface toward the Arctic Ocean, as discussed in earlier posts, such as at this one and this one.

As the image below shows, the April ocean temperature anomaly on the Northern Hemisphere in 2020 was 0.97°C or 1.75°F higher than the 20th century average, and the highest on record.


Arctic sea ice is getting very thin and, at this time of year, it is melting rapidly from below, due to rising temperature of the Arctic Ocean.

Arctic sea ice volume has been at record low since the start of 2020, while 2019 volume was at a record low from October, making that volume has now been at record low for almost 8 months straight.

An earlier analysis indicates that there is a tipping point at 1°C at which the sea ice underneath the surface of the Arctic Ocean disappears, which means that there will be little or no buffer left to consume the influx of ever warmer and salty water from the Atlantic Ocean and Pacific Ocean.

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.

But there is ever less sea ice volume left to absorb ocean heat, and the amount of energy absorbed by melting ice is as much as it takes to heat an equivalent mass of water from zero to 80°C.


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


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. The danger is that this heat will destabilize the ice and the hydrates, resulting in huge releases of methane.


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


Links

• NASA GISS maps - Land Surface Air Temperature and Sea Surface Temperature
https://data.giss.nasa.gov/gistemp/maps/index_v4.html

• NOAA Global Climate Report - April 2020
https://www.ncdc.noaa.gov/sotc/global/202004

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

• Arctic Hit By Ten Tipping Pointshttps://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

• 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

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

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




Monday, May 4, 2020

Very High Greenhouse Gas Levels

Carbon Dioxide

On May 3, 2020, NOAA recorded a daily average carbon dioxide (CO₂) level of 418.12 ppm at Mauna Loa, Hawaii.

The image below shows hourly average CO₂ levels approaching 419 ppm at Mauna Loa in May 2020.
The image below shows hourly (red circles) and daily (yellow circles) averaged CO₂ values from Mauna Loa, Hawaii for the last 31 days, with some recent hourly averages showing up with values above 419 ppm.

By comparison, the highest daily average CO₂ level recorded by NOAA in 2019 at Mauna Loa was 415.64 ppm, as discussed in an earlier post. The image below shows how CO₂ growth has increased over the decades.
The daily average CO₂ level recorded by scripps.ucsd.edu at Mauna Loa, Hawaii, was 418.04 ppm on May 25, 2020. One hourly average the day before exceeded 420 ppm, at which time emissions by people had raised CO₂ levels by some 160 ppm compared to the situation thousands of years ago, and by even more if levels had continued to follow a natural trend, as illustrated by the image and inset below.

A rise of 100 ppm CO₂ has historically corresponded with a global temperature rise of more than 10°C or 18°F, when looking at CO₂ levels and temperatures over the past 420,000 years, as illustrated by the image below.


Concentrations of carbon dioxide, methane (CH₄) and nitrous oxide (N₂O) in 2018 surged by higher amounts than during the past decade, according to a 2019 WMO news release and as illustrated by the image on the right, from an earlier post, which shows that CH₄, CO₂ and N₂O levels in the atmosphere in 2018 were, respectively, 259%, 147% and 123% of their pre-industrial (before 1750) levels.

So, methane levels have been rising much faster than CO₂ since 1750 and there is much potential for an even faster rise in methane levels due to seafloor hydrate releases.

Furthermore, as industrial activity declines in the wake of COVID-19, loss of aerosol masking alone could trigger a rapid rise, as discussed by Guy McPherson in recent papers here and here.

Given this, the 160 ppm rise in CO₂ could lead to a global temperature rise of 18°C or 32.4°F from 1750, and such a rise could unfold soon, as oceans and ice take up ever less heat and further feedbacks kick in, as also discussed in earlier post such as this one and this one.

The rise in levels of nitrous oxide is also worrying. Levels for methane and nitrous oxide were very high in May 2020, as further discussed below.

Methane

MetOp-1 recorded peak methane levels of 2917 ppb at 469 mb on the afternoon of May 22, 2020.


MetOp-1 recorded mean methane levels of 1896 ppb at 336 mb on the morning of May 22, 2020.


MetOp-2 recorded peak methane levels of 1918 ppb at 586 mb on the afternoon of May 24, 2020.


Siberian Heatwave

A heatwave hit Siberia in May 2020.


Above image shows that temperature anomalies were forecast to be at the high end of the scale over Siberia on May 22, 2020, 06:00 UTC, i.e. 30°C or 54°F higher than 1979-2000. At the same time, cold temperatures are forecast for much of eastern Europe.

What enables such a strong heatwave to develop is that the Jet Stream is getting more wavy as the temperature difference between the North Pole and the Equator is narrowing, causing both hot air to move up into the Arctic (red arrow) and cold air to descend out of the Arctic (blue arrow).

The Siberian heatwave threatens to trigger forest fires that can cause large amounts of black carbon to settle on the snow and ice cover, speeding up its demise. Furthermore, the heatwave threatens rivers to heat up that carry large amounts of water into the Arctic Ocean.

Nitrous Oxide

N20 recorded peak nitrous oxide levels of 366 ppb at 840 mb on the morning of May 21, 2020.


N20 recorded somewhat lower peak nitrous oxide levels of 346.9 ppb at 487.2 mb on the afternoon of May 23, 2020, but look at how much of Antarctica is covered by the magenta color, reflecting levels at the top end of the scale.


In addition to being a potent greenhouse gas, nitrous oxide is also an ozone depleting substance that affects the ozone layer. A recent study found that the Devionian mass extinction event 360 million years ago, that killed much of the Earth's plant and freshwater aquatic life, was caused by a brief breakdown of the ozone layer. Lead researcher Professor Marshall says: "Current estimates suggest we will reach similar global temperatures to those of 360 million years ago, with the possibility that a similar collapse of the ozone layer could occur again, exposing surface and shallow sea life to deadly radiation. This would move us from the current state of climate change, to a climate emergency."

Super Typhoon Amphan hits India and Bangladesh

Also in May 2020, super typhoon Amphan hit India and Bangladesh, with high waves and heavy rainfall. Waves as high as 14.2 m or 46.6 ft were forecast (at the green circle) for May 20, 2020, 06:00 UTC as Amphan approached Bangladesh.

"Once once-in-a-century, now once-in-a-decade", comments Sam Carana on this and other events.


The sea surface temperature image below shows that, on May 17, 2020, ocean temperatures were as high as 32.9°C or 91.1°F.


The combination image below shows high sea surface temperatures on May 15, 2020, 12:00 UTC, in the left panel.


Anomalies in the Indian Ocean were as high as 3.4°C or 6.0°F, in the Arctic Ocean as high as 1°C or 1.8°F and in the Pacific Ocean as high as 5.1°C or 9.1°F. Anomalies are from daily average during years 1981-2011.

The right panel of the combination image shows how these high ocean temperatures cause circular wind patterns. Wind speed was as high as 255 km/h or 159 mph in the Indian Ocean, at the location of super typhoon Amphan, on May 18, 2020, 06:00 UTC, while instantaneous wind power density was as high as 177.2 kW/m².

The combination image below shows the temporary cooling impact of Amphan.


The bottom panel shows that on May 18, 2020 09:00 UTC, the temperature at a location in India was 42.6°C or 108.6°F, as Amphan was approaching from the South.

The middle panel shows that, two days later, at the same location and at same time of day, the temperature had fallen to 23.4°C or 74°F as Amphan hit the area.

The cooling is only temporary. The top panel shows that a temperature of 47.9°C or 118.1°F is forecast for that location, same time of day, for May 26, 2020.

Arctic sea ice volume

Arctic sea ice volume has been at record low since the start of 2020, while 2019 volume was at a record low from October, making that volume has now been at record low for almost 8 months straight.

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


Links

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

• Climate Plan (June 1, 2019 version)
https://arctic-news.blogspot.com/2019/06/climate-plan.html

• The Keeling Curve - Scripps Institution of Oceanography at UC San Diego
https://scripps.ucsd.edu/programs/keelingcurve

• 417.93 parts per million (ppm) CO2 in air 24-May-2020
https://twitter.com/Keeling_curve/status/1264955470655025152

• Greenhouse Gas Levels Keep Accelerating
https://arctic-news.blogspot.com/2019/05/greenhouse-gas-levels-keep-accelerating.html

• Will COVID-19 Trigger Extinction of All Life on Earth? - by Guy McPherson
https://opastonline.com/wp-content/uploads/2020/04/will-covid-19-trigger-extinction-of-all-life-on-earth-eesrr-20-.pdf

• Earth is in the Midst of Abrupt, Irreversible Climate Change - by Guy McPherson
https://www.onlinescientificresearch.com/articles/earth-is-in-the-midst-of-abrupt-irreversible-climate-change.pdf

• Extinction
https://arctic-news.blogspot.com/p/extinction.html

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

• Methane
https://arctic-news.blogspot.com/p/methane.html

• Study shows erosion of ozone layer responsible for mass extinction event
https://www.eurekalert.org/pub_releases/2020-05/uos-sse052620.php

• UV-B radiation was the Devonian-Carboniferous boundary terrestrial extinction kill mechanism - by John Marshall et al.
https://advances.sciencemag.org/content/6/22/eaba0768

• Care for the Ozone Layer
https://arctic-news.blogspot.com/2019/01/care-for-the-ozone-layer.html

• Arctic Ocean November 2019
https://arctic-news.blogspot.com/2019/11/arctic-ocean-november-2019.html





Sunday, April 19, 2020

The Fatal Road To 4 Degrees Celsius

The fatal road to +4°Celsius
Extreme GHG and T°C rise rates exceed climate tipping thresholds

Andrew Glikson

Precis

Global CO₂ rise and warming rates have reached a large factor to an order of magnitude higher than those of the past geological and mass extinction events, with major implications for the shift in climate zones and the nature and speed of current extreme weather events. Given the abrupt change in state of the atmosphere-ocean-cryosphere-land system, accelerating since the mid-20ᵗʰ century, the terms climate change and global warming no longer reflect the nature of the climate extremes consequent on this shift. Further to NASA’s reported mean land-ocean temperature rise to +1.18°C for March 2020, relative to the 1951-1980 baseline, large parts of the continents, including Siberia, central Asia, Canada, parts of west Africa, eastern South America and Australia are warming toward mean temperatures of +2°C and higher. The rate exceeds that of the Last Glacial Termination (LGT) (21–8 kyr), the Paleocene-Eocene hyperthermal event (PETM) (55.9 Ma) and the Cretaceous-Tertiary boundary (K-T) (64.98 Ma) impact event. A principal question arises regarding the relationships between the warming rate and the nature and progression of the current migration climate zones toward the poles, including changes in the atmosphere and ocean current systems. Significant transient cooling pauses, or stadials, are projected as a consequence of the flow of cold ice melt water from Greenland and Antarctica into the oceans.

Figure 1. Global temperature distribution in March 2020, relative to a 1951-1980 baseline. NASA GISS.


The K-T impact and subsequent warming: According to Beerling et al. (2002) the CO₂ change triggered by the K-T impact event 65 Ma years ago involved a rise from about 400-500 ppm to 2300 ppm over 10.000 years from the impact (Fig. 2) at a rate of 0.18 ppm/year. This is less than the mean Anthropocene CO₂ rise rate of 0.415 ppm/year and an order of magnitude less than the 2 to 3 ppm/year rise rate in the 21ˢᵗ century. Likewise the Anthropocene temperature rise rate of ~ 0.0074°C/year is high by an order of magnitude as compared to the K-T impact event rate of~ 0.00075°C/year (Table 1) reported by Beerling et al. (2002).

Figure 2. Reconstructed atmospheric CO₂ variations during the Late Cretaceous–Early Tertiary derived from the SI
(Stomata index) of fossil leaf cuticles calibrated by using inverse regression and stomatal ratios. Beerling et al. (2002).
Beerling et al.’s (2002) estimate, based on fossil fern proxies, implies an initial injection of at least 6,400 GtCO₂  and possibly as high as 13,000 GtCO₂ into the atmosphere, significantly higher than values derived by Pope et al. (1997). This would increase climate forcing by +12 Wm⁻² and mean warming of ~7.5°C, which would have strongly stressed ecosystems already affected by cold temperatures and the blockage of sunlight during the impact winter and associated mass extinction at the KT boundary (O’Keefe et al. 1989).

The PETM hyperthermal event: The Palaeocene–Eocene Thermal Maximum, about 55.9 Ma, triggered the release of a large mass of light ¹³C-depleted carbon suggestive of an organic source, likely methane, has led to a global surface temperature rise of 5 – 9°C within a few thousand years (Table 1; Fig. 3). Deep-sea carbonate dissolution indices and stable carbon isotope composition were used to estimate the initial carbon pulse to a magnitude of 3,000 PgC or less. As a result, atmospheric carbon dioxide concentrations increased during the main event by up to 70% compared with pre-event levels, leading to a global surface temperatures rose by 5–9°C within a few thousand years.

Figure 3. Simulated atmospheric CO2 at and after the Palaeocene-Eocene boundary (after Zeebe et al. (2009).

The last glacial termination: Paleoclimate indices based on ice cores and isotopic evidence suggest temperature rise generally correlates with CO₂ during the Last Glacial Termination between 17.5 kyr to 10 kyr. Whereas the rise rates of CO₂ and temperature are broadly parallel the temperature somewhat lags behind CO₂ (Figure 2). Changes of CO₂ – 186 - 265 ppm and of temperature of T°C -3.3°C - +0.2°C (Fig. 4). A rise rate of ~0.010 ppm CO₂/year and of temperature ~0.00046°C/year are indicated (Table 1) (Shakun et al., 2012). Differences between temperature changes of the Northern Hemisphere and Southern Hemisphere correspond to variations in the strength of the Atlantic meridional overturning circulation.
Figure 4. Global CO₂ and temperature during the last glacial termination (After Shakun et al. 2012).
(LGM – Last Glacial Maximum; OD – Older Dryas; B-A - Bølling–Allerød; YD Younger Dryas).
Trajectories and rates of global CO₂ rise and warming

The rates at which atmospheric composition and climate changes occur constitute major control over the survival versus extinction of species. Based on paleo-proxy estimates of greenhouse gas levels and of mean temperatures, using oxygen and carbon isotopes, fossil plants, fossil organic matter, trace elements, the rate of CO₂ rise since ~1750 (Anthropocene) (CO₂ ᴀɴᴛʜ) exceeds that of the last glacial termination (CO₂ ʟɢᴛ) by an order of magnitude (CO₂ ᴀɴᴛʜ/CO₂ ʟɢᴛ = 41) and that of the Paleocene-Eocene Thermal Maximum (CO₂ ᴘᴇᴛᴍ) by a high factor (CO₂ ᴀɴᴛʜ/CO₂ ᴘᴇᴛᴍ ~ 3.8–6.9)(Table 1). The rise rate of mean global temperature exceeds that of the LGT and the PETM by a large factor to an order of magnitude (Table 1; Figs 5 and 6). It can be expected that such extreme rates of change will be manifest in real time by observed shifts in state of global and regional climates and the intensity and frequency of extreme weather events, including the following observations:
The rapid increase in extreme weather events,including droughts, heat waves, fires, cyclones and storms.
Figure 5. Cenozoic and Anthropocene CO₂ and temperature rise rates.

Figure 6. A comparison between rates of mean global temperature rise during:
(1) the last Glacial Termination (after Shakun et al. 2012);
(2) the PETM (Paleocene-Eocene Thermal Maximum, after Kump 2011);
(3) the late Anthropocene (1750–2019), and
(4) an asteroid impact. In the latter instance, temperature associated with
CO₂ rise would lag by some weeks or months behind aerosol-induced cooling.
Figure 7. An updated Köppen–Geiger climate zones map.

By contrast to linear IPCC climate projections for 2100-2300, climate modelling for the 21st century by Hansen et al. 2016 suggests major effects of ice melt water flow into the oceans from the ice sheets, leading to stadial cooling of parts of the oceans, changing the global temperature pattern from that of the early 21ˢᵗ century (Figs 8, 9a) to the late 21ˢᵗ century (Fig. 9b).
Figure 8. Global temperature patterns during El Nino and La Nina events. NASA GISS

Figure 9. a. An A1B model of surface-air temperature change for 2055-2060 relative
to 1880-1920 (+1 meters sea level rise) for modified forcing (Hansen et al. 2016);
b. A1B model surface-air temperatures in 2096 relative to 1880-1920 (+5 meters sea level rise) for 10 years
ice melt doubling time in the southern hemisphere and partial global cooling of -0.33
°C (Hansen et al. 2016).

Summary and conclusions

  1. Late 20th century to early 21asrt century global greenhouse gas levels and regional warming rates have reached a high factor to an order of magnitude faster than those of past geological and mass extinction events, with major implications for the nature and speed of extreme weather events.
  2. The Anthropocene CO₂ rise and warming rates exceed that of the Last Glacial Termination (LGT) (21–8kyr), the Paleocene-Eocene hyperthermal event (PETM) (55.9 Ma) and the post-impact Cretaceous-Tertiary boundary (K-T) (64.98 Ma). 
  3. Further to NASA’s reported mean land-ocean temperature rise of +1.18°C in March 2020, relative to the 1951-1980 baseline, large parts of the continents, including central Asia, west Africa eastern South America and Australia are warming toward mean temperatures of +2°C and higher. 
  4. Major consequences of the current shift in state of the climate system pertain to the weakening of the polar boundaries and the migration of climate zones toward the poles. Transient cooling pauses are projected as a result of the flow of cold ice melt water from Greenland and Antarctica into the oceans, leading to stadial cooling intervals.
  5. Given the abrupt shift in state of the atmosphere-ocean-cryosphere-land system, the current trend signifies an abrupt shift in state of the atmosphere, accelerating since the mid-20th century. Terms such as climate change and global warming no longer reflect the extreme nature of the climate events consequent on this shift, amounting to a climate catastrophe on a geological scale.
Andrew Glikson
Dr Andrew Glikson
Earth and Paleo-climate scientist
ANU Climate Science Institute
ANU Planetary Science Institute
Canberra, Australian Territory, Australia
geospec@iinet.net.au

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 

From Stars to Brains: Milestones in the Planetary Evolution of Life and Intelligence

The Plutocene: Blueprints for a Post-Anthropocene Greenhouse Earth

Added below is a video with an August 6, 2019, interview of Andrew Glikson by Guy McPherson and Kevin Hester, as edited by Tim Bob.