Showing posts with label paleoclimate. Show all posts
Showing posts with label paleoclimate. Show all posts

Sunday, June 13, 2021

Could temperatures keep rising?

Orbital changes are responsible for Milankovitch cycles that make Earth move in and out of periods of glaciation, or Ice Ages. Summer insolation on the Northern Hemisphere reached a peak some 10,500 years ago, in line with the Milankovitch cycles, and insolation has since gradually decreased.
Summer insolation on the Northern Hemisphere in red and in langleys
per day (left axis, adapted from Walker, 2008). One langley is 1 cal/cm²
(thermochemical calorie per square centimeter), or 41840 J/m² (joules
per square meter), or about 11.622 Wh/m² (watt-hours per square meter). 
In blue is the mean annual sea surface temperature, given as the difference
from the temperature over the last 1000 years (right axis, from Bova, 2021).

Snow and ice cover acting as a buffer

While temperatures rose rapidly, especially before the insolation peak was reached, the speed at which temperatures rose was moderated by the snow and ice cover, in a number of ways:
  • snow and ice cause sunlight to get reflected back into space
  • energy from sunlight is consumed in the process of melting snow and ice, and thawing permafrost
  • meltwater from sea ice and runoff from melting glaciers and thawing permafrost cools oceans.
In other words, the snow and ice cover acted as a buffer, moderating the temperature rise. While this buffer has declined over time, it is still exercizing this moderation today, be it that the speed at which this buffer is reducing in size is accelerating, as illustrated by the image below, showing the rise of the sea surface temperature on the Northern Hemisphere.

[ from earlier post ]

Will the snow and ice cover ever grow back?

More recently, the temperature rise has been fueled by emissions caused by people. While emission of greenhouse gases did rise strongly since the start of the Industrial Revolution, the rise in emission of greenhouse gases by people had already started some 7,000 years ago with the rise in modern agriculture and associated deforestation, as illustrated by the image below, based on Ruddiman et al. (2015).


The temperature has risen accordingly since those times. At the start of the Industrial Revolution, as the image at the top shows, temperatures already had risen significantly, compared to some 6000 years before the Industrial Revolution started. When also taking into account that the temperature would have fallen naturally (i.e. in the absence of these emissions), the early temperature rise caused by people may well be twice as much.

Temperatures could keep rising for many years, for a number of reasons:
  • Snow & Ice Cover Loss - A 2016 analysis by Ganapolski et al. suggests that even moderate anthropogenic cumulative carbon dioxide emissions would cause an absence of the snow and ice cover in the next Milankovitch cycle, so there would be no buffer at the next peak in insolation, and temperatures would continue to rise, making the absence of snow and ice a permanent loss.
  • Brighter Sun - The sun is now much brighter than it was in the past and keeps getting brighter.
  • Methane - Due to the rapid temperature rise, there is also little or no time for methane to get decomposed. Methane levels will skyrocket, due to fires, due to decomposition of dying vegetation and due to releases from thawing of terrestrial permafrost and from the seafloor as hydrates destabilize.
  • No sequestration - The rapidity of the rise in greenhouse gases and of the associated temperature rise leaves species little or no time to adapt or move, and leaving no time for sequestration of carbon dioxide by plants and by deposits from other species, nor for formation of methane hydrates at the seafloor of oceans.
  • No weathering - The rapidity of the rise also means that weathering doesn't have a chance to make a difference. Rapid heating is dwarfing what weathering can do to reduce carbon dioxide levels. 
  • Oceans and Ozone Layer Loss - With a 3°C rise, many species including humans will likely go extinct. A 2013 post warned that, with a 4°C rise, Earth will enter a moist-greenhouse scenario. A 2018 study by Strona & Bradshaw indicates that most life on Earth would disappear with a 5°C rise. As temperatures kept rising, the ozone layer would disappear and the oceans would keep evaporating and eventually disappear into space, further removing elements and conditions that are essential to sustain life on Earth.

Paris Agreement

All this has implications for the interpretation of the Paris Agreement. At the Paris Agreement, politicians pledged to take efforts to ensure that the temperature will not exceed 1.5°C above pre-industrial levels.

So, what is pre-industrial? To calculate how much the temperature has risen, let's start at 2020 and go back one century. According to NASA data, the temperature difference between 1920 and 2020 is 1.29°C (image below). 


The NASA ocean data are for sea surface temperatures, so another 0.10°C can be added to obtain global air near surface temperatures (2 m). Furthermore, it makes sense to add another 0.10°C for higher polar anomalies. This would bring the temperature rise from 1920 up to 1.49°C.  


Of course, 1920 is not pre-industrial. As the IPCC mentions, the 'pre-' in pre-industrial means 'before', implying that 'pre-industrial' refers to levels as they were in times well befóre (as opposed to when) the Industrial Revolution started.

When taking the rise over the past century and adding 0.30°C for the rise over the previous 170 years, that brings the rise up to 1.79°C (from ≈1750, the start of the Industrial Revolution). Carbon dioxide and methane levels started to rise markedly about 6000 years ago, causing a 0.29°C rise for the years from 3480 BC to 1520 (see image at top). Finally, there will also have been a rise for the years from 1520 to 1750 that, when estimated at 0.20°C, would mean that emissions by people could have caused the temperature to rise by 2.28°C (4.122°F), compared to the temperature some 5500 years ago (see inset on above image).

A huge temperature rise by 2026?

A recent post suggests that the 1.5°C threshold was already crossed in 2012, i.e. well before the Paris Agreement was adopted by the U.N. (in 2015), while there could be a temperature rise of more than 3°C by 2026.

Such a rise could be facilitated by a number of events and developments, including:

[ from earlier post see CH4 GWP]
• The Arctic sea ice latent heat tipping point and the seafloor methane hydrates tipping point look set to get crossed soon (see above image).

• Continued emissions. Politicians are still refusing to take effective action, even as greenhouse gas emissions appear to be accelerating. The warming impact of carbon dioxide reaches its peak a decade after emission, while methane's impact over a few years is huge.

• Sunspots. We're currently at a low point in the sunspot cycle. As the image on the right shows, the number of sunspots can be expected to rise as we head toward 2026, and temperatures can be expected to rise accordingly. According to James Hansen et al., the variation of solar irradiance from solar minimum to solar maximum is of the order of 0.25 W/m⁻².

• Temperatures are currently also suppressed by sulfate cooling, and their impact is falling away as we progress with the necessary transition away from fossil fuel and biofuel, toward the use of more wind turbines and solar panels instead. Aerosols typically fall out of the atmosphere within a few weeks, so as the transition progresses, this will cause temperatures to rise over the next few years.

• El Niño events, according to NASA, occur roughly every two to seven years. As temperatures keep rising, ever more frequent strong El Niño events are likely to occur. NOAA anticipates the current La Niña to continue for a while, so it's likely that a strong El Niño will occur between 2023 and 2025.

• Rising temperatures can cause growth in sources of greenhouse gases and a decrease in sinks, as discussed in an earlier post.

The mass extinction event that we are currently in is rapidly progressing, even faster than the Great Permo-Triassic Extinction, some 250 million years ago, when the temperature rose to about 28°C, i.e. some 14.5°C higher than pre-industrial.

In the video below, Guy McPherson discusses the current mass extinction.


In the video below, Ye Tao introduces and discusses the MEER ReflEction idea.


In conclusion, there could be a huge temperature rise by 2026 and with a 3°C rise, humans will likely go extinct, which is a daunting prospect. Even so, the right thing to do is to help avoid the worst things from happening, through comprehensive and effective action as described in the Climate Plan.


Links

• Climate change and ecosystem response in the northern Columbia River basin - A paleoenvironmental perspective - by Ian R. Walker and Marlow G. Pellat (2008)
https://cdnsciencepub.com/doi/10.1139/A08-004

• Vance, R.E. 1987. "Meteorological Records of Historic Droughts as Climatic Analogues for the Holocene." In N.A. McKinnon and G.S.L. Stuart (eds), Man and the Mid-Holocene Climatic Optimum - Proceedings of the Seventeenth Annual Conference of the Archaeological Association of the University of Calgary. The University of Calgary Archaeological Association, Calgary: 17-32.

• Seasonal origin of the thermal maxima at the Holocene and the last interglacial - by Samantha Bova et al. (2021)
https://www.nature.com/articles/s41586-020-03155-x

• Palaeoclimate puzzle explained by seasonal variation (2021)
https://www.nature.com/articles/d41586-021-00115-x

• Important Climate Change Mystery Solved by Scientists (news release 2021)
https://www.rutgers.edu/news/important-climate-change-mystery-solved-scientists

• Milankovitch (Orbital) Cycles and Their Role in Earth's Climate - by Alan Buis (NASA news, 2020)
https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate

• Milankovitch cycles - Wikipedia
https://en.wikipedia.org/wiki/Milankovitch_cycles

• Insolation changes
https://energyeducation.ca/encyclopedia/Insolation
http://www.geo.umass.edu/faculty/bradley/bradley2003x.pdf

• Late Holocene climate: Natural or anthropogenic? - by William Ruddiman et al. (2015)
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015RG000503

• Critical insolation–CO2 relation for diagnosing past and future glacial inception - by Andrey Ganapolski et al. (2016)
https://www.nature.com/articles/nature16494

• Co-extinctions annihilate planetary life during extreme environmental change - by Giovanni Strona & Corey Bradshaw (2018)

• Earth is on the edge of runaway warming
https://arctic-news.blogspot.com/2013/04/earth-is-on-the-edge-of-runaway-warming.html

• Paris Agreement
https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement
https://unfccc.int/sites/default/files/english_paris_agreement.pdf

• IPCC Special Report: Global warming of 1.5 ºC — Box SPM.1: Core Concepts 
https://www.ipcc.ch/sr15/chapter/spm/

• IPCC AR5 Synthesis Report — Figure 2.8
https://www.ipcc.ch/report/ar5/syr/synthesis-report

• IPCC AR5 Report, Summary For Policymakers
https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_SPM_FINAL.pdf

• NASA Analysis Graphs and Plots - LSAT and SST change

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

• Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing - by M. Etminan et al.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071930

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

• Possible climate transitions from breakup of stratocumulus decks under greenhouse warming - by Tapio Schneider et al.
https://www.nature.com/articles/s41561-019-0310-1

• A World Without Clouds
https://www.quantamagazine.org/cloud-loss-could-add-8-degrees-to-global-warming-20190225

• How close are we to the temperature tipping point of the terrestrial biosphere? - by Katharyn Duffy et al.

• What Carbon Budget?


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Friday, February 12, 2021

The extreme rate of global warming: IPCC Oversights of future climate trends

by Andrew Glikson

Intergovernmental Panel on Climate Change (IPCC) reports and comprehensive summaries of the peer-reviewed literature raise questions regarding the assumptions inherent in computer modelling of future climate changes, including the supposed linearity of future global temperature trends (Figure 1).

Figure 1. Global mean surface temperature increase as a function of cumulative total global carbon dioxide (CO2) emissions from various lines of evidence. IPCC

Computer modelling does not necessarily capture the sensitivity, complexity and feedbacks of the atmosphere-ocean-land system as observed from paleoclimate studies. Underlying published IPCC computer models appears to be an assumption of mostly gradual or linear responses of the atmosphere to compositional variations. This overlooks self-amplifying effects and transient reversals associated with melting of the ice sheets. 

Leading paleoclimate scientists have issued warnings regarding the high sensitivity of the atmosphere in response to extreme forcing, such as near-doubling of greenhouse gas concentrations: According to Wallace Broecker, “The paleoclimate record shouts out to us that, far from being self-stabilizing, the Earth's climate system is an ornery beast which overreacts to even small nudges, and humans have already given the climate a substantial nudge”. As stated by James Zachos, “The Paleocene hot spell should serve as a reminder of the unpredictable nature of climate”.

Holocene examples are abrupt stadial cooling events which followed peak warming episodes which trigger a flow of large volumes of ice melt water into the oceans, inducing stadial events. Stadial events can occur within very short time, as are the Younger dryas stadial (12.9-11.7 kyr) (Steffensen et al. 2008) (Figure 2) and the 8.2 kyr Laurentian cooling episode,

Despite the high rates of warming such stadial cooling intervals do not appear to be shown in IPCC models (Figure 1).

Figure 2. The younger dryas stadial cooling (Steffensen et al., 2008). Note the abrupt freeze and thaw boundaries of ~3 years and ~1 year.

Comparisons with paleoclimate warming rates follow: The CO₂ rise interval for the K-T impact is estimated to range from instantaneous to a few 10³ years or a few 10⁴ years (Beerling et al, 2002), or near-instantaneous (Figure 3A). An approximate CO₂ growth range of ~0.114 ppm/year applies to the Paleocene-Eocene Thermal Maximum (PETM) (Figure 3B) and ~0.0116 ppm/year to the Last Glacial Termination (LGT) during 17-11 kyr ago (Figure 3C). Thus the current warming rate of 2 to 3 ppm/year is about or more than 200 times the LGT rate (LGT: 17-11 kyr; ~0.0116 ppm/yr) and 20-30 times faster than the Paleocene-Eocene Thermal Maximum (PETM) rate of ~0.114 ppm/year.

Therefore the term “climate change” for the extreme warming reaching +1.5°C over the continents and more than +3°C over the Arctic over a period of less than 100 years, requires reconsideration.

However, comparisons between the PETM and current global warming may be misleading since, by distinction from the current existence of large ice sheets on Earth, no ice was present about 55 million years ago.

Figure 3. (A) Reconstructed atmospheric CO₂ variations during the Late Cretaceous–early Tertiary, based on -
Stomata indices of fossil leaf cuticles calibrated 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);
(C) Global CO₂ and temperature during the last glacial termination (After Shakun et al., 2012) (LGM - Last Glacial Maximum; OD – Older dryas; BA - Bølling–Alerød; YD - Younger dryas)

Observed climate complexities leading to the disturbance of linear temperature variations include:
  1. The weakening of climate zone boundaries, such as the circum-Arctic jet stream, allowing cold air and water masses to shift from polar to mid-latitude zones and tropical air masses to penetrate polar zones (Figure 4), induce collisions between air masses of contrasted temperatures and storminess, with major effects on continental margins and island chains.

  2. Amplifying feedbacks, including release of carbon from warming oceans due to reduced CO₂ solubility and therefore reduced intake from the atmosphere, release of methane from permafrost and from marine sediments, desiccated vegetation and extensive bush fires release of CO₂.

  3. The flow of cold ice melt water into the oceans from melting ice sheets—Greenland (Rahmstorf et al., 2015) and Antarctica (Bonselaer et al., 2018)—ensuing in stadial cooling effects, such as the Younger dryas and following peak interglacial phases during the last 800,000 years (Cortese et al., 2007; Glikson, 2019).
Figure 4. Weakening and undulation of the jet stream, shifts of climate zones and penetration of air masses across the weakened climate boundary. NOAA.

In the shorter term such international targets as “zero emissions by 2050” apparently do not include the export of petroleum, coal and gas, thus allowing nations to circumvent domestic emission limits. Australia, the fifth biggest miner and third biggest exporter of fossil fuels, is responsible for about 5% of global greenhouse gas emissions.

At present the total CO₂+CH₄+N₂O level (mixing ratio) is near 500 ppm CO₂-equivalent (Figure 5). From the current atmospheric CO₂ level of above ~415 ppm, at the rise rate of 2 - 3 ppm/year, by 2050 the global CO₂ level would reach about 500 ppm and the CO₂-equivalent near 600 ppm, raising mean temperatures to near-2°C above preindustrial level, enhancing further breakdown of the large ice sheets and a further rise of sea levels.

Figure 5. Evolution of the CO₂+CH₄+N₂O level (mixing ratio)


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




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Monday, November 16, 2020

Accelerated global warming and stadial cooling events: IPCC oversights regarding future climate trends

 by Andrew Glikson

The linear nature of global warming projections by the IPCC (2014) Assessment Report (AR5) (Figure 1) appears to take little account of stadial cooling events, such as have followed peak temperature rises in previous interglacial stages. The linear trends appear to take only limited account of amplifying positive feedback effects of the warming from land and ocean. A number of factors cast doubt on IPCC climate change projections to 2100 AD and 2300 AD, including:
Figure 1 (a) IPCC average surface temperature change to 2100 relative to 1986-2005 IPCC AR5;
(b) IPCC average surface temperature change to 2300 relative to 1986-2005 IPCC AR5

However, global temperature measurements for 2015-2020 indicate accelerated warming due to both the greenhouse effect reinforced by a solar radiation maximum (Hansen and Sato 2020) (Figure 2).

Figure 2. Accelerated Global Warming reinforced by both greenhouse 
gases and a solar maximum Hansen and Sato, 2020

The weakening of the northern Jet stream, due to polar warming and thus reduced longitudinal temperature contrasts, allows penetration of warm air masses into the polar region and consequent fires (Figure 3). The clash between tropical and polar air and water masses (Figure 3A) leads to regional storminess and contrasting climate change trajectories in different parts of the Earth, in particular along land-ocean boundaries and island chains. 

The weakening of the jet stream and migration of climate zones constitute manifestations of an evolving Earth’s energy imbalance¹, namely a decrease in reflection of solar radiation from Earth to space and thereby global warming. Earth retained 0.6 Watt/m² during 2005-2010 and 0.87 Watt/m² during 2010-2020 (Hansen and Sato 2020), primarily due to a rise in greenhouse gases but also due to a solar radiation peak. During 2015-2020 global warming rates exceeded the 1970-2015 warming rate of 0.18°C/per decade, a deviation greater than climate variability. Hansen and Sato (2020) conclude the accelerated warming is caused by an increasing global climate forcing, specifically by the role of atmospheric aerosols.

Figure 3 A. Undulating and weakening jet stream and the polar vortex and penetration
of warm air, inducing Arctic warming and fires.     B. Satellite images of Wildfires
ravaging parts of the Arctic, with areas of Siberia, Alaska, Greenland and Canada
engulfed in flames and smoke. While wildfires are common at this time of year, record-
breaking summer temperatures and strong winds have made 2020 fires particularly bad.

Bronselaer et al., 2018 modelled a meltwater-induced cooling of the southern hemisphere toward the end 21st century by as low as -1.5°C (Figure 4A). Hansen et al. 2016 estimated the time frame of 21st century stadial cooling event as dependent on the rates of ice melt (Figure 4B), reaching near global extent toward the end of the century (Figure 4C).

Figure 4 A. 2080–2100 meltwater-induced sea-air temperature anomalies relative to
the standard RCP8.5 ensemble (Bronselaer et al., 2018). Hatching indicates where the
anomalies are not significant at the 95% level;  B. Negative temperature anomalies
through the 21st-22nd centuries signifying stadial cooling intervals (Hansen et al., 2016);
C. A model of Global warming for 2096, where cold ice melt water occupies large parts
of the North Atlantic and circum-Antarctica, raises sea level by about 5 meters and
decreases global temperature by -0.33°C (Hansen et al., 2016).

With the concentration of greenhouse gases rising by approximately 47% during the last century and a half, faster than almost any observed rise in the Cenozoic geological record, the term “climate change” refers to an extreme shift in state of the atmosphere-ocean system. The greenhouse gas rise and temperature rise rates are faster than those of the K-T mass extinction, the Paleocene-Eocene extinction and the last glacial termination.

The consequences for future climate change trends include:
  • Further expansion of the tropical climate zones and a polar-ward shift of intermediate climate zones, leading to encroachment of subtropical deserts over fertile Mediterranean zones. 
  • Spates of regional to continent-scale fires, including in Brazil, Siberia, California, around the Mediterranean, Australia.
  • A weakened undulating jet stream (Figure 3) allowing penetration of and clashes between warm and cold air and water masses, with ensuing storms. 
  • In Australia the prolonged drought, low vegetation moisture, high temperatures and warm winds emanating from the northern Indian Ocean and from the inland, rendering large parts of the continent tinder dry and creating severe fire weather subject to ignition by lightning.
  • The delayed melting of the large ice sheets due to hysteresis², would be followed by sea level rise to Pliocene levels, ~25 meters above pre-industrial levels, once sea level reaches equilibrium with temperature of 2 to 3 degrees Celsius or higher, changing the geography of the continents.
It would follow from these considerations that succeeding periods of peak temperatures, extensive melting of the ice sheets, flow of ice melt into the oceans and thereby stadial cooling would lead to clashes between tropical fronts and cooling masses of air, producing storminess, in particular along continental margins and island chains. The modelled time frame of these developments (Figure 4B) may be cyclical, or may extend further in time and place as long as the ice sheets continue to breakdown.

¹ Earth's energy imbalance is the difference between the amount of solar energy
absorbed by Earth and the amount of energy the planet radiates to space as heat.
If the imbalance is positive, more energy coming in than going out, we can expect
Earth to become warmer in the future — but cooler if the imbalance is negative.
² Hysteresis is the dependence of the state of a system on its history. For example the 
melting of an ice sheet may occur slowly depending on its previous state.

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





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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, Australiageospec@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.


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