Friday, September 27, 2019

IPCC Report Ocean and Cryosphere in a Changing Climate


The IPCC has issued another special report: The Ocean and Cryosphere in a Changing Climate.

How much carbon is there in the Arctic?

[ click on images to enlarge ]
How much carbon is present in the northern circumpolar permafrost region (map)?

According to the report, there is 1460 to 1600 billions of tons of carbon (GtC¹) present in the soil on land. The report also mentions that there is additional carbon present on shallow Arctic sea shelves, but the report doesn't add figures.

Natalia Shakhova et al. once estimated the accumulated methane potential for the Eastern Siberian Arctic Shelf alone to be about 500 Gt of organic carbon, with an additional amount in hydrates of about 1000 Gt and a further amount of methane in free gas of about 700 Gt. Back in 2008, Natalia Shakhova et al. considered release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time.

Note ¹: 1 billion ton of carbon = 1 GtC = 1.33 Gt of CH₄ (methane) and 1 GtC = 3.67 Gt of CO₂ (carbon dioxide)

How much of these vast amounts could be released to the atmosphere?

The IPCC report projects permafrost near the surface (top 3–4 m) to decrease in area by up to 89% by 2100 under a high emissions scenario (RCP8.5), leading to cumulative release of tens to hundreds of billions of tons of carbon in the form of carbon dioxide and methane to the atmosphere by 2100.

The report fails to warn that, as the Arctic Ocean keeps heating up, huge seafloor methane eruptions could be triggered, and that this could happen within years, as discussed at the extinction page. Abrupt release of 10 Gt of methane would triple the amount of methane in the atmosphere, resulting in huge heating, while it would also trigger the clouds feedback tipping point to be crossed that in itself could push global temperatures up by 8°C within a few years, as earlier discussed in this post and this post.

Sea ice

The report notes that between 1979 and 2018, the areal proportion of multi-year Arctic sea ice at least five years old has declined by approximately 90%. The report refers to a study by Pistone that concludes that the additional heating due to complete Arctic sea ice loss would hasten global warming by an estimated 25 years. Below is a NASA video showing the melting away of the multi-year sea ice over the years.


The image below shows the difference in Arctic sea ice extent between the years, from an earlier post.


The report concludes that Antarctic sea ice extent overall has had no statistically significant trend. At the same time, the report notes that the Southern Ocean's share of the total heat gain in the upper 2000 m global ocean increased to 45–62% between 2005 and 2017. Below is an image illustrating the difference in Antarctic sea ice extent between the years.


The image below shows how much global sea ice extent has decreased over the past few years.

Sea ice decline makes that less sunlight gets reflected back into space and more heat gets absorbed by the ocean. The report also mentions latent heat changes and increased water vapor and increased cloudiness over the Arctic Ocean. Furthermore, as the temperature difference between the North Pole and the Equator narrows, the Jet Stream changes, which makes it more likely that a large influx of hot, salty water can enter the Arctic Ocean.


Meanwhile, the MetOp-1 satellite recorded a mean global methane level as high as 1914 parts per billion, on September 30, 2019, pm at 293 mb.


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


Links

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

• IPCC special report, The Ocean and Cryosphere in a Changing Climate
https://www.ipcc.ch/srocc/home

• 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

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

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

• Radiative Heating of an Ice‐Free Arctic Ocean, by Kristina Pistone et al.
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL082914

• Weekly Arctic Sea Ice Age with Graph of Ice Age By Area: 1984 - 2019, by NASA
https://svs.gsfc.nasa.gov/4750

• IPCC Report Climate Change and Land
https://arctic-news.blogspot.com/2019/08/ipcc-report-climate-change-and-land.html

• IPCC keeps feeding the addication
https://arctic-news.blogspot.com/2018/10/ipcc-keeps-feeding-the-addiction.html

• IPCC seeks to downplay global warming
https://arctic-news.blogspot.com/2018/02/ipcc-seeks-to-downplay-global-warming.html

• Just do NOT tell them the monster exists
https://arctic-news.blogspot.com/2013/10/just-do-not-tell-them-the-monster-exists.html




Saturday, September 14, 2019

Critical Tipping Point Crossed In July 2019


In July 2019, a critical tipping point was crossed. July sea surface temperatures on the Northern Hemisphere were 1.07°C above what they were during the 20th century, as illustrated by above image which has a trend added that points at 5°C above the 20th century by 2033.

Why is 1°C above 20th century's temperature such a critical tipping point for the sea surface on the Northern Hemisphere? Let's first take a look at where global heating is going.



Oceans are absorbing over 90% of global heating, as illustrated by above image. Due to the high greenhouse gas levels resulting from people's emissions, oceans keep on getting hotter, and given oceans' huge heat-absorbing capacity, it has taken many years before this tipping point was crossed.

In July 2016, the tipping point was touched at 0.99°C. In July 2017, the July temperature anomaly was on the tipping point, at exactly 1°C. In July 2018, the sea surface was a bit cooler, and the tipping point was crossed in July 2019 when the temperature anomaly was 1.07°C above the 20th century average.


Arctic sea ice used to absorb 0.8% of global heating (in 1993 to 2003). Ocean heat keeps flowing into the Arctic Ocean, carried by ocean currents, as illustrated by above image. As peak heat arrives in the Arctic Ocean, it melts sea ice from below.

The image below shows sea surface temperatures on August 13, 2019 (left) and on September 9, 2019 (right). The light blue line forms a line indicating the sea surface temperature there is 0°C. That light blue line has moved pole-ward in September, due to rivers that kept adding warm water and also due to more warmer water entering the Arctic Ocean from the Atlantic Ocean and the Pacific Ocean.


As above image also shows, the sea surface near Svalbard was 20.4°C (or 68.7°F) at the area marked by the green circle on August 13, 2019 (left), and 20.3°C (or 68.5°F) on September 9, 2019 (right), indicating how high the temperature of the water can be underneath the surface, as it moves into the Arctic Ocean. In other words, further ocean heat is still entering the Arctic Ocean.

From mid August 2019, ocean heat could no longer find any sea ice to melt, since the thick sea ice that hangs underneath the surface had already disappeared. A thin layer of sea ice at the surface was all that remained, as air temperatures didn't come down enough to melt it from above.


This indicates that the buffer has gone that has until now been consuming ocean heat as part of the melting process. 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. 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.

The image below, created with NOAA 2007-2019 June-August sea surface temperature data, shows how extra heating of the sea surface on the Northern Hemisphere from 2012 caused the buffer to disappear and the 1°C tipping point to be crossed in 2019.


Once the buffer is gone, further heat arriving in the Arctic Ocean must go elsewhere.


The image below illustrates the difference in extent between the years, as recorded by ads.nipr.ac.jp. On September 13, 1980, Arctic sea ice extent was 7.77 million km². On September 17, 2019, Arctic sea ice extent was 3.96 million km². On September 16, 2012, extent was 3.18 million  million km².


Arctic sea ice will soon be growing in extent, sealing off the water, meaning that less ocean heat will be able to escape to the atmosphere.


This situation comes at a time that methane levels are very high globally. Mean global methane levels were as high as 1911 parts per billion on September 3, 2019, as discussed in a recent post. This post, as well as many earlier posts, also discussed the danger that ocean heat will reach sediments at the seafloor of the Arctic Ocean and cause huge methane releases.

Ominously, methane levels at Barrow, Alaska, were very high recently, as illustrated by above image showing methane levels peaking at over 2500 parts per billion. The satellite image below shows the global situation on the afternoon of September 13, 2019, when peak methane levels as high as 2605 ppb were recorded by the MetOp-1 satellite at 586 mb.


In the videos below, Paul Beckwith discusses the situation.





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


Links

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

• Arctic Sea Ice Gone By September 2019?
https://arctic-news.blogspot.com/2019/07/arctic-sea-ice-gone-by-september-2019.html

• July 2019 Hottest Month On Record
https://arctic-news.blogspot.com/2019/08/july-2019-hottest-month-on-record.html

• Cyclone over Arctic Ocean - August 24, 2019
https://arctic-news.blogspot.com/2019/08/cyclone-over-arctic-ocean-august-24-2019.html

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

• Arctic Ocean overheating
https://arctic-news.blogspot.com/2019/09/arctic-ocean-overheating.html


Sunday, September 8, 2019

Arctic Ocean overheating


The Arctic Ocean is overheating, as illustrated by above image.
[ from earlier post ]

Heating of the water in the Arctic Ocean is accelerating, as illustrated by above map that uses 4-year smoothing and that shows temperatures in the Arctic that are up to 4.41°C hotter than the average global temperature during 1880-1920.

The NOAA image on the right shows the sea surface temperature difference from 1961-1990 in the Arctic at latitudes 60°N - 90°N on September 7, 2019.

Where Arctic sea ice disappears, hot water emerges on the image, indicating that the temperature of the ocean underneath the sea ice is several degrees above freezing point.

The nullschool.net image on the right shows sea surface temperature differences from 1981-2011 on the Northern Hemisphere on September 8, 2019, with anomalies reaching as high as 15.2°C or 27.4°F (near Svalbard, at the green circle).

Accelerating heating of the Arctic Ocean could make global temperatures skyrocket in a matter of years.

Decline of the sea ice comes with albedo changes and further feedbacks, such as the narrowing temperature difference between the North Pole and the Equator, which slows down the speed at which the jet stream circumnavigates Earth and makes the jet stream more wavy.


Disappearance of the sea ice also comes with loss of the buffer that has until now been consuming ocean heat as part of the melting process. 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. 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. Once the sea ice is gone, further heat must go elsewhere.

[ click on images to enlarge ]
The Naval Research Laboratory image on the right shows a forecast for Sep. 8, 2019, run on Sep. 7, 2019, of the thickness of the sea ice. Sea ice has become terribly thin, indicating that the heat buffer constituted by the sea ice has effectively gone. Only a very thin layer of sea ice remains in place throughout much of the Arctic Ocean.

This remaining sea ice is stopping a lot of ocean heat from getting transferred to the air, so the temperature of the water of the Arctic Ocean is now rising rapidly, with the danger that some of the accumulating ocean heat will reach sediments at the seafloor and cause eruptions of huge amounts of methane.


This situation comes at a time that methane levels are very high globally. Mean global methane levels were as high as 1911 parts per billion on the morning of September 3, 2019, a level recorded by the MetOp-1 satellite at 293 mb (image below).


[ from an earlier post ]
As the image on the right shows, mean global levels of methane (CH₄) have risen much faster than carbon dioxide (CO₂) and nitrous oxide (N₂O), in 2017 reaching, respectively, 257%, 146% and 122% their 1750 levels.

Compared to carbon dioxide, methane is some 150 times as potent as a greenhouse gas during the first few years after release.

Huge releases of seafloor methane alone could make marine stratus clouds disappear, as described in an earlier post, and this clouds feedback could cause a further 8°C global temperature rise.

In total, global heating by as much as 18°C could occur by the year 2026 due to a combination of elements, including albedo changes, loss of sulfate cooling, and methane released from the ocean seafloor.

from an earlier post (2014)  

In the image below, a global warming potential (GWP) of 150 for methane is used. Just the existing carbon dioxide and methane, plus seafloor methane releases, would suffice to trigger the clouds feedback tipping point to be crossed that by itself could push up global temperatures by 8°C, within a few years time.


Progression of heating could unfold as pictured below.

[ from an earlier post ]

In the video below, John Doyle describes out predicament.



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


Links

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

• Arctic Sea Ice Gone By September 2019?
https://arctic-news.blogspot.com/2019/07/arctic-sea-ice-gone-by-september-2019.html

• July 2019 Hottest Month On Record
https://arctic-news.blogspot.com/2019/08/july-2019-hottest-month-on-record.html

• Cyclone over Arctic Ocean - August 24, 2019
https://arctic-news.blogspot.com/2019/08/cyclone-over-arctic-ocean-august-24-2019.html

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


Sunday, September 1, 2019

Blueprints of future climate trends

Blueprints of future climate trends

Extreme GHG and temperature rise rates question linear climate projections

Andrew Glikson
Earth and climate scientist
Australian National University
geospec@iinet.net.au

Abstract

The extreme greenhouse gas (GHG) and temperature rise rates since the mid-1970th raise questions over linear climate projections for the 21st century and beyond. Under a rise of CO₂-equivalent reaching +500 ppm and 3.0 W/m⁻² relative to 1750, the current rise rates of CO₂ by 2.86 ppm per and recent global temperature rise rate (0.15-0.20°C per decade) since 1975 are leading to an abrupt shift in state of the terrestrial climate and the biosphere. By mid-21st century at >750 ppm CO₂-e climate tipping points indicated by Lenton et al. 2008 and Schellnhuber 2009 are likely to be crossed. Melting of the Greenland and Antarctic ice sheets has increased by a factor of more than 5 since 1979–1990. As the ice sheets and sea ice melt, the albedo flip between reflective ice surfaces and dark infrared-absorbing water results in significant increase of radiative forcing, and complete removal of Arctic sea ice would result in a forcing of about 0.7 W/m⁻² (Hudson, 2011). The confluence of climate events, including a breach of the circum-Arctic jet stream boundary and a polar-ward migration of climate zones at a rate of 56-111 km per decade, induce world-wide extreme weather events including bushfires, methane release from Arctic permafrost and sediments. For a climate sensitivity of 3±1.5°C per doubling of atmospheric CO₂, global warming has potentially reached between +2°C to +3°C above mean pre-industrial temperatures at a rate exceeding the fastest growth rate over the last 55 million years. As ice melt water flow into the oceans temperature polarities between warming continents and cooling tracts of ocean would further intensify extreme weather events under non-linear climate trajectories. The enrichment of the atmosphere in GHG, constituting a shift in state of the terrestrial climate, is predicted to delay the onset of the next glacial state by some 50,000 years.

GHG and temperature rise

The paleoclimate record suggests that no event since 55 million years ago, the Paleocene-Eocene Thermal Maximum (PETM), when global temperatures rose by more than +5 to +8°C over a period of ~20,000 years, with a subsequent warming period of up to 200,000 years, has been as extreme as atmospheric disruption since the onset of the industrial age about 1750 AD (the Anthropocene), accelerating since 1975. During this period greenhouse gas levels have risen from ~280 ppm to above >410 ppm and to 496 ppm CO₂-equivalent (Figure 1), the increase of CO₂ reaching near-47 percent above the original atmospheric concentration. However, linear climate change projections are rare in the recent climate history (Figure 2) and linear future climate projections may not account for the effects of amplifying feedbacks from land and oceans. Given an Anthropocene warming rate faster by ~X200 times than the PETM (Figure 3), linear warming trajectories such as are projected by the IPCC may overlook punctuated tipping points, transient reversals and stadial events.
Figure 1. Growth of CO₂-equivalent level and the annual greenhouse gas Index (NOAA AGGI).
Measurements of CO₂ to the 1950s are from (Keeling et al., 2008) and from air trapped in ice and
snow between CO₂ concentrations and radiative forcing from all long-lived greenhouse gases.

According to NOAA, GHG forcing in 2018 has reached 3.101 W/m⁻² relative to 1750 (CO₂ = 2.044 W/m⁻²; CH₄ = 0.512 W/m⁻²; N₂O = 0.199 W/m⁻²; CFCs = 0.219 W/m⁻²) with a CO₂-equivalent of 492 ppm (Figure 1). The rise in GHG forcing during the Anthropocene since about 1800 AD, intensifying since 1900 AD and sharply accelerating since about 1975, has induced a mean of ~1.5°C over the continents above pre-industrial temperature, or >2.0°C when the masking role of aerosols is discounted, implying further warming is still in store.

According to Hansen et al. 2008, the rise in radiative forcing during the Last Glacial Termination (LGT - 18,000 -11,000 years BP), associated with enhancing feedbacks, has driven GHG radiative forcing by approximately ~3.0 W/m⁻² and a mean global temperature rise of ~4.5°C (Figure 2), i.e. of similar order as the Anthropocene rise since about 1900. However the latter has been reached within a time frame at least X30 times shorter than the LGT, underpinning the extreme nature of current global warming.
Figure 2. (Hansen et al. 2008). Glacial-temperature and GHG forcing for the last 420,000 years based on the Vostok
ice core, with the time scale expanded for the Anthropocoene. The ratio of temperature and forcing scales is 1.5°C
per 1 W/m⁻². The temperature scale gives the expected equilibrium response to GHG change including slow feedback
surface albedo change. Modern forcings include human-made aerosols, volcanic aerosols and solar irradiance.
The CO₂-equivalent levels and radiative forcing levels constitute a rise from Holocene levels (~280 ppm CO₂) to >410 ppm compared with Miocene-like levels (300-600 ppm CO₂), at a rate reaching 2 to 3 ppm/year, within a century or so, driving the fastest temperature rise rate recorded since 55 million years ago (Figure 3).

Figure 3. 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 (1750–2016), and (4) an asteroid impact. In the latter instance temperature
due to CO₂ rise would lag by some weeks or months behind aerosol-induced cooling

Considering the transient mitigating albedo effects of clouds, seasonal land surface albedo, ice albedo, atmospheric aerosols including sulphur dioxide and nitrate, the potential rise of land temperature could have reached -0.4 to -0.9 W/m⁻² in 2018, masking approximately 0.6 to 1.3°C potential warming once the short lived aerosol effect is abruptly reduced.

Accelerated melting of the ice sheets

The fast rate of the Anthropocoene temperature rise compared to the LGT and PETM (Figure 3) ensues in differences in terms of the adaptation of flora and fauna to new conditions. The shift in state of the Earth’s climate is most acutely manifested in the poles, where warming leads to weakening of the jet stream boundaries which are breached by outflow of cold air fronts, such as the recent “Beast from the East” event, and penetration of warm air masses.

As the poles keep warming, to date by a mean of ~2.3°C, the shrinking of the ice sheets per year has accelerated by a factor of more than six fold (Figure 4). Warming of the Arctic is driven by the ice-water albedo flip, where dark sea-water absorbing solar energy alternates with high-albedo ice and snow, and by the weakening of the polar boundary and jet stream.

Greenland. The threshold of collapse of the Greenland ice sheet, retarded by hysteresis, is estimated in the range of 400-560 ppm CO₂, already transgressed at the current 496 ppm CO₂equivalent (Figure 4). The Greenland mass loss increased from 41 ± 17 Gt/yr in 1990–2000, to 187 ± 17 Gt/yr in 2000–2010, to 286 ± 20 Gt/yr in 2010–2018, or six fold since the 1980s, or 80 ± 6 Gt/yr per decade, on average.

Antarctica. The greenhouse gas level and temperature conditions under which the East Antarctic ice sheet formed during the late Eocene 45-34 million years ago are estimated as ~800–2000 ppm and up to 4 degrees Celsius above pre-industrial values, whereas the threshold of collapse is estimated as 600 ppm CO₂ or even lower. The total mass loss from the Antarctic ice sheet increased from 40 ± 9 Gt/yr in 1979–1990 to 50 ± 14 Gt/yr in 1989–2000, 166 ± 18 Gt/yr in 1999–2009, and 252 ± 26 Gt/yr in 2009–2017. Based on satellite gravity data, the East Antarctic ice sheet is beginning to breakdown in places (Jones 2019), notably the Totten Glacier (Rignot et al., 2019), which may be irreversible. According to Mengel and Levermann (2014), the Wilkes Basin in East Antarctica alone contains enough ice to raise global sea levels by 3–4 meters.

Figure 4. (A) New elevation showing the Greenland and Antarctic current state of the ice sheets accurate to a few meters in height, with elevation changes indicating melting at record pace, losing some 500 km³ of ice per-year into the oceans; (B) Ice anomaly relative to the 2002-2016 mean for the Greenland ice sheet (magenta) and Antarctic ice sheet (cyan). Data are from GRACE; (C) the melting of sea ice 1978-2017, National Snow and Ice Data Center (NCIDC)

C. Migration of climate zones

The expansion of warm tropical zones and the polar-ward migration of subtropical and temperate climate zones are leading to a change in state in the global climate pattern. The migration of arid subtropical zones, such as the Sahara, Kalahari and central Australian deserts into temperate climate zones ensues in large scale droughts, such in inland Australia and southern Africa. In the northern hemisphere expansion of the Sahara desert northward, manifested by heat waves across the Mediterranean and Europe (Figure 5).
Figure 5. (A) Migration of the subtropical Sahara climate zone (red spots) northward into the Mediterranean climate
zone leads to warming, drying and fires over extensive parts of Spain, Portugal, southern France, Italy, Greece and
Turkey, and to melting of glaciers in the Alps. Migration, Environment and Climate Change, International
Organization for Migration Geneva – Switzerland (GMT +1); Source: https://environmentalmigration.iom.int/maps

Figure 5. (B) Southward encroachment of Kalahari Desert conditions (vertical lines and red spots) leading to
warming and drying of parts of southern Africa. Source: https://environmentalmigration.iom.int/maps
Figure 5. (C) Drying parts of southern Australia, including Western Australia, South Australia and parts of the
eastern States, accompanied with increasing bushfires. Source: https://environmentalmigration.iom.int/maps
Climate extremes

Since the bulk of terrestrial vegetation has evolved under glacial-interglacial climate conditions, where GHG range between 180 - 300 ppm CO₂, global warming is turning large parts of Earth into a tinderbox, ignited by natural and human agents. By July and August 2019, as fires rage across large territories, including the Amazon forest, dubbed the Planet’s lungs as it enriches the atmosphere in oxygen. When burnt the rainforest becomes of source of a large amount of CO₂ (Figure 6.B), with some 72,843 fires in Brazil this year and extensive bushfires through Siberia, Alaska, Greenland, southern Europe, parts of Australia and elsewhere, the planet’s biosphere is progressively transformed. As reported: ‘Climate change is making dry seasons longer and forests more flammable. Increased temperatures are also resulting in more frequent tropical forest fires in non-drought years. And climate change may also be driving the increasing frequency and intensity of climate anomalies, such as El Niño events that affect fire season intensity across Amazonia.’

Extensive cyclones, floods, droughts, heat waves and fires (Figure 6.B) increasingly ravage large tracts of Earth. However, despite its foundation in the basic laws of physics (the black body radiation laws of Planck, Kirchhoff' and Stefan Boltzmann), as well as empirical observations around the world by major climate research bodies (NOAA, NASA, NSIDC, IPCC, World Meteorological Organization, Hadley-Met, Tindale, Potsdam, BOM, CSIRO and others), the anthropogenic origin, scale and pace of climate change remain subject to extensively propagated denial and untruths.

Figure 6. (A) Extreme weather events around the world 1980-2018,
including earthquakes, storms, floods, droughts. Munich Re-insurance.
Figure 6. (B) A satellite infrared image of South America fires (red dots) during July and August, 2019, NASA.

An uncharted climate territory

Whereas strict analogies between Quaternary and Anthropocene climate developments are not possible, elements of the glacial-interglacial history are relevant for an understanding of current and future climate events. The rise of total greenhouse gas (GHG), expressed as CO₂-equivalents, to 496 ppm CO₂-e (Figure 1), within less than a century represents an extreme atmospheric event. It raised GHG concentrations from Holocene levels to the range of the Miocene (34–23 Ma) when CO₂ level was between 300 and 530 ppm. As the glacial sheets disintegrate, cold ice-melt water flowing into the ocean ensue in large cold water pools, a pattern recorded following peak interglacial phases over the last 450,000 years, currently manifested by the growth of cold regions in north Atlantic Ocean south of Greenland and in the Southern Ocean fringing Antarctica (Figure 7).

Warming of +3°C to +4°C above pre-industrial levels, leading to enhanced ice-sheet melt, would raise sea levels by at least 2 to 5 meters toward the end of the century and, delayed by hysteresis, likely by 25 meters in the longer term. Golledge et al. (2019) show meltwater from Greenland will lead to substantial slowing of the Atlantic overturning circulation, while meltwater from Antarctica will trap warm water below the sea surface, increasing Antarctic ice loss. Whereas the effect of low-density ice melt water on the surrounding oceans is generally not included in many models, depending on amplifying feedbacks, prolonged Greenland and Antarctic melting and consequent cooling of surrounding ocean sectors as well as penetration of freezing air masses through weakened polar boundaries may have profound effect on future climate change trajectories (Figure 8).

Figure 7. (A) Global warming map (NASA 2018). Note the cool ocean regions south of Greenland and 
along the Antarctic. Credits: Scientific Visualization Studio/Goddard Space Flight Center; 
(B) 2012 Ocean temperatures around Antarctica (NASA 2012).
Climate projections for 2100-2300 by the IPCC AR5 Synthesis Report, 2014 portray predominantly linear to curved models of greenhouse gas, global temperatures and sea level changes. These models however appear to take limited account of amplifying feedbacks from land and ocean and of the effects of cold ice-melt on the oceans. According to Steffen et al. (2018) “self-reinforcing feedbacks could push the Earth System toward a planetary threshold” and “would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene”.

Amplifying feedbacks of global warming include:
  • The albedo-flip of melting sea ice and ice sheets and the increase of the water surface area and thereby sequestration of CO₂. Hudson (2011) estimates a rise in radiative forcing due to removal of Arctic summer sea ice as 0.7 W/m², a value close to the total of methane release since 1750.
  • Reduced ocean CO₂ intake due to lesser solubility of the gas with higher temperatures.
  • Vegetation desiccation and burning in some regions, and thereby released CO₂ and reduced evaporation and its cooling effect. This factor and the increase of precipitation in other regions lead to differential feedbacks from vegetation as the globe warms (Notaro et al. 2007).
  • An increase in wildfires, releasing greenhouse gases (Figure 6).
  • Release of methane from permafrost, bogs and sediments and other factors.
Linear temperature models appear to take limited account of the effects on the oceans of ice melt water derived from the large ice sheets, including the possibility of a significant stadial event such as already started in oceanic tracts fringing Greenland and Antarctica (Figure 7) and modeled by Hansen et al, (2016). In the shorter to medium term sea level rises would ensue from the Greenland ice sheet (6-7 meter sea level rise) and West Antarctic ice sheet melt (4.8 meter sea level rise). Referring to major past stadial events, including the 8200 years-old Laurentian melt and the 12.7-11.9 younger dryas event, a protracted breakdown of parts of the Antarctic ice sheet could result in major sea level rise and extensive cooling of southern latitudes and beyond, parallel with warming of tropical and mid-latitudes (Figure 8) (Hansen et al. 2016). The temperature contrast between polar-derived cold fronts and tropical air masses is bound to lead to extreme weather events, echoed among other in Storms of my grandchildren (Hansen, 2010).

Figure 8. (A) Model Surface-air temperature (°C) for 2096 relative to 1880–1920 (Hansen et al. 2016).
The projection betrays major cooling of the North Atlantic Ocean, cooling of the circum-Antarctic Ocean
and further warming in the tropics, subtropics and the interior of continents; (B) Modeled surface-air
temperatures (°C) to 2300 AD relative to 1880–1920 for several ice melt rate scenarios, displaying a stadial cooling event at a time dependent on the ice melt doubling time (Hansen et al., 2016). Courtesy Prof James Hansen;.
Within and beyond 2100-2300 projections (Figure 8.A, B) lies an uncharted climate territory, where continuing melting of the Antarctic ice sheet, further cooling of neighboring sectors of the oceans and climate contrasts with GHG-induced warming of land areas (Figure 8.A), ensue in chaotic climate disruptions (Figure 8.B). Given the thousands to tens of thousands years longevity of atmospheric greenhouse gases (Solomon et al., 2009; Eby et al 2009), the onset of the next ice age is likely to be delayed on the scale of tens of thousands of years (Berger and Loutre, 2002) through an exceptionally long interglacial period (Figure 9).

These authors state: ‘The present day CO₂ concentration (now >410 ppm) is already well above typical interglacial values of ~290 ppmv. This study models increases to up to 750 ppmv over the next 200 years, returning to natural levels by 1000 years. The results suggest that, under very small insolation variations, there is a threshold value of CO₂ above which the Greenland Ice Sheet disappears. The climate system may take 50,000 years to assimilate the impacts of human activities during the early third millennium. In this case, an “irreversible greenhouse effect” could become the most likely future climate. If the Greenland and west Antarctic Ice Sheets disappear completely, then today’s “Anthropocene” may only be a transition between the Quaternary and the next geological period.’

Figure 9. Simulated Northern Hemisphere ice volume (increasing downward) for the period 200,000 years BP to 130,000 years in the future, modified after a part of Berger and Loutre 2002. Time is negative in the past and positive in the future. For the future, three CO2 scenarios were used: last glacial-interglacial values (solid line), a human-induced concentration of 750 ppm (dashed line), and a constant concentration of 210 ppm inducing a return to a glacial state (dotted line).
As conveyed by leading scientists “Climate change is now reaching the end-game, where very soon humanity must choose between taking unprecedented action or accepting that it has been left too late and bear the consequences” (Prof. Hans Joachim Schellnhuber) …“We’ve reached a point where we have a crisis, an emergency, but people don’t know that ... There’s a big gap between what’s understood about global warming by the scientific community and what is known by the public and policymakers” (James Hansen).

Climate scientists find themselves in a quandary similar to medical doctors, committed to help the ill, yet need to communicate grave diagnoses. How do scientists tell people that the current spate of extreme weather events, including cyclones, devastating islands from the Caribbean to the Philippine, floods devastating coastal regions and river valleys from Mozambique to Kerala, Pakistan and Townsville, and fires burning extensive tracts of the living world, can only intensify in a rapidly warming world? How do scientists tell the people that their children are growing into a world where survival under a mean temperature higher than +2 degrees Celsius (above pre-industrial temperature) is likely to be painful and, in some parts of the world, impossible, let alone under +4 degrees Celsius projected by the IPCC?

Summary and conclusions
  1. The current growth rate of atmospheric greenhouse gas is the fastest recorded for the last 55 million years.
  2. By the mid-21st century, at the current CO₂ rise rates of 2 to 3 ppm/year, a CO₂-e level of >750 ppm is likely to transcend the climate tipping points indicated by Lenton et al. 2008 and Schellnhuber 2009.
  3. The current extreme rise rates of GHG (2.86 ppm CO₂/year) and temperature (0.15-0.20°C per decade since 1975) raise doubt with regard to linear future climate projections.
  4. Global greenhouse gases have reached a level exceeding the stability threshold of the Greenland and Antarctic ice sheets, which are melting at an accelerated rate.
  5. Allowing for the transient albedo-enhancing effects of sulphur dioxide and other aerosols, mean global temperature has reached approximately 2.0 degrees Celsius above per-industrial temperatures.
  6. Due to hysteresis the large ice sheets would outlast their melting temperatures.
  7. Land areas would be markedly reduced due to a rise to Miocene-like sea levels of approximately 40±15 meters above pre-industrial levels.
  8. Cold ice melt water flowing from the ice sheets into the oceans at an accelerated rate is reducing temperatures in large tracts in the North Atlantic and circum-Antarctic.
  9. Strong temperature contrasts between cold polar-derived and warm tropical air and water masses are likely to result in extreme weather events, retarding habitats and agriculture over coastal regions and other parts of the world.
  10. In the wake of partial melting of the large ice sheets, the Earth climate zones would continue to shift polar-ward, expanding tropical to super-tropical regions such as existed in the Miocene (5.3-23 million years ago) and reducing temperate climate zones and polar ice sheets.
  11. Current greenhouse gas forcing and global mean temperature are approaching Miocene Optimum-like composition, bar the hysteresis effects of reduced ice sheets (Figure 4.A).
  12. The effect of high atmospheric greenhouse gas levels would be for the next ice age to be delayed on a scale of tens of thousands of years, during which chaotic tropical to hyperthermal conditions would persist until solar radiation and atmospheric CO₂ subsided below ~300 ppm.
  13. Humans will survive in relatively favorable parts of Earth, such as sub-polar regions and sheltered mountain valleys, where gathering of flora and hunting of remaining fauna may be possible.

A Postscript

The author, while suggesting the projections made in this paper are consistent with the best climate science with which he is aware, sincerely hopes the implications of these projections would not eventuate.