The myth of “net zero emissions by 2050”

by Andrew Glikson

[ Oil and gas fracking pads in Texas. Photo: Dennis Dimick ]

It should raise people’s hopes to believe “net zero emissions by 2050” will arrest or at least slow-down global warming, had it not been yet another cruel hoax perpetrated in the wake of more than 50 years of obfuscation and denial of environment and climate science.

This is because:

• The proposed zero emission by 2050 overlooks the long term nature of ongoing investments, mining and drilling for carbohydrates, such as new oil fields as in the North Atlantic and the sub-Arctic, new coal fields such as in the Galilee Basin, or fracking for coal seam gas in North America and Australia. According to Columbia University, “The gas industry and investors have plans to build over $70 billion of new gas-fired power plants through 2025, according to two Rocky Mountain Institute reports”.
  
  Thus it is reported “the State Bank of India might lend $1 billion to Bravus, the absurdly renamed Adani Mining, to finance its Carmichael coal and rail project in the Galilee Basin”. Likewise “At the end of last year Australia overtook Qatar to become the world’s largest exporter of LNG, and now even more companies are investing in infrastructure throughout the region to turn Western Australia into a global LNG hub.”
  
  
• The proposed reductions in emissions are to be mainly confined to domestic emissions, neglecting carbon exports that end up mixing in the atmosphere and oceans, returning to harm life on Earth. Australia, China and the US are the largest CO2 emitters and Saudi Arabia, Russia and Australia are the largest CO2 exporters. On a per capita basis, Australia’s carbon footprint, including exports, is nine times higher than China’s, four times that of the US, and 37 times that of India.
  
  National emissions inventories exclude the large CO2 transfers associated with international trade, such as has grown dramatically since the early 1990s. This hampered overall progress to cut total CO2 emissions over the past few decades. When CO2 imports are considered, the reduction in emissions achieved by many developed countries is much smaller than would otherwise appear.
  
  Australia mines about 57 tonnes of CO2 potential per person each year, about 10 times the global average, and is the world's third-biggest exporter of hydrocarbons behind Russia and Saudi Arabia. In total Australia emits about five per cent of global total CO2 once exports are included. A Fact Check estimated that Australia's domestic emissions plus the emissions embedded in its exports added to 1,712 million tonnes in 2016. The total falls from 3.6 per cent to 3.3 per cent of global emissions.
  
  
• The proposed reductions take no account of the accelerated rise of temperatures due to the radiative effects of the rising greenhouse gas concentration in the atmosphere, which by 2050 will be tracking toward 600 parts per million CO2-equivalent of combined carbon and nitrous oxide gases. These are already generating amplifying feedbacks from land and ocean which drive temperatures higher, rendering reductions of emissions ineffective. At that stage the large ice sheets would experience irreversible melting.

For this reason, the essential reductions in emission must be accompanied with sequestration of atmospheric greenhouse gases by at least the amount of annual emissions.

The authorities are not listening to what climate science is indicating. Instead they are consulting with economists ignorant of the physics and chemistry of the atmosphere and of the consequences of global heating. An example is the absurd idea as if “a rise of 4°C in global average temperature would be “optimal” when the costs and benefits of mitigating climate change are balanced”.

Currently, CO2 concentrations in the atmosphere are increasing at the approximate rate of 2 to 3 parts per million per year. This leaves the fundamental question unanswered: What, if anything, would halt the fatal progression toward +4 degrees Celsius above pre-industrial temperatures, given that according to the IPCC (cited by the World Bank) a “four degree world would be one of unprecedented heatwaves, severe drought and major floods in many regions”. In perspective, global warming of the 20-21st centuries is at least 70 times faster than the rise of about 5 degrees Celsius over a period of about 7000 years since the last interglacial period. At this rate of environmental change mass extinctions are inevitable. When Professor Hans Joachim Schellnhuber (former climate adviser to the German Chancellor and the EU) was asked about the difference between a +2°C and a +4°C world, he replied: “Human civilization”.

 

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

Polar-ward climate zones shift and consequent tipping points

by Andrew Glikson

The concept of a global climate tipping point/s implies a confluence of climate change processes in several parts of the world where regional climate changes can combine as a runaway shifts to a new climate state. Conversely the shift of climate zones can constitute the underlying factor that triggers extreme weather events which culminate in tipping points. These shifts include the expansion of the tropics, tropical cyclones, mid-latitude storms and weakening of boundaries of the polar vortex, allowing breach of air masses of contrasting temperatures through the jet stream polar boundary, with ensuing snow storms and heatwaves.

Figure 1. Climate tipping points (McSweeney 2020)

The migration of climate zones toward the poles appears to constitute a major factor in triggering tipping points in the Earth system (Figures 1 and 2), including (from north to south):

1. permafrost loss 
2. expansion of the Boreal forest at the expense of the tundra
3. disintegration of the Greenland ice sheet
4. breakdown of the Atlantic meridional overturning circulation (AMOC) caused by an increased influx of freshwater into the North Atlantic 
5. Amazon forest dieback 
6. West African monsoon shift 
7. Indian monsoon shift 
8. Coral reef die-off
9. West Antarctic ice disintegration

Not included in this list are the increased desertification and the extensive fires in parts of the continents, including the Arctic, Siberia, western North America, the Mediterranean, Brazil and Australia.

Figure 2. Monthly anomalies for October 2020 by NOAA (National Centers for Environmental Information)

A conflation of regional climate developments into global climate tipping point/s, namely a shift in state of the Earth climate is likely, although the details of this process are not clear. Alternatively it is the migration of climate zones toward the poles, indicated by climate zone maps, which is triggering regional events.

Figure 3. High anomalies over the Arctic from Nov. 2019 to Oct. 2020 (NASA image)

Here I list some of these likely relationships: 

• In the Arctic sea ice extent in October 2020 was lower by 36.8% than during 1981-2010 (Figure 2). High anomalies have hit the Artic Ocean and Siberia over the 12-month period from November 2019 to October 2020 (Figure 3). The warming of the Arctic is driven by (1) a decline in albedo due to ice melt and exposure of open water surfaces; (2) the albedo flip generated by formation of thin water surfaces above ice sheets and glaciers, and (3) the penetration of warm air masses through the weakened circum-Arctic jet stream (Figure 4.). 
  
• The tropics are expanding at a rate of near-50 km per decade (Jones 2018) and have widened about 0.5° latitude per decade since 1979 (Staten et al. 2018). With warming and desertification effects across North Africa and the Mediterranean Sea this is leading to draughts and fires in southern Europe. The shift of climate zones toward the poles, at a rate approximately 50 to 100 km per decade, as well as sea level rise, is changing the geography of the planet. Once sea level reaches equilibrium temperatures it will attain at least 25 meters above the present, by analogy to Pliocene level (before 2.6 million years ago).
• As climate zones shift northward an increase of winter precipitation of up to 35% is recorded in mid to northern Europe during the 21st century, with increases of up to 30% in north-eastern Europe. In 2020 Europe had the warmest October on record and North America the heaviest snow precipitation on record (Figure 2). 
• In Australia a southward migration of the tropical North Australia climate zone and the high pressure ridge separating it from the southern terrain dominated by the Westerlies and the precipitation-bearing spirals of the Antarctic-sourced vortex southward, with consequent droughts in southern and southwestern parts of the continent. 

Figure 4. The Arctic jet stream, summer, 1988, NASA. Extreme melting in 
Greenland’s ice sheet is linked to warm air delivered by the wandering jet 
stream, a fast-moving belt of westerly winds created by the convergence of 
cold air masses descending from the Arctic and rising warm air masses from 
the tropics that flow through the lower layers of the atmosphere.

As evident from the above the shift in climate zones constitutes the underlying factor which triggers extreme weather events and tipping points.

Figure 5. Arctic surface-air temperature anomalies for July 2020.

Since the onset of the industrial age, in particular since about 1960-70, global warming accelerated at by one to two orders of magnitude faster than during the last glacial termination (~16000 – 8000 years ago) and much earlier. Mass extinction events in the Earth history have occurred when environmental changes took place at a rate to which species could not adapt. Plants and animals are currently dying off at a rate 100 to 1000 times faster than the mean rate of extinction over geological timescales.

The Intergovernmental Panel for Climate Change (IPCC AR5) projects linear warming to 2300 and 2500, which however does not take full account of amplifying feedbacks from a range of sources (Trajectories of the Earth system in the Anthropocene). These include reduced CO2 sequestration in the warming oceans, albedo changes due to melting of ice, enrichment of the atmosphere in water vapor, desiccation and burning vegetation, release of methane from permafrost. Nor do these linear trends take account of the stadial effects of the flow of cold ice melt water into the oceans (Glikson, 2019).

According to the National Oceanic and Atmospheric Agency (NOAA) global warming has accelerated significantly during 2015-2020. The danger inherent in temperature rise to about 4 degrees Celsius by 2100 is underpinned by the consequences at lower temperature rise of +1 to +2 degrees Celsius, already in evidence. Thus, whereas the mean land-ocean temperature rise between 1880-2020 is +1.16 degrees Celsius, the average rise in continental temperatures during this period has already reached +1.6 degrees Celsius, beyond the upper limit proposed by the Paris Accord. The rise in temperatures is driving a three-fold to six-fold rise in extreme weather events since 1980 (Figure 6.), including severe storms, tropical storms, flooding, droughts and wildfires (NOAA 2018).

Figure 6. The growth in the frequency of extreme weather events in the US during 1980-2018

Large-scale melting of the Greenland and Antarctica ice sheets, discharging cold ice melt water, is already cooling of parts of the oceans. The clash between cold air masses and tropical fronts would increase storminess, in particular along coastal boundaries and islands. Such storminess, along with intensified tropical cyclones, would render island chains increasingly vulnerable.

To date most suggestions for mitigation and adaptation are woefully inadequate to arrest global warming. Reductions in carbon emissions, which are absolutely essential, may no longer be adequate to arrest accelerating greenhouse gas and temperature levels. At the current level of carbon dioxide (>500 parts per million equivalent CO2+methane+nitrous oxide), reinforced by amplifying feedbacks from land and oceans, the remaining option would be to sequester (down-draw) greenhouse gases from the atmosphere.

A global imperative.

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

There is no time to lose

Carbon dioxide levels continue at record levels, despite COVID-19 lockdown, the WMO reports. The increase in carbon dioxide from 2018 to 2019 was larger than that observed from 2017 to 2018 and larger than the average annual growth rate over the last decade.

The rise has continued in 2020. The lockdown did cut emissions of many pollutants and greenhouse gases, but any impact on carbon dioxide levels - the result of cumulative past and current emissions - is in fact no bigger than the normal year to year fluctuations. 

“Carbon dioxide remains in the atmosphere for centuries and in the ocean for even longer. The last time the Earth experienced a comparable concentration of CO₂ was 3-5 million years ago, when the temperature was 2-3°C warmer and sea level was 10-20 meters higher than now. But there weren’t 7.7 billion inhabitants,” said WMO Secretary-General Professor Petteri Taalas.

“The COVID-19 pandemic is not a solution for climate change. However, it does provide us with a platform for more sustained and ambitious climate action to reduce emissions to net zero through a complete transformation of our industrial, energy and transport systems. The needed changes are economically affordable and technically possible and would affect our everyday life only marginally. It is to be welcomed that a growing number of countries and companies have committed themselves to carbon neutrality,” he said. “There is no time to lose.”

Above image illustrates the steep rise in methane, compared to carbon dioxide and nitrous oxide. Levels of carbon dioxide, methane and nitrous oxide reached new highs in 2019, reports the WMO. Carbon dioxide (CO₂) rose to 410.5 ppm (148% of its pre-industrial level), methane (CH₄) to 1877 ppb (260% of pre-industrial) and nitrous oxide (N₂O) to 332.0 ppb (123% of pre-industrial).

So, given that there's no time to lose, why mention carbon neutrality, and not 100% clean, renewable energy? Also, let's not lose sight of other emissions such as N₂O. Yes, dramatic cuts in CO₂ emissions do need to happen rapidly, and yes, this does require a complete transformation of industry, energy and transport. Nonetheless, N₂O emissions are also important and most N₂O emissions result from land use, such as food production and waste handling, which must also change. 

[ from earlier post ]

The IPCC (AR5) gave N₂O a lifetime of 121 years and a 100-year global warming potential (GWP) of 265 times that of carbon dioxide. Furthermore, N₂O also causes stratospheric ozone depletion. 

The IPCC, in special report Climate Change and Land, found that agriculture, forestry and other land use activities accounted for some 13% of CO₂, 44% of CH₄, and 82% of N₂O emissions from human activities globally during 2007-2016, representing 23% of total net anthropogenic emissions of greenhouse gases.

If emissions associated with pre- and post-production activities in the global food system are included, the emissions could be another 14% higher, i.e. as high as 37% of total net anthropogenic greenhouse gas emissions, the IPCC added.

Let's get back to that 23%. The IPCC calculates this 23% by using a GWP of 28 for CH₄. Over the first few years, however, the GWP of CH₄ is more than 150, as discussed in an earlier post. When using a GWP of 150, land use emissions rise from 23% to 31%, as the image on the right shows. Add another 14% from further food-related emissions and the total share for land use becomes 45% of people's emissions. 

[ click on images to enlarge ]

In other words, all polluting emissions need to be reduced. Moreover, a recent paper by Jorgen Randers et al. points out that, even if all greenhouse gas emissions by people could stop immediately and even if the temperature anomaly could fall to 0.5°C above pre-industrial, greenhouse gas levels would start rising again after 2150 and keep rising for centuries to come. Another recent paper, by Tapio Schneider et al., points out that solar geoengineering may not prevent strong warming from direct effects of CO₂ on stratocumulus cloud cover. 

This means that the threat is even more menacing when including large methane releases that threaten to occur as temperatures keep rising in the Arctic and sediments at the seafloor of the Arctic Ocean threaten to get destabilized, resulting in the eruption of huge amounts of methane. 

What is the joint impact of carbon dioxide and methane? The WMO reported CO₂ levels of 410.5 ppm and CH₄ levels of 1877 ppb in 2019. As discussed in an earlier post, over the first few years after release, methane's GWP is more than 150 times higher than carbon dioxide. Accordingly, the 2019 level of 1877 ppb of methane translates into global heating of 281.55 ppm CO₂e. Together, that makes 692.5 ppm CO₂e, which is 507.5 ppm CO₂e away from the 1200 ppm CO₂e cloud tipping point. 

The image below illustrates that the joint impact of carbon dioxide and methane could cause the 1200 ppm CO₂e tipping point to be crossed in 2040. The image uses IPCC and WMO through 2019 to display three lines, with added trends: 

- Black line: CO₂ in parts per million (ppm);
- Red line: CH₄ in ppm CO₂e, using a GWP of 150;
- Purple line: CO₂ and CH₄ in ppm CO₂e.

Trends for CH₄ are selected to reflect a steep rise as a result of methane hydrate destabilization. 

How could such a steep rise in methane levels occur?

Stronger methane releases from subsea permafrost can be expected, says a paper by Natalia Shakhova et al. A 1000-fold methane increase could occur, resulting in a rise of as much as 6°C within 80 years, with more to follow after that, according to a paper by Atsushi Obata et al.

Seafloor methane releases could be triggered by strong winds causing an influx of warm, salty water into the Arctic ocean (see this earlier post and this page). 

Since little hydroxyl is present in the atmosphere over the Arctic, it is much harder for this methane to get broken down.

Even relatively small methane releases could cause tremendous heating, if they reach the stratosphere.

Methane rises from the Arctic Ocean concentrated in plumes, pushing away the aerosols and gases that slow down the rise of methane elsewhere, which enables methane erupting from the Arctic Ocean to rise straight up fast and reach the stratosphere. 

The IPCC (AR5) gave methane a lifetime of 12.4 years. The IPCC (TAR) gave stratospheric methane a lifetime of 120 years, adding that less than 7% of methane did reach the stratosphere at the time.

The images on the right illustrate this. On November 20 pm, 2020, the MetOp-1 satellite recorded high methane levels over the Arctic Ocean at 293 mb (top image on the right). This corresponds with an altitude of some 9 km altitude, which is where the Stratosphere starts at the North Pole. The global mean methane level at that altitude was 1921 ppb.

The next images show areas with high levels of methane, as indicated by the magenta color, remaining present over the Arctic Ocean even at higher altitudes.

The higher the altitude, the more methane will concentrate over the Equator. Yet at 229 mb, high methane levels are still visible north of Siberia, while global mean methane levels were still very high, i.e. 1916 ppb. 

Even at 156 mb, there still are high methane levels visible (green circle, third image right). 

The conversion table shows that the Tropopause, which separates the Troposphere from the Stratosphere, is lower over the North Pole (at about 9 km altitude) than over the Equator (17 km altitude). 

The fifth image on the right, from an earlier post, shows that methane has accumulated more at higher altitudes over the years. 

The sixth image on the right shows that the MetOp-1 satellite recorded mean methane levels of 1925 ppb at 293 mb on December 2, 2020 am, with high methane levels present over the Arctic Ocean.

The next image shows that a peak methane level of 2715 ppb was recorded by the SNPP satellite on November 30, 2020 pm at 399.1 mb.

The animation on the right shows high methane levels recorded by the MetOp-2 satellite on December 2, 2020 pm, at a number of altitudes: 

- At 1000 mb (close to ground/sea level) a peak methane level of 2129 ppb shows up north of Svalbard. 

- At 918 mb, methane peaks at 2408 ppb and high methane levels show up over the Artic Ocean.

- At 815 mb, methane reaches a peak of 2582 ppb and high methane levels are visible over larger parts of the Arctic Ocean. 

- At 742 mb, methane reaches a peak of 2663 ppb and high methane levels are visible over even larger parts of the Arctic Ocean. 

- At 586 mb, methane reaches a peak of 2518 ppb and high methane levels are visible over a huge part of the Arctic Ocean, while hardly any high levels of methane are visible over land. 

- At 293 mb, methane reaches a peak of 2411 ppb and high levels of methane are still visible over the Arctic Ocean, even at this high altitude. 

[ from earlier post ]

In conclusion, a huge temperature rise could occur soon, even with a relatively small increase in carbon dioxide and methane releases. 

As above image illustrates, a temperature rise of more than as 10°C could eventuate as soon as 2026 when taking into account aerosol changes, albedo changes, water vapor, nitrous oxide, etc., as an earlier analysis shows. 

The joint impact of these warming elements threatens the cloud tipping point to be crossed and the resulting 8°C rise would then come on top of the 10°C rise, resulting in a total rise of 18°C, as illustrated by the image on the right, from an earlier post.

Indeed, there is no time to lose. It is high time to stop the denial of the size of the threats and challenges that the world faces, the harm inflicted and the speed at which developments could strike. 

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

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

• IPCC AR5 Workgroup 1
https://www.ipcc.ch/assessment-report/ar5/

and

https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter08_FINAL.pdf

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

• WMO Greenhouse GasBulletin
https://public.wmo.int/en/resources/library/wmo-greenhouse-gas-bulletin

• WMO news release: Carbon dioxide levels continue at record levels, despite COVID-19 lockdown
https://public.wmo.int/en/media/press-release/carbon-dioxide-levels-continue-record-levels-despite-covid-19-lockdown

• Understanding the Permafrost–Hydrate System and Associated Methane Releases in the East Siberian Arctic Shelf, by Natalia Shakhova, Igor Semiletov and Evgeny Chuvilin (2019)
https://www.mdpi.com/2076-3263/9/6/251

• Damage of Land Biosphere due to Intense Warming by 1000-Fold Rapid Increase in Atmospheric Methane: Estimation with a Climate–Carbon Cycle Model - by Atsushi Obata et al. (2012) 

https://journals.ametsoc.org/doi/full/10.1175/JCLI-D-11-00533.1

• Possible climate transitions from breakup of stratocumulus decks under greenhouse warming, by Tapio Schneider et al. (2019)
https://www.nature.com/articles/s41561-019-0310-1

• Solar geoengineering may not prevent strong warming from direct effects of CO2 on stratocumulus cloud cover - by Tapio Schneider et al. 

https://www.pnas.org/content/early/2020/11/10/2003730117

• An earth system model shows self-sustained thawing of permafrost even if all man-made GHG emissions stop in 2020 - by Jorgen Randers et al.
https://www.nature.com/articles/s41598-020-75481-z

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

• A Temperature Rise Of 18 Degrees Celsius

https://arctic-news.blogspot.com/p/a-temperature-rise-of-18-degrees-celsius.html

• Cold freshwater lid on North Atlantic

https://arctic-news.blogspot.com/p/cold-freshwater-lid-on-north-atlantic.html

• A rise of 18°C or 32.4°F by 2026?

https://arctic-news.blogspot.com/2019/02/a-rise-of-18c-or-324f-by-2026.html

• Temperatures threaten to become unbearable

https://arctic-news.blogspot.com/2020/09/temperatures-threaten-to-become-unbearable.html

• Warning of mass extinction of species, including humans, within one decade

https://arctic-news.blogspot.com/2017/02/warning-of-mass-extinction-of-species-including-humans-within-one-decade.html

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:

• The flow of large volumes of cold ice melt water into the oceans, leading to stadial cooling effects, such as in the North Atlantic (Rahmstorf et al 2015; Glikson, 2019) and around Antarctica (Bonselaer et al., 2018).
• Paleoclimate observations indicate that during the Pleistocene glacial-interglacial cycles, at least for the 800,000 years, every time temperatures reached a peak a sharp cooling followed (Cortese et al. 2007).
• Amplifying feedbacks from land and ocean drive non-linear climate trajectories, due to a lowered capacity of the warming oceans to absorb CO₂, the release of CO₂ from desiccated vegetation and extensive bushfires, decrease in reflection due to melting of ice sheets, increase in infrared absorption by open water and exposed rock surfaces, discharge of methane from melting permafrost and from methane clathrates.

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