Amplifying feedbacks leading to accelerated planetary temperatures
by Andrew Glikson
“The paleoclimate record shouts to us that, far from being self-stabilizing, the Earth's climate system is an ornery beast which overreacts even to small nudges” (Wally Broecker)
Many climate change models, including by the IPCC, appear to minimize or even neglect the amplifying feedbacks of global warming, which are pushing temperatures upward in a runaway chain reaction-like process, as projected by Wally Broecker and other:
Lateral and vertical ice melt, including formation of water films on ice;
These feedbacks drive a chain reaction of events, accelerating the warming, as follows:
Melting snow and ice expose dark rock surfaces, reducing the albedo of the polar terrains and sea ice in surrounding oceans, enhancing infrared absorption and heating.
Fires create charred low-albedo land surfaces.
An increase in evaporation raises atmospheric vapor levels, enhancing the greenhouse gas effect.
Whereas an increase in plant leaf area enhances photosynthesis and evapotranspiration, creating a cooling effect, the reduction in vegetation in darkened burnt areas works in the opposite direction, warming land surfaces.
Figure 1. The 2021 global climate trends (Hansen, 2021, by permission)
The current acceleration of global warming is reflected by the anomalous rise of temperatures, in particular during 2010-2020 (Hansen 2021, Figure 1 above). Consequently, extensive regions are burning, with 4 to 5 million fires per year counted between about 2004 and 2019. In 2021, global April temperatures are much less than in 2020, due to a moderately strong La Nina effects.
Figure 2. The Palaeocene-Eocene Thermal Maximum recorded by benthic plankton isotopic data from sites in the Antarctic, south Atlantic and Pacific (Zachos et al., 2003). The rapid decrease in oxygen isotope ratios is indicative of a large increase in atmospheric temperatures associated with a rise in greenhouse gases CO₂ and CH₄ signifies approximately +5°C warming.
Analogies between Anthropocene climate change and major geological climate events reveal the rate of current rise in greenhouse gas levels and temperatures as compared to major geological warming events is alarming. A commonly cited global warming event is the Paleocene-Eocene boundary thermal maximum (PETM) at 55 Ma-ago, reaching +5 degrees Celsius and over 800 ppm CO₂ within a few thousand years (Figures 2 above and 3A below).
Figure 3. (A) Simulated atmospheric CO₂ at and following the Palaeocene-Eocene boundary (after Zeebe et al., 2009); (B) 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). Glikson (2020).
The triggering of a mass extinction event by the activity of organisms is not unique to the Anthropocene. The end Permian mass extinction, the greatest calamity for life in geologic history, is marked in marine carbonates by a negative δ¹³C shift attributed to oceanic anoxia and the emission of methane (CH₄) and hydrogen sulphide (H₂S) related to the activity of methanogenic algae (“purple” and “green” bacteria) (Ward, 2006; Kump, 2011). As a corollary anthropogenic climate change constitutes a geological/biological process where the originating species (Homo sapiens) has not to date discovered an effective method of controlling the calamitous processes it has triggered.
Andrew Glikson
A/Prof. Andrew Glikson
Earth and Paleo-climate scientist The University of New South Wales, Kensington NSW 2052 Australia
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:
A high rate of ice melt and development of cool ocean pools south of Greenland and around Antarctica (Fig. 8a) developing into cool ocean regions and stadial climate conditions (Fig. 8b).
Reduced temprature differences between the polar zones and mid-latitudes and thereby weakening of the polar boundaries and the polar jet stream boundary.
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.
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
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.
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).
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.
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.
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
Carbon, the essential element underpinning photosynthesis and life, is transformed into toxic substances in the remnants of plants and organisms buried in sediments. Once released to the atmosphere in the form of CO₂, CO and methane, in large quantities these gases become lethal and have been responsible for mass extinctions of species (Fig. 1).
Given amplifying feedbacks from land and oceans triggered by rising temperatures, the concept of an upper limit of warming determined by limitation on carbon emissions alone is unlikely, since, under a rising high greenhouse gas concentration, amplifying feedbacks triggered by methane release, bushfires, warming oceans and loss of reflectivity of melting ice, temperatures would keep rising. As an example, findings show that warmer ocean water is melting hydrates and releasing methane into the sediment and waters off the coast of Washington state, at levels that reach the same amount of methane from the Deepwater Horizon blowout. Carana (2019) finds a potential for abrupt warming of 18°C or 32.4°F (Fig. 2).
Attempts at CO₂ drawdown (sequestration), if urgently applied on a global scale, may conceivably be able to slow down further warming. This article refers to natural methane reservoirs and human-induced methane emissions, indicating that, once temperatures supersede a critical level, a further rise in methane release would result regardless of restrictions of emissions.
According to Kelley (2003) a planetary “runaway greenhouse event” may be triggered when a planet overheats due to absorption of more solar energy than it can give off to retain equilibrium. As a result, the oceans may boil filling its atmosphere with steam, which leaves the planet uninhabitable, as Venus is now. Planetary geologists think there is good evidence that Venus was the victim of a runaway greenhouse effect which turned the planet into the boiling hell we see today. According to Hansen (2010): “If we burn all fossil fuels, the forcing will be at least comparable to that of the PETM, but it will have been introduced at least ten times faster. [. .] The warming ocean can be expected to affect methane hydrate stability at a rate that could exceed that in the PETM, where the rate of change was driven by the speed of the methane hydrate climate feedback, not by the nearly instantaneous introduction of all fossil fuel carbon.” In a critical review of the theory of runaway greenhouse warming, Goldblatt and Watson (2012) state: “We cannot therefore completely rule out the possibility that human actions might cause a transition, if not to full runaway, then at least to a much warmer climate state than the present one.”
The concentration of fossil carbon deposits in the form of coal, oil, natural gas, coal seam gas, permafrost methane, ice clathrates, shale oil, and oil sands, once released to the atmosphere in large quantities, generates powerful feedbacks from land, ocean, atmosphere and cryosphere. This includes further release of greenhouse gases, warming oceans, loss of reflectivity of melting ice, and bushfires, pushing temperatures further upward. With carbon dioxide concentrations rising at a rate of 2–3 parts per million (ppm) per year (October 2018: 406.00 ppm; October 2019: 408.53 ppm) and the Earth heating-up by 0.98°C since 1951-1980, the ultimate consequences of this trend belong to the unthinkable.
A 2016 IPCC analysis found that no more than 275 GtC of the world’s reserves of fossil fuels of 746 GtC could be emitted, if the global temperature rise is to be restricted to 2°C above pre-industrial temperatures, an impossible target since amplifying carbon feedbacks would push temperatures upwards.
According to Heede and Oreskes (2016), global reserves of oil (~171 GtC), natural gas (~95) and coal (479 GtC) add up to a total of 746 GtC. Hansen et al. (2013) estimates that recoverable fossil fuel reserves include ~120 GtC gas, ~80 GtC oil, >10,000 GtC coal, >2000 GtC unconventional gas, and ~700 GtC unconventional oil, adding up to a total of ~13,000 GtC (Fig. 3).
The amount of unstable methane deposits in permafrost and methane hydrates (clathrates) in ocean sediments is of a similar order of magnitude as the amount of fossil fuel reserves. Vulnerable carbon pools include methane hydrates in sediments (~10,000 GtC), solubility and biological pump (~6000 GtC), permafrost methane (~900 GtC), and peatlands and vulnerable vegetation (~1150 GtC), adding up to a total of ~18,050 GtC (Fig. 4).
Unoxidized metastable deposits of methane and methane hydrates, accumulated during the Pleistocene glacial-interglacial cycles and vulnerable to temperature rise, are already leaking as indicated by atmospheric concentrations which have risen from 1988 (~1700 ppb CH₄) to 2019 (~1860 ppb CH₄) at a rate of ~5.2 ppb/year, a rise of more than 4 ppm CO₂-equivalent at GWP25xCO₂ or 24 ppm CO₂-e at GWP150xCO₂.
Meinshausen et al. (2011) estimated global-mean surface temperature increases, applying a climate sensitivity of 3°C per doubling of CO₂, resulting by 2100 in a temperature rise of between 1.5°C to 4.5°C relative to pre-industrial levels. By 2300, under constant emissions, CO₂ concentrations would rise to ~2000 ppm, methane to 3.5 ppm and nitrous oxide to 0.52 ppm (Fig. 5). Amplifying feedbacks are taken into account, but the effects of tipping points and of cold ice-melt pools formed in the oceans near Greenland and Antarctica ice sheets are unclear.
Given the estimated total of exploitable hydrocarbon resources (~13.000 GtC) and of vulnerable carbon pools (~18,050 GtC), the amount released under different future climate conditions is subject to estimates:
Assuming mean global temperature of +2°C (above pre-industrial), with allowance made for the masking effects of sulphur aerosols, the combustion of ~2% of the fossil fuel reserves (13,000 GtC), i.e. ~260 GtC, would raise CO₂ concentration by ~130 ppm (100 GtC = 50 ppm CO₂) (Fig. 3). Combustion of ~5% of the fossil fuel reserve would raise CO₂ concentration by ~325 ppm.
Under +2°C above pre-industrial, release of CO₂ from fires and other feedback effects such as melting of permafrost and release of methane would raise atmospheric carbon by at least 1 percent of vulnerable carbon pools (~18,050 GtC).
The flow of ice melt water from Greenland and Antarctica into the oceans would create large regions of cold water capable of absorption of atmospheric CO₂.
Hansen (2010) concludes: “if we burn all reserves of oil, gas, and coal, there's a substantial chance that we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome [runaway greenhouse warming] is a dead certainty”. Stephen Hawking (2017) appears to agree with Hansen’s warning, stating: “if the US pulls out of the Paris climate agreement it may lead to runaway global warming, eventually turning Earth's atmosphere into something resembling Venus”. Goldblatt and Watson (2012) wrote: “The ultimate climate emergency is a ‘runaway greenhouse’: a hot and water-vapor-rich atmosphere limits the emission of thermal radiation to space, causing runaway warming … This would evaporate the entire ocean and exterminate all planetary life … We cannot therefore completely rule out the possibility that human actions might cause a transition, if not to full runaway, then at least to a much warmer climate state than the present one … However, our understanding of the dynamics, thermodynamics, radiative transfer and cloud physics of hot and steamy atmospheres is weak.”
An analysis by Carana (2013) suggests that accelerated release of methane from permafrost and methane hydrates (clathrates) could trigger runaway global warming (Fig. 6). A polynomial trend for the Arctic shows temperature anomalies of +4°C by 2020, +7°C by 2030 and +11°C by 2040, threatening major feedbacks, further albedo changes and methane releases leading to global temperature anomalies of 20°C+ by 2050.
Figure 6. A polynomial 2 trend line points at global temperature anomalies (Carana 2013). A polynomial function is a function such as a quadratic, a cubic, a quartic, and so on, involving only non-negative integer powers of x.
The magnitude of the runaway greenhouse effect that now threatens to eventuate becomes evident when looking at the geological record. For example, the 55 million years-old PETM event (Paleocene-Eocene Thermal Maximum), lasting for about 100,000 years, driven by CO₂ levels as hugh as 1700 ppm, does not appear to have triggered a runaway greenhouse process. The PETM is attributed to ¹³C-depleted methane (Zeebe et al. 2009), reaching 5 - 8°C and leading to a mass extinction of 35-50% of benthic foraminifera. By sharp contrast, the current Anthropocene hyperthermal event, commencing with the industrial age and re-accelerating since about 1975, constitutes a temporally abrupt development exceeding the rate of geological hyperthermal events (Fig. 7), a rate which does not allow biological adaptation and thereby enhances a mass extinction of species (Barnosky et al. 2011).
Figure 7. A comparison of Cenozoic CO₂ rise rates and temperature rise rates, highlighting the extreme rise rates in the Anthropocene. From an earlier post.
As Australia burns, the IPCC maintains there is time left to consume a carbon budget and to keep handing out offsets and carbon credits; at the 25th meeting of the Conference of the Parties to the United Nations Convention on Climate Change in Madrid, Australia is seeking to use "carry-over credits" to meet its pledged emissions reductions. The situation is illustrated by Sam Carana in the image below.
Andrew Glikson
Dr Andrew Glikson Earth and climate scientist Australian National University
• Contributions to accelerating atmospheric CO₂ growth from economic activity, carbon intensity, and efficiency of natural sinks, by J. Canadell et al. (2007) https://www.pnas.org/content/104/47/18866
Andrew Glikson Earth and Climate scientist Australian National University 12-8-2019
Preamble
The inhabitants of planet Earth are in the process of destroying the habitability of their world through the perpetration of the largest mass extinction of species since 66 million years ago, when a large asteroid impacted Earth, and 55 million years since the Paleocene-Eocene Thermal Maximum (PETM) reaching 5–8°C. The late Holocene-Anthropocene climate change represents an unprecedented event, triggering a fast shift in climate zones and a series of extreme weather events, with consequences for much of nature and civilization. The changes are manifest where green forests are blackened by fire, droughts are turning grassy planes to brown semi-deserts, brilliant white snow and ice caps are melting into pale blue water and clear blue skies turn grey due to aerosols and jet contrails, most particularly in the northern hemisphere. Unless effective efforts are undertaken at CO₂ drawdown, the consequence would include demise of much of nature and a collapse of human civilization.
1. The scorched Earth
The transfer of hundreds of billions of tonnes of carbon from the Earth crust, the residues of ancient biospheres, to the atmosphere and oceans, condemning the bulk of life through the most extreme shift in the composition of the atmosphere and ocean Earth has experienced since 55 million years ago, with changes taking place in front of our eyes. Since the industrial revolution, about 375 billion tonnes of carbon (or 1,374 billion tonnes CO₂) have been emitted by humans into the atmosphere. The consequences are everywhere, from mega-droughts, to heat waves, fires, storms and floods. With atmospheric CO₂-equivalent rising above 500 ppm and mean temperatures by more than 1.5°C (Figure 1) look no further than the shift in climate zones, displayed for example on maps of the expanding wet tropical zones, drying sub-tropical latitudes and polar-ward migration of temperate climate zone. The ice sheets and sea ice are melting, huge fires overtake Siberia, the Sahara is shifting northward, large parts of southern Europe are suffering from droughts, heat waves and fires, the Kalahari Desert dunes are shifting and much of southern Australia is affected by warming and draughts. This is hardly compensated by a minor increase in precipitation and greening such as at the southern fringes of the Sahara Desert and parts of northern Australia.
Induced by anthropogenic carbon emissions reaching 37.1 billion tonnes CO₂ in 2018 and their amplifying feedbacks from land and oceans and, ranging from 16.5 tonnes CO₂ per capita per year from the US to 35.5 tonnes CO₂ per capita per year from Saudi Arabia and 44 tonnes CO₂ per capita per year from Australia, the inexorable link between these emissions and the unfolding disaster is hardly mentioned by mainstream political classes and the media.
Figure 1 (A) Growth of CO₂-equivalent level and the annual greenhouse gas Index (AGGI¹). Measurements of CO₂ to
the 1950s are from (Keeling et al., 1958) and air trapped in ice and snow above glaciers. Pre-1978 changes are based
on ongoing measurements of all greenhouse gases. Equivalent CO₂ amounts (in ppm) are derived from the relationship
between CO₂ concentrations and radiative forcing from all long lived gases; (B) showing how much warmer each
month of the GISTEMP data is than the annual global mean. For July (2019) temperatures rose by about +1.5°C.
¹The AGGI index uses 1990 as a baseline year with a value of 1. The index increased every year since 1979.
2. Migrating climate zones
As the globe warms, to date by a mean of near ~1.5 °C, or ~2.0°C when the masking effects of sulphur dioxide and other aerosols are considered, and by a mean of ~2.3°C in the polar regions, the expansion of warm tropical latitudes and the pole-ward migration of subtropical and temperate climate zones (Figure 2) ensue in large scale droughts such as parts of inland Australia and southern Africa. A similar trend is taking place in the northern hemisphere where the Sahara desert is expanding northward, with consequent heat waves across the Mediterranean and Europe.
In southern Africa “Widespread shifts in climate regimes are projected, of which the southern and eastern expansion of the hot desert and hot steppe zones is most prominent. From occupying 33.1 and 19.4 % of southern Africa under present-day climate, respectively, these regions are projected to occupy between 47.3 and 59.7 % (hot desert zone) and 24.9 and 29.9 % (hot steppe zone) of the region in a future world where the mean global temperature has increased by ~3°C.
Closely linked to the migration of climate zones is the southward drift of Antarctic- sourced cold moist fronts which sustain seasonal rain in south-west and southern Australia. A feedback loop has developed where deforestation and decline in vegetation in southern parts of the continent result in the rise of thermal plumes of dry air masses that deflect the western moist fronts further to the southeast.
Figure 2. Köppen-Geiger global Climate zones classification map
Since 1979 the planet’s tropics have been expanding pole-ward by 56 km to 111 km per decade in both hemispheres, leading one commentator to call this Earth’s bulging waistline. Future climate projections suggest this expansion is likely to continue, driven largely by human activities – most notably emissions of greenhouse gases and black carbon, as well as warming in the lower atmosphere and the oceans.”
An analysis of the origin of Australian droughts suggests, according to both observations and climate models, that at least part of this decline is associated with changes in large-scale atmospheric circulation, including shrinking polar ice and a pole-ward movement of polar-originated westerly wind spirals, as well as increasing atmospheric surface pressure and droughts over parts of southern Australia (Figure 3). Simulations of future climate with this model suggest amplified winter drying over most parts of southern Australia in the coming decades in response to changes in radiative forcing. The drying is most pronounced over southwest Australia, with total reductions in austral autumn and winter precipitation of approximately 40% by the late twenty-first century. Thus rainfall in southwestern Australia has declined sharply from about 1965 onward, concomitant with the sharp rise of global temperatures.
Figure 3 (A) Bureau of Meteorology (BOM) drought map, showing rainfall levels for the southern wet season from
April 1 to July 31 in 2019; (B) NASA satellite image displaying a southward deflection of Antarctic-sourced moist
cold fronts from southern Australia, a result of (1) southward migration of climate zones; (2) increasing aridity of
southern and southwestern Australia due to deforestation; (3) rising hot plumes from warming arid land.
3. Extreme weather events
The consequences of the migration of climate zones are compounded by changes in flow patterns of major river systems around the world, for example in southern an southeastern Asia, including the Indus, Ganges, Brahmaputra and Mekong river basins, the home and bread basket for more than a billion people. With warming, as snow cover declines in the mountainous source regions of rivers, river flows are enhanced, with ensuing floods, in particular during the Monsoon. For example, in 2010 approximately one-fifth of Pakistan's total land area was affected by floods (Figure 4A), directly affecting about 20 million people, with a death toll close to 2,000. And about 700 people in cyclone Isai in Mozambique (Figure 4B, C). Such changes in climate and geography are enhanced once sea level rise increases from the scale of tens of centimeters, as at present, to meters, as predicted to take place later this and next century.
An increasing frequency and intensity of cyclones constitute an inevitable consequence of rising temperatures over warm low pressure cell tracks in tropical oceans, already affecting large populations in the Caribbean and west Pacific island chains, encroaching into continental coastal zones, China, southeast USA, southeast Africa, India, northern Australia, the Pacific islands. According to Sobel et al. (2016)“We thus expect tropical cyclone intensities to increase with warming, both on average and at the high end of the scale, so that the strongest future storms will exceed the strength of any in the past”. Likewise increasing temperatures, heat waves and droughts, compounded by deforestation over continents, constitute an inevitable consequence of heat waves and droughts. A prime example is the Siberian forest fires (Figure 5B), covering an area larger than Denmark and contributing significantly to climate change. Since the beginning of the year a total of 13.1 million hectares has burned. Total losses from natural catastrophes on 2018 stated as US$160 billion.
Figure 4 (A) Pakistan flooding, shows the 2010 Indus River spanning well over 10 kilometers, completely filling
the river valley and spilling over onto nearby land. Floodwaters have created a lake almost as wide as the swollen
Indus that inundates Jhatpat; (B) Before-and-after satellite imagery of Mozambique showing massive flood
described as an "inland ocean" up to 30 miles wide following the landfall of Tropical Cyclone Idai, 2019.
Figure 5 (A) Global fire zones, NASA. The Earth data fire map accumulates the locations of fires detected by
moderate-resolution imaging radiometer (MODIS) on board the Terra and Aqua satellites over a 10-day period.
Each colored dot indicates a location where MODIS detected at least one fire during the compositing period. Color ranges from red where the fire count is low to yellow where number of fires is large; (B) An ecological
catastrophe in Russia: wildfires have created over 4 million square km smoke lid over central northern Asia.
Big Siberian cities are covered with toxic haze that had already reached Urals.
4. Shrinking Polar ice sheets
Last but not least, major changes in the Polar Regions are driving climate events in the rest of the globe. According to NOAA Arctic surface air temperatures continued to warm at twice the rate of the rest of the globe, leading to major thaw at the fringes of the Arctic (Figure 6A) and a loss of 95 percent of its oldest ice over the past three decades. Arctic air temperatures during 2014-18 since 1900 have exceeded all previous records and are driving broad changes in the environmental system both within the Arctic as well as through the weakening of the jet stream which separates the Arctic from warmer climate zones. The recent freezing storms in North America represent penetration of cold air masses through an increasingly undulating jet stream barrier, as well as allowing warm air masses to move northward, further warming the Arctic and driving further ice melting (Figure 6B).
According to Rignot et al. (2011) in 2006 the Greenland and Antarctic ice sheets experienced a combined mass loss of 475 ± 158 billion tons of ice per year. IPCC models of future climate change contain a number of departures from the paleoclimate evidence, including the major role of feedbacks from land and water, estimates of future ice melt, sea level rise rates, methane release rates, the role of fires in enhancing atmospheric CO₂, and the already observed onset of transient freeze events consequent on the flow of ice melt water into the oceans. Ice mass loss would raise sea level on the scale of meters and eventually tens of meters (Hansen et al. 2016). The development of large cold water pools south and east of Greenland (Rahmstorf et al. 2015) and at the fringe of West Antarctica, signify early stages in the development of a North Atlantic freeze, consistent with the decline in the Atlantic Meridional Ocean Circulation (AMOC). As the Earth warms the increase in temperature contrasts across the globe, in particular between warming continental regions and cooling ocean regions, leads to storminess and extreme weather events, which need to be taken into account when planning adaptation measures, including preparation of coastal defenses, construction of channel and pipelines from heavy precipitation zones to drought zones.
Figure 6 (A)Thawing at the fringes of Siberia and Canada. Scientists say 2019 could be another annus
horribilis for the Arctic with record temperatures already registered in Greenland—a giant melting ice
sheet that threatens to submerge the world's coastal areas one day; (B) Weakening and increasing undulation of the polar vortex, allowing penetration of cold fronts southward and of warm air masses northward.
Figure 7 (A) Surface air temperature (°C) change in 2055–2060 relative to 1880–1920 according to.
A1B model + modified forcings and ice melt to 1 meter sea level rise; (B) Surface-air temperature
change in 2096 relative to 1880–1920 according to IPCC model AIB adding Ice melt with 10-year
doubling of ice melt leading to +5 meters sea level rise; (C) Surface air temperature (°C) relative to
1880–1920 for several scenarios taking added ice melt water into account (Hansen et al. 2016)
Postscript
None of the evidence and projections summarized above appears to form a priority consideration on the part of those in power—in parliaments, in corporations, among the wealthy elites and vested interests. Having to all intents and purposes given up on the habitability of large parts of the Earth and on the survival of numerous species and future generations—their actions and inactions constitute the ultimate crime against life on Earth.
Andrew Glikson
Dr Andrew Glikson
Earth and climate scientist Australian National University Canberra, Australian Territory, Australia
geospec@iinet.net.au
Books:
The Archaean: Geological and Geochemical Windows into the Early Earth
