Arctic News

Wednesday, January 15, 2020

The Australian firestorms: portents of a planetary future

by Andrew Glikson
Earth and climate scientist
Australian National University

Global warming and its disastrous consequences are now truly with us since the second part of 2019. At the moment a change in the weather has given parts of the country a respite from the raging fires, some of which are still burning or smoldering, waiting for another warm spell to flare up. The danger zones include the Australian Capital Territory, from where these lines are written. To date, 18.6 million hectares (186,000 square kilometers) were burnt, including native forests, native animals, homesteads and towns, and 24 people died. The firestorms betray harbingers of a planetary future, or a lack of such, under ever rising temperatures and extreme weather events inherent in fossil fuel driven global warming.

Global heating

As the atmospheric concentration of the well-mixed greenhouse gases rise (CO₂ >411.76 ppm; CH₄ >1870.5 ppb; N₂O >333 ppb plus trace greenhouse gases) land temperatures soar (NASA global sea-land mean of 1.05°C since 1880). According to Berkeley Earth global land temperatures have increased by 1.5C over the past 250 years and mean Arctic temperatures have risen by 2.5°C to 3.0°C between 1900 and 2017. According to NASA :

“Extreme heatwaves will become widespread at 1.5 degrees Celsius warming. Most land regions will see more hot days, especially in the tropics.
At 1.5°C about 14 percent of Earth’s population will be exposed to severe heatwaves at least once every five years, while at 2 degrees Celsius warming that number jumps to 37 percent.”
“Risks from forest fires, extreme weather events and invasive species are higher at 2 degrees warming than at 1.5 degrees warming.”
“Ocean warming, acidification and more intense storms will cause coral reefs to decline by 70 to 90 percent at 1.5 degrees Celsius warming, becoming all but non-existent at 2 degrees warming.”

Figure 1. The distribution of global fires. NASA.

However, bar the transient masking effects of sulphur aerosols, which according to estimates by Hansen et al. (2011) induce more than 1.0°C of cooling, global temperatures have already reached near 2.0°C (by analogy to the requirement for a patient’s body temperature to be measured before and not after aspirin has been taken). As aerosols are not homogeneously distributed, in some parts of the world temperatures have already soared to such levels. Thus the degree to which aerosols cool the earth, which depends on aerosol particle size range, has been grossly underestimated.

The rate of global warming, at ~2 to 3 ppm year and ~1.5°C in about one century, faster by an order of magnitude then geological climate catastrophe such as the PETM and the KT impact, has taken scientists by surprise, requiring a change from the term climate change to climate calamity.

The Australian firestorms

In Australia mean temperatures have risen by 1.5°C between 1910 and 2019 (Figure 2), as a combination of global warming and the ENSO conditions, as reported by the Bureau of Meteorology.

“The Indian Ocean Dipole (IOD) has returned to neutral after one of the strongest positive IOD events to impact Australia in recent history ... the IOD’s legacy of widespread warm and dry conditions during the second half of 2019 primed the Australian landscape for bushfire weather and heatwaves this summer. In the Pacific Ocean, although indicators of the El Niño–Southern Oscillation (ENSO) are neutral, the tropical ocean near and to the west of the Date Line remains warmer than average, potentially drawing some moisture away from Australia.”

Figure 2. (A) Australian mean temperature. (B) Severe fire weather. (C) Drought. (D) Driest year.
Bureau of Meteorology

The prolonged drought (Figure 2 C, D), low fuel moisture, high temperatures (Figure 2A) and warm winds emanating from the inland have rendered large parts of the Australian continent tinder dry, creating severe fire weather (Figure 2B) subject to ignition by lightning and human factors. Fires on a large scale create their own weather (see: bushfire raging in Mount Adrah and firestorm). Observations of major conflagrations, including the 2003 Canberra fires, indicate fires can form atmospheric plumes which can migrate and as hot plumes radiating toward the ground (fire tornadoes).

The underlying factor for rising temperatures and increasingly severe droughts in Australia is the polar-ward shift in climate zones (see map Oceania) as the Earth warms, estimated as approximately 56-111 km per decade, where dry hot subtropical zones encroach into temperate zones, as is also the case in South Africa and the Sahara.

Smoke signals emanating from the Australian fires are now circling around the globe (Figure 3) signaling a warning of the future state of Earth should Homo sapiens, so called, not wake up to the consequences of its actions.

Figure 3. (A) Smoke emanating from the southeastern Australian fires (January 4, 2020);
(B) smoke from the pyro-cumulonimbus clouds of the Australian fires drifting across the Pacific Ocean.
The fire clouds have lofted smoke to unusual heights in the atmosphere. The CALIPSO satellite observed smoke soaring between 15 to 19 kilometers on January 6, 2020—high enough to reach the stratosphere. NASA.

Andrew Glikson

Dr Andrew Glikson
Earth and climate scientist
Australian National University

15.1.2020

Books:
- The Archaean: Geological and Geochemical Windows into the Early Earth
- The Asteroid Impact Connection of Planetary Evolution
- Asteroids Impacts, Crustal Evolution and Related Mineral Systems with Special Reference to Australia
- Climate, Fire and Human Evolution: The Deep Time Dimensions of the Anthropocene
- The Plutocene: Blueprints for a Post-Anthropocene Greenhouse Earth
- Evolution of the Atmosphere, Fire and the Anthropocene Climate Event Horizon
- From Stars to Brains: Milestones in the Planetary Evolution of Life and Intelligence

Thursday, December 26, 2019

Planetary arson and amplifying feedbacks: No alternative to CO2 drawdown

by Andrew Glikson

Earth and climate scientist

Australian National University

No one knows how to impose 1.5 or 2.0 degrees Celsius limits on the mean global temperature, unless drawdown/carbon sequestration of atmospheric CO₂ is attempted, nor are drawdown methods normally discussed in most political or economic forums. According to Kevin Drum (2019), “Meeting the climate goals of the Paris Agreement is going to be nearly impossible without removing carbon dioxide from the atmosphere”.

The release of some 910 billion tons of carbon dioxide is leading human society, indeed much of nature, to an existential impasse. The widest chasm has developed between what climate science is indicating and between climate policies and negotiations controlled by governments, politicians, economists and journalists—none of whom fully comprehends, or is telling the whole truth about, the full consequences of the current trend in the atmosphere-ocean-land system.

The evidence for future projections, as understood by climate scientists, has been largely put to one side, mainly because it is economically and politically “inconvenient” or is frightening. Reports from the Madrid climate COP-25 Conference suggest negotiations, focusing on emission reductions, are overlooking the evidence that at the current concentration of CO₂, which have reached 412 ppm and 496 ppm-equivalent (when the CO₂-equivalents of methane and nitrous oxide are included), amplifying feedbacks from land and ocean are pushing temperatures further upwards. This is driven by the replacement of sea ice and land ice and snow surfaces by open water surfaces, by methane leaks, desiccated vegetation, fires and reduced CO₂ absorption by warming oceans. Given the long atmospheric residence time of CO₂ (Solomon et al. 2009, Eby et al. 2009) and the short life span of aerosols, attempts at CO₂ drawdown are essential if complete devastation of the biosphere is to be avoided.

Figure 1. (A) 1990-2019 Global growth of CO₂ emissions (gigaton);
(B) 1960-2019 Annual fossil CO₂ emissions from coal, oil, natural gas and cement (gigaton).
From: CSIRO News Release

The prevailing political and economic focus in international climate projects, conferences and advisory councils is concerned with (a) limits on, or a decrease of, carbon emissions from power generation, industry, agriculture, transport and other sources; (b) limits on the current rise in global temperatures to +1.5 degrees Celsius, and a maximum of +2.0 degrees Celsius, above mean pre-industrial (pre-1750) temperatures.

However, no one knows how to impose these limits unless drawdown/sequestration of atmospheric CO₂ is attempted, nor are drawdown methods normally discussed in most forums.

Figure 2. (A) Distribution of global fires (NASA);
(B) Fire storms over the southwest USA;
(C) Pine forest fire California.

At the present the concentration of greenhouse gases of just under-500 ppm CO₂-equivalent is activating amplifying feedbacks of greenhouse gases from land, oceans and melting ice sheets, namely further warming:

An increase in evaporation due to warming of land and oceans leads to further warming due to the greenhouse effect of water vapor but also to increased cloudiness which retards warming. The water vapor factor, significant in the tropics, is somewhat less important in the dry subtropical zones and relatively minor in the Polar Regions (Figure 3).
The melting of ice sheets, reducing reflective (high-albedo) ice and snow surfaces, and concomitant opening of open water surfaces (heat absorbing low-albedo) is generating a powerful positive (warming) feedback. Hudson (2011) estimates the rise in warming due to total removal of Arctic summer sea ice as approximately +1.0 degrees Celsius.
The release of methane from melting permafrost and bubbling of methane hydrates from the oceans has already raised atmospheric methane levels from about 800 to 1863 parts per billion which, given the radiative forcing of methane of X25< times, renders methane highly significant.
As the oceans warm they become less capable of taking up carbon dioxide. As a result, more of our carbon pollution will stay in the atmosphere, exacerbating global warming.
As tropical and subtropical climate zones overtake temperate Mediterranean-type climate zones, desiccated and burnt vegetation release copious amounts of carbon dioxide to the atmosphere. For example the current bushfires in Australia have already emitted 250 million tonnes of CO₂, almost half of country's annual emissions in 2018.

Figure 3. Total water vapor that can precipitate, as observed by
the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite.

With rising global temperatures and further encroachment of subtropical climate zones desertification and warming can only become more severe.

Abrupt reductions in emissions may be insufficient to stem global warming, unless accompanied by sequestration of greenhouse gases from the atmosphere, recommended as below 350 ppm CO₂. According to Hansen et al. (2008) carbon sequestration in soil (the biochar method) has significant potential, applying pyrolysis of residues of crops, forestry and animal waste. Biochar helps soil retain nutrients and fertilizers, reducing release of greenhouse gases such as N₂O. Replacing slash-and-burn agriculture with a slash-and-char method and the use of agricultural and forestry wastes for biochar production could provide a CO₂ drawdown of ~8 ppm or more in half a century.

Stabilization and cooling of the climate could include two principle approaches (Table 1): (a) solar shielding, and (b) CO₂ drawdown/sequestration. However, solar shielding by injected aerosols or water vapor is bound to be transient, requiring constant replenishment.

Table 1. Solar shielding and atmospheric CO₂ sequestration methods.

Method	Supposed advantages	Problems
SO2 injections	Relatively cheap and rapid application	Short atmospheric residence time; ocean acidification; retardation of precipitation and of monsoons
Space satellite-mounted sunshades/mirrors	Rapid application. No direct effect on ocean chemistry	Longer space residence time. Does not mitigate ocean acidification by CO2 emissions.
Streaming of air through basalt and serpentine (Figure 4)	CO2 capture by Ca and Mg carbonates	In operation on a limited scale in Iceland. Significant potential
Soil carbon burial/biochar	Effective means of controlling the carbon cycle (plants+ soil exchange more than 100 GtC/year with the atmosphere)	Requires a collaborative international effort by millions of farmers. Significant potential
CO2 capture by seaweeds	An effective method applied in South Korea	Decay of seaweeds releases CO₂ to ocean water. Significant potential
Ocean iron filing fertilization enhancing phytoplankton	CO2 sequestration	Phytoplankton residues would release CO2 back to the ocean water and atmosphere.
Ocean pipe system for vertical circulation of cold water to enhance CO2 sequestration	CO2 sequestration	Further warming would render such measure transient.
“Sodium trees” – pipe systems of liquid NaOH sequestering CO2 to sodium carbonate Na2CO3, followed by separation and burial of CO2.	CO2 sequestration, estimated by Hansen et al. (2008) at a cost of ~$200/ton CO₂ where the cost of removing 50 ppm of CO₂ is ~$20 trillion.	Unproven efficiency; need for CO2 burial; $trillions expense, though no more than the military expenses since WWII.

Figure 4. Iceland: The streaming of CO₂-containing air and of water through
basaltic rocks and CO₂-capture as carbonate minerals.

The big question is how effective are the above methods in reducing CO₂ levels on a global scale, at the very least to balance emissions, currently 36.8 billion tons CO₂ per year. Whereas each of the methods outlined in Table 1 has advantages and disadvantages, it is hard to see an alternative way of cooling the atmosphere and oceans than a combination of several of the more promising methods. Budgets on a scale of military spending ($1.7 trillion in 2017) are required in an attempt to slow down the current trend across climate tipping points. The choice humanity is facing is whether to spend resources on this scale on wars or on defense from the climate calamity.

Time is running out.

Andrew Glikson

Tuesday, December 17, 2019

Extinction in 2020?

Above image depicts how humans could go extinct as early as 2020. The image was created with NASA LOTI 1880-Nov.2019 data, 0.78°C adjusted to reflect ocean air temperatures (as opposed to sea surface temperatures), to reflect higher polar temperature anomalies (as opposed to leaving out 'missing' data) and to reflect a 1750 baseline (as opposed to a 1951-1980 baseline), with two trends added. Blue: a long-term trend based on Jan.1880-Nov.2019 data. Red: a short-term trend, based on Jan.2009-Nov.2019 data, to illustrate El Niño/La Niña variability and how El Niño could be the catalyst to trigger huge methane releases from the Arctic Ocean.

How was above image created? Let's first look at the baseline. The NASA default baseline is 1951-1980. The added trend in the image below shows early 1900s data to be well below this 1951-1980 baseline. In this analysis, a 0.28°C adjustment was therefore used to reflect this, and to reflect a 1750 baseline, a further 0.3°C was used, adding up to a 0.58°C baseline adjustment.

Furthermore, the NASA Land+Ocean temperature index (LOTI) uses sea surface temperatures, but ocean air temperatures seem more appropriate, which adds a further 0.1°C adjustment. Also, when comparing current temperatures with preindustrial ones, it's hard to find data for the polar areas. Treating these data as 'missing' would leave important heating out of the picture. After all, the polar areas are heating up much faster than the rest of the world, and especially so in the Arctic region. Therefore, a further 0.1°C adjustment was used to reflect higher polar temperature anomalies, resulting in the above-mentioned 0.78°C adjustment.

Finally, the red trend illustrates El Niño/La Niña variability. As discussed in a recent post, an El Niño is forecast for 2020 and this could be the catalyst to trigger huge methane releases from the Arctic Ocean.

The image below shows El Niño/La Niña variability going back to 1950, added to the NOAA monthly temperature anomaly.

As said, the Arctic region is heating up much faster than the rest of the world. There are several reasons why this is the case. Decline of the sea ice makes that less sunlight gets reflected back into space and that more sunlight is reaching the Arctic Ocean. This also causes more water vapor and clouds to appear over the Arctic Ocean. Furthermore, Arctic sea ice has lost most of the thicker multi-year ice that used to extend meters below the surface, consuming huge amounts of ocean heat entering the Arctic Ocean along ocean currents from the North Atlantic and the North Pacific oceans.

[ created with NOAA Arctic Report Card 2019 image ]

Above-mentioned feedbacks (albedo changes and more water vapor and clouds) contribute to higher temperatures in the Arctic. Furthermore, as the temperature difference between the North Pole and the Equator narrows, the jet stream changes, which can lead to further Arctic heating, i.e. higher temperatures of the atmosphere over the Arctic Ocean and over land around the Arctic Ocean, which in turn causes higher temperatures of the water flowing into the Arctic Ocean from rivers.

Furthermore, jet stream changes can also cause additional heating of parts of the Pacific Ocean and the Atlantic Ocean.

[ click on images to enlarge ]

Above image shows that sea surface temperature anomalies off the East Coast of North America as high as 13.6°C or 24.4°F were recorded on December 18, 2019.

Ocean currents can bring huge amounts of heat into the Arctic Ocean, and this can be amplified due to cyclones speeding up the inflow of water from the Atlantic Ocean and the Pacific Ocean into the Arctic Ocean.

As above image shows, the temperature rise of the oceans on the Northern Hemisphere is accelerating. This constitutes a critical tipping point, i.e. there are indications that a rise of 1°C will result in most of the sea ice underneath the surface to disappear. This sea ice used to consume the inflow of warm, salty water from the Atlantic Ocean and the Pacific Ocean. So, while there may still be sea ice left at the surface, since low air temperatures will cause freezing of surface water, the latent heat buffer has gone.

As long as there is sea ice, this 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 danger is that, as Arctic Ocean heating accelerates further, hot water will reach sediments at the Arctic Ocean seafloor and trigger massive methane eruptions, resulting in a huge abrupt global temperature rise. As discussed in an earlier post, a 3°C will likely suffice to cause extinction of humans.

Earlier this year, an Extinction Alert was issued, followed by a Stronger Extinction Alert.

In a rapid heating scenario:

a strong El Niño would contribute to
early demise of the Arctic sea ice, i.e. latent heat tipping point +
associated loss of sea ice albedo,
destabilization of seafloor methane hydrates, causing eruption of vast amounts of methane that further speed up Arctic warming and cause
terrestrial permafrost to melt as well, resulting in even more emissions,
while the Jet Stream gets even more deformed, resulting in more extreme weather events
causing forest fires, at first in Siberia and Canada and
eventually also in the peat fields and tropical rain forests of the Amazon, in Africa and South-east Asia, resulting in
rapid melting on the Himalayas, temporarily causing huge flooding,
followed by drought, famine, heat waves and mass starvation, and
collapse of the Greenland Ice Sheet.

[ from an earlier post ]

The precautionary principle calls for appropriate action when dangerous situations threaten to develop. How can we assess such danger? Risk is a combination of probability that something will eventuate and severity of the consequences. Regarding the risk, there is growing certainty that climate change is an existential threat, as discussed in a recent post. There's a third dimension, i.e. timescale. Imminence alone could make that a danger needs to be acted upon immediately, comprehensively and effectively. While questions may remain regarding probability, severity and timescale of the dangers associated with climate change, the precautionary principle should prevail and this should prompt for action, i.e. comprehensive and effective action to reduce damage is imperative and must be taken as soon as possible.

The image below gives a visual illustration of the danger.

Polynomial trendlines can point at imminent danger by showing that acceleration could eventuate in the near future, e.g. due to feedbacks. Polynomial trendlines can highlight such acceleration and thus warn about dangers that could otherwise be overlooked. This can make polynomial trendlines very valuable in climate change analysis. In the image below, the green linear trend and the blue polynomial trend are long-term trends (based on Jan.1880-Nov.2019 data), smoothing El Niño/La Niña variability, but the blue polynomial trend better highlights the recent temperature rise than the green linear trend does. The red short-term trend (based on Jan.2009-Nov.2019 data) has the highest R² (0.994) and highlights how El Niño could be the catalyst for huge methane eruptions from the Arctic Ocean, triggering a huge global temperature rise soon.

The image below, from an earlier post, explains the speed at which warming elements can strike, i.e. the rise could for a large part occur within years and in some cases within days and even immediately.

As the image below shows, peak methane levels as high as 2737 parts per billion (ppb) were recorded by the MetOp-2 satellite in the afternoon of December 20th, 2019, at 469 mb. Ominously, a large part of the atmosphere over the East Siberian Arctic Shelf (ESAS) is colored solid magenta, indicating methane levels above 1950 ppb.

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

Wednesday, December 11, 2019

The portent of runaway greenhouse warming

by Andrew Glikson
Earth and climate scientist
Australian National University

Figure 1. Relations between CO₂ levels in the atmosphere and mass extinctions of genera.

Data cited from D. Royer et al. (2002), from G. Keller (2016) and P. Wignall et al. (2002).

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).

Figure 2. Potential heating, Carana (2019)

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.

Through 2012, total accumulated emissions are estimated to have reached 384 GtC, with an annual amount of 43.1 billion tonnes of carbon dioxide expected to be added in 2019.

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).

Figure 4. Vulnerable carbon pools. (A) Land: Permafrost ~900 GtC; High-latitude peatlands ~400 GtC;
Tropical peatlands ~100 GtC; Vegetation subject to fire and/or deforestation ~650 GtC;
(B) Oceans: Methane hydrates ~10,000 GtC; Solubility pump ~2700 GtC; Biological pump ~3300 GtC;
Total (A) + (B): ~18,050 GtC (Canadell 2007)

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.