Showing posts with label rate. Show all posts
Showing posts with label rate. Show all posts

Tuesday, November 5, 2019

A record CO2 rise rate since the KT dinosaur extinction 66 million years ago

By Andrew Glikson
Earth and climate scientist
Australian National University

As the concentration of atmospheric CO₂ has risen to 408 ppm and the total greenhouse gas level, including methane and nitrous oxide, combine to near 500 parts per million CO₂-equivalent, the stability threshold of the Greenland and Antarctic ice sheets, currently melting at an accelerated rate, has been exceeded. The consequent expansion of tropics and the shift of climate zones toward the shrinking poles lead to increasingly warm and dry conditions under which fire storms, currently engulfing large parts of South America (Fig. 1), California, Alaska, Siberia, Sweden, Spain, Portugal, Greece, Angola, Australia and elsewhere have become a dominant factor in the destruction of terrestrial habitats.

Figure 1. Sensors on NASA satellites Terra and Aqua captured a record of thousands of points
of fire in Brazil in late August. Credit: NASA Earth Observatory
Since the 18th century, combustion of fossil fuels has led to the release of more than 910 billion tons of carbon dioxide (GtCO₂) by human activity, raising CO₂ to about 408.5 ppm (Fig. 2), as compared to the 280-300 ppm range prior to the onset of the industrial age. By the early-21st century the current CO₂ rise rate has reached of 2 to 3 ppm/year.

Figure 2. Global temperature and carbon dioxide - Climate Central
Allowing for the transient albedo enhancing effects of sulphur dioxide and other aerosols, mean global temperature has potentially reached ~2.0 degrees Celsius above pre-industrial temperatures. Current greenhouse gas forcing and global mean temperatures are approaching Miocene-like (5.3-23 million years-ago) composition.

The current carbon dioxide rise rate exceeds the fastest rates estimated for the K-T asteroid impact (66.4 million years-ago) and the PETM (Paleocene-Eocene Temperature Maximum) hyperthermal event (55.9 million years ago) by an order of magnitude (Fig. 3). The current growth rate of atmospheric greenhouse gases, in particular over the last 70 years or so, may appear gradual in our lifetime, but it constitutes an extreme event in the recorded history of Earth.
Figure 3. Cenozoic CO₂ and temperature rise rates. Current rise rates of CO₂ (2.86 ppm CO2/year) and temperature (0.15-0.20°C per decade since 1975) associated with extreme weather events raise doubt regarding gradual linear climate projections. Instead, chaotic climate conditions may arise from the clash between northward-shifting warm air masses which intersect the weakened undulating Arctic jet stream boundary and freezing polar air fronts penetrating Siberia, North America and Europe.
The definition of a “tipping point” in the climate system is a threshold which, once exceeded, can lead to large changes in the state of the system, or where the confluence of individual factors combines into a single stream. The term “tipping element” describes subcontinental-scale subsystems of the Earth system that are susceptible to being forced into a new irreversible state by small perturbations. In so far as a tipping point can be identified in current developments of the climate system, the weakening of the Arctic boundary, indicated by slowing down and increased disturbance of the jet stream heralds a likely tipping point, an example being the recent ‘Beast from the East” freeze in northern Europe and North America (Fig. 4).

Figure 4. The cold fronts penetrating Europe from Siberia and the North Atlantic and North America from the Arctic, 2018. UK Met Office.
A report by the National Academy Press 2011 states: “As the planet continues to warm, it may be approaching a critical climate threshold beyond which rapid (decadal-scale) and potentially catastrophic changes may occur that are not anticipated.”

Direct evidence for changing climate patterns is provided by the expansion of the tropics and migration of climate zones toward the poles, estimated at a rate of approximately 56-111 km per decade. As the dry subtropical zones shift toward the poles, droughts worsen and overall less rain falls in temperate regions. Poleward shifts in the average tracks of tropical and extratropical cyclones are already happening. This is likely to continue as the tropics expand further. As extratropical cyclones move, they shift rain away from temperate regions that historically rely on winter rainfalls for their agriculture and water supply. Australia is highly vulnerable to expanding tropics as about 60 percent of the continent lies north of 30°S.

Low-lying land areas, including coral islands, delta and low coastal and river valleys would be flooded due to sea level rise to Miocene-like (5.3-23 million years ago) sea levels of approximately 40±15 meters above pre-industrial levels. Accelerated flow of ice melt water flow from ice sheets into the oceans is reducing temperatures over tracts in the North Atlantic and circum-Antarctic oceans. Strong temperature contrasts between cold polar-derived fronts and warm tropical-derived air masses lead to extreme weather events, retarding habitats, in particular over coastal regions. As partial melting of the large ice sheets proceeds the Earth’s climate zones continue to shift polar-ward (Environmental Migration Portal, 2015). This results in an expansion of tropical regions such as existed in the Miocene, reducing the size of polar ice sheets and temperate climate zones.

According to Berger and Loutre (2002) the effect of high atmospheric greenhouse gas levels would delay the next ice age by tens of thousands of years, during which chaotic tropical to hyper-tropical conditions including extreme weather events would persist over much of the Earth, until atmospheric CO₂ and insolation subside. Humans are likely to survive in relatively favorable parts of Earth, such as sub-polar regions and sheltered mountain valleys, where cooler conditions would allow flora and fauna to persist.

To try and avoid a global calamity, abrupt reduction in carbon emissions is essential, but since the high level of CO₂-equivalent is activating amplifying feedbacks from land and ocean, global attempts to down-draw about of 50 to 100 ppm of CO₂ from the atmosphere, using every effective negative emissions, is essential. Such efforts would include streaming air through basalt and serpentine, biochar cultivation, sea weed sequestration, reforestation, sodium hydroxide pipe systems and other methods.

But while $trillions continue to be poured into preparation of future wars, currently no government is involved in any serious attempt at the defense of life on Earth.


Andrew Glikson
Dr Andrew Glikson
Earth and climate scientist
Australian National University

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



Saturday, March 23, 2019

Climate Tipping Points

Paleoclimate perspectives of 21st-23rd centuries, IPCC projections and tipping points

by Andrew Glikson
Earth and paleo-climate scientist
Australian National University

Abstract

IPCC models of future climate trends contain a number of departures from patterns deduced from the paleoclimate evidence. With CO₂ levels reaching 411.8 ppm in January 2019 and CH₄ levels reaching 1.867 ppm in October 2018, for a greenhouse radiative forcing factor of CH₄=25 CO₂ equivalents, the total CO₂-equivalent of 457.5 ppm¹ approaches the stability limit of the Greenland ice sheet, estimated at a greenhouse gas forcing of approximately 500 ppm CO₂ although ephemeral ice may have existed as far back as the middle Eocene. As the concentration of greenhouse gases is rising and amplifying feedbacks from land, oceans and ice sheet melting increase, transient temperature reversals (stadials) accentuate temperature polarities between warming land masses and oceanic regions cooled by the flow of cold ice melt water from the ice sheets, leading to extreme weather events. The rise in Arctic temperatures, at a rate twice as fast as that of lower latitudes, weakens the polar boundary and results in undulation of the jet stream, allowing warm air masses to shift north across the boundary, further heating the polar region. The weakened boundary further allows cold air masses to breach the boundary shifting away from the Arctic. Combined with the flow of ice melt water from Greenland, these developments are leading to a cooling of sub-polar oceans and adjacent land. Similar growth of cold water pools occur along the fringes of Western Antarctica. The cold water pools cover deeper warmer salt water layers which melt the frontal glaciers. The slow-down of the AMOC is analogous to Pleistocene (2.6-0.01 Ma) and early Holocene stadial freeze events such as the Younger Dryas (12.9 – 11.7 kyr) and the 8.5 kyr Laurentide ice melt, where peak temperatures were followed closely by sharp cooling. Climate projections by Hansen et al. (2016) suggest a stadial event associated with significant sea level rise and involving sharp cooling of approximately -2°C, lasting several decades between the mid-21 st century and the mid-22nd century, a time dependent on the rate of Greenland and Antarctic ice melt. Accelerating ice melt and nonlinear sea level rise would reach multi-meters levels over a timescale of 50–150 years.

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¹ January 2019: CO₂ = 410.8 ppm https://www.esrl.noaa.gov/gmd/ccgg/trends/ ; October 2018: CH₄ 1.8676 ppm (CO₂ equivalent x25 = 46.7 CO₂e) https://www.esrl.noaa.gov/gmd/ccgg/trends_ch4/

Paleoclimate records

Pleistocene paleo-climate records are marked by abrupt warming and cooling events during both glacial periods (Dansgaard-Oeschger (D-O) cycles; Ganopolski and Rahmstorf 2001; Camille and Born, 2019) and stadial interglacial periods, the latter defined as stadial freeze events (Figure 1). The paleo-climate record indicates that during the last ~450,000 years peak interglacial temperatures were repeatedly succeeded by temporary freeze events, attributed to the flow of cold ice melt water flow into the North Atlantic Ocean (Cortese et al. 2007) (Figure 1), associated with rapid rises in sea level, as during the last glacial termination (Figure 2). The rise in extreme weather events associated with current global warming to ~0.9°C above 1884 level (NASA, 2018) compares with temperatures and extreme weather events associated with the early Holocene Period (~11.6 –7.0 kyr), a period of major sea level rise of ~60 meters (Smith et al. 2011) and with the Eemian interglacial (128-116 kyr). During the Eemian tropical and extratropical North Atlantic cyclones may have been more intense than at present, and may have produced waves larger than those observed historically, as evidenced by large boulders transported by waves generated by intense storms and cliff erosion (Roverea et al. 2017). Sea levels during the Eemian, when temperatures were about +1°C or and sea levels were +6 to +9 m higher than during the late Holocene, offer analogies with current developments (Roverea A et al. 2017; Kaspar et al. 2007).

Figure 1. (A) Evolution of sea surface temperatures in 5 glacial-interglacial transitions recorded in ODP
1089 at the sub-Antarctic Atlantic Ocean. Lower grey lines – δ¹⁸O measured on Cibicidoides plankton;
Black lines – sea surface temperature. Marine isotope stage numbers are indicated on top of diagrams.
Note the stadial temperature drop events following interglacial peak temperatures, analogous
to the Younger Dryas preceding the onset of the Holocene (Cortese et al. 2007⁽²⁵⁾).
(B) Mean temperatures for the late Pleistocene and early Holocene.

With CO₂ levels reaching 411.8 ppm in January 2019 and CH₄ reaching 1.867 ppm in October 2018, for a greenhouse radiative forcing factor of CH₄=25 CO₂e, the total CO₂-equivalent of 457.5 ppm¹ approaches Miocene levels (Gasson et al. 2016). Levy et al. (2016), Tripati and Darby (2018) and other considered the implications of the rise of greenhouse levels above about 500 ppm CO₂ for the future of the Greenland ice sheet. Whereas due to hysteresis² of the ice sheets may delay complete melting, the extreme rate of warming (Figure 3) may in part override this effect.

Anthropocene tipping points

During the late Anthropocene³, accelerating since about 1960, the rise of radiative forcing due mainly to increasing greenhouse gas concentration above >457 ppm CO₂-equivalent, accounts for a rise of mean global temperatures by 0.98°C since 1880 (NASA (2018) A further rise by more than >0.5°C is masked by aerosols, mainly sulphur dioxide and sulfuric acid (Hansen et al., 2011).

The temperature rise is potentially further enhanced by amplifying feedbacks from land and oceans, including infrared absorption by water surfaces following sea ice melting, reduction of CO₂ concentration in warming water, release of methane and fires. However, climate change trajectories are likely to be highly irregular as a result of stadial ocean cooling events affected by flow of ice melt. Whereas similar temperature fluctuations including stadial events have occurred during past interglacial periods (Cortese et al. 2007; figure 1), with a further rise in atmospheric greenhouse gases the intensity and frequency of extreme weather events would enter uncharted territory unlike any recorded during the Pleistocene, potentially rendering large parts of the continents uninhabitable (Wallace-Wells, 2019).

Figure 2. Tipping points in the Earth system (Lenton et al., 2008)
https://www.pik-potsdam.de/services/infodesk/tipping-elements/kippelemente
Creative Commons BY-ND 3.0 DE license.

Expressions of climate tipping points include intensifying climate feedbacks such ice sheet and sea ice melting, declining Atlantic circulation, intensifying monsoons, increasing El-Nino events, heatwaves and fires, rainforest dieback, melting permafrost and breakdown of methane clathrates (Figure 2) (Lenton et al., 2008). According to the Potsdam Climate Impacts Institute (PIK), tipping points include transformation of the Amazon Rainforest, retreat of the Northern Boreal Forests, destruction of Coral Reefs and weakening of the Marine Carbon Pump, melting of the Arctic Sea Ice, loss of the Greenland Ice Sheet, collapse of the West Antarctic Ice Sheet, partial Collapse in East Antarctica, melting of the Yedoma Permafrost and methane Emissions from the Ocean (Schellnhuber, 2009).

Figure 3. Atmospheric carbon dioxide rise rates and global warming events: a comparison between current
global warming, the Paleocene-Eocene Thermal Event (PETM) and the last Glacial Termination. 

The rate at which atmospheric greenhouse gases and temperatures are rising exceeds global warming rates of the PETM and of last glacial termination and is the fastest recorded in Cenozoic record, excepting that associated with asteroid impacts (Figure 3). Ice mass loss would raise sea level by several meters in an exponential rather than linear response, with doubling time of ice loss yielding multi-meter sea level rise. Modelled 2055-2100 AIB model forcing of +1.19°C above 1880-1920 leads to a projected global warming trend which includes a transient drop in temperature, reflecting stadial freezing events in the Atlantic Ocean and the sub-Antarctic Ocean, reaching -2°C over several decades (Figure 7) (Hansen et al., 2016). These authors used paleoclimate data and modern observations to estimate the effects of ice melt water from Greenland and Antarctica, showing cold low-density meltwater tends to cap increasingly warm subsurface ocean water, affecting an increase ice shelf melting. This affects acceleration of ice sheet mass loss (Figure 4) and slowing of deep water formation (Figure 5).

Figure 4. Greenland and Antarctic ice mass change. GRACE data are extension of Velicogna et al. (2014)
gravity data. MBM (mass budget method) data are from Rignot et al. (2011). Red curves are gravity data for
Greenland and Antarctica only; small Arctic ice caps and ice shelf melt add to freshwater input. (Hansen et al. 2016)
Figure 5. (a) AMOC (in Sverdrup) at 28°N in simulations (i.e., including freshwater injection of 720 Gt year⁻¹ in 2011
                around Antarctica, increasing with a 10-year doubling time, and half that amount around Greenland).
(b) SST (°C) in the North Atlantic region (44–60°N, 10–50°W).

Future trends and Tipping points

Whereas the precise nature tipping point/s ensuing from the confluence of numerous processes (Figure 2) remains little defined, the weakened boundaries between the Arctic and sub-Arctic zones (Figure 7) and the build-up of cold ice melt pools in the oceans fringing Greenland and Antarctica represent an initial stage in the development of a stadial freeze. The warming of the Arctic, formed approximately 3.6-2.2 million years ago when CO₂ levels were about 400 ppm and polar temperatures near 2°C higher than in the late Holocene, heralds conditions somewhat similar to those of the Pliocene. Whereas reports of the International Panel of Climate Change (IPCC, 2018) (Figure 9), based on thousands of peer reviewed science papers and reports, offer a confident documentation of past and present processes in the atmosphere (Climate Council 2018), the portrayal of mostly linear temperature rise trends need to be questioned. Already early stages of a stadial event are manifest by the build-up of a large pools of cold water in the North Atlantic Ocean south of Greenland (Figure 6A) (Rahmstorf et al., 2015) and at the fringe of West Antarctica (Figure 6A) signify early stages in the development of a stadial freeze in large parts of the oceans, consistent with the decline in the Atlantic Meridional Ocean Circulation (AMOC) (Figure 6A).

Figure 6. (A) 2018 global temperature (NASA);
(B) projected 2055-2100 surface-air temperature to +1.19°C above 1880-1920
(AIB model modified forcing, ice melt to 1 meter) (Hansen et al., 2016).
These projections differ markedly from linear model trends (Figure 9) of IPCC models, which mainly assume long term ice melt (Ahmed, 2018). Rignot et al. (2011) report that in 2006 the Greenland and Antarctic ice sheets experienced a combined mass loss of 475 ± 158 Gt/yr, equivalent to 1.3 ± 0.4 mm/yr sea level rise”. For the Antarctic ice sheet the IEMB team (2017) states the sheet lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimeter (IMBIE team 2017). Hansen et al. (2008) consider global temperature higher than 1.0°Celsius due to CO₂ level of ~450 ppm would lead to irreversible ice sheet loss, given most climate models did not include amplifying feedbacks effects such as ice sheet disintegration, vegetation migration, and greenhouse gas release from soils, tundra, or ocean sediments. Such feedbacks can lead to climate tipping points leading to irreversible runaway climate change (Ahmed, 2018).

Figure 7. Global surface-air temperature to the year 2300 in the North Atlantic and Southern Oceans,
including stadial freeze events as a function of Greenland and Antarctic ice melt doubling time (Hansen et al., 2018)

According to NOAA (2018) Arctic surface air temperatures continue to warm at twice the rate relative to the rest of the globe (Figure 8B), leading to a loss of 95 percent of its oldest ice over the past three decades. Arctic air temperatures for 2014-18 have exceeded all previous records since 1900 and are driving broad changes within the Arctic as well he sub-Arctic through 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 a weakening and increasingly undulating jet stream barrier (Figure 8A). This weakening also allows warm air masses to move northward, further warming the Arctic and driving further ice melting. The freezing storms in North America (Figure 8C) are cheering those who refuse to discriminate between the climate and the weather.

Figure 8. – A. The weakened undulating Jet stream bounding the polar vortex.
Red represents the fastest air flow (Berwyn 2016). The "big freeze" in North America
results from a slow-moving depression of a Rossby wave⁵. The troughs and ridges of
these waves carry wind around the world and generally have a speed rating
of six or seven, with higher numbers representing faster moving winds;
B. The North American and Siberian freeze event 30 January 2019 (NOAA Global
Forecast system model) (Francis 2019). Predicted near-surface air temperature
differences from normal, relative to 1981-2010. Pivotal Weather, CC BY-ND (Francis 2019);
C. North America is experiencing the weather pattern on the left, while Europe enjoys the other one.

IPCC models of future climate change (Figure 9) contain a number of departures from patterns deduced from the paleoclimate evidence. The role of feedbacks from land and water, estimates of future ice melt rates, sea level rise rates, rates of methane release from permafrost and the extent of fires in enhancing atmospheric CO₂, and the already observed onset of ocean cooling south of Greenland and fringes of Antarctica freeze events need to be quantified. According to Hansen et al. (2016) ice mass loss would raise sea level by several meters in an exponential rather than linear response even within the 21st century. According to Rignot et al. (2011) the Greenland and Antarctic ice sheets experienced in 2006 a combined mass loss of 475 ± 158 billion tons per year.

According to a Met Office briefing evaluating the implications of the UN report, once we go past 1.5°C, we dramatically increase the risks of floods, droughts, and extreme weather that would impact hundreds of millions of people. According to the IPCC this would just be the beginning: as we are currently on track to hit 3-4°C by end of century (Figure 9), which would lead to a largely unlivable planet (Ahmed, 2018). The progressive melting of Greenland and the Arctic Sea ice, formed in the Pliocene approximately 3.6-2.2 million years ago when CO₂ levels were about 560-400 ppm (Stone et al. 2010). Future climate model projections by the IPCC (Figure 9) contain a number of significant departures from observations based on the paleoclimate evidence. This includes factors related to amplifying feedbacks from land and water, ice melt rates, temperature trajectories, sea level rise rates, methane release rates, the role of fires, and observed onset of transient stadial (freeze) events. As the Earth continues to heat, cold air masses breach the Arctic boundary and move southward and warm air penetrates into the Arctic, temperature contrasts between polar and subpolar climate zones decrease, further weakening the polar divide. Temperature contrasts between Arctic-derived cold air masses and subtropical air masses result in an increase in the intensity and frequency of extreme weather events.

Figure 9. IPCC AR5: Time series of global annual mean surface air temperature anomalies relative to 1986–2005
from CMIP5 (Coupled Model Inter-comparison Project) concentration-driven experiments.
Projections are shown for each RCP for the multi model mean (solid lines) and the 5–95% range
(±1.64 standard deviation) across the distribution of individual models (shading) (Easterbrook 2014).⁽⁴⁾

As the Earth warms, the increase in temperature contrasts across the globe, and thereby an increase in storminess and extreme weather events, occurring at present, 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 draught zones. A non-linear climate warming trend, including stadial freeze events, bears significant implications for planning future adaptation efforts, including preparations for transient deep freeze events in parts of Western Europe and eastern North America for periods lasting several decades (Figure 7) and coastal defenses against enhanced sea levels and storms. In Australia this should include construction of water pipelines and channels from the flooded north to parched regions such as the Murray-Darling basin.

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² Hysteresis: The phenomenon in which the value of a physical property lags behind changes in the effect causing it, as for instance when magnetic induction lags behind the magnetizing force.
³ The Anthropocene is a proposed epoch dating from the commencement of significant human impact on the Earth's 
geology and ecosystems. https://en.wikipedia.org/wiki/Anthropocene
⁴ Steve Easterbrook, New IPCC Report (Part 6). Azimuth. https://johncarlosbaez.wordpress.com/2014/04/16/what-does-the-new-ipcc-report-say-about-climate-change-part-6/
https://oceanservice.noaa.gov/facts/rossby-wave.html
https://www.dw.com/en/understanding-the-polar-vortex/a-17347788


Andrew Glikson
Dr Andrew Glikson
Earth and Paleo-climate science, Australia National University (ANU) School of Anthropology and Archaeology,
ANU Planetary Science Institute,
ANU Climate Change Institute,
Honorary Associate Professor, Geothermal Energy Centre of Excellence, University of Queensland.

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


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