Wednesday, May 1, 2019

Greenhouse Gas Levels Keep Accelerating

Carbon Dioxide



Weekly CO₂ levels at Mauna Loa, Hawaii, at the end of April 2019 reached 414.32 ppm, as above image shows. An ominous trendline points at 415 ppm in 2019 and 420 ppm in 2020.


The daily average CO₂ level recorded by NOAA at Mauna Loa, Hawaii, on May 15, 2019, was 415.64 ppm, as above image shows. The image below also shows hourly average levels from April 15, 2019, to May 15, 2019.


Current CO₂ levels far exceed levels that were common during the past 800,000 years, as the image below shows. CO₂ levels moved between roughly 180 and 280 ppm, while the temperature went up and down by some 10°C or 18°F.


The daily average CO₂ level recorded by scripps.ucsd.edu at Mauna Loa, Hawaii, on May 13, 2019, was 415.5 ppm and the May 15, 2019, level was 415.7 ppm. On May 14, 2019, one hourly average exceeded 417 ppm.


The situation is dire

This level of 417 ppm is 139 ppm above the CO₂ level in the year 1750 and more than 157 ppm above what the CO₂ level would have been if levels had followed a natural trend. As shown by the inset (from Ruddiman et al.) in above image, a natural trend points at levels below 260 ppm.

Furthermore, methane levels are rising even faster than CO₂ levels. While CO₂ levels did rise by 146% since 1750, methane levels did rise by 257% since that time and there is much potential for an even faster rise in methane levels due to seafloor hydrate releases. Levels of nitrous oxide also keep rising rapidly.

Such a rise in greenhouse gas levels has historically corresponded with more than 10°C or 18°F of warming, when looking at greenhouse gas levels and temperatures over the past 800,000 years, as illustrated by the image below.


Given that a 100 ppm rise in CO₂ did historically cause temperatures to rise by 10°C or 18°F, how much warming would be in line with a 157 ppm CO₂ and how fast could such a rise unfold?

A temperature of 10°C or 18° above 1750 seems in line with such high greenhouse gas levels. This is illustrated by above graph, based on 420,000 years of ice core data from Vostok, Antarctica, and as the post What Does Abrupt Climate Change Look Like? describes.


Why isn't it much warmer now? Why hasn't such a rise happened yet? Oceans and ice are still holding off such a rise, by absorbing huge amounts of warming. Of 1993-2003 warming, 95.5% was absorbed by oceans and ice. However, ocean stratification and ice loss are making the atmosphere take up more and more heat.

There are further warming elements, in addition to the accelerating rise in greenhouse gas levels. Mentioned above is the loss of the snow and ice cover. The domino effect is a popular way to demonstrate a chain reaction. It is typically sequential and typically uses dominoes that are equal in size. A chain reaction can be achieved with solid dominoes each as much as 1.5 times larger than the previous one. The exponential function is discussed in the video below by Guy McPherson. Rather than following a linear order, warming elements can be self-reinforcing feedback loops and can influence each other in ways that multiply (rather than pass on) their impact, which can speed up the temperature rise exponentially.

So, how fast and by how much could temperatures rise? As oceans and ice are taking up ever less heat, rapid warming of the lower troposphere could occur very soon. When including the joint impact of all warming elements, as described in a recent post, abrupt climate change could result in a rise of as much as 18°C or 32.4°F by 2026. This could cause most life on Earth (including humans) to go extinct within years.

Methane

Next to carbon dioxide, there are further greenhouse gases. Methane is important, because of its high short-term potency as a greenhouse gas and because methane levels in the atmosphere have hugely risen since 1750, and especially recently, as illustrated by the image on the right.

Carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) levels in the atmosphere in 2017 were, respectively, 257%, 146% and 122% their 1750 levels.

A recent study by Turetsky et al. concludes that, since sudden collapse releases more carbon per square metre because it disrupts stockpiles deep in frozen layers, and since abrupt thawing releases more methane than gradual thawing does, the impact of thawing permafrost on Earth’s climate could be twice that expected from current models.

As said, there also is a huge and growing danger of large abrupt methane releases from clathrates contained in sediments at the seafloor of the Arctic Ocean.

As illustrated by the image below, methane levels are rising and this rise is accelerating.


The graph shows July 1983 through December 2018 monthly global methane means at sea level, with added trend. Higher methane means can occur at higher altitude than at sea level. On Sep 3, 2018, daily methane means as high as 1905 ppb were recorded at 307 mb, an altitude at which some of the strongest growth in methane has occurred, as discussed in earlier posts such as this one.

Nitrous Oxide

Next to carbon dioxide and methane, there are further greenhouse gases, of which nitrous oxide is particularly important. Nitrous oxide is up to 300 times as potent as a greenhouse gas as carbon dioxide and has a lifetime of 121 years. Several recent studies point at the danger of huge releases of nitrous oxide from permafrost.

According to a 2017 study by Voigt et al., Arctic permafrost contains vast amounts of nitrogen (more than 67 billion tons). Warming of the Arctic permafrost is accelerating, causing rapid thaw of permafrost soils, and this now threatens to cause huge releases of nitrous oxide to the atmosphere. The study concluded that nitrous oxide emissions in the Arctic are likely substantial and underestimated, and show high potential to increase with permafrost thaw.

In the video below, Paul Beckwith discusses nitrous oxide.


In the video below, Paul Beckwith discusses the recent study by Wilkerson et al.


The study by Wilkerson et al. shows that nitrous oxide emissions from thawing Alaskan permafrost are about twelve times higher than previously assumed. A 2018 study by Yang et al. points at the danger of large nitrous oxide releases from thawing permafrost in Tibet. Even more nitrous oxide could be released from Antarctica. The danger is illustrated by the image below, which shows that massive amounts of nitrous oxide were recorded over Antarctica on April 29, 2019.


Depletion of the Ozone Layer

In addition to being a potent greenhouse gas, nitrous oxide is also an ozone depleting substance (ODS). As the left panel of the image below shows, growth in the levels of chlorofluorocarbons (CFCs) has slowed over the years, yet their impact will continue for a long time, given their long atmospheric lifetime (55 years for CFC-11 and 140 years for CFC-12). Since nitrous oxide levels continue to increase in the atmosphere, while the impact of CFC-11 and CFC-12 is slowly decreasing over time, the impact (as an ODS) of nitrous oxide has relatively grown, as the right panel of the image below shows.

[ from an earlier post ]
James Anderson, co-recipient of the 1995 Nobel Prize in chemistry for his work on ozone depletion, said in 2018 that "we have five years to save ourselves from climate change".

Comprehensive Action

In conclusion, while it's important to reduce emissions of all greenhouse gases, reducing emissions of methane and nitrous oxide is particularly important. To both reduce polluting emissions and to remove greenhouse gases from the atmosphere and oceans, the Climate Plan recommends feebates as depicted in the image below. As the image also mentions, further lines of action will be needed to avoid a rapid rise in temperature.

[ from an earlier post ]
Meanwhile, Arctic sea ice reached a new record low for April, as illustrated by the NSIDC image below.

In the video below, Guy McPherson describes what threatens to eventuate soon. This is an edit of the April 22, 2019, video in which Guy McPherson was interviewed by Peter B. Collins for the community television station in Marin County, California.


In the video below, Guy McPherson gives a presentation at the Center for Spiritual Living, in Chico, April 28, 2019.


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


Links

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

• Permafrost collapse is accelerating carbon release, by Merritt Turetsky et al. (30 April 2019)
https://www.nature.com/articles/d41586-019-01313-4

• Permafrost nitrous oxide emissions observed on a landscape scale using the airborne eddy-covariance method, by Jordan Wilkerson et al. (April 3, 2019)
https://www.atmos-chem-phys.net/19/4257/2019/

• Can natural or anthropogenic explanations of late-Holocene CO2 and CH4 increases be falsified?, by William Ruddiman et al. (2011)
https://journals.sagepub.com/doi/10.1177/0959683610387172

• Magnitude and Pathways of Increased Nitrous Oxide Emissions from Uplands Following Permafrost Thaw, by Guibiao Yang et al. (July 9, 2018)
https://pubs.acs.org/doi/10.1021/acs.est.8b02271

• Increased nitrous oxide emissions from Arctic peatlands after permafrost thaw, by Carolina Voigt et al.
https://www.pnas.org/content/early/2017/05/23/1702902114

• We Have Five Years To Save Ourselves From Climate Change, Harvard Scientist Says - James Anderson (January 15, 2018)
https://www.forbes.com/sites/jeffmcmahon/2018/01/15/carbon-pollution-has-shoved-the-climate-backward-at-least-12-million-years-harvard-scientist-says/

• A rise of 18°C or 32.4°F by 2026?
https://arctic-news.blogspot.com/2019/02/a-rise-of-18c-or-324f-by-2026.html

• Care for the Ozone Layer
https://arctic-news.blogspot.com/2019/01/care-for-the-ozone-layer.html

• What Does Runaway Warming Look Like?
https://arctic-news.blogspot.com/2018/10/what-does-runaway-warming-look-like.html

• Rapid ice loss in early April leads to new record low - NSIDC
https://nsidc.org/arcticseaicenews/2019/05/rapid-ice-loss-in-early-april-leads-to-new-record-low/



Wednesday, April 17, 2019

How long do we have?

The March 2019 temperature is in line with an earlier analysis that 2019 could be 1.85°C warmer than preindustrial and that a rapid temperature rise could take place soon, as illustrated by the image below.


A catastrophe of unimaginable proportions is unfolding. Life is disappearing from Earth and all life could be gone within a decade. At 5°C of warming, most life on Earth will have disappeared. When looking at near-term human extinction, 3°C will likely suffice. Study after study is showing the size of the threat, yet many people seem out to hide what we're facing.

Above image asks 'How long do we have?' The image is created with NASA LOTI data, adjusted 0.78°C to reflect a 1750 baseline, ocean air temperature and higher polar anomaly. Trends are added based on 1880-2019 (purple) and 2000-2019 data (red). The long-term purple trend points at 2025 as the year when 3°C rise from preindustrial could be crossed, while the red trend that focuses on short-term events shows how a 3°C rise from preindustrial could be reached as early as in 2020.

The chart below shows elements contributing to the warming, adding up to a rise of as much as 18°C by 2026.

[ from an earlier post ]
The situation is dire and calls for comprehensive and effective action, as described at the Climate Plan.


If we accept that crimes against humanity include climate crimes, then politicians who inadequately act on the unfolding climate catastrophe are committing crimes against humanity and they should be brought before the International Criminal Court in The Hague, the Netherlands.




Links

• Co-extinctions annihilate planetary life during extreme environmental change, by Giovanni Strona and Corey Bradshaw (2018)
https://www.nature.com/articles/s41598-018-35068-1

• How much warming have humans caused?
https://arctic-news.blogspot.com/2016/05/how-much-warming-have-humans-caused.html

• Extinction
https://arctic-news.blogspot.com/p/extinction.html

• A rise of 18°C or 32.4°F by 2026?
https://arctic-news.blogspot.com/2019/02/a-rise-of-18c-or-324f-by-2026.html

• Stronger Extinction Alert
https://arctic-news.blogspot.com/2019/03/stronger-extinction-alert.html

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


Sunday, April 14, 2019

As Winds Start To Growl


Late last month, wind patterns over the North Pacific and North America resembled a screaming face.

The Arctic was as much as 7.7°C or 13.86°F warmer than 1979-2000, while in parts of Alaska the temperature anomaly was at the top end of the scale, i.e. 30°C or 54°F above 1979-2000.

On April 14, 2019, wind patterns over the North Atlantic resembled a growling face, as highlighted by the red ellipse on the image.

Temperatures over Greenland were as high as 14.9°C or 58.7°F at 1000 hPa at the spot marked by the green circle.

On the left, the image shows winds at 250 hPa dipping over the U.S., enabling cold winds to descend deep down over North America.


Temperatures in Colorado that day were as low as -13.5°C or 7.6°F, as illustrated by above image.

The map below shows the jet streams stretched out from North Pole to South Pole, while the jet stream is also crossing the Equator over the Pacific Ocean.


Meanwhile, Arctic sea ice extent remains at a record low for the measurements at ads.nipr.ac.jp for the time of year. As the image below shows, Arctic sea ice extent was 12.9 million km² on April 14, 2019.


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


Links

• An infinite scream passing through nature
https://arctic-news.blogspot.com/2019/04/an-infinite-scream-passing-through-nature.html

• Arctic Warming Up Fast
https://arctic-news.blogspot.com/2019/03/arctic-warming-up-fast.html

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


Monday, April 8, 2019

Blue Ocean Event Consequences

A Blue Ocean Event looks set to occur in the Arctic when there will be virtually no sea ice left. At first, the duration of this event will be a few weeks in September, but as more heat accumulates in the Arctic, the event will last longer each year thereafter.

Indeed, a Blue Ocean Event will come with accumulation of more heat, due to loss of latent heat, as a dark (blue) ocean absorbs more sunlight than the reflective ice, etc. Consequences will extend far beyond the Arctic, as shown on the image below that features Dave Borlace's Blue Ocean Top Ten Consequences.


Dave Borlace goes into more detail regarding these consequences in the video Blue Ocean Event : Game Over?


A Blue Ocean Event could happen as early as September 2019. The image below shows that Arctic sea ice extent on April 7, 2019, was 12.97 million km², a record low for measurements at ads.nipr.ac.jp for the time of year. By comparison, on May 28, 1985, extent was larger (13.05 million km²) while it was 51 days later in the year.


In the video below, Paul Beckwith also discusses the rapid decline of the sea ice and the consequences.


Clearly, the rapid decline of the sea ice has grave consequences. When also looking beyond what's happening in the Arctic, there are further events, tipping points and feedbacks that make things worse. An earlier post contains the following rapid warming scenario:
  1. a stronger-than-expected El Niño would contribute to
  2. early demise of the Arctic sea ice, i.e. latent heat tipping point +
  3. associated loss of sea ice albedo, 
  4. destabilization of seafloor methane hydrates, causing eruption of vast amounts of methane that further speed up Arctic warming and cause
  5. terrestrial permafrost to melt as well, resulting in even more emissions,
  6. while the Jet Stream gets even more deformed, resulting in more extreme weather events
  7. causing forest fires, at first in Siberia and Canada and
  8. eventually also in the peat fields and tropical rain forests of the Amazon, in Africa and South-east Asia, resulting in
  9. rapid melting on the Himalayas, temporarily causing huge flooding,
  10. followed by drought, famine, heat waves and mass starvation, and
  11. collapse of the Greenland Ice Sheet.


Importantly, depicted above is only one scenario out of many. Things may eventuate in different order and occur simultaneously, i.e. instead of one domino tipping over the next one sequentially, many events reinforcing each other. Further points should be added to the list, such as falling away of sulfate cooling due to economic changes, ocean stratification and stronger storms that can push large amounts of warm salty water into the Arctic Ocean.

Global sea ice extent is also at a record low for the time of year. Global sea ice extent on April 8, 2019, was 17.9 million km². On April 8, 1982, global sea ice extent was 22.32 million km², i.e. a difference of 4.42 million km². That constitutes a huge albedo loss.


As discussed in an earlier post, this all adds up to further global warming that may eventuate very rapidly. The image below shows how a total rise of 18°C or 32.4°F from preindustrial could eventuate by 2026.



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


Links

• Blue Ocean Event : Game Over? - by Dave Borlace
https://www.youtube.com/watch?v=qo3cznpfIpA

• Climate System Upheaval: Arctic Sea-Ice, Snow Cover, Jet-Stream, Monsoonal Consequences - by Paul Beckwithhttps://www.youtube.com/watch?v=ZtpF--rqZZ8

• Jet Stream Center-of-Rotation to Shift 17 degrees Southward from North Pole to Greenland with Arctic Blue Ocean Event - by Paul Beckwith
https://www.youtube.com/watch?v=bFme3C9e-cs

• Blue Ocean Event
https://arctic-news.blogspot.com/2018/09/blue-ocean-event.html

• Stronger Extinction Alert
https://arctic-news.blogspot.com/2019/03/stronger-extinction-alert.html

• It could be unbearably hot in many places within a few years time
https://arctic-news.blogspot.com/2016/07/it-could-be-unbearably-hot-in-many-places-within-a-few-years-time.html

• Feedbacks
https://arctic-news.blogspot.com/p/feedbacks.html

• Latent Heat
https://arctic-news.blogspot.com/p/latent-heat.html

• Albedo and more
https://arctic-news.blogspot.com/p/albedo.html

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

• How much warming have humans caused?
https://arctic-news.blogspot.com/2016/05/how-much-warming-have-humans-caused.html

• The Threat
https://arctic-news.blogspot.com/p/threat.html

• A rise of 18°C or 32.4°F by 2026?
https://arctic-news.blogspot.com/2019/02/a-rise-of-18c-or-324f-by-2026.html

• Extinction
https://arctic-news.blogspot.com/p/extinction.html

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


Monday, April 1, 2019

An infinite scream passing through nature


Wind patterns on March 30, 2019, resembled what Edvard Munch wrote in his diary in 1892, i.e. "I sensed an infinite scream passing through nature", a feeling Munch expressed in his iconic artwork The Scream, part of which is added on the right in above image.


Indeed, at the end of March 2019, it felt like an infinite scream passing through nature! On March 31, 2019, 12:00 UTC, the Arctic was 7.7°C or 13.86°F warmer than 1979-2000, as above image shows, while in parts of Alaska the anomaly was at the top end of the scale, i.e. 30°C or 54°F above 1979-2000, as discussed in an earlier post.

What caused this to eventuate? Firstly, as the Arctic is warming faster than the rest of the world, the temperature difference between the North Pole and the Equator is narrowing, which is slowing down the overall speed at which the jet stream is circumnavigating Earth, while it also is making the jet stream wavier, enabling warm air from the Atlantic Ocean and Pacific Ocean to more easily enter the Arctic, while also enabling cold air from the Arctic to more easily descend over Asia and North America.


At the same time, global warming is making oceans warmer. Sea surface temperatures were high in the path of the jet stream on March 15, 2019, as above image shows. The sea surface was 10.8°C or 19.4°F warmer than 1981-2011 at the green circle in the left panel of above image. On that day, surface air temperature there was as high as 7.9°C or 46.2°F, and there were cyclonic wind patterns, as the right panel of above image shows.

High sea surface temperatures are causing winds over oceans to get much stronger than they used to be at this time of year.

The image on the right shows that, on March 15, 2019, the jet stream reached speeds as high as 386 km/h or 240 mph at the green circle. These stronger winds then collide at high speed with the air in front of them. This collision occurs with an even greater force, due to low temperatures over North America and due to the lower overall speed at which the jet stream circumnavigates Earth. All this makes that air gets strongly pushed aside toward the Arctic and the Equator.

On March 30, 2019, strong winds pushed warm air into Bering Strait, resulting in temperatures as high as 2.5°C or 36.4°F, as the image below illustrates.


On March 30, 2019, Arctic sea ice extent fell to a record low for the time of year, as discussed in an earlier post. Ominously, methane reached peak levels as high as 2,967 ppb on March 29, 2019, as the image below shows.


With Arctic sea ice extent this low and with temperatures rising relentlessly, fears are that the sea ice won't be able to act as a buffer to absorb heat for long, and that a strong influx of warm, salty water will reach the seafloor of the Arctic Ocean and trigger methane eruptions from destabilizing hydrates.

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


Links

• Arctic Warming Up Fast
https://arctic-news.blogspot.com/2019/03/arctic-warming-up-fast.html

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



Sunday, March 31, 2019

Arctic Warming Up Fast

On March 30, 2019, Arctic sea ice extent was 13.42 million km², a record low for the measurements at ads.nipr.ac.jp for the time of year.


[ click on images to enlarge ]
As the Arctic warms up faster than the rest of the world, the temperature difference between the North Pole and the Equator narrows, making the jet stream wavier, thus enabling warm air over the Pacific Arctic to move more easily into the Arctic.

The image on the right shows that, on March 31, 2019, the Arctic was 7.5°C or 13.5°F warmer than 1979-2000.

The earlier forecast below shows a temperature anomaly for the Arctic of 7.6°C or 13.68°F for March 31, 2019, 12:00 UTC and in places 30°C or 54°F warmer. The inset shows the Jet Stream moving higher over the Bering Strait, enabling air that has been strongly warmed up over the Pacific Ocean to move into the Arctic.


A wavier Jet Stream also enables cold air to more easily move out of the Arctic. The inset shows the Jet Stream dipping down over North America where temperatures lower than were usual were recorded.

The later forecast below shows a temperature anomaly for the Arctic of 7.7°C or 13.86°F for March 31, 2019, 12:00 UTC.


The image below shows that El Niño can be expected to push temperatures up higher in 2019 during the Arctic sea ice retreat.

A warmer sea surface can cause winds to grow dramatically stronger, and they can push warm, moist air into the Arctic, while they can also speed up sea currents that carry warm, salty water into the Arctic Ocean.

Rivers can also carry huge amounts of warm water from North America and Siberia into the Arctic Ocean, as these areas are getting hit by ever stronger heatwaves that are hitting the Arctic earlier in the year.

With Arctic sea ice at a low, it won't be able to act as a buffer to absorb heat for long, with the danger that an influx of warm, salty water will reach the seafloor and trigger methane eruptions.

As warmer water keeps flowing into the Arctic Ocean and as air temperatures in the Arctic are now starting to rise on the back of a strengthening El Niño, fears for a Blue Ocean Event in 2019 are rising, which would further accelerate the temperature rise as less sunlight gets reflected back into space.

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

Links

• Arctic sea ice extent
https://ads.nipr.ac.jp/vishop/#/extent

• Climate Reanalyzer
https://climatereanalyzer.org

• ENSO Update by Climate Prediction Center / NCEP 25 March 2019
https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

• Blue Ocean Event
https://arctic-news.blogspot.com/2018/09/blue-ocean-event.html

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


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.

___________________
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.

_________________________
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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