The unthinkable consequences of global warming

The unthinkable consequences of global warmingby Andrew Glikson
“We’re simply talking about the very life support system of this planet”. Hans Joachim Schellnhuber 2009.
“Burning all fossil fuels would create a different planet than the one that humanity knows. The paleoclimate record and ongoing climate change make it clear that the climate system would be pushed beyond tipping points, setting in motion irreversible changes, including ice sheet disintegration with a continually adjusting shoreline, extermination of a substantial fraction of species on the planet, and increasingly devastating regional climate extremes” and “this equates to 400,000 Hiroshima atomic bombs per day 365 days per yearJames Hansen et al. 2012.
Humanity is fast reaching our moment of truth. What Hansen, Schellnhuber and others have warned us is based on evidence consistent with the basic laws of science, the discipline which, contrary to medieval superstition, is founded on direct observations, calculations and on reason.

Figure 1. The change in state of the planetary climate since the onset of the industrial age in the 17ᵗʰ century.

To elaborate on the nature of the threat humanity and nature are now facing:

A. The rise in greenhouse gas levels (Figure 1) and temperatures at the Earth surface, rising by more than 1°Celsius since 1880, has been underestimated. This is because the temperature values take little account of the masking effects of sulphur dioxide and other aerosols, which transiently mitigates global temperatures by at least ~ -0.5°C. The actual rise could already be as much as 1.5 degrees Celsius, the upper level recommended by the Madrid climate conference. On present trends temperatures will rise to above 2 degrees relative to pre-industrial levels Celsius by 2030. Further temperature rises are likely to be irregular and affected by the flow of ice melt water from melting ice sheets into the oceans by mid-century.
B. The rise in temperature of large ocean regions, with much of the warming occurring to ~800 meter deep levels, reduces the ocean’s ability to absorb CO₂. This means that more CO₂ is trapped in the atmosphere, causing further warming. Also, as ocean temperatures rise, the oceans are depleted in oxygen, which leads to increased production of methane and hydrogen sulphide, which are poisonous to marine life.
C. Models projecting global warming as a linear trajectory, as outlined by the International panel of Climate Change (IPCC), take only limited account of the weakening of climate zone boundaries, as temperatures rise in the polar regions, notably the circum-Arctic jet stream. The weakening of the boundaries allows penetration of warm air masses from the south, as expressed by fires in the Tundra and the Arctic. Conversely, the injection of freezing air masses from the Arctic into North America and Europe (The so-called Beast from the East) provides further evidence for the weakening of the Arctic boundary. These are likely to produce more violent winter storms and heavier snowfalls, forming direct results of global warming. Cooling of large surface areas of the ocean by ice melt water flowing from Greenland and the Antarctica, and accumulation of warmer water in depth, lead to irregular warming trends, with a consequent three-fold rise in extreme weather events (Figure 2), especially where high temperature and cold air masses collide.

Figure 2. The number (bars, left axis), type (colors), and annual cost (right vertical axis) of U.S. billion-dollar disasters from 1980-2018. Running annual cost (grey line), along with the 95% confidence interval, and 5-year average costs (black line).The number and costs of disasters are increasing. Inland flooding (blue bars) and severe storms (green bars) are making in increasingly large contribution to the number of U.S. billion-dollar disasters.

D. An estimated 1,400 billion tons (400 GTC) of carbon is embedded in the world’s permafrost, mostly in the Arctic and sub-Arctic, from where large amounts of carbon are released under the fast warming conditions. By comparison, the atmosphere presently contains 750 billion tons of carbon. Should a large part of the existing permafrost thaw, Earth could experience dramatic, fast and very dangerous warming. Huge amounts of methane (CH₄), the gas considered responsible for mass extinctions in the history of Earth about 251 million years ago (Permian -Triassic boundary) and 56 million years ago (Paleocene-Eocene boundary), are being released from melting permafrost and Arctic sediments, raising the atmospheric concentration of the gas by more than three-fold (from <600 to 1800 parts per billion) (Figure 3). Temperature rises during the PETM event are estimated as 5 to 8 degrees Celsius. When emitted the warming induced by methane is more than 84 times that of CO₂, declining to 25 times over some 20 years. The release to the atmosphere of a significant part of the stored carbon (permafrost ~900 billion ton carbon [GtC]), peatland 500 GtC and vegetation prone to fires (650 GtC), is sufficient to shift most of the Earth’s climate into a tropical to hyper-tropical state.

Figure 3. Global reserves and growth in the release of methane 1988-2019

E. The 2019-2010 wildfires in Australia have unleashed about 900 million tons of carbon dioxide into the atmosphere, which is equivalent to nearly double the country's total yearly fossil fuel emissions. As the planet warms, wildfires become more frequent and accelerate the warming process.
F. Sea level rise will flood the very regions where civilization has emerged, low river valleys, delta and coastal planes, which are also vital to food production. This is estimated to displace 100 million people initially, and more over time as major coastal cities are flooded.
G. The rising energy levels in warming regions of the Earth, notably tropical island chains such as the Caribbean and the Philippines, generate devastating tropical storms known as cyclones and typhoons. These wreak havoc on coastal regions of southeast North America, India, southern Africa, the Pacific and Australia.
H. Rising heat levels in tropical, subtropical and intermediate Mediterranean climate zones may render large areas unsuitable for agriculture and are physiologically difficult for humans to live in as “heat bulb” conditions set in.

An outline of the migration of climate zones in Australia and the southwestern Pacific is given in Figure 4. Further to NASA’s reported mean land-ocean temperature rise to +1.18°C for March 2020 relative to 1951-1980, large parts of the continents, including Siberia, central Asia, Canada, parts of west Africa, eastern South America and Australia, are warming toward mean temperatures of +2°C and higher. The rate exceeds that of the Last Glacial Termination (LGT) during 21–8 thousand years ago and earlier warming events. These includes the Paleocene-Eocene hyperthermal event (PETM) (about 55.9 million years ago [Ma]) and the Cretaceous-Tertiary boundary (K-T) (64.98 Ma) impact event. The relationships between the global warming rate and the migration of climate zones toward the poles are portrayed in detail on global climate maps (Figure 4).

Figure 4. The migration of the northward into southern Europe. Note the drying up of Spain,
Italy, Greece and Turkey and the increased in precipitation in Northern Europe.

In the 20th century the Earth climate has reached a tipping point, namely a point of no return. Global CO₂ and other greenhouse gases rise have reached a large factor to an order of magnitude higher than those of the past geological and mass extinction events, as have the rate of warming, the shift of climate zones and the rate of extreme weather events (Figure 2). Given the abrupt change in state of the atmosphere-ocean-cryosphere-land system, accelerating since the mid-20ᵗʰ century, the terms “climate change” and “global warming” no longer reflect the extreme scale and rate of these shifts.
Time is running out.

Andrew Glikson

Dr Andrew Glikson
Earth and Paleo-climate scientist
ANU Climate Science Institute
ANU Planetary Science Institute
Canberra, Australia
The Asteroid Impact Connection of Planetary Evolution
The Archaean: Geological and Geochemical Windows into the Early Earth
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
Asteroids Impacts, Crustal Evolution and Related Mineral Systems with Special Reference to Australia
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