As the CO2 level rises to 408 ppm and the total greenhouse gas concentrations in the atmosphere, including CO2, methane and nitrous oxide, reaches about 500 parts per million CO2-equivalent, the stability threshold of the Greenland and Antarctic ice sheets, currently melting at an accelerated rate, is exceeded. Under warming drought conditions, firestorms currently engulfing California, large parts of South America, Siberia, Australia and elsewhere are a direct consequence of the extreme changes in the composition of the atmosphere.
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 (September 2019), 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 2 to 3 ppm/year.
The current carbon dioxide rise rate exceeds the fastest geological 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. The current growth rate of atmospheric greenhouse gases, in particular over the last 70 years or so, constitutes an extreme event in the recorded history of Earth.
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 doubts 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 boundary and freezing polar air fronts penetrating Siberia, North America and Europe.
Allowing for the temperature-lowering influence of the transient albedo (reflection) enhancing effects of atmospheric 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 (prior to 5.3 million years-ago) conditions.
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.
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—because of complex feedback dynamics and existing computational limitations—by climate models that are tuned to modern conditions.”
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, deltas and low coastal and river valleys, would be flooded due to sea level rise to Miocene-like 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 (5.3-23 million years ago), 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 to below ~300 ppm. Humans are likely to survive only in relatively favourable parts of Earth, such as sub-polar regions and sheltered mountain valleys, where cooler conditions would allow fauna to remain.
To try and avoid such calamities abrupt reduction in carbon emissions is essential, but since the high level of CO2-e is activating amplifying feedbacks from land and ocean, global attempts to down-draw 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.
As trillions of dollars continue to be poured into preparation of future wars, currently no government is involved in serious attempts at defending life on Earth.
Andrew Glikson, Earth and paleoclimate scientist.
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