Current mean greenhouse gas concentrations have reached a level similar to those of the Miocene (5.3 – 23 million years ago) when average temperatures exceeded 4 degrees Celsius and, while terrestrial adversaries keep pushing the Earth toward wars and a possible nuclear catastrophe, looming in the background are increasing heat waves, extreme fires and flood events, manifesting the huge calamity of irreversible global warming. False promises of emission cuts are negated by overlooked fossil fuel exports, new fossil fuel projects and accounting questions. Consequently the current rise in atmospheric greenhouse gas levels ― the single most critical parameter in controlling the climate ― continues to rise at a rate of 2 to 3 ppm per year, reaching 419.28 by February 2022 (Figure 1).
Following the onset of the industrial age about ~1750, and most acutely in the wake of WWII about ~1950 (Figure 1b), CO2 and other greenhouse gases (CH4, NO2) have grown at an accelerated rate to a total of ~500 ppm CO2-equivalent. This included a rise from ~315 ppm CO2 in 1950 to ~419 ppm in 2022, rising at an average rate of ~1.35 ppm/year and up to 2.5 – 3 ppm/year, a rate unprecedented in Cenozoic (since 65 Ma) record, except perhaps in the aftermath of the K-T dinosaur mass extinction event, when temperature rise reached ~7.5°C. According to Beerling et al. (2002) CO2 level rose from 350–500 ppm to at least 2,300 ppm within 10,000 years following the K-T impact, at an average rate of ~0.2 ppm/year, significantly less than the ~2 to 3 ppm/year rate since 1970 (Figure 1b).
Figure 1. Global mean CO2 level rising toward Miocene-like (~5.3 – 23 million years ago) conditions, when, about 14.8 Ma ago central European temperatures reached about 35oC (Figure 4), more than double the current mean global temperature of ~13.9oC.
Figure 2. Annual mean carbon dioxide growth rates for Mauna Loa, NOAA.
At the present CO2 growth rate of between 2 and 3 ppm/year (Figures 1 and 2) the terrestrial atmosphere would reach CO2 level above 500 ppm (2 ppm x 78 = 156 ppm; 419 ppm + 156 ppm = 575 ppm) and temperature of at least 4oC and higher before the end of the 21st century, consistent with IPCC projections and commensurate with the atmospheric conditions during parts of the Miocene (Figure 3 and 4).
Figure 3. Comparison between different proxy-based pCO2 estimates for the past 40 Ma.
Figure 4. Mid-Miocene continental climate records. Red arrow – The 2022 average global temperature of 13.9oC; NOAA.
Can the current climate trend be arrested, or even reversed?
The current global greenhouse gas trend, rising at 2 to 3 ppm/year, is leading to one of the largest mass extinction of species in the geological record, one of the species being human civilization. The current focus on emission reduction overlooks a major factor, namely the amplifying feedbacks from land and oceans (Steffen et al., 2018). There is a desperate need, in addition to emission reduction, for urgent large-scale sequestration of atmospheric greenhouse gases,
The role of amplifying GHG feedbacks from land and oceans, leading to enhanced heating, appears to be neglected in climate negotiations. Amplifying feedbacks include (A) an increase in evaporation, raising atmospheric vapor levels, which enhances the greenhouse gas effect; (B) a decline in the polar albedo (reflection) due to large-scale lateral and vertical melting of ice; (C) release of methane from melting permafrost and from polar sediments; (D) reduced CO₂ intake by warming oceans. Currently the oceans absorb between 35-42% of all CO₂ and around 90% of the excess heat; (E) warming, desiccation, deforestation and fires over land areas.
Numerous species have been unable to survive the accelerated global heating following the K-T impact event, nor are many species likely to survive the even higher rate of the of the Anthropocene catastrophe. A connection between climate change and human wars is evident from the accelerated global warming in the wake of the industrial-scale world wars I and II and subsequent industrial developments. It is possible that climate change could have been arrested in the 1960s had global efforts been directed at the time for abrupt cuts in emissions, transformation of agricultural and land clearing practices, and effort at CO2 drawdown/sequestration. By the onset of the 21st century however, such efforts have hardly been undertaken and could yet turn out to be too late. The repetitions of humanity’s old warlike habits, investing resources in industries of death, genocidal wars associated with intensive carbon emissions, forecasted in “The Fate of the Earth”, yield little promise for a change of direction.
A/Prof Andrew Glikson, Earth and paleoclimate scientist
