by Andrew Glikson
Earth and climate scientist
Australian National University
No one knows how to impose 1.5 or 2.0 degrees Celsius limits on the mean global temperature, unless drawdown/carbon sequestration of atmospheric CO₂ is attempted, nor are drawdown methods normally discussed in most political or economic forums. According to Kevin Drum (2019), “Meeting the climate goals of the Paris Agreement is going to be nearly impossible without removing carbon dioxide from the atmosphere”.
The release of some 910 billion tons of carbon dioxide is leading human society, indeed much of nature, to an existential impasse. The widest chasm has developed between what climate science is indicating and between climate policies and negotiations controlled by governments, politicians, economists and journalists—none of whom fully comprehends, or is telling the whole truth about, the full consequences of the current trend in the atmosphere-ocean-land system.
The evidence for future projections, as understood by climate scientists, has been largely put to one side, mainly because it is economically and politically “inconvenient” or is frightening. Reports from the Madrid climate COP-25 Conference suggest negotiations, focusing on emission reductions, are overlooking the evidence that at the current concentration of CO₂, which have reached 412 ppm and 496 ppm-equivalent (when the CO₂-equivalents of methane and nitrous oxide are included), amplifying feedbacks from land and ocean are pushing temperatures further upwards. This is driven by the replacement of sea ice and land ice and snow surfaces by open water surfaces, by methane leaks, desiccated vegetation, fires and reduced CO₂ absorption by warming oceans. Given the long atmospheric residence time of CO₂ (Solomon et al. 2009, Eby et al. 2009) and the short life span of aerosols, attempts at CO₂ drawdown are essential if complete devastation of the biosphere is to be avoided.
|Figure 1. (A) 1990-2019 Global growth of CO₂ emissions (gigaton);|
(B) 1960-2019 Annual fossil CO₂ emissions from coal, oil, natural gas and cement (gigaton).
From: CSIRO News Release
However, no one knows how to impose these limits unless drawdown/sequestration of atmospheric CO₂ is attempted, nor are drawdown methods normally discussed in most forums.
|Figure 2. (A) Distribution of global fires (NASA); |
(B) Fire storms over the southwest USA;
(C) Pine forest fire California.
- An increase in evaporation due to warming of land and oceans leads to further warming due to the greenhouse effect of water vapor but also to increased cloudiness which retards warming. The water vapor factor, significant in the tropics, is somewhat less important in the dry subtropical zones and relatively minor in the Polar Regions (Figure 3).
- The melting of ice sheets, reducing reflective (high-albedo) ice and snow surfaces, and concomitant opening of open water surfaces (heat absorbing low-albedo) is generating a powerful positive (warming) feedback. Hudson (2011) estimates the rise in warming due to total removal of Arctic summer sea ice as approximately +1.0 degrees Celsius.
- The release of methane from melting permafrost and bubbling of methane hydrates from the oceans has already raised atmospheric methane levels from about 800 to 1863 parts per billion which, given the radiative forcing of methane of X25< times, renders methane highly significant.
- As the oceans warm they become less capable of taking up carbon dioxide. As a result, more of our carbon pollution will stay in the atmosphere, exacerbating global warming.
- As tropical and subtropical climate zones overtake temperate Mediterranean-type climate zones, desiccated and burnt vegetation release copious amounts of carbon dioxide to the atmosphere. For example the current bushfires in Australia have already emitted 250 million tonnes of CO₂, almost half of country's annual emissions in 2018.
|Figure 3. Total water vapor that can precipitate, as observed by |
the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite.
Abrupt reductions in emissions may be insufficient to stem global warming, unless accompanied by sequestration of greenhouse gases from the atmosphere, recommended as below 350 ppm CO₂. According to Hansen et al. (2008) carbon sequestration in soil (the biochar method) has significant potential, applying pyrolysis of residues of crops, forestry and animal waste. Biochar helps soil retain nutrients and fertilizers, reducing release of greenhouse gases such as N₂O. Replacing slash-and-burn agriculture with a slash-and-char method and the use of agricultural and forestry wastes for biochar production could provide a CO₂ drawdown of ~8 ppm or more in half a century.
Stabilization and cooling of the climate could include two principle approaches (Table 1): (a) solar shielding, and (b) CO₂ drawdown/sequestration. However, solar shielding by injected aerosols or water vapor is bound to be transient, requiring constant replenishment.
Table 1. Solar shielding and atmospheric CO₂ sequestration methods.
|Figure 4. Iceland: The streaming of CO₂-containing air and of water through|
basaltic rocks and CO₂-capture as carbonate minerals.
Time is running out.
Earth and climate scientist
Australian National University
- 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