Tipping Elements At Risk

Unabated continuation of business-as-usual emissions of greenhouse gases to the atmosphere would rapidly risk triggering tipping elements which would result in an irreversible cascade of climate change to a hothouse Earth where very few life forms are able to survive (Lenton et al. 2008; Steffen et al. 2018).

A tipping point in our climate system is a threshold which, if exceeded, leads to abrupt and large changes in the state of the system. Some of these changes can be irreversible. Timothy Lenton and colleagues (2008) identified nine tipping points and Will Steffen and colleagues (2018) identified which tipping elements are most at risk.

Figure 1: Tipping elements at risk (Steffen et al. 2018)

Because different climate systems are interconnected, one system can have an impact on another. The arrows in Figure 1 show the potential interactions among tipping elements. Each increase in global warming risks a domino like cascade where a series of tipping point thresholds are exceeded.

The Greenland ice sheet, Arctic summer sea ice, alpine glaciers, coral reefs, and West Antarctic ice sheets have already undergone change with a 1.0°C increase in global warming above preindustrial levels. Sea ice reflects more sunlight into outer space than uncovered water where sea ice used to be. With each melting of sea ice, the oceans absorb more heat which increases the level of global warming. The melting of sea ice involves a positive feedback loop where the melting of sea ice results in an acceleration in the melting of more sea ice.

Figure 2: Positive feedback loop of melting of melting of sea ice

The units of carbon stock in Figure 4 are in Petagrams. That is one gram multiplied by ten to the power of fifteen - in other words multiplied by 10 fifteen times. The atmosphere holds about 589 Petagrams and permafrost stores about 1,700 Petagrams. There is much more carbon locked in permafrost than is currently in the Earth’s atmosphere.

Carbon is also stored in the ground in the form of fossil fuel reserves. These reserves include gas (383 - 1,134 Petagrams), oil (173 - 264 Petagrams), and coal (446 - 541 Petagrams). The carbon locked in these fossil fuels far exceed that of carbon in the atmosphere.

A year before the 2015 Paris Agreement, Christophe McGlade and Paul Ekins (2014) cautioned that most of these fossil fuel reserves must stay in the ground.

At the 2015 Paris Agreement, nations agreed to restrict their use of fossil fuels and keep within a carbon budget in order to achieve net zero greenhouse emissions by 2050. But many countries have continued to explore for more reserves of fossil fuels. By doing so, these countries contravene the spirit of the 2015 Paris Agreement and use part of the agreed global carbon budget in exploration for more fossil fuels which should be used to transition from fossil fuels to renewable energy and infrastructure

Figure 4: Tundra in arctic regions

There is already evidence of permafrost thawing. Large scale thawing of permafrost would result in irreversible change in climate. The result would be a hothouse Earth where no life forms can survive. It is important to take into account the dynamics of changes in any system.

Here is one dynamic which is not so well known with regards to the mitigation of climate change. The combustion of fossil fuels produces emissions of CO₂, which is a long-lived gas and also short-lived pollutants such as sulphur dioxide (SO₂) etc. which contribute to the formation of atmospheric aerosols. Short-lived atmospheric aerosols cool the planet and masks the full potential of global warming due to emissions of greenhouse gases.

Aerosol particulates are highly toxic when inhaled, leading to millions of premature deaths per year. Phasing out of fossil fuel combustion will provide health benefits, but will also reduce the extent to which the warming induced by greenhouse gases is masked by aerosols. There are trade-offs between the rate of change in reductions in aerosols (flue-gas desulphurisation of coal-fired power plants) and reductions in CO₂ emissions. According to Shindell and Smith (2019), if aerosols alone are rapidly removed, then the rate of warming could accelerate from current levels of about 0.2 °C per decade to 0.4 to 0.8 °C per decade.

China and other countries are undergoing programmes of reductions in SO₂, but global levels of CO₂ are currently not decreasing. Shindell and Smith (2019) conclude that “The apparent success of ongoing efforts to reduce air pollution such as China therefore adds to the urgency to phase out the use of fossil fuels.” Reductions in CO₂ levels need to keep up pace with reductions in SO₂ and other pollutants so as to avoid a pulsing effect of a sharp increase in global warming.

In their study of tipping elements at risk, Will Steffen and colleagues (2018) conclude: “Our analysis suggests that the Earth System may be approaching a planetary threshold that could lock in a continuing rapid pathway toward much hotter conditions - Hothouse Earth”.

Figure 6: Hot house Earth (Steffen et al. 2018)

In 2021 the International Panel on Climate Change (IPCC) reported that global temperatures are likely to rise by more than 1.5°C above pre-industrial levels over the next two decades. This would cause widespread devastation and more extreme weather. Only rapid and drastic reductions in greenhouse gases in this decade can prevent climate breakdown. Every fraction of a degree of further heating is likely to compound the accelerating effects of climate change.