2.2.5 Potential for Earth system tipping points to magnify or accelerate impacts of global warming

Some tipping points might also be expected to potentially alter the rate of global warming by changing the increase in radiative forcing, either by modifying the airborne fraction of anthropogenic emissions through changes in natural sinks and sources of greenhouse gases (permafrost, Amazon rainforest, boreal forests, methane hydrates) or by changing the albedo of the planet (sea ice, ice sheets). This could change the time at which we reach specific Global Warming Levels (GWLs) such as 2°C and hence the time of reaching the associated climate hazards. This could alter the overall impact on human society because the socioeconomic conditions would be different, leading to different levels of exposure and vulnerability. If a particular level of hazard were to be reached sooner if global change were accelerated by passing one or more tipping points, this may mean that vulnerability (and potentially exposure) is higher because there has been less time to prepare/adapt. On the other hand, exposure may be smaller if (for example) the population has not grown so much when the hazard level occurs.

Wang et al., (2023) used the Finite Amplitude Impulse-Response (FAIR) simple climate model to provide a preliminary estimate of the increase in global warming that would arise from the collective effects of several Earth System tipping points for which quantitative estimates could be made with reasonable confidence. These were release of CO₂ and/or CH₄ from permafrost thaw, marine methane hydrate destabilisation, Amazon forest dieback; and increased shortwave radiative forcing from Arctic sea ice loss. With the SSP2-4.5 scenario (which could approximately represent the trajectory of global emissions under current policies), and without tipping points being passed, global warming was projected to reach approximately 3.0°C (2.8-4.2°C) in 2100 and 3.5°C (2.2-5.2°C) in 2300. Using specific, quantitative assumptions for the contribution of each tipping point to greenhouse gas release or radiative forcing, and with several different assumptions on equilibrium climate sensitivity, it was estimated that the combined effect of passing those tipping points would be to increase global warming by 0.13°C (0.06-0.23°C) in 2100 and 0.24°C (0.11-0.49°C) in 2100. With a hypothetical very high emissions scenario SSP5-8.5, global warming of 5.0°C (3.0-7.5°C) at 2100 was increased by 0.21°C (0.10-0.36°C), and warming of 8.5°C (5.5-12.7°C) at 2300 was increased by 0.52°C (0.25-1.09°C).

Importantly, the use of the simple climate model for the above estimates did not allow for dynamical tipping behaviour or interactions between tipping points, and moreover did not include other tipping points such as rapid ice sheet loss, boreal forest loss or AMOC collapse, so should certainly not be regarded as a complete estimate of the impacts of Earth system tipping points on the projected rate of future global warming. However, the above estimates do provide a means to place the potential additional collective impacts arising from those specific, selected tipping points in context with other impacts assessments.

Table 2.2.1: Impacts of tipping points on sectors. Note that all impacts could potentially be increased by contributions of tipping points to acceleration of global warming, especially if several tipping points occur.

	Water security	Food security	Energy security	Health	Biodiversity and ecosystem services	Communities and economies
AMOC collapse	Changes in regional rainfall globally (both increases and decreases)	Large losses of crop productivity in regions affected by reduced rainfall	Increased demand for heating in Northern Hemisphere	Widespread risks to health from reduced water and food availability in regions affected by reduced precipitation, and from more severe cold weather in winter	Radical changes to North Atlantic ecosystems including fisheries	Severe challenges for North Atlantic region countries
Ice sheet collapse	Salination of groundwater in coastal regions	Impacts on coastal crop productivity through salination Disruption to Sahel agriculture inland through reduced West African monsoon rainfall	Potential for flooding of coastal energy infrastructure, e.g. power stations	Spread of diseases due to inundation of coastal areas	Loss of coastal ecosystems	Potential loss of atoll nations 480 million people vulnerable to annual coastal flood event by 2100 with 2m sea level rise
Arctic sea ice loss	Potential to affect regional climates, but uncertain. Specific impacts on water not assessed	Potential to affect regional climates, but uncertain. Specific impacts on food not assessed	Potential for increased fossil fuel extraction and export	Potential to affect regional climates, but uncertain. Specific impacts on food not assessed	Risks to Arctic biodiversity, both direct through loss of sea ice as part of a habitat, and indirect through amplified warming	New shipping routes and potential for increased mineral extraction and export
Permafrost thawing	Reduced water quality through release of contaminants	Challenges to traditional practices for provision and storage of food	Damage to energy infrastructure	Risks to health from contaminated drinking water supplies and food chains	Changes in species composition in permafrost ecosystems	70% of current infrastructure in permafrost regions is in areas with high potential for thaw by 2050
Amazon dieback	Reduced river flows	Risks to agricultural productivity through reduced availability of time for outdoor working due to heat stress risks	Hydropower productivity in Xingu basin reduced to 25% of installed capacity due to decreased river flows	Exposure of 6 million people to extreme heat stress risk Reduced air quality from wildfires	Shifts from rainforest tree species to dry forest or savanna tree and grass species, with associated loss of animal species adapted to closed-canopy conditions	Economic damages of US$957bn and US$3,589bn Transport difficulties due to reduced river flows Risks to communities from wildfires Potential migration to cities