2.3.4.1 Earth system destabilisation and displacement

Displacement is usually a forced or involuntary, reactive movement between places, which can be short or long-term, within or between nations. Both acute and slow-onset environmental pressures, such as extreme weather events, drought and sea level rise, are projected to increase under Earth system tipping scenarios.

Measurement challenges, definitional debates, and the complex drivers of human mobility can make it difficult to document and identify causal evidence of climate-induced migration and displacement (Boas et al., 2019; Carvajal and Pereira, 2010). Climate mobilities – including cross-border and internal movements and immobility – occur along a spectrum from voluntary to pre-emptive, to forced (Capisani, 2023). These are exacerbated by weather events and deteriorating environmental conditions, but are also a product of the global state system, and historical and current political, social and economic decisions about infrastructure, housing, public services, rights, and governance responses. Nevertheless, increasing Earth system destabilisation will impact the migration (voluntary movement), displacement (involuntary movement), and immobility (inability to leave a high-risk or impacted area) of a large proportion of the population through direct and indirect effects. These include: increased hazard exposure, flooding, coastal erosion, sea level rise, droughts and heatwaves, effects on water supplies and other vital human systems and infrastructures, and threats to livelihoods and housing security, among others (Hauer et al., 2020; Mueller et al., 2014). Indeed, there are already examples of the forced and involuntary displacement of populations due to the impacts of extreme weather events (Thalheimer and Oh, 2023; IPPC, 2022; Clement et al., 2021). And many, in particular irreversible climate change effects such as sea level rise, are projected to be extremely costly, not least because of their impact on (forced) human mobility (Hauer et al., 2020; Neumann et al., 2015). Breaching Earth system tipping points would further amplify these effects.

Acute, short-term hazards result in increased migration and forced displacement, at least temporarily, especially within communities with limited adaptive capacity or resilience (McLeman, 2018). Recent estimates show that 95 million people are involuntarily on the move across the globe, many internally displaced due to extreme weather (Lenton et al., 2023). The Groundswell global modelling efforts predict 140 million people displaced within the borders of their own countries by 2030 (Rigaud et al., 2018). Additionally, the proportion of the global population living in coastal regions likely to be affected by sea level rise is growing and likely to surpass one billion people this century. Indeed, internal displacement often leads to large-scale and rapid urbanisation (Adger et al., 2020) and many of the urban centres that attract migrants and displaced people are close to the sea. These populations are likely to experience repeated displacement, which often leads to poorer outcomes for these communities (Hauer et al., 2020). Ultimately, vulnerability and risk in a shifting and shrinking human climate niche are not equally distributed, and how they are spread across the planet is likely to change with the crossing of Earth system tipping points.