2022/02/02 by Intergovernmental Panel on Climate Change (IPCC) · 3 citations
Social Sciences · #Island Studies and Pacific Affairs #Climate Change, Adaptation, Migration
paper · pdf · doi:10.1017/9781009157964.006
openalex publication_date 2022/02/02 · openalex created_date 2022/02/08 · openalex updated_date 2026/08/05
This chapter assesses past and future contributions to global, regional and extreme sea level changes, associated risk to low-lying islands, coasts, cities, and settlements, and response options and pathways to resilience and sustainable development along the coast. ObservationsGlobal mean sea level (GMSL) is rising (virtually certain 1 ) and accelerating (high confidence 2 ).The sum of glacier and ice sheet contributions is now the dominant source of GMSL rise (very high confidence).GMSL from tide gauges and altimetry observations increased from 1.4 mm yr -1 over the period 1901-1990 to 2.1 mm yr -1 over the period 1970-2015 to 3.2 mm yr -1 over the period 1993-2015 to 3.6 mm yr -1 over the period 2006-2015 (high confidence).The dominant cause of GMSL rise since 1970 is anthropogenic forcing (high confidence).4.2.2.1.1,4.2.2.2 GMSL was considerably higher than today during past climate states that were warmer than pre-industrial, including the Last Interglacial (LIG; 129-116 ka), when global mean surface temperature was 0.5C-1.0Cwarmer, and the mid-Pliocene Warm Period (mPWP; ~3.3 to 3.0 million years ago), 2C-4C warmer.Despite the modest global warmth of the Last Interglacial, GMSL was likely 6-9 m higher, mainly due to contributions from the Greenland and Antarctic ice sheets (GIS and AIS, respectively), and unlikely more than 10m higher (medium confidence).Based on new understanding about geological constraints since the IPCC 5th Assessment Report (AR5), 25 m is a plausible upper bound on GMSL during the mPWP (low confidence).Ongoing uncertainties in palaeo sea level reconstructions and modelling hamper conclusions regarding the total magnitudes and rates of past sea level rise (SLR).Furthermore, the long (multi-millennial) time scales of these past climate and sea level changes, and regional climate influences from changes in Earth's orbital configuration and climate system feedbacks, lead to low confidence in direct comparisons with near-term future changes.Cross-Chapter Box 5 in Chapter 1, 4.2.2, 4.2.2.1, 4.2.2.5, SM 4.1 Non-climatic anthropogenic drivers, including recent and historical demographic and settlement trends and anthropogenic subsidence, have played an important role in increasing low-lying coastal communities' exposure and vulnerability to SLR and extreme sea level (ESL) events (very high confidence).In coastal deltas, for example, these drivers have altered freshwater and sediment availability (high confidence).In 1 Each finding is grounded in an evaluation of underlying evidence and agreement.A level of confidence is expressed using five qualifiers: very low, low, medium, high and very high, and typeset in italics, e.g., medium confidence.The following terms have been used to indicate the assessed likelihood of an outcome or a result: virtually certain 99-100% probability, very likely 90-100%, likely 66-100%, about as likely as not 33-66%, unlikely 0-33%, very unlikely 0-10%, exceptionally unlikely 0-1%.Assessed likelihood is typeset in italics, e.g., very likely.This is consistent with AR5 and the other AR6 Special Reports.Additional terms (extremely likely 95-100%, more likely than not >50-100%, more unlikely than likely 0-<50%, extremely unlikely 0-5%) are used when appropriate.This Report also uses the term 'likely range' or 'very likely range' to indicate that the assessed likelihood of an outcome lies within the 17-83% or 5-95% probability range.For more details see 1.9.2, Figure 1.4. 2Statements about uncertainty in Section 4.2 are contingent upon the RCP or other emissions assumptions that accompany them.In Section 4.4, the entirety of information facing a decision maker is taken into consideration, including the unknown path of future emissions, in assessing uncertainty.Depending on which perspective is chosen, uncertainty may or may not be characterised as 'deep'.low-lying coastal areas more broadly, human-induced changes can be rapid and modify coastlines over short periods of time, outpacing the effects of SLR (high confidence).Adaptation can be undertaken in the short-to medium-term by targeting local drivers of exposure and vulnerability, notwithstanding uncertainty about local SLR impacts in coming decades and beyond (high confidence).4.2.2.4,4.3.1,4.3.2.2, 4.3.2.3 Coastal ecosystems are already impacted by the combination of SLR, other climate-related ocean changes, and adverse effects from human activities on ocean and land (high confidence).Attributing such impacts to SLR, however, remains challenging due to the influence of other climate-related and non-climatic drivers such as infrastructure development and human-induced habitat degradation (high confidence).Coastal ecosystems, including saltmarshes, mangroves, vegetated dunes and sandy beaches, can build vertically and expand laterally in response to SLR, though this capacity varies across sites (high confidence).These ecosystems provide important services that include coastal protection and habitat for diverse biota.However, as a consequence of human actions that fragment wetland habitats and restrict landward migration, coastal ecosystems progressively lose their ability to adapt to climate-induced changes and provide ecosystem services, including acting as protective barriers (high confidence). 4.3.2.3Coastal risk is dynamic and increased by widely observed changes in coastal infrastructure, community livelihoods, agriculture and habitability (high confidence).As with coastal ecosystems, attribution of observed changes and associated risk to SLR remains challenging.Drivers and processes inhibiting attribution include demographic, resource and land use changes and anthropogenic subsidence.4.3.3, 4. 3.4A diversity of adaptation responses to coastal impacts and risks have been implemented around the world, but mostly as a reaction to current coastal risk or experienced disasters (high confidence).Hard coastal protection measures (dikes, embankments, sea walls and surge barriers) are widespread, providing predictable levels of safety in northwest Europe, East Asia, and around many coastal cities and deltas.Ecosystem-based adaptation (EbA) is continuing to gain traction worldwide, providing multiple co-benefits, but there is still low agreement on its cost and long-term effectiveness.Advance, which refers to the creation of new land by building into the sea (e.g., land reclamation), has a long history in most areas where there are dense coastal populations.Accommodation measures, such as early warning systems (EWS) for ESL events, are widespread.Retreat is observed but largely restricted