Editing IPCC:AR6/WGII/Chapter-3 (section)

==== 3.4.3.2 Phenological Shifts and Trophic Mismatches ====

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===== 3.4.3.2.1 Observed changes =====

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SROCC reported ''high confidence'' in phenological shifts towards earlier onset of biological events (Table 3.18), with phenological shifts among epipelagic species attributed to ocean warming ( ''high confidence'' ).

'''Table 3.18 |''' Summary of previous IPCC assessments of phenological shifts and trophic mismatches

{| class="wikitable"
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! Observations

! Projections

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| ''AR5 WGII ( [[#Hoegh-Guldberg--2014|Hoegh-Guldberg et al., 2014]] ; [[#Larsen--2014|Larsen et al., 2014]] )''

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| ‘Changes to sea temperature have altered the phenology, or timing of key life-history events such as plankton blooms, and migratory patterns, and spawning in fish and invertebrates, over recent decades ( ''medium confidence'' ). There is ''medium to high agreement'' that these changes pose significant uncertainties and risks to fisheries, aquaculture and other coastal activities.’

The highly productive high-latitude spring bloom systems in the northeast Atlantic are responding to warming ( ''medium evidence, high agreement'' ), with the greatest changes being observed since the late 1970s in the phenology, distribution and abundance of plankton assemblages, and the reorganisation of fish assemblages, with a range of consequences for fisheries ( ''high confidence'' ).

‘Observed changes in the phenology of plankton groups in the North Sea over the past 50 years are driven by climate forcing, in particular regional warming ( ''high confidence'' ).’

‘On average, spring events in the ocean have advanced by 4.4 ± 0.7 days per decade (mean ± SE).’

‘Shifts in the timing and magnitude of seasonal biomass production could disrupt matched phenologies in the food webs, leading to decreased survival of dependent species ( ''medium confidence'' ). If the timing of primary and secondary production is no longer matched to the timing of spawning or egg release, survival could be impacted, with cascading implications to higher trophic levels. This impact would be exacerbated if shifts in timing occur rapidly ( ''medium confidence'' ).’

‘There is ''medium to high confidence'' that climate-induced disruptions in the synchrony between timing of spawning and hatching of some fish and shellfish and the seasonal increases in prey availability can result in increased larval or juvenile mortality or changes in the condition factor of fish and shellfish species in the Arctic marine ecosystems.’

| Projections of phenological shifts and trophic mismatches were not assessed in this report.

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|
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| ''SROCC ( [[#Bindoff--2019a|Bindoff et al., 2019a]] )''

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| ‘Phenology of marine ectotherms in the epipelagic systems related to ocean warming ( ''high confidence'' ) and the timing of biological events has shifted earlier ( ''high confidence'' ).’

‘Timing of spring phenology of marine organisms is shifting to earlier in the year under warming, at an average rate of 4.4 ± 1.1 days per decade, although it is variable among taxonomic groups and among ocean regions.’

| Projections of phenological shifts and trophic mismatches were not assessed in this report.

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| ''WGI AR6 [[IPCC:Wg2:Chapter:Chapter-2|Chapter 2]] ( [[#Gulev--2021|Gulev et al., 2021]] )''

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| ‘Phenological metrics for many species of marine organisms have changed in the last half century ( ''high confidence'' ), though many regions and many species of marine organisms remain under-sampled or even unsampled. The changes vary with location and with species ( ''high confidence'' ). There is a strong dependence of survival in higher trophic-level organisms (fish, exploited invertebrates, birds) on the availability of food at various stages in their life cycle, which in turn depends on the phenologies of both ( ''high confidence'' ). There is a gap in our understanding of how the varied responses of marine organisms to climate change, from a phenological perspective, might threaten the stability and integrity of entire ecosystems.’

| Projections of phenological shifts and trophic mismatches were not assessed in this report.

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'''Table 3.19 |''' Assessment of phenological shifts by taxon based on time series from field observations spanning at least 19 years published over the past 25 years

{| class="wikitable"
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! Taxon

! Rate of consistency of observations with climate change

! Estimated mean rate of change in seasonal timing

! Confidence

! Notes

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| Phytoplankton

| 78.41%

( ''n'' = 85)

| −7.5 d per decade

( ''n'' = 83)

| ''Very high confidence''

| ''Evidence most robust'' for changes in timing of blooms in the North Atlantic (e.g., [[#Chivers--2020|Chivers et al., 2020]] ) and Baltic (e.g., [[#Scharfe--2019|Scharfe and Wiltshire, 2019]] ; [[#Wasmund--2019|Wasmund et al., 2019]] ), with ''limited evidence'' from the Southern Hemisphere.

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| Holozooplankton

| 79.74%

( ''n'' = 77)

| −4.27 d per decade

( ''n'' = 58)

| ''Very high confidence''

| ''Evidence most robust'' in the northeast Atlantic (e.g., [[#Chevillot--2017|Chevillot et al., 2017]] ), but sparse elsewhere.

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| Meroplankton (taxa that are only temporarily in the plankton)

| 81.06%

( ''n'' = 72)

| −4.34 d per decade

( ''n'' = 64)

| ''Very high confidence''

| Includes earlier peak abundance of fish larvae in upwelling systems (e.g., [[#Asch--2015|Asch, 2015]] ).

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| Benthic invertebrates

| 72.34%

( ''n'' = 5)

| −8.5 d per decade

( ''n'' = 5)

| ''Low confidence'' ( ''limited evidence, medium agreement'' )

| ''Evidence is limited'' , uncertainty levels are high. Rate of consistency of responses with climate change is not significantly different from random chance.

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| Plants

| 100%

( ''n'' = 1)

| No estimate available

| ''Very low confidence''

| Just a single study for seagrasses, and only for consistency ( [[#Diaz-Almela--2007|Diaz-Almela et al., 2007]] ).

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| Fish

| 65.48%

( ''n'' = 109)

| −3.02 d per decade

( ''n'' = 43)

| ''Very high confidence''

| Includes earlier appearance of migratory fish in estuaries (e.g., [[#Chevillot--2017|Chevillot et al., 2017]] ), earlier spawning migrations for anadromous fish such as salmon (e.g., [[#Rubenstein--2019|Rubenstein et al., 2019]] ), earlier migrations for sole (e.g., [[#Fincham--2013|Fincham et al., 2013]] ) and tuna (e.g., [[#Dufour--2010|Dufour et al., 2010]] ), and earlier spawning of key commercial demersal (bottom-dwelling) species such as cod (e.g., [[#McQueen--2017|McQueen and Marshall, 2017]] ).

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| Marine reptiles

| 100.0%

( ''n'' = 4)

| −2.89 d per decade

( ''n'' = 4)

| ''Low confidence'' ( ''limited evidence, low agreement'' )

| ''Evidence is limited'' , uncertainty levels are high. Mean phenological shift is not significantly different from zero.

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| Seabirds

| 42.36%

( ''n'' = 56)

| +0.77 d per decade

( ''n'' = 51)

| ''Very low confidence'' ( ''limited evidence, low agreement'' )

| Neither the rate of consistency with climate change nor the phenological shift differ significantly from null expectations (50% consistency and no shift). Many seabirds are breeding earlier ( [[#Byrd--2008|Byrd et al., 2008]] ; [[#Sydeman--2009|Sydeman et al., 2009]] ), while breeding among others in temperate and polar regions has been delayed, which has been linked to later sea ice breakup or limited prey resources ( [[#Barbraud--2006|Barbraud and Weimerskirch, 2006]] ; [[#Wanless--2009|Wanless et al., 2009]] ; [[#Chambers--2014|Chambers et al., 2014]] ). Although the response of lifecycle events for many seabird species is variable in direction, there has usually been a more complex driver associated with climate that has been considered to be responsible ( [[#Sydeman--2015|Sydeman et al., 2015]] ). For many species, seasonal timing is moving earlier, especially in the Arctic (e.g., [[#Byrd--2008|Byrd et al., 2008]] ; [[#Descamps--2019|Descamps et al., 2019]] ), but for many species in the Southern Ocean, it is not ( [[#Barbraud--2006|Barbraud and Weimerskirch, 2006]] ; [[#Chambers--2014|Chambers et al., 2014]] ). This could be because of a much slower rate of warming in most of the Southern Ocean than in the Arctic.

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| Marine mammals

| 100.0%

( ''n'' = 4)

| −0.34 d per decade ( ''n'' = 4)

| ''Very low confidence'' ( ''limited evidence, low agreement'' )

| All studies of phenological changes for marine mammals have focused on whales (e.g., [[#Ramp--2015|Ramp et al., 2015]] ; [[#Hauser--2017|Hauser et al., 2017]] ; [[#Loseto--2018|Loseto et al., 2018]] ) or polar bears (e.g., [[#Cherry--2013|Cherry et al., 2013]] ; [[#Atwood--2016|Atwood et al., 2016]] ; [[#Escajeda--2018|Escajeda et al., 2018]] ) and have related timing to aspects of sea ice dynamics, highlighting the complexity of such processes. Mean phenological shift is not significantly different from zero at the global scale.

|}

Since SROCC, field data have continued to show that the phenology of biological events in the ocean is ''very likely'' ( ''high to very high confidence'' ) advancing in response to climate change, with 71.9% of published observations consistent with these anticipated effects (Figure 3.16a,b; Table 3.19), although most reports (95.6%) were from the Northern Hemisphere (Figure 3.16a). Biological events that are shifting earlier in response to climate change include phytoplankton blooms ( [[#Scharfe--2019|Scharfe and Wiltshire, 2019]] ; [[#Chivers--2020|Chivers et al., 2020]] ) such as: (a) those of HAB species ( [[#Forsblom--2019|Forsblom et al., 2019]] ; [[#Bucci--2020|Bucci et al., 2020]] ); (b) peaks in zooplankton abundance ( [[#Chevillot--2017|Chevillot et al., 2017]] ; [[#Forsblom--2019|Forsblom et al., 2019]] ); (c) the migration ( [[#Otero--2014|Otero et al., 2014]] ; [[#Kovach--2015|Kovach et al., 2015]] ; [[#Chust--2019|Chust et al., 2019]] ) and spawning of commercial fish ( [[#McQueen--2017|McQueen and Marshall, 2017]] ; [[#Kanamori--2019|Kanamori et al., 2019]] ), including crabs and squid ( [[#Henderson--2017|Henderson et al., 2017]] ); and (d) breeding of marine reptiles ( [[#Mazaris--2008|Mazaris et al., 2008]] ; [[#Cherkiss--2020|Cherkiss et al., 2020]] ). Moreover, different trophic levels within epipelagic food webs are responding at different rates ( ''very high confidence'' ) (Table 3.19; Figure 3.16b,c), with greater and more consistent responses by lower trophic levels (phytoplankton, holozooplankton and meroplankton) but less consistent, weaker and more varied responses by higher trophic levels. There were too few independent time series to make robust estimates for benthic invertebrates, plants, marine reptiles and mammals. This differential response across trophic levels could lead to trophic mismatches ( [[#Neuheimer--2018|Neuheimer et al., 2018]] ), where predators and their prey respond asynchronously to climate change ( [[#Edwards--2004|Edwards and Richardson, 2004]] ; [[#Rogers--2019|Rogers and Dougherty, 2019]] ; [[#Rubenstein--2019|Rubenstein et al., 2019]] ; [[#Émond--2020|Émond et al., 2020]] ), with potential population-level consequences, including declines in fish recruitment ( [[#Burthe--2012|Burthe et al., 2012]] ; [[#Chevillot--2017|Chevillot et al., 2017]] ; [[#McQueen--2017|McQueen and Marshall, 2017]] ; [[#Asch--2019|Asch et al., 2019]] ; [[#Durant--2019|Durant et al., 2019]] ; [[#Régnier--2019|Régnier et al., 2019]] ). Available evidence also suggests that feeding relationships could modulate species responses to climate change, as seen in breeding of surface-feeding and deeper-diving seabirds ( [[#Descamps--2019|Descamps et al., 2019]] ). These differential responses could determine ‘winners’ and ‘losers’ under future climate change ( [[#Lindén--2018|Lindén, 2018]] ).

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[[File:d1f25a14a1580fe6eb4b371e588bddc3 IPCC_AR6_WGII_Figure_3_016.png]]

'''Figure 3.16 |''' '''Observed responses to climate change based on a systematic Web of Science review of marine phenology studies exceeding 19 years in length to update the assessment in WGII AR5 Chapter 30 (Hoegh-Guldberg et al.''' ''', 2014).''' Error bars indicate 95% confidence limits (i.e., the ''extremely likely'' range).

'''(a)''' Global data shows changes in seasonal cycles of biota that are attributed (at least partly) to climate change (blue, ''n'' = 297 observations), and changes that are inconsistent with climate change (white, ''n'' = 116 observations). Each circle represents the centre of a study area.

'''(b)''' The proportion of phenological observations (showing means and ''extremely likely'' ranges) that are attributed to climate change (i.e., generally showing earlier timing) by taxonomic group.

'''(c)''' Observed shifts in timing (days per decade, showing means and ''extremely likely'' ranges), by taxonomic group, that are attributed to climate change. Negative shifts are earlier, positive shifts are later. (Details and additional plots are presented in 3.SM.3.3, Figure 3.SM.3 and Table 3.SM.1.)

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===== 3.4.3.2.2 Projected changes =====

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The CMIP6 ESM ensembles project that, by 2100, 18.8 ± 19.0% (mean ± ''very likely'' range) and 38.9 ± 9.4% of the ocean surface will ''very likely'' undergo a change of 20 d or more (advance or delay) in the start of the phytoplankton growth period under SSP1-2.6 and SSP5-8.5, respectively (Figure 3.17a,b) ( ''low confidence'' due to the dependence with the projected changes in phytoplankton biomass, the trends of which are reported with ''low confidence'' ) ( [[#3.4.3.4|Section 3.4.3.4]] ; SROCC [[IPCC:Wg2:Chapter:Chapter-5#5.2|Section 5.2.3]] ; [[#Bindoff--2019a|Bindoff et al., 2019a]] ). Phytoplankton growth is projected to begin later in the Northern Hemisphere subtropics, and earlier at high latitudes in some regions around the Antarctic Peninsula, and over large areas in the Northern Hemisphere ( ''low to medium confidence'' as there are improved constraints from historical variability in this region and consistency with CMIP5-based-studies results) ( [[#Henson--2018b|Henson et al., 2018b]] ; [[#Asch--2019|Asch et al., 2019]] ). There is ''high agreement'' in model projections that the start of the phytoplankton growth period will ''very likely'' advance in the Arctic Ocean under a high-emission scenario for CMIP5 and CMIP6 (Figure 3.17b; [[#Henson--2018b|Henson et al., 2018b]] ; [[#Asch--2019|Asch et al., 2019]] ; [[#Tedesco--2019|Tedesco et al., 2019]] ; [[#Lannuzel--2020|Lannuzel et al., 2020]] ). The CMIP6 ensemble projections further show limited changes in phenology across most of the Southern Ocean but large regional variations in the tropics (Figure 3.17). Overall, the regional patterns are qualitatively similar under SSP1-2.6 and SSP5-8.5 but with greater magnitude and larger areas under SSP5-8.5 ( ''low confidence'' ).

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[[File:aae03dd90e97291b745b7a026d4210dd IPCC_AR6_WGII_Figure_3_017.png]]

'''Figure 3.17 |''' '''Projected phytoplankton phenology.''' (a,c) Spatial patterns and (b,d) density distributions of projected change in phytoplankton phenology by 2100 under Shared Socioeconomic Pathway (SSP)1-2.6 and SSP5-8.5, respectively. Difference in the start of the phytoplankton growth period is calculated as 2090–2099 minus 1996–2013. Negative (positive) values indicate earlier (later) start of the phytoplankton growth period by 2100. The ensemble projections of global changes in phytoplankton phenology include, under SSP1-2.6 and SSP5-8.5, respectively, a total of five Coupled Model Intercomparison Project 6 Earth system models containing coupled ocean biogeochemical models that cover a wide range of complexity ( [[#Kwiatkowski--2019|Kwiatkowski et al., 2019]] ). (The phenology calculations are based on [[#Racault--2017|Racault et al., 2017]] , using updated data.)

At latitudes &gt;40°N, temperature-linked phenology of fish reproduction with high geographic fidelity to spawning grounds (geographic spawners) is projected to change at double the rate of that for phytoplankton, which will ''likely'' cause phenological mismatches resulting in increased risk of starvation for fish larvae ( ''medium to high confidence'' ) (WGI AR6 [[IPCC:Wg2:Chapter:Chapter-2#2.3|Section 2.3.4.2.3]] ; [[#Asch--2019|Asch et al., 2019]] ; [[#Durant--2019|Durant et al., 2019]] ; [[#Régnier--2019|Régnier et al., 2019]] ; [[#Gulev--2021|Gulev et al., 2021]] ; [[#Laurel--2021|Laurel et al., 2021]] ). Furthermore, under RCP8.5, trophic mismatch events exceeding ±30 days ( [[#Asch--2019|Asch et al., 2019]] ) leading to fish-recruitment failure are expected to increase tenfold for geographic spawners across much of the North Atlantic, North Pacific and Arctic Ocean basins ( ''low confidence'' ) ( [[#Neuheimer--2018|Neuheimer et al., 2018]] ). In contrast, temporal mismatches between fish that relocate spawning grounds in response to environmental variations (environmental spawners) and phytoplankton blooms are projected to remain shorter and less varied, suggesting that across ocean basins, range shifts by environmental spawners may increase their resilience. Nevertheless, this compensation mechanism might fail at locations where phytoplankton bloom phenology is not controlled by temperature-driven water-column stratification, leading to a possible sixfold local increase in extreme mismatches under climate change ( [[#Asch--2019|Asch et al., 2019]] ).

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