Editing IPCC:AR6/WGII/Chapter-11 (section)

=== 11.3.11 Detection and Attribution of Observed Climate Impacts ===

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Detection and attribution of observed climate trends and events is called ‘climate attribution’. This has been assessed by IPCC WGI ( [[#Gutiérrez--2021|Gutiérrez et al., 2021]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; [[#Seneviratne--2021|Seneviratne et al., 2021]] ) and summarised in Chapter 16. Trends that have been formally attributed in part to anthropogenic climate change include regional warming trends and sea level rise (SLR), decreasing rainfall and increasing fire risk in southern Australia. Events include extreme rainfall in New Zealand during 2007–2017, the 2007/2008 and 2012/2013 droughts in New Zealand, high temperatures in Australia during 2013–2020, the 2016 northern Australian marine heatwave, the 2016/2017 and 2017/18 Tasman Sea marine heatwaves and 2019/2020 fires in Australia.

Detection and attribution of climate impacts on natural and human systems is called ‘impact attribution’. This often involves a two-step approach (joint attribution) that links climate attribution to observed impacts. Impact attribution is complicated by confounding factors, for example, changes in exposure arising from population growth, urban development and underlying vulnerabilities.

Impact attribution is considered in Sections 11.3.1–11.3.10 and summarised in Table 11.9. More literature is available for natural systems than human systems, which represents a knowledge gap rather than an absence of impacts that are attributable to anthropogenic climate change. Fundamental shifts in the structure and composition of some ecosystems are partly due to anthropogenic climate change ( ''high confidence'' ). In human systems, the costs of droughts and floods in New Zealand, and heat-related mortality and fire damage in Australia, are partly attributed to anthropogenic climate change ( ''medium confidence'' ).

'''Table 11.9 |''' Examples of observed impacts that can be partly attributed to climate change.

{| class="wikitable"
|-
! Impact

! Source

|-
| Mass bleaching of GBR in 2016/2017 due to a marine heatwave

| Box 11.2

|-
| In the New Zealand southern Alps, extreme glacier mass loss, which was at least 6 times more likely in 2011 and 10 times more likely in 2018, due to warming

| 11.2.1, 11.3.3

|-
| In the Australian Alps bioregion, loss of habitat for endemic and obligate species due to snow loss and increases in fire, drought and temperature

| Table 11.4

|-
| In the Australian wet tropics world heritage area, some vertebrate species have declined in distribution area and population size due to increasing temperatures and length of dry season

| Table 11.4

|-
| Extinction of Bramble Cay melomys due to loss of habitat caused by storm surges and SLR in Torres Strait

| Table 11.4

|-
| In New Zealand, increasing invasive predation pressure on endemic forest birds surviving in cool forest refugia due to anthropogenic warming

| Table 11.4

|-
| In New Zealand, erosion of coastal habitats due to more severe storms and SLR

| Table 11.4, Box 11.6

|-
| In Australia, estuaries warming and freshening with decreasing pH

| Table 11.6

|-
| Changes in life-history traits, behaviour or recruitment of fish and invertebrates due to ocean acidification or warming, severe decline in recruitment of coral on GBR due to ocean warming, aquaculture stock deaths due to heat stress

| Table 11.6

|-
| New diseases and toxins due to warming and extension of East Australian Current

| Table 11.6

|-
| Changes in almost 200 marine species’ distributions and abundance due to ocean warming

| Table 11.6

|-
| Temperate marine species replaced by seaweeds, invertebrates, corals and fishes characteristic of sub-tropical and tropical waters

| Table 11.6

|-
| River flow decline in southern Australia is largely due to the decline in cool-season rainfall partly attributed to anthropogenic climate change

| 11.3.3

|-
| In New Zealand, the 2007/2008 drought and 2012/2013 drought were 20% attributed to anthropogenic climate change

| 11.3.3

|-
| In New Zealand, about 30% of the insured damage for the 12 costliest flood events from 2007 to 2017 can be attributed to anthropogenic climate change

| 11.3.8

|-
| In Australia, 35–36% of heat-related excess mortality in Melbourne, Sydney and Brisbane from 1991–2018 can be attributed to anthropogenic climate change

| 11.3.6

|}

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