Editing IPCC:AR6/WGI/Chapter-Atlas (section)

=== Atlas.6.2 Assessment and Synthesis of Observations, Trends and Attribution ===

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Reliable station observations are available from around 1900 in Australasia, but in some regions the coverage was and remains poor. Australia and New Zealand have continued to warm, and many rainfall trends have continued since AR5. Changes and trends in temperature and precipitation from 1961 to 2015 from three different global datasets are displayed in Figure Atlas.11 and the Interactive Atlas, and show significant (at 0.1 significance level) warming trends over southern and eastern Australia. Most of the observed changes in precipitation over the region are not significant over this period. Although observed datasets (e.g., GPCC and GPCP) generally agree on a significant drying trend in the southern regions of New Zealand during the shorter 1980–2015 period, this is in fact the reverse of the longer-term trends in 1961–2015 (Interactive Atlas).

For a longer-term perspective based on high-quality regional datasets, Figure Atlas.20 shows Australasia has warmed over the last century ( ''very high confidence'' ). Australian mean temperature has increased by 1.44°C ± 0.24°C during the period 1910–2019 using the updated observed temperature dataset ACORN-SATv2.1, with 2019 Australia’s hottest year on record and nine out of 10 of the warmest years on record occurring since 2005 ( [[#Trewin--2020|Trewin et al., 2020]] ). Much of the warming has occurred since 1960, there is clear anthropogenic attribution of this change and emergence of the signal from the1850–1900 climate ( [[#BOM%20and%20CSIRO--2020|BOM and CSIRO, 2020]] ; [[#Hawkins--2020|Hawkins et al., 2020]] ). Warming has been more rapid than the national average in central and eastern Australia, with a warming minimum and non-significant trends since the 1960s in the north-west ( [[#CSIRO%20and%20BOM--2015|CSIRO and BOM, 2015]] ; [[#BOM%20and%20CSIRO--2020|BOM and CSIRO, 2020]] ). The National Institute of Water and Atmospheric Research temperature record, NIWA NZ, shows a warming of 1.13°C ± 0.27°C during the period 1909–2019, although several stations show non-significant trends since 1960 (Figure Atlas.20), including a warming minimum in the south-east at least partly due to a persistent shift in atmospheric circulation ( [[#Sturman--2013|Sturman and Quénol, 2013]] ; [[#MfE%20and%20Stats%20NZ--2017|MfE and Stats NZ, 2017]] , 2020).

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[[File:1613874b91602f0ca427f4419cd0d8b5 IPCC_AR6_WGI_Atlas_Figure_20.png]]

'''Figure Atlas.20''' '''|''' '''Observed trends in mean annual temperature (a, b) and summer (December–January–February, DJF) and winter (June–July–August, JJA) precipitation (c, d) for Australia and New Zealand from high-quality regional datasets.''' Time series show anomalies from the 1961–1990 average and 10-year running mean; maps show annual linear trends for 1960–2019; rainfall trends are shown in % per decade, crosses show areas and stations with a lack of significant trend and regions of seasonally dry conditions (&lt;0.25 mm day–1) are masked and outlined in red. Datasets are Australian Climate Observation Reference Network – Surface Air Temperature version 2.1 (ACORN-SATv2.1) for Australian temperature, the Australian Gridded Climate Data (AGCD) for Australian rainfall ( [[#Evans--2020|Evans et al., 2020]] ), and the 30-station high-quality network for New Zealand temperature and rainfall. Further details on data sources and processing are available in the chapter data table (Table Atlas.SM.15).

Since 1960, precipitation has increased in much of mainland Australia in austral summer and decreased in many regions of southern and eastern Australia in austral winter (Figure Atlas.20). A detectable anthropogenic signal of increases in precipitation in Australia has been reported particularly for north central Australia and for a few regions along the south-central coast for the period 1901–2010 ( [[#Knutson--2018|Knutson and Zeng, 2018]] ). Seasonally, there is a significant decline in winter rainfall in the south-west of the state of Western Australia (Figure Atlas.20), with an attributable human influence ( ''high confidence,'' ''robust evidence'' , ''medium agreement'' ) ( [[IPCC:Wg1:Chapter:Chapter-10#10.4|Section 10.4]] and references therein, e.g., [[#Delworth--2014|Delworth and Zeng, 2014]] ). Rainfall trends in the south-east are not significant since 1960 but have shown a notable reduction since the 1990s, and there is ''limited evidence'' for the attribution of this change to human influence (e.g., [[#Rauniyar--2020|Rauniyar and Power, 2020]] ). In New Zealand between 1960 and 2019 in both summer and winter, rainfall increased in some stations in the South Island and decreased at many stations in the North Island, however most station trends are not statistically significant (Figure Atlas.20; [[#MfE%20and%20Stats%20NZ--2020|MfE and Stats NZ, 2020]] ). In JJA, Milford Sound (increasing) and Whangaparaoa (decreasing) trends are significant.

In Australia, there has been a decrease in snow depth and area since the late 1950s, especially in spring ( [[#BOM%20and%20CSIRO--2018|BOM and CSIRO, 2018]] ). Based on a reconstructed snow cover record, the recent rapid decrease in the past five decades has been shown to be larger by more than an order of magnitude than the maximum loss for any five-decade period over the past 2000 years ( [[#McGowan--2018|McGowan et al., 2018]] ). In New Zealand, from 1977 to 2018, glacier ice volume decreased from 26.6 km <sup>3</sup> to 17.9 km <sup>3</sup> (a loss of 33%; [[#Salinger--2019|Salinger et al., 2019]] ).

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