Assessment of the Earth s Energy and Sea Level Changes

Transcription

1 Assessment of the Earth s Energy and Sea Level Changes John A. Church1, Ma0hew D. Palmer2 and Susan Wijffels1 1CSIRO Oceans and Atmosphere, Hobart, Australia 2Met Office Hadley Centre, Exeter, United Kingdom OCEANS AND ATMOSPHERE NATIONAL RESEARCH FLAGSHIP

2 Earth s energy imbalance: the driver of global climate change von Schuckmann et al [2016]

3 Surface temperature is a weak indicator of Earth s energy imbalance on decadal Jmescales Palmer and McNeall [2014] von Schuckmann et al [2016]

4 Ocean heat content change is a reliable on Earth s energy imbalance on decadal Jmescales Palmer and McNeall [2014] von Schuckmann et al [2016]

5 Oceans absorbed >90% of the energy storage and account for a third of radiajve forcing 5 IPCC WGI Ch 3 &13

6 The Argo Array provides high-quality, global coverage to 2000 m, from about 2006 Map ocean heat content and steric sea level Quality control of data important. Beware of biases from historical data bases. Coverage not complete prior to

7 Argo heat content esjmates to late 2015 Steady heajng of ocean, parjcularly Southern Ocean and from 300 m to 2000 m Wijffels et al

8 Deep Ocean Warming SPM-4 and Chapter 3.2: Deep Ocean Warming Since the 1990s, when sufficient deep-ocean observauons have become available to allow an assessment, the deep ocean below 3000 m depth has likely warmed. Fig 3.3 Mean warming rates below 4000 m centered on SUppled areas not significant at 95%. Thick black lines - Repeat oceanographic transects used to esumate warming rates. Data from Purkey and Johnson(2010).

9 Total energy storage consistent with climate model ensemble (but significant variability between models) Upper 2000 m of ocean sampled by Argo = W m -2 Full ocean area & deep ocean = W m W m -2 incl lithosphere, cryosphere, atmosphere 9 Model results from Church et al. 2013, IPCC WGI AR5 Ch13

10 Rate of heat storage has increased, with significant storage in deep ocean Gleckler et al [2016]

11 Progress towards a deep ocean observing system need to maintain GO-SHIP and extend Argo to full depth GO-SHIP now provides observauons in the deep ocean (> 2000 m) Straw-plan for 5 x 5 degree Deep Argo float array m and m floats are currently being deployed in pilot studies

12 Global sea level and energy budgets linked Warming (cooling) of the ocean (thermal expansion/ contracuon) Change in mass of glaciers and ice sheets (BarystaUc) Changes in liquid water storage on land (BarystaUc) Fig 13.1 RelaUve sea level is also affected by ocean density and circulauon, land movement, and distribuuon of mass on the Earth

13 Sea level is conjnuing to rise at a faster rate than the average during the 20 th century 13 Time of emergence for regional sea-level change

14 The trend is not uniform globally 14 Time of emergence for regional sea-level change

15 The strong El Niño has resulted in high sea level anomalies in the eastern Pacific at the end of 2015

16 As well as thermal expansion and glacier contribujons, the Greenland and AntarcJc Ice Sheets are losing mass 16 Time of emergence for regional sea-level change Velicogna et al. 2014

17 Past climate variajons important for sea level rise prior to 1950 Anthropogenic forcing dominates a`er 1970 Slangen et al., in review

18 Conclusions Ocean heat content criucal element of keeping track of climate change and understanding the Earth s radiauon and sea level budgets. Argo allows much improved esumates of upper (< 2 km) ocean heat content - need to extend to full depth and full ocean coverage, complemented by repeat secuons. Unequivocal warming over decades EsUmates consistent with CMIP5 model esumates of ocean heat content. Sea level conunuing to rise; Strong El Niño in late 2015 resulted in higher sea levels in the eastern Pacific. ContribuUons from thermal expansion and the addiuon of mass from glaciers and ice sheets. Anthropogenic climate change dominates recent rise. Heat content and sea level are criucal measures of efficacy of miugauon. Long term commitment! 18

19 In situ data suggests reprocessed aljmeter data has smaller trend and a posijve (not significant) accelerajon (rather than a decelerajon) Watson et al. 2015

20 ObservaUon-based esumate N o created by averaging satellite and AMIP simulauons Good agreement (r=0.82) with ensemble mean of CMIP5 coupled models VariaUons dominated by volcanic erupuons (Agung 1963, El Chichon 1982 and Pinatubo 1991) Absolute values of N for different periods in reasonable agreement with CMIP5 and IPCC Smith et al. 2014

21 Improved understanding of 20 th century sea level change Observed contribuuons explain observed GMSLR Anthropogenic influence Data from Table 13.1 Figure 13.7

22 Measure ocean mass and its components significant uncertainjes remain Compare oceanic and gravitajonal esjmate of regional ocean mass change Dieng et al Purkey et al Can we back out ice sheet and land water contribuuons? (e.g. Reager et al. 2016)

23 AlJmeter and steric sea level trends 2006 to Time of emergence for regional sea-level change

24 Differences between AlJmeter and steric ( m) trends mean removed 24 Time of emergence for regional sea-level change

25 The global ocean dominates the energy budget on Jmescales > 1 year Palmer and McNeall [2014] von Schuckmann et al [2016]

26 RadiaJve forcing, climate feedbacks and storage of energy within the climate system are consistent with the likely range of climate sensijvity Box 13.1, Figure 1 IPCC AR5, Box 13.1 Fig1, Church et al. 2013