INSIGHTS INTO THE ROLE OF THE OCEANS IN THE EARTH ENERGY BUDGET

Transcription

1 INSIGHTS INTO THE ROLE OF THE OCEANS IN THE EARTH ENERGY BUDGET Karina von Schuckmann 5TH INTERNATIONAL CONFERENCE ON REANALYSIS, NOV 2017, ROME

2 EARTH CLIMATE. A practical way to monitor climate variations at different time scales is to continually assess the transfer of energy in the Earth system.

3 EARTH ENERGY IMBALANCE (EEI) Perturbations of the equilibrium state from internal or external climate variations postive or negative Earth energy imbalance, manifested as a radiative flux imbalance at the top of the atmosphere von Schuckmann at al., 2016

4 EARTH ENERGY IMBALANCE (EEI): Climate forcing Effective radiative forcing Earth energy imbalance IPCC, 2013 EEI forcing due to: Internal climate variability (e.g. ENSO, PDO) Times-scales: months to decadal External climate forcing: Changes in solar output Milankovitch cycle Large volcanic eruptions human activities Times-scales: decadal and longer Dieng et al., 2017

5 Global warming is unequivocal and contemporary increases in the Earth Energy Imbalance are directly attributable to increases in carbon dioxide and other greenhouse gases in the atmosphere from human activities (IPCC, 2013) Earth Energy Budget from Climate feedback (climate sensitivity) Cummulative energy flow into the Earth system (ES) Balanced by warming of ES increase in outgoing radiation inferred from changes global SST IPCC, 2013

6 EARTH S ENERGY IMBALANCE: INDEPENDENT ESTIMATES Period EEI estimate Reference [W/m 2 ] ± 0.1 Cheng et al., ± 0.1 Trenberth et al., 2011; Trenberth and Fasullo, 2011; Hansen et al., 2011; Balmaseda et al., 2013b ± 0.1 Hansen et al., ± 0.1 von Schuckmann et al., ± 0.43 Loeb et al., 2012 (TOA) Trenberth et al., ± 0.15 Hansen et al., ± 0.1 Dieng et al., ± 0.1 Trenberth et al., 2016, Johnson et al., ± 0.1 von Schuckmann et al., 2017

7 EARTH S ENERGY IMBALANCE: INDEPENDENT ESTIMATES Period EEI estimate Reference [W/m 2 ] ± 0.1 Cheng et al., ± 0.1 Trenberth et al., 2011; Trenberth and Fasullo, 2011; Hansen et al., 2011; Balmaseda et al., 2013b ± 0.1 Hansen et al., ± 0.1 von Schuckmann et al., ± 0.43 Loeb et al., 2012 (TOA) Trenberth et al., ± 0.15 Hansen et al., ± 0.1 Dieng et al., ± 0.1 Trenberth et al., 2016, Johnson et al., ± 0.1 von Schuckmann et al., 2017 The absolute value of EEI represents the most fundamental metric defining the status of global climate change.

8 Determining Earth s energy imbalance: 4 different approaches Radiation at TOA Loeb et al., 2012 Ocean heat content Climate models Surface flux radiative turbulent Josey et al., 2015 IPCC, 2013

9 EARTH ENERGY IMBALANCE von Schuckmann at al., 2016

10 The Earth energy imbalance can best be estimated from changes in ocean heat content, complemented by radiation measurements from space (von Schuckmann et al., 2016, NCC) Correlation in total system energy & ocean heat content as a function of trend length Correlation Palmer and McNeal, 2014 IPCC, 2013 Trend length [month] Climate models suggest that the global ocean becomes the dominant term in the Earth s energy budget on timescales longer than about 1 year

11 Close correspondence: Rate of ocean heat content change and net flux at TOA Change in TOA net radiation and rate of global ocean heat storage from independent global climate observing systems should be in phase and of the same magnitude on annual and longer time scales (e.g. Loeb et al., 2012) Estimate of the ocean energy budget Reconstructed net flux at TOA (Allan et al., 2014) Cheng et al., 2017 All other forms of heat storage are factors of 10 smaller at that time scale (Trenberth et al., 2009; Loeb et al., 2012, Palmer and Mc Neal 2014, von Schuckmann et al., 2016).

12 The accumulation of thermal energy in the Earth system is the root cause of the various facets of observed climate change von Schuckmann at al., 2016

13 Monitoring Earth s surface temperature: A symptom of a positive EEI Global mean surface temperature (GMST) annual mean 5-year mean The picture is complicated by substantial short-term variations owing to internal climate variability within the Earth system 11-year trends with 1 year overlap GMST AMO PDO Dieng et al., 2017

14 Monitoring Earth s surface temperature: A symptom of a positive EEI Steady increase of ocean heat content No evidence that global warming has paused 2-monthly means El Niño events La Niña events Cheng et al., 2017 Tracking changes in ocean heat content is the most robust indicator for global warming monitoring

15 Methods for global Ocean Heat Content (OHC) estimates 1 DIRECT ESTIMATES 2 INDIRECT ESTIMATES 3 OCEAN REANALYSES

16 Methods for global Ocean Heat Content (OHC) estimates < In situ Altimetry 1993 onwards TOA net flux 2000 onwards Golden period Ocean mass 2002 onwards

17 OHC: Historical in situ measurements < In situ Era of historical measurements 1960 Abraham et al.,

18 Global Ocean Heat Content: Historical & Argo era Linear trend Abraham et al., 2013 Boyer et al., 2016 Differences in upper-ocean heat storage between analyses due to mapping, bias correction, baseline climatology & data quality ( Differences in interannual to decadal variability between analyses. All estimates show a multi-decadal increase in OHC in both, upper and deep ocean regions.

19 OHC: ARGO ERA Global Ocean Heat Content trend : 0.5±0.1 Wm -2 von Schuckmann and Le Traon, 2011 von Schuckmann et al., 2014

20 OHC: ARGO ERA Decadal OHC (upper 2000m) changes ( ) von Schuckmann et al. (2016) Still too large spread in different estimates!!! Coverage is not yet truly global, as Argo does not cover: the deep ocean below 2000m depth the shelf areas and marginal seas pole wards of 60 latitude the near surface layer

21 Ocean heat content estimates from reanalyses Comparison to net flux at TOA & Argo based estimates monthly mean Trenberth et al., 2016 annual mean

22 Ocean heat content estimates from reanalyses In the last decade, about 30% of the warming has occurred below 700 m, contributing significantly to an acceleration of the warming trend. Balmaseda et al., 2013 The warming below 700 m remains even when the Argo observing system is withdrawn although the trends are reduced.

23 Ocean heat content estimates from reanalyses Further evaluation under the physical budget constraint of the Earth energy imbalance Ensemble mean of 3 ORAs & 2 in situ products trend: 0.8 ± 0.2 W/m 2 von Schuckmann et al., 2017 Improved budget constraint closure when changes in the m depth are taken into account.

24 Ocean heat content estimates from reanalyses The ORA-IP intercomparison project: OHC 5-year rolling trends Ensemble mean of 15 ORAs Palmer et al., 2015

25 Ocean heat content estimates from reanalyses Constraining the Global Ocean Heat Content through assimilation of CERES derived TOA energy imbalance estimates Storto et al., 2017

26 Ocean heat content estimates from reanalyses GOHC anomaly sensitivity to reanalysis components & atmos. forcing Initial conditions In situ uncertainty SST nudging Sea ice nudging Assimilation setup Model physics uncertainty Atmospheric forcing Storto et al., 2016 Bias correction and preprocessing of in situ observations represent the most crucial component of the reanalysis, whose perturbation accounts for up to 60% of the ocean heat content anomaly variability in the pre-argo period

27 Summary - ROLE OF THE OCEANS IN THE EARTH ENERGY BUDGET The absolute value of EEI represents the most fundamental metric defining the status of global climate change, and will be more useful than using global surface temperature. EEI can best be estimated from changes in ocean heat content, complemented by radiation measurements from space. Ocean reanalyses are key for the evaluation of Earth s system regulations, but improvements need to go hand in hand with sustained and expanded global ocean and climate observing systems Progress can be best achieved with a concerted international effort.

28 CLIVAR research focus CONCEPT-HEAT: Consistency between planetary energy balance and ocean heat storage An overall goal is to bring together different climate research communities all concerned with the energy flows in the Earth s System to advance on the understanding of the uncertainties through budget constraints: Chairs: K. von Schuckmann, T. L Ecyuer Atmospheric radiation Ocean Heat Content Earth s surface fluxes Climate variability and change Data assimilation & operational services (R&D) Climate projection Global sea level Remote sensing In situ Reanalysis systems Numerical model

29 A COST Action to improve the coordination of European efforts in the evaluation of ocean syntheses: better understanding of the value and use of ocean syntheses promote the use of ocean syntheses Chairs: Aida Alvera-Azcárate (University of Liège, BE) Keith Haines (University of Reading, UK) a.alvera@ulg.ac.be Earth System Science and Environmental Management

30 THANK YOU.