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Scientific gaps and vulnerabilities Observations: Oceanic Climate Change and Sea Level Nathan Bindoff ACECRC, IASOS, CSIRO MAR University of Tasmania TPAC 02 October 2007 WCRP Meeting Observations: Oceanic climate change and sea level • Global scale temperature and salinity change • Regional scale ocean changes • Ocean bio-geochemical change (ocean carbon cycle) • Changes in sea level • Synthesis “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level (see Figure SPM-3).” 02 October 2007 WCRP Meeting Do we understand the observed heat content record in the oceans? Key points for 19612003: •consistency of products • oceans absorbed 0.21 ± 0.04 W m–2 (0-3000m) over the earth’s surface. •70% of this energy is absorbed in top 700 m •0.1°C warming (0-700m) •1993-2003 has higher rates of warming (0.50 ± 0.18 W m–2) •decadal variability, cooling since 2003 Key issue: •Excessive internal variability 02 October 2007 WCRP Meeting Do we understand the heat content record? • Issues – Spatial sampling (eg Southern Ocean) • Sub-sampling experiments (Achatao et al, 2005 ) – Instrumental biases • Gouretski and Koltermann (2006), others – Robustness – more global analyses needed with closure – Capturing the deep ocean change (below ~2000m) 02 October 2007 Gaps: • Can we close the earth energy budget? (some papers) • How does heat penetrate the ocean? • Is heat uptake slowing? • Has the ocean stratified more? • How does this affect ocean renewal (ventilation) WCRP Meeting Salinity change 02 October 2007 WCRP Meeting Ocean climate change: salinity • Why important – P-E estimates – Air-ocean exchanges – Combine with terrestrial networks – Potential for increased ice sheet melt Issues and science gaps are same for heat content 02 October 2007 WCRP Meeting Observed change in overturning circulation? “…we assess that over that over the modern instrumental record no coherent evidence for a trend in the mean strength of the [Atlantic] MOC has been found.” Based on: •1970’s to 1990’s MOC increased by 10% (SST and models) •1970’s to 1995 convection strong in Labrador sea (increased MOC) but convection now weak ( decrease in MOC) •Denmark overflow mean strength unchanged (record to short) •Atlantic subpolar gyre (from direct measurements) unchanged in strength •Hydrographic data at 25°N show a 30% decrease (1957-2004) 02 October 2007 WCRP Meeting Observed change in overturning circulation? • Issues – Difficult to observe. – Need data + models (eg reanalyses of available data with models). – Southern Hemisphere OT changes Illustrates the power of assimilation to monitor the MOC. 02 October 2007 WCRP Meeting Ocean bio-geochemical changes 02 October 2007 WCRP Meeting Is ocean carbon cycle changing? Depth integrated Anthropogenic Carbon Upwelling Deep overturning Subduction zone It is more likely than not that the fraction of all the emitted CO2 that was taken up by the oceans has decreased….. 02 October 2007 WCRP Meeting Is Ocean ventilation changing? •There is evidence for decreased oxygen concentrations, likely to be driven by reduced rates of water renewal in most ocean basins from the early 1970’s to the late 1990’s. 02 October 2007 WCRP Meeting Is ocean carbon cycle changing? • Issues – Robustness – more global analyses needed with closure – Is the ~10 year sampling timely enough given the increasing urgency, and increasing signal? – Can we analyse the data faster enough? 02 October 2007 Gaps: • Can we estimate changes in ocean carbon storage? • Are the changes consistent with ventilation changes? WCRP Meeting Can we close the sea level rise budget? Has the last decade of sea-level rise accelerated? Are sea-level extremes changing? 02 October 2007 WCRP Meeting Accounting for observed sea level rise 1961-2003: Sea level budget not quite closed. 1993-2003: Sea level budget is closed. 02 October 2007 WCRP Meeting The sea level budget The main contributions to sea level: Slr = thermal exp. + (glaciers + ice-caps) + Greenland + Antarctica + Terrestrial +……. The solutions for hydrology (recommendation) • re-invigorate terrestrial analysis on basis • use multiple analyses (GCM’s), GRACE •Must be complete (P-E, runoff, hydrology) Other terms are “in hand”, ie confident of analysis 02 October 2007 WCRP Meeting Has last sea-level accelerated over the last decade? Issues: •Signal is increasing •Risk of more rapid Tide-gauges change, and poor models of ice sheets 3.1 mm yr-1 Last decade means rapid 1.8 mm yr-1 analysis •PMSL is slow in reporting tide data •Statistical methods aren’t good enough Steric Sea-level •Should resort to more representative “It is unknown whether the higher rate in 1993–2003 is due to decadal variability or an increase in the longer termmethods trend.” 02 October 2007 WCRP Meeting Are sea-level extremes changing? Global analysis of records: • changes in extremes in tide gauges (1 global study in AR4, many individual studies) • Examine impacts of observed wind changes and intensity • Global maps of changes in return periods 02 October 2007 WCRP Meeting General gaps and recommendations Science Gaps or needs: • Response time has to decrease… interested in differences on shorter time scales. • Greater skill at separating natural variations from climate induced variations. • Insufficient global analyses, too many regional analyses, with mixed messages. 02 October 2007 Recommendations: • Accelerate tide gauge reporting (?) • Use more ocean reanalyses (ECCO, GECCO, GODAE, ECMWF) unfold changes (eg OT, Sea Level Rise rates) • Accelerate CO2 analyses of extant data sets and related data sets • Foster global analyses WCRP Meeting Three underlying issues for ocean observations 1. Sustained observations (big risks) - Transitioning a research endeavor into a sustained, operational capability - Insitu programs (ARGO, SOO, etc) 2. Timely data access – How to ensure timely access to data so that all may derive benefit 3. The non-specialist needs….this is multidisciplinary research 02 October 2007 Courtesy Stan WCRPWilson Meeting Observational Risk – potential failures 91 05 92 06 93 07 94 08 95 09 96 10 97 11 98 12 99 13 00 14 01 15 02 16 03 17 04 18 05 19 66°-inclination climate reference orbit Jason-3 Jason-1 SWOT RA/ERS-1 Jason-2 High-inclination complementary orbit Envisat SARAL GFO Sentinel 3 – 2-satellite series Cryosat-2 HY-2A HY-2B HY-2C On going mission Approved mission GMES mission beginning development Pending Jason follow-on NASA mission pending approval 02 October 2007 Stan Wilson WCRP Meeting HY-2D IPCC: team effort •Lead authors 11 •Review editors 2 •Contributing authors 52 02 October 2007 WCRP Meeting