02 October 2007WCRP Meeting Scientific gaps and vulnerabilities Observations: Oceanic Climate Change and Sea Level Nathan Bindoff ACECRC, IASOS, CSIRO MAR University of Tasmania TPAC

02 October 2007WCRP Meeting “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).” 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

02 October 2007WCRP Meeting Do we understand the observed heat content record in the oceans? Key points for : 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) has higher rates of warming (0.50 ± 0.18 W m –2 ) decadal variability, cooling since 2003 Key issue: Excessive internal variability

02 October 2007WCRP 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) 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)

02 October 2007WCRP Meeting Salinity change

02 October 2007WCRP 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 2007WCRP 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 ( )

02 October 2007WCRP 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 2007WCRP Meeting Ocean bio-geochemical changes

02 October 2007WCRP Meeting Is ocean carbon cycle changing? Depth integrated Anthropogenic Carbon Upwelling Subduction zone Deep overturning 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 2007WCRP 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 2007WCRP 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? Gaps: Can we estimate changes in ocean carbon storage? Are the changes consistent with ventilation changes?

02 October 2007WCRP 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 2007WCRP Meeting Accounting for observed sea level rise : Sea level budget not quite closed : Sea level budget is closed.

02 October 2007WCRP Meeting 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 The sea level budget

02 October 2007WCRP Meeting Has last sea-level accelerated over the last decade? Steric Sea-level 3.1 mm yr -1 Tide-gauges 1.8 mm yr -1 “It is unknown whether the higher rate in 1993–2003 is due to decadal variability or an increase in the longer term trend.” Issues: Signal is increasing Risk of more rapid change, and poor models of ice sheets Last decade means rapid analysis PMSL is slow in reporting tide data Statistical methods aren’t good enough Should resort to more representative methods

02 October 2007WCRP 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 2007WCRP 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. Recommendations: Accelerate tide gauge reporting (?) Use more ocean reanalyses (ECCO, GECCO, GODAE, ECMWF) unfold changes (eg OT, Sea Level Rise rates) Accelerate CO 2 analyses of extant data sets and related data sets Foster global analyses

02 October 2007WCRP 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 multi- disciplinary research Courtesy Stan Wilson

02 October 2007WCRP Meeting Observational Risk – potential failures RA/ERS-1 GFO On going mission SARAL Envisat Approved missionGMES mission beginning development Jason-3 Pending Jason follow-on 66°-inclination climate reference orbit High-inclination complementary orbit Jason-1 Sentinel 3 – 2-satellite series Jason-2 Cryosat-2 NASA mission pending approval SWOT HY-2BHY-2CHY-2DHY-2A Stan Wilson

02 October 2007WCRP Meeting IPCC: team effort Lead authors 11 Review editors 2 Contributing authors 52