01 March 2007Royal Society Meeting Climate Change 2007: The Physical Science Basis Chapter 5:Observations: Oceanic Climate Change and Sea Level The Working Group I Report of the Intergovernmental Panel on Climate Change Fourth Assessment Report Nathan Bindoff and lead authors ACECRC, IASOS, CSIRO MAR University of Tasmania TPAC

01 March 2007Royal Society Meeting IPCC: team effort Lead authors 11 Review editors 2 Contributing authors 52

01 March 2007Royal Society 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

01 March 2007Royal Society Meeting Vertical overturning ocean circulation Blue: Antarctic Green: North Atlantic Red : Southern Ocean Schmitz 1996

01 March 2007Royal Society Meeting Heat content change: vertical distribution Linear trend

01 March 2007Royal Society Meeting Global heat content change: spatial pattern Linear trend Warming not uniform Equatorial Pacific cooling warming

01 March 2007Royal Society Meeting Heat content change: time evolution 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

01 March 2007Royal Society Meeting Earth’s overall energy balance Key points: > 80% of energy change is stored in the oceans ice sheets, glaciers and ice caps about 1% energy ice sheets, glaciers and ice caps about 40% sea level

01 March 2007Royal Society Meeting Salinity change

01 March 2007Royal Society Meeting Ocean climate change: salinity Atlantic Ocean Pacific Ocean

01 March 2007Royal Society Meeting Ocean climate change: salinity Summary of salinity changes Large-scale, coherent trends of salinity are observed for 1955– 1998 –global freshening in subpolar latitudes –increasing salinity in shallower parts of the tropics and subtropics. Freshening is pronounced in the Pacific while increasing salinities prevail over most of Atlantic and Indian Oceans. Relevant to the atmosphere and climate These trends are consistent with changes in precipitation and inferred larger water transport in the atmosphere from low latitudes to high latitudes and from the Atlantic to the Pacific.

01 March 2007Royal Society 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 ( )

01 March 2007Royal Society Meeting Ocean bio-geochemical changes

01 March 2007Royal Society Meeting Ocean carbon cycle: surface pCO2, pH Increased pC02 implies decreased pH pH decreasing at a rate of 0.02 pH units per decade. 20 years

01 March 2007Royal Society Meeting Ocean carbon cycle: vertical distribution Pacific and Indian Ocean Atlantic Ocean Anthropogenic carbon Dissolved inorganic carbon Chloroflourocarbons Pre-industrial (~1750) Estimate of added DIC Water chemistry

01 March 2007Royal Society Meeting Ocean carbon cycle: spatial pattern Depth integrated Anthropogenic Carbon Upwelling Subduction zone Deep overturning Largest zone of carbon storage is in the Southern ocean.

01 March 2007Royal Society Meeting Ocean carbon cycle: global uptake It is more likely than not that the fraction of all the emitted CO 2 that was taken up by the oceans has decreased….. Implying reduced rates of renewal of key ocean water masses

01 March 2007Royal Society Meeting Oxygen changes: North Pacific Ocean 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.

01 March 2007Royal Society Meeting Sea-level rise observations

01 March 2007Royal Society Meeting The main contributions to sea level: Slr = thermal exp. + (glaciers + ice-caps) + Greenland + Antarctica + ……. Focus on two periods in the report: The sea level budget

01 March 2007Royal Society Meeting 20th century sea level Rates of sea level rise: 1.8 ± 0.5 mm yr -1, ± 0.5 mm yr-1, 20 th Century 3.1 ± 0.7 mm yr -1, Consistency of sea level data Variability of sea level data Are rates increasing?

01 March 2007Royal Society Meeting Thermal expansion’s contribution to sea-level Sea-level rise Thermal expansion Sea level rise is spatially non-uniform Thermal expansion controls spatial pattern Observed thermal expansion 1.6 ± 0.5 mm yr -1, ± 0.1 mm yr -1, SLRThe. Exp.

01 March 2007Royal Society Meeting Glacier contribution to sea-level since 1961 Increased glacier retreat since the early nineties Mass loss from glaciers and ice caps: 0.5 ± 0.18 mm yr -1, ± 0.22 mm yr -1,

01 March 2007Royal Society Meeting Ice sheet contributions to sea level rise Antarctic ice sheet loses mass mostly through increased glacier flow Greenland mass loss is increasing Loss: glacier discharge, melting Mass loss of Greenland: 0.05 ± 0.12 mm yr -1 SLE, ± 0.07 mm yr -1 SLE, Mass loss of Antarctica: 0.14 ± 0.41 mm yr -1 SLE, ± 0.35 mm yr -1 SLE,

01 March 2007Royal Society Meeting Accounting for observed sea level rise : Sea level budget not quite closed : Sea level budget is closed.

01 March 2007Royal Society Meeting Ocean climate change and sea level

01 March 2007Royal Society Meeting Synthesis The patterns of observed changes in global ocean heat content and salinity, sea-level, thermal expansion, water mass evolution and bio-geochemical parameters described in this chapter are broadly consistent with the observed ocean surface changes and the known characteristics of the large-scale ocean circulation.

01 March 2007Royal Society Meeting The has high rate of rise compared with the period. Other periods have had sea-level rise as high as On longer term (since 19 th century) sea-level rise rate has increased Has the sea level rise rate increased? 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.”

01 March 2007Royal Society Meeting Synthesis

01 March 2007Royal Society Meeting The IPCC is a “remarkable example” of mobilizing expert analysis to inform policymakers Jeffrey Sachs (Nature, 12 August 2004) The IPCC assessments are “dull as dishwater” Tim Flannery, The Weather Makers IPCC: process

01 March 2007Royal Society Meeting Salinity change: vertical distribution

01 March 2007Royal Society Meeting

01 March 2007Royal Society Meeting Ocean climate change: temperature

01 March 2007Royal Society Meeting Thermal expansion’s contribution to sea-level Thermal Expansion ± 0.1 mm yr -1

01 March 2007Royal Society Meeting Greenland and Antarctic ice sheets of are shrinking Greenland mass loss is increasing Loss: glacier discharge, melting Greenland gains mass in the interior, but loses more at the margins Mass loss of Greenland: to 0.17 mm yr -1 SLE, to 0.28 mm yr -1 SLE,

01 March 2007Royal Society Meeting Greenland and Antarctic ice sheets of are shrinking Antarctic ice sheet loses mass mostly through increased glacier flow Mass loss of Antarctica: to 0.55 mm yr -1 SLE, to 0.55 mm yr -1 SLE,

01 March 2007Royal Society Meeting Sea Level: progress since the TAR In observations: Mass balance of Antarctica Mass balance of Greenland Better records of glaciers Extended records of global sea- level to 1870’s New records of altimeter data Different error analysis- combined in quadrature Errors are quoted as 90% confidence intervals compared with 95% intervals in TAR In interpretation: Assessed errors in observations are now smaller relative to TAR Largest uncertainties in thermal expansion ( ), Antarctica, and sea level observations Causes of difference between sea level and its contributions in long term records ( ) is unresolved - either the observations or un-quantified processes. Climate contributions to sea level can explain the observations in the short term ( )

01 March 2007Royal Society Meeting Sea-level rise

01 March 2007Royal Society Meeting Sea-level rise:

01 March 2007Royal Society Meeting

01 March 2007Royal Society Meeting Sea-level rise: at islands

01 March 2007Royal Society Meeting Steric sea-level rise:

01 March 2007Royal Society Meeting Sea-level rise: ENSO

01 March 2007Royal Society Meeting

01 March 2007Royal Society Meeting

01 March 2007Royal Society Meeting Glacier contribution to sea-level since 1961 Increased glacier retreat since the early nineties Mass loss from glaciers and ice caps: 0.5 ± 0.18 mm yr -1, ± 0.22 mm yr -1,

01 March 2007Royal Society Meeting Ice sheet contributions to sea level rise Antarctic ice sheet loses mass mostly through increased glacier flow Greenland mass loss is increasing Loss: glacier discharge, melting Mass loss of Greenland: 0.05 ± 0.12 mm yr -1 SLE, ± 0.07 mm yr -1 SLE, Mass loss of Antarctica: 0.14 ± 0.41 mm yr -1 SLE, ± 0.35 mm yr -1 SLE,

01 March 2007Royal Society Meeting Accounting for observed sea level rise : Sea level budget not quite closed : Sea level budget is closed.