18 April 2007 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

18 April 2007 IPCC: team effort Chapter 5 Team Lead authors 11 Review editors 2 Contributing authors 52 Four reviews ~2000 comments Every comment has a response ~6000 s

18 April 2007 “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

18 April 2007 Vertical overturning ocean circulation Blue: Antarctic Green: North Atlantic Red : Southern Ocean Schmitz 1996

18 April 2007 Heat content change: vertical distribution Linear trend

18 April 2007 Global heat content change: spatial pattern Linear trend Warming not uniform Equatorial Pacific cooling warming

18 April 2007 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

18 April 2007 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

18 April 2007 Salinity change

18 April 2007 Ocean climate change: salinity Atlantic Ocean Pacific Ocean

18 April 2007 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.

18 April 2007 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 ( )

18 April 2007 Ocean bio-geochemical changes

18 April 2007 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

18 April 2007 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

18 April 2007 Ocean carbon cycle: spatial pattern Depth integrated Anthropogenic Carbon Upwelling Subduction zone Deep overturning Largest zone of carbon storage is in the Southern ocean.

18 April 2007 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

18 April 2007 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.

18 April 2007 Global oxygen decreases

18 April 2007 Sea-level rise observations

18 April 2007 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

18 April th 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?

18 April 2007 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.

18 April 2007 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,

18 April 2007 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,

18 April 2007 Accounting for observed sea level rise : Sea level budget not quite closed : Sea level budget is closed.

18 April 2007 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.”

18 April 2007 Ocean climate change and sea level

18 April 2007 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.

18 April 2007 Synthesis

18 April 2007 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

18 April 2007 Salinity change: vertical distribution

18 April 2007

Ocean climate change: temperature

18 April 2007 Thermal expansion’s contribution to sea-level Thermal Expansion ± 0.1 mm yr -1

18 April 2007 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,

18 April 2007 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,

18 April 2007 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 ( )

18 April 2007 Sea-level rise

18 April 2007 Sea-level rise:

18 April 2007

Sea-level rise: at islands

18 April 2007 Steric sea-level rise:

18 April 2007 Sea-level rise: ENSO

18 April 2007

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,

18 April 2007 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,

18 April 2007 Accounting for observed sea level rise : Sea level budget not quite closed : Sea level budget is closed.