* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download IASOS - chapter 5
Media coverage of global warming wikipedia , lookup
Hotspot Ecosystem Research and Man's Impact On European Seas wikipedia , lookup
Effects of global warming on human health wikipedia , lookup
Attribution of recent climate change wikipedia , lookup
Scientific opinion on climate change wikipedia , lookup
General circulation model wikipedia , lookup
Politics of global warming wikipedia , lookup
Iron fertilization wikipedia , lookup
Climate change, industry and society wikipedia , lookup
Surveys of scientists' views on climate change wikipedia , lookup
Public opinion on global warming wikipedia , lookup
Effects of global warming on humans wikipedia , lookup
Global warming wikipedia , lookup
Ocean acidification wikipedia , lookup
Climate change and poverty wikipedia , lookup
Instrumental temperature record wikipedia , lookup
Climate change in the Arctic wikipedia , lookup
Global warming hiatus wikipedia , lookup
Global Energy and Water Cycle Experiment wikipedia , lookup
Effects of global warming wikipedia , lookup
Years of Living Dangerously wikipedia , lookup
Climate change feedback wikipedia , lookup
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 emails 18 April 2007 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).” 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 1955-2003 18 April 2007 Global heat content change: spatial pattern Linear trend 1955-2003 18 April 2007 •Warming not uniform •Equatorial Pacific cooling warming Heat content change: time evolution 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 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 (1957-2004) 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 Anthropogenic carbon Atlantic Ocean 18 April 2007 •Dissolved inorganic carbon •Chloroflourocarbons •Pre-industrial (~1750) •Estimate of added DIC •Water chemistry Ocean carbon cycle: spatial pattern Depth integrated Anthropogenic Carbon Upwelling Largest zone of carbon storage is in the Southern ocean. 18 April 2007 Deep overturning Subduction zone Ocean carbon cycle: global uptake It is more likely than not that the fraction of all the emitted CO2 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 sea level budget The main contributions to sea level: Slr = thermal exp. + (glaciers + ice-caps) + Greenland + Antarctica + ……. Focus on two periods in the report: •1961-2003 •1993-2003 18 April 2007 20th century sea level Rates of sea level rise: •1.8 ± 0.5 mm yr-1, 1961-2003 •1.7 ± 0.5 mm yr-1, 20th Century •3.1 ± 0.7 mm yr-1, 1993-2003 •Consistency of sea level data •Variability of sea level data •Are rates increasing? 18 April 2007 Thermal expansion’s contribution to sea-level The. Exp. SLR Sea-level rise 1993-2003 Thermal expansion 1993-2003 • Sea level rise is spatially non-uniform • Thermal expansion controls spatial pattern • Observed thermal expansion 1.6 ± 0.5 mm yr-1, 1993-2003 0.4 ± 0.1 mm yr-1, 1961-2003 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, 19612003 • 0.77 ± 0.22 mm yr-1, 19912003 18 April 2007 Ice sheet contributions to sea level rise Mass loss of Greenland: • 0.05 ± 0.12 mm yr-1 SLE, 1961-2003 • 0.21 ± 0.07 mm yr-1 SLE, 1991-2003 Antarctic ice sheet loses mass mostly through increased glacier flow Greenland mass loss is increasing Loss: glacier discharge, melting 18 April 2007 Mass loss of Antarctica: • 0.14 ± 0.41 mm yr-1 SLE, 1961-2003 • 0.21 ± 0.35 mm yr-1 SLE, 1991-2003 Accounting for observed sea level rise 1961-2003: Sea level budget not quite closed. 1993-2003: Sea level budget is closed. 18 April 2007 Has the sea level rise rate increased? •The 1993-2003 has high rate of rise compared with the 1961-2003 period. Tide-gauges 3.1 mm yr-1 1.8 mm yr-1 Steric Sea-level •Other periods have had sea-level rise as high as 1993-2003 •On longer term (since 19th century) sea-level rise rate has increased “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 IPCC: process 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 18 April 2007 Salinity change: vertical distribution 18 April 2007 18 April 2007 Ocean climate change: temperature 18 April 2007 Thermal expansion’s contribution to sea-level Thermal Expansion 1961-2003 •1961-2003 0.4 ± 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 Mass loss of Greenland: • -0.07 to 0.17 mm yr-1 SLE, 1961-2003 • 0.14 to 0.28 mm yr-1 SLE, 1991-2004 Greenland gains mass in the interior, but loses 18 April more at2007 the margins Greenland and Antarctic ice sheets of are shrinking Mass loss of Antarctica: • -0.28 to 0.55 mm yr-1 SLE, 1961-2003 • -0.14 to 0.55 mm yr-1 SLE, 1991-2004 Antarctic ice sheet loses mass mostly through increased glacier flow 18 April 2007 Sea Level: progress since the TAR In observations: In interpretation: •Mass balance of Antarctica •Assessed errors in observations are now smaller relative to TAR •Mass balance of Greenland •Better records of glaciers •Extended records of global sealevel to 1870’s •New records of altimeter data •Different error analysiscombined in quadrature • Errors are quoted as 90% confidence intervals compared with 95% intervals in TAR 18 April 2007 •Largest uncertainties in thermal expansion (1993-2003), Antarctica, and sea level observations •Causes of difference between sea level and its contributions in long term records (1961-2003) is unresolved - either the observations or un-quantified processes. •Climate contributions to sea level can explain the observations in the short term (1993-2003) Sea-level rise 18 April 2007 Sea-level rise: 18 April 2007 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 18 April 2007 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, 19612003 • 0.77 ± 0.22 mm yr-1, 19912003 18 April 2007 Ice sheet contributions to sea level rise Mass loss of Greenland: • 0.05 ± 0.12 mm yr-1 SLE, 1961-2003 • 0.21 ± 0.07 mm yr-1 SLE, 1991-2003 Antarctic ice sheet loses mass mostly through increased glacier flow Greenland mass loss is increasing Loss: glacier discharge, melting 18 April 2007 Mass loss of Antarctica: • 0.14 ± 0.41 mm yr-1 SLE, 1961-2003 • 0.21 ± 0.35 mm yr-1 SLE, 1991-2003 Accounting for observed sea level rise 1961-2003: Sea level budget not quite closed. 1993-2003: Sea level budget is closed. 18 April 2007