Evidence for climate Change The Working Group I Report of the Intergovernmental Panel on Climate Change Fourth Assessment Report Nathan Bindoff and others ACECRC, IASOS, CSIRO MAR University of Tasmania TPAC Royal Society of Tasmania

Projected impacts of climate change 1°C2°C5°C4°C3°C Sea level rise threatens major cities Falling crop yields in many areas, particularly developing regions Food Water Ecosystems Risk of Abrupt and Major Irreversible Changes Global temperature change (relative to pre-industrial) 0°C Falling yields in many developed regions Rising number of species face extinction Increasing risk of dangerous feedbacks and abrupt, large-scale shifts in the climate system Significant decreases in water availability in many areas, including Mediterranean and Southern Africa Small mountain glaciers disappear – water supplies threatened in several areas Extensive Damage to Coral Reefs Extreme Weather Events Rising intensity of storms, forest fires, droughts, flooding and heat waves Possible rising yields in some high latitude regions Stern report (2006) Why the concern about climate change?

Changing Atmosphere

Radiative change Role of aerosols

Global mean temperatures are rising faster with time Warmest 12 years: 1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999,1990,2000 SPM-3a

Sea level is rising in 20 th century Rates of sea level rise: mm yr -1, mm yr-1, 20 th Century mm yr -1, SPM-3b

Other evidence from observations Oceans have warmed Oceans becoming more acidic Patterns of rainfall/evaporation are changing Evidence over both land and oceans Droughts are more frequent Extremes events are changing More warm nights More storm surges Strengthening westerlies Reduced snow, shrinking Arctic Sea-Ice Melting Glaciers, melting Greenland ice sheet, mass loss from Antarctica “……evidence for climate change is unequivocal….”

Climate models, essential to hypothesis testing Observations Mean Model

What is attribution? Anthropogenic greenhouse gas increases very likely caused most of the observed warming since mid-20 th century extremely unlikely due to natural variation Observations Solar + volcanic TS-23 Attribution to man All forcing = GHG + Aerosols + solar + volcanic

Continental warming likely shows a significant anthropogenic contribution over the past 50 years Observations All forcingnatural forcing SPM-4

Scenarios of future change

Projections of Future Changes in Climate Best estimate for low scenario (B1) is 1.8°C (likely range is 1.1°C to 2.9°C), and for high scenario (A1FI) is 4.0°C (likely range is 2.4°C to 6.4°C). Broadly consistent with span quoted for SRES in TAR, but not directly comparable

Spatial patterns: greater warming over land, greater warming at high latitudes Albedo changes in high latitudes, less snow and sea-ice. Figure SPM-5, TS-28, 10.8, Projections of Future Changes in Climate High Emissions Low Emissions

Precipitation increases are very likely in high latitudes in Decreases are likely in most subtropical land regions in Figure SPM-6, TS-30, 10.9 Projections of Future Changes in Climate

Scenarios for sea-ice North. Hem. Summer South. Hem. Winter

Future Climate: Greenland Ice Sheets =1.4m Ice Sheets: a key risk for future climate

Post 2100 changes, Greenland: “…..and that the surface mass balance becomes negative at a global average warming (relative to ) in excess of 1.2 to 3.9°C. If a negative surface mass balance were sustained for millennia, that would lead to virtually complete elimination of the Greenland ice sheet and a resulting contribution to sea level rise of about 7 m.” Almost all marker scenarios exceed 1.2 to 3.9 °C tipping points. “.. If radiative forcing were to be stabilized in 2100 at A1B levels11, thermal expansion alone would lead to 0.3 to 0.8 m of sea level rise by 2300 (relative to 1980–1999). “ Implication, while not stated, is that there will be large sea level changes beyond 2100 (eg by 2300 something like 1.5 to 3.5m) Projections of Future Climate: Ice Sheets

Scenarios for Extremes- frost, heat waves, growth

“The balance of evidence suggests a discernible human influence on global climate.” (SAR, 1995) “There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.” (TAR, 2001) “ Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. ” (AR4, 2007) “Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns.” (AR4, 2007) The IPCC WGI “Headlines”

Past successes –Montreal Protocol (1988) –Pollution controls for Sulphur emissions (acid rain) There are alternatives –Problem is the number of choices and which is best? Important to act sooner than later –Already locking in future change –Harder to mitigate or adapt to dangerous change –Important to act gradually –Its cheap Causes for optimism

Global mean temperatures compared with past (NH) Very likely that last 50 years was warmer than any period in last 500 years

Emission Scenarios High – fossil fuel intensive future Low – greater alternative energy sources Mix of economics, technology change. Do not include mitigation Aerosols HighLowMedium

Scenarios for sea-ice Antarctic Winter Arctic Summer

Very likely that the Atlantic meridional overturning circulation (MOC) will slow down over the course of the 21st century. Very unlikely that the MOC will undergo a large abrupt transition during the 21st century. Longer-term changes in the MOC cannot be assessed with confidence Studies with additional fresh water from melting of the Greenland Ice Sheet suggest that this will not lead to a complete MOC shutdown in the 21 st century. Ch. 10, Fig

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,

125,000 years ago, higher Arctic temperatures likely resulted in sea level 4-6m above present - contributions may have come from both Arctic Ice Fields (especially Greenland) and Antarctica Simulated and observed Arctic warming at 125,000 yr B.P. Estimated reduction in Greenland Ice Sheet Area and Thickness A paleoclimate perspective

The most important spatial pattern (top) of the monthly Palmer Drought Severity Index (PDSI) for 1900 to The time series (below) accounts for most of the trend in PDSI. Drought is increasing most places

Example from South West Australia

AWBM Assumption: no change in land use Tasmania Water Catchment Models

 Factor of 1.0 represents no change in inflows  Factors <1.0 represents drying  Factors >1.0 represents wetter  Great Lake factors well below 1.0 and thus drying predicted  Others have drier Summers/Autumns and wetter Winters Example: Hydro Tasmania Inflow Prediction Most important lake