Evidence for climate Change The Working Group I Report of the Intergovernmental Panel on Climate Cha

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Evidence for climate ChangeThe 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

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Projected impacts of climate change
Why the concern about climate change?
Global temperature change (relative to
pre-industrial)
1C
2C
5C
4C
3C
0C
Food
Falling crop yields in many areas, particularly
developing regions
Falling yields in many developed regions
Possible rising yields in some high latitude
regions
Water
Significant decreases in water availability in
many areas, including Mediterranean and Southern
Africa
Small mountain glaciers disappear water
supplies threatened in several areas
Sea level rise threatens major cities
Ecosystems
Extensive Damage to Coral Reefs
Rising number of species face extinction
Extreme Weather Events
Rising intensity of storms, forest fires,
droughts, flooding and heat waves
Risk of Abrupt and Major Irreversible Changes
Increasing risk of dangerous feedbacks and
abrupt, large-scale shifts in the climate system
Stern report (2006)
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Changing Atmosphere
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Radiative change 1750-2005

• Role of aerosols

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Global mean temperatures are rising faster with
time
SPM-3a
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Sea level is rising in 20th century

• 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

SPM-3b
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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.

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Climate models, essential to hypothesis testing
Observations 1980-2000
Mean Model 1980-2000
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Attribution to man
All forcing GHG Aerosols solar volcanic

• What is attribution?
• Anthropogenic greenhouse gas increases very
  likely caused most of the observed warming since
  mid-20th century
• extremely unlikely due to natural variation

Observations
Solar volcanic
TS-23
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Continental warming
SPM-4
Observations All forcing natural forcing

• likely shows a significant anthropogenic
  contribution over the past 50 years

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

• 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, 10.28
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Projections of Future Changes in Climate
Figure SPM-6, TS-30, 10.9

• Precipitation increases are very likely in high
  latitudes in 2090-2099
• Decreases are likely in most subtropical land
  regions in 2090-2099

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Scenarios for sea-ice
North. Hem. Summer
South. Hem. Winter
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Future Climate Greenland Ice Sheets
1900
3660
2170
2610
3030
1.4m
Ice Sheets a key risk for future climate
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Projections of Future Climate Ice Sheets
Post 2100 changes, Greenland

• ..and that the surface mass balance becomes
  negative at a global average warming (relative to
  1961-1990) in excess of 1.2 to 3.9C. 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 19801999).
• 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)

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Scenarios for Extremes- frost, heat waves, growth
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The IPCC WGI Headlines

• 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)

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Causes for optimism

• 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

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

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

High
Low
Medium
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Scenarios for sea-ice
1980-2000
2080-2100
Arctic Summer
Antarctic Winter
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Ch. 10, Fig. 10.15
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 21st century.
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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
• Mass loss of Antarctica
• 0.14 0.41 mm yr-1 SLE, 1961-2003
• 0.21 0.35 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
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A paleoclimate perspective
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
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Drought is increasing most places
The most important spatial pattern (top) of the
monthly Palmer Drought Severity Index (PDSI) for
1900 to 2002. The time series (below) accounts
for most of the trend in PDSI.
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Example from South West Australia
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Tasmania Water Catchment Models
AWBM
Assumption no change in land use
Assumption no change in land use
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Example Hydro Tasmania Inflow Prediction
Most important lake

• Factor of 1.0 represents no change in inflows
• Factors lt1.0 represents drying
• Factors gt1.0 represents wetter
• Great Lake factors well below 1.0 and thus drying
  predicted
• Others have drier Summers/Autumns and wetter
  Winters