Title: Global Warming: Earth evolution or man made? The case for being man made.
1Global Warming Earth evolution or man made?
The case for being man made.
- Nathan Bindoff
- ACECRC, IASOS, CSIRO MAR
- University of Tasmania
- TPAC
2Projected 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)
3Changing Atmosphere
4Radiative change 1750-2005
5Global mean temperatures are rising faster with
time
SPM-3a
6Global mean temperatures compared with past (NH)
Very likely that last 50 years was warmer than
any period in last 500 years
7Sea 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
8Other 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.
9Climate models, essential to hypothesis testing
Observations 1980-2000
Mean Model 1980-2000
10Attribution 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
11Continental warming
SPM-4
Observations All forcing natural forcing
- likely shows a significant anthropogenic
contribution over the past 50 years
12Summary for the affirmative case
- Affirmative case has shown
- many strands of evidence for climate change over
a broad range of variables, that are consistent
with conceptual/qualitative models of climate
change - that known man induced changes in atmosphere are
very likely to explain global and continental
surface temperature records for the last century - it is extremely unlikely that solar variations
can explain global mean observations - The above results are quantitative, formally
rigorous, and robust, combining both observations
and physical models - There are many more formal attribution and
detection studies for other climate variables
(precipitation, ocean warming) that support the
above case.
13A 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
14Projections 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
15I am not the only one, 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)
16Emission Scenarios
- High fossil fuel intensive future
- Low greater alternative energy sources
- Mix of economics, technology change.
- Do not include mitigation
- Aerosols
High
Low
Medium
17Role of volcanoes on radiative forcing
18Projections 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
19Projections 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
20Scenarios for sea-ice
North. Hem. Summer
South. Hem. Winter
21Scenarios for sea-ice
1980-2000
2080-2100
Arctic Summer
Antarctic Winter
22Other observed changes in the climate system
23Future Climate Greenland Ice Sheets
1900
3660
2170
2610
3030
1.4m
Ice Sheets a key risk for future climate
24Projections 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)
25Scenarios for Extremes- frost, heat waves, growth
26Causes for optimism
- Past successes
- Montreal Protocol (1987,1989)
- 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
27Global atmospheric CO2 budget Pep Canadell,
Corinne LeQuere, Mike Raupach, Gregg Marland,
Skee Houghton, Tom Conway, Philippe Ciais
Atmospheric accumulation FFoss FLUC
FLandAir FOceanAir
28Projections of Future Changes in Climate
29The 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
30The structure of the IPCC for the Fourth
Assessment Report
Co-chairs Susan Solomon, USA Dahe Qin, China
31Ch. 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.
32Glacier 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, 1961-2003
- 0.77 0.22 mm yr-1, 1991-2003
33Ice 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
34Attribution
All forcing GHG Aerosols solar volcanic
- are observed changes consistent with expected
responses to forcings - inconsistent with alternative explanations
Observations
Solarvolcanic
TS-23
35Climate models, and climate model credibility
Observations 1980-2000
Mean Model 1980-2000
36Heat content change time evolution
- Key points for 1961-2003
- consistency of products
- oceans absorbed 0.21 0.04 W m2 (0-3000m) over
the earths surface. - 70 of this energy is absorbed in top 700 m
- 0.1C warming (0-700m)
- 1993-2003 has higher rates of warming (0.50
0.18 W m2) - decadal variability, cooling since 2003