Transcript Tasmanian Royal Society

Climate Change Science -- the Present
Stuart Godfrey (retired CSIRO Oceanographer)
What is it like being a Greenhouse climate scientist?
Perth, WA river inflows -- a wake-up call
Are such trends global, and if so, why?
Sea level rise, thermal expansion and icemelt
Do models reproduce the trends we see?
GLOBAL WARMING IS A LEARNING
EXPERIENCE!
Annual Inflows to Perth Reservoirs, 1911-1998
CSIRO and Bureau of Met were asked:
Is this human-induced Climate Change? Or is it climate variability?
(Still to come from Aspendale)
3x3 panels, showing rainfall trends over Australia, from
9 climate models with Greenhouse gaes included. 7 of 9
showed a maximum drying trend in SWWA. However, all
of them showed a drying rate much slower than the observed one.
CSIRO and BoM concluded that --while it was NOT certain -Greenhouse was probably the main cause.
What has happened since 1998?
Is this global, and if so why?
How widespread is this kind of drying?
Is it due to rainfall? Or to temperature rise?
Or to increasing winds?
Land precipitation is changing significantly over broad areas
Increases
Decreases
Smoothed annual anomalies for precipitation (%) over land from
1900 to 2005; other regions are dominated by variability.
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.
Rainfall -- and
temperature
Warm nights are increasing; cold nights decreasing
1979-2003
1951-1978
1901-1950
fewer
more
fewer
10th (left) and 90th (right) percentiles
more
Frequency of occurrence of cold or warm temperatures for 202
global stations with at least 80% complete data between 1901 and
2003 for 3 time periods:
1901 to 1950 (black), 1951 to 1978 (blue) and 1979 to 2003 (red).
Sea Level Rise
Sea level is rising in 20th century
SPM-3b
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
(still mostly from “thermal expansion”, but ice loss is growing)
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
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
Mass loss of Antarctica:
• 0.14 ± 0.41 mm yr-1 SLE,
1961-2003
• 0.21 ± 0.35 mm yr-1 SLE,
1991-2003
How well do climate models simulate such trends?
Coupled climate models do well at forecasting
temperature, and fairly well at predicting winds -but they do not do well at predicting rainfall.
Experience suggests that the average of climates
simulated by many models is more “skilful” than any
single model forecast.
In the following, observed temperatures are compared to
the average of (16 +23?? -- see Bindoff’s slide 29)
simulations.
Observations
Attribution
• are observed
changes
consistent with
expected
responses to
forcings
inconsistent with
alternative
explanations
All forcing
Solar+volcanic
TS-23
Observations
• Anthropogenic
greenhouse gas
increases very
likely caused
most of the
observed
warming since
mid-20th century
All forcing
Solar+volcanic
TS-23
Continental warming
SPM-4
likely shows a
significant
anthropogenic
contribution
over the past 50
years
Observations
All forcing
natural forcing
IF EUROPE CAN DO THIS, WHY CAN’T WE?
(www.
trecers.
net)