Climate Change Science -- the Present

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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!
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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?
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(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.
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What has happened since 1998?
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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?
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Land precipitation is changing significantly over
broad areas
Smoothed annual anomalies for precipitation ()
over land from 1900 to 2005 other regions are
dominated by variability.
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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.
Rainfall -- and temperature
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Warm nights are increasing cold nights decreasing
?fewer more?
?fewer more?
10th (left) and 90th (right) percentiles
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).
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Sea Level Rise
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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
(still mostly from thermal expansion, but ice
loss is growing)
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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, 1961-2003
• 0.77 0.22 mm yr-1, 1991-2003

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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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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 Bindoffs slide 29) simulations.
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Observations
Attribution

• are observed changes consistent with expected
  responses to forcings
• inconsistent with alternative explanations

All forcing
Solarvolcanic
TS-23
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Observations

• Anthropogenic greenhouse gas increases very
  likely caused most of the observed warming since
  mid-20th century

All forcing
Solarvolcanic
TS-23
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Continental warming
SPM-4
likely shows a significant anthropogenic
contribution over the past 50 years
Observations All forcing natural forcing
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IF EUROPE CAN DO THIS, WHY CANT WE?
(www. trecers. net)