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 callAre 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 LEARNINGEXPERIENCE!

CSIRO and Bureau of Met were asked:

Is this human-induced Climate Change? Or is it climate variability?

Annual Inflows to Perth Reservoirs, 1911-1998

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.

(Still to come from Aspendale)

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?

Smoothed annual anomalies for precipitation (%) over land from 1900 to 2005; other regions are dominated by variability.

Land precipitation is changing significantly over broad areas

Increases

Decreases

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.

Drought is increasing most places

Rainfall -- andtemperature

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).

1979-2003

1951-1978

1901-1950

Warm nights are increasing; cold nights decreasing

fewer more fewer more

Sea Level Rise

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)

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

Ice sheet contributions to sea level rise

Antarctic ice sheet loses mass mostly through increased glacier flowGreenland mass loss is increasingLoss: glacier discharge, melting

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

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.

Attribution• are observed

changes consistent with expected responses to forcings

inconsistent with alternative explanations

Observations

All forcing

Solar+volcanic

TS-23

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

Observations

All forcing

Solar+volcanic

TS-23

Continental warming

likely shows a significant anthropogenic contribution over the past 50 years

Observations All forcing natural forcing

SPM-4

IF EUROPE CAN DO THIS, WHY CAN’T WE?

(www.trecers.net)