Burning Off Australia

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Randolf Wilfrid Rodgers
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1 Burning Off Australia Climate Change in Aboriginal Australia by Carl Drews May 4, 2007 ATOC : Human Impacts on Weather and Climate University of Colorado at Boulder Dr. Roger Pielke Senior, Instructor

Australia from Indonesia about 45,000 years ago. 2.

and burned off the entire continent within a short

This change in vegetation altered the climate of

2 Hypothesis 1. The Aboriginal people arrived in a forested Australia from Indonesia about 45,000 years ago. 2. The Aborigines used fire as a hunting technique, and burned off the entire continent within a short period of time. 3. This change in vegetation altered the climate of Australia, transforming it from a forested continent into the arid landscape we see today.

3 Testing the Hypothesis There should be a stable forested state of the Australian climate. The pre-human Australian forest should maintain itself through increased precipitation. At the very least, a pre-human forested version of the continent should produce more precipitation than the current un-forested version. How much more rainfall? Run a climate model to find out...

4 CAM Community Atmosphere Model National Center for Atmospheric Research Community Land Model (CLM) Run parameters: Resolution: 32 latitude x 64 longitude divisions x degrees 10 simulated years Special thanks to Chuck Bardeen and Jason English of ATOC for help with CAM!

5 What did the Aborigines do? 1. Burned all the trees: Land Use Change. 2. Released a huge cloud of carbon dioxide and soot: Anthropogenic CO2. This scenario roughly corresponds to what humans are doing now. Can the Australian event serve as an analog to the present day? Can we separate the effects of elevated CO2 and land use change?

6 Three Cases to Run Prehuman: forested, CO2 at 355 ppm. Co2puff: forested + elevated CO2. Today: no forest, CO2 at 355 ppm. Calculate changes in precipitation and surface temperature. CO2 effect = co2puff prehuman. Land use effect = today - prehuman.

7 How Much CO2? Dr. JB Friday, University of Hawaii at Manoa (high school classmate): "So you could start with estimates of 100 to 200 t/ha biomass and combust 60% to 80% of that." Pilot Analysis of Global Ecosystems: Grassland Ecosystems", report by Robin P. White, Siobhan Murray, and Mark Rohweder, "Here again, carbon storage potential appears highest in the tropical and boreal forests (with carbon storage values ranging from metric tons per hectare), (Map 22)." (page 50).

8 Biomass Burning White et al. publish Table 18 on page 52: Global Estimates of Annual Amounts of Biomass Burning : Source Quantity burned (Tg/yr) Carbon released (Tg/yr) Tropical forests Temperate forests These numbers tell us the fraction of combusted biomass that ends up as atmospheric carbon (about 45%).

9 CO2 Released Use: 120 metric tons of CO2 released per hectare of Australian forest burned. Carbon dioxide release = 3.41 metric gigatons Annually, for a period of 100 years. Total atmospheric CO2 = 3 metric teratons. Assume no uptake; CO2 levels will increase by 11.38% at the end of 100 years. Set CO2VMR = 395 ppm. Default value is 355 ppm.

10 Current Vegetation

11 Pre-human Vegetation

12 Vegetation Codes PFT = Plant Functional Type in CAM Change PFT codes within Australian landmass to: North of Tropic of Capricorn: 3 broadleaf_evergreen_tropical_tree South of Tropic of Capricorn: 6 broadleaf_deciduous_temperate_tree

13 Run the CAM model... 5 calendar days to simulate 10 climate years. Dell Optiplex GX 280 Linux workstation.

14 Prehuman World Temperature

15 Prehuman World Precipitation Graphics by Unidata's Integrated Data Viewer (IDV).

16 Prehuman Australian Precipitation

17 Co2puff Anomalies Change from 'prehuman' case to 'co2puff' case. Effects of carbon dioxide alone. Recall CO2 increased from 355 ppm to 395 ppm. The global circulation patterns did not change, but some contours are slightly shifted. Precipitation changed more than temperature. Largest temp changes in Antarctica.

18 Co2puff: World Temp Change

19 Co2puff: Australian Temp Change

20 Co2puff: World Precipitation Change

21 Co2puff: Australian Precip Change

22 Land Use Anomalies Forests burnt, replaced by arid landscape. Effects of land use change alone. Teleconnections are big! Indonesia especially affected. Antarctica is also sensitive.

23 Land Use: World Temp Change

24 Land Use: Australian Temp Change

25 Land Use: World Precip Change

26 Land Use: Australian Precip Change

27 Hypothesis? The Aborigines didn't do it! Australia is in an arid latitude. See South America and South Africa. Forest burning may have caused some drying and permanent loss of forested area around the edges of the continent. But the interior is naturally arid. If you planted trees throughout Australia, most of them would die from lack of water. Ancient forested Australia had other causes.

28 Conclusions Australia really affects Antarctica! Shifts the Rossby waves in the polar vortex? Precipitation changes were greater than temperature changes. And more complex over the whole globe. Land use changes were generally larger than CO2 changes. As much as 40% greater delta precipitation. Dry out Australia, soak Indonesia.

Ecosystems on land are grouped into biomes primarily based on the plant communities within them.

Section 2: Ecosystems on land are grouped into biomes primarily based on the plant communities within them. K What I Know W What I Want to Find Out L What I Learned Essential Questions How is latitude