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7/29/09 

Heat in, Heat Out  Too cold 
•  If all the heat coming in went out the average 
temperature on the Earth’s surface would be 

‐19 

How? 
•  Some molecules absorb the heat coming up 
from the earth, 
•  They then reemit in in random direcFons – 
50% of it comes back. 

Some of the gases that do this are 
And it is: 
increasing – a lot! 

1

7/29/09 

So? It might make Canberra’s winter 
more bearable… 
•  But we are already seeing increases in: 
–  Floods 
–  Droughts 
–  Cyclones  Ice is melFng 
•  In some places the monsoon are failing 
•  Some diseases are more widespread 
•  Salt is intruding into groundwater 

And 

Understand the Size Understand the Scale of the Challenges
of the Challenges Satellite Image early Marc
h 2000

Measure
it 2
11,000 km

295 km
km
37

Iceberg B15 calving from The Edg
the Ross Ice Shelf e of B15
A

Go in for a closer look Iceberg Alley

2

7/29/09 

Sea levels do change 
•  During the last ice age (20,000 years ago) sea 
levels were about 120m lower. 
•  14,000 years ago sea levels rose 20m in just 
400 years as some major ice sheets melted. 

But when they wrote the report you  •  Current sea levels have been remarkably 
have been asked to read, no one  stable since about 3000 years ago  
thought this would happen  •  about the Fme humans started building things, mostly 
by the sea. 

Greenland and AntarcFca  So what might this look like: 
•  Greenland is now clearly melFng much faster  •  hZp://flood.firetree.net 
than previously thought. AntarcFca probably is 
too. 

•  Each could raise sea levels by 5m, that’s 10m 
in total. And it could happen within this 
century.  

Will Steffen @ ANU 
What we are risking at a 2 degree rise: 
says things can change in a hurry: 
…the rapid disintegraFon of the large ice sheets  •  Sea levels 
on Greenland and AntarFca or large scale and 
uncontrollable feedbacks in the carbon cycle:  •  15‐40% plant and animal species 
acFvaFon of the methane clathrates [frozen  •  Ocean acidificaFon 
water and methane] buried under sediments in 
the ocean floor, the rapid loss of methane from  •  Widespread drought and deserFficaFon  
warmer and drier tundra ecosystems, increasing  •  Increasing heatwaves 
wildfires in the boreal and tropical zones, the  •  Monsoon failure 
conversion of the Amozon rainforest to savannah, 
the release of carbon dioxide from warming  •  Glacial water supply – Asia and South America 
soils…  •  Loss of major agricultural lands 

3

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