The document discusses how greenhouse gases trap heat in the atmosphere and raise the planet's average temperature. If all the heat entering the atmosphere escaped back into space, the average temperature would be -19°C. Greenhouse gas levels are increasing significantly and causing sea levels to rise, more extreme weather events, species loss, and other problems. Allowing temperatures to rise 2°C above pre-industrial levels risks major impacts like significantly higher sea levels from ice sheet melting, droughts, and loss of many plant and animal species. Immediate action is needed to reduce emissions to avoid potentially catastrophic climate change.

1. 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!
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2. 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
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3. 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
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