Transcript Document

The Science of Climate Change
and its Implications
Kim M. Cobb
[email protected]
April 15, 2008
Which of the following are scientific statements?
1) Slowing global warming would hurt the economy.
2) Hurricane Katrina provides direct proof of global warming.
3) A warming of 1ºC over the next 50yrs should be avoided.
4) The Earth was warmer than today 100 million years ago.
5) Improved technology is the best way to mitigate
global warming.
Which of the following are scientific statements?
1) Slowing global warming would hurt the economy.
2) Hurricane Katrina provides direct proof of global warming.
3) A warming of 1ºC over the next 50yrs should be avoided.
4) The Earth was warmer than today 100 million years ago.
5) Improved technology is the best way to mitigate
global warming.
Average Global Temperature
0.5
Atmospheric CO2 (ppm)
0.0
Temperature (°C)
1.0
360
340
Atmospheric CO2
320
300
280
1860
1880
1900
1920
1940
1960
1980
2000
The ‘instrumental’ record of climate shows a ~1ºC warming over the last century,
doesn’t sound like much, but last Ice Age was only 5ºC cooler…
Why do 99.999% of climate scientists believe
that CO2 is warming the planet?
1. Theory predicts that increasing atmospheric CO2 should warm
the planet.
2. Geologic evidence links CO2 and temperature in the past.
3. The warming is unprecedented in the most recent centuries
(dwarfs natural variability).
4. Climate models show that rising CO2 is necessary to simulate
20th century temperature trends (solar and volcanic minor
players).
Ice core climate and CO2 records
tiny gas bubbles
in the ice trap
ancient air samples
#2
Atmospheric CO2 and temperature over
the past 650 thousand years
CO2 and temperature
are closely linked
on geologic timescales
To understand how climate has changed in
the past, we need to use records of climate
preserved in ice cores, ancient tree rings,
coral bands, and other “paleoclimatic”
sources:
key is to CALIBRATE to temperature records
#3
The “Hockey Stick”
Key Points:
error bars increase as you go back in time
natural variability accounts for <0.5ºC over the last millennium
late 20th century temperature trend is unprecedented
#4
Intergovernmental
Panel on
Climate Change
(IPCC) 2001
Consequences of Global Warming (IPCC SPM-AR4)
1)
2)
3)
4)
5)
6)
7)
8)
9)
Reduced uptake of CO2 by land and ocean in warmer climate
Rising sea levels (0.3 to 0.6m by 2100)…. at a minimum
Ocean pH will decrease by 0.14 to 0.35 (already down 0.1)
Snow cover will decrease, permafrost melt, sea ice melt
Extreme events (temperature and precipitation) will become more frequent
Tropical cyclones will become more intense
Storm tracks will move poleward
Rainfall will increase in the high latitudes, decrease in the subtropics
Meridional overturning of Atlantic ocean will decrease
The uncertain climate future
Range of CO2 scenarios:
Strict international agreements  CO2 at 600ppm by 2100
Mid-ground  850ppm by 2100
Business as usual  1550ppm by 2100
*390ppm today
280ppm 1800
Model scenarios:
20 models tell
different stories,
especially at
high CO2
Sea level rise:
IPCC says 7” to 22” by 2100,
much more if rapid ice sheet collapse occurs
most scientists would go on record for 1m rise (30 inches)
Projected precipitation change: regional view
change in yearly
average precipitation
# heavy rain days
# dry days
Diffenbaugh et al, 2005
So we should prepare for more uneven rainfall (longer dry periods
separated by intense rainfall).
IPCC says increase
in hurricane intensity
“likely” (66%)
What is a country to do?
There are only three (prudent) options:
1)use less energy
- drive less, drive smaller (plug-in?) cars
- conserve electricity
- recycle, reuse
2) make “clean” energy
- solar power, wind power, nuclear energy
3) take CO2 out of the sky (much more difficult)
…. but how much at what cost?
Scientific Summary
Strong evidence supports the idea that anthropogenic CO2 is warming the planet.
Future climate changes in a warming environment are still uncertain, although:
-sea level rise certain (but how much by when?, prepare for ~1m)
- SE precipitation will become more erratic (water resource management)
-prospect for increasing hurricane activity
A Climate Scientist’s Plea
Evaluate the scientific evidence for yourselves, from a scientific source.
Distinguish between the science of global warming and the politics/economics
of global warming.
My homepage: http://shadow.eas.gatech.edu/~kcobb