1. Chapter 14: Climate Change
The earth’s changing climate
Possible causes of climatic change
Global warming

2. The Earth’s Changing Climate
18,000 years ago
The earth’s climate is
always changing
20,000 years ago the
sea level was so low
that the English
Channel didn’t
even exist

3. Determining Past Climates
fossil evidence: pollen
sediment cores: ocean, lake
ice cores: Antarctic, Greenland
oxygen isotope ratios
dendrochronology: tree-ring
Isotopes are atoms whose nuclei have the same number of protons but different numbers of neutrons.
As the global warming debate has intensified in recent years, many methods of reconstructing past climates have undergone close scrutiny.

4. Climate During Past 1000 Years and since 1860
“Hockey Stick” graph
The global warming of the
past 100 years has not been constant

5. Climate Change and Feedback Mechanisms
Feedbacks cause climate changes to be either amplified or reduced.
positive feedback mechanisms: reinforce the interaction
negative feedback mechanisms: weaken the interaction
water vapor-greenhouse feedback: positive
snow-albedo feedback: positive
Cloud feedback: uncertain; overall negative

6. Possible Causes of Climate Change
external: changes in incoming solar radiation
external (e.g., volcano) or human (e.g., CO2): changes in the composition of the atmosphere
external (e.g., mountain uplifting) or human (e.g., land use): changes in the earth’s surface
Emissions of CO2 and other greenhouse gases are by no means the only way to change the climate.

7. Climate Change and Atmospheric Particles (decadal-century)
sulfate aerosols
volcanic aerosols
Sulfate aerosols are thought to cool the climate and therefore counteract global warming to some extent.

8. Climate Change and Variations in Solar Output (decadal-century)
sunspots

9. Climate Change and Variations in the Earth’s Orbit (10K-100K years)
Milankovitch theory: - eccentricity (100K yr) - obliquity (41K yr)
- precession (23K yr)

10. Climate Change, Plate Tectonics, and Mountain-Building (100M yr)
theory of plate tectonics
Landmasses 150M years ago Today

11. Warming is Unequivocal
Rising atmospheric temperature
Rising sea level
Reductions in NH snow cover
And oceans..
And upper atmosphere….

12. Human and Natural Drivers of Climate Change
Carbon dioxide is causing the bulk of the forcing.
On average, it lives more than a hundred years in the atmosphere and therefore affects climate over long time scales.
without air, the earth surface temperature would be 33C colder

13. Natural versus human-caused temperature increase
Climate models are needed:
aerosols;
cloud;
precipitation;
land processes; ….

14. Understanding and Attributing Climate Change
Anthropogenic warming is likely discernible on all inhabited continents
Observed
Expected for all forcings
Natural forcing only

15. What’s in the pipeline and what could come
Warming will increase if GHG increase. If GHG were kept fixed at current levels, a committed 0.6°C of further warming would be expected by More warming would accompany more emission.
CO2 Eq
3.4oC = 6.1oF
850
2.8oC = 5.0oF
600
1.8oC = 3.2oF
B1 and A1B have similar population projections – ca 7 billion at A2 population more than double at 15 billion. GDP/capita is 47k$, 75k$, 16k$ for B1, A1B, A2.
0.6oC = 1.0oF
400

16. A1B is a typical “business as usual” ( ) scenario: Global mean warming 2.8oC; Much of land area warms by ~3.5oC Arctic warms by ~7oC; would be less for less emission

17. What else happens in a hotter world?
Observations of sea level rise from satellites,
The global average SLR for the 20th century was about 6 inches (0.17m), mostly from expansion of the hot ocean, and with contributions from glacier melt (Alaska, Patagonia, Europe….).
Future changes just from these processes could be up to 1.5 feet (0.5 m) by 2100, and up to 3 feet (1 meter) within about 2-3 centuries, depending on how much GHGs are emitted.
But what about other processes? Rapid ice flow?

18. Other related issues Drought Tropical forest dieoff
Hurricane activities
Kyoto Protocol