1. Earth’s Climate System
Climate – long term atmospheric conditions in a region
Earth’s climate includes interactions of:
Atmosphere
Hydrosphere
Geosphere
Biosphere
Cryosphere
Climate system – exchanges of energy and moisture between these spheres

2. Earth’s Climate System

3. Earth’s Climate System
Feedback loops – modify atmospheric processes
Positive feedback loops – enhance initial change
Negative feedback loops – counteract initial change

4. Determining Causes of Earth’s Climate Change
Paleoclimatology
Proxy data – indirect evidence using natural recorders of climate variability
Sea floor sediments
Coral deposits
Glacial ice rings
Tree rings
Pollen
Historical documents

5. Temperature: the last 400,000 years
From the Vostok ice core (Antarctica)
That there is a link between CO2 and global temperatures is irrefutable as this diagram shows, but exact details of the link and all the possible feedback mechanisms are not clear.
The interaction of positive and negative feedback effects associated with the greenhouse effect is currently a critical issue for the scientific community.

6. Natural Climate Change
External Forcing:
Internal Forcing:
The agent of change is outside of the Earth-atmosphere system
The agent of change is within the Earth-atmosphere system itself

7. External Forcing
Variations in solar output
Orbital variations
Meteors

8. Natural Causes of Climate Change
Solar energy changes
Variable energy from the Sun over time
Luminosity
Sunspots

9. Solar Variations Sunspots correlate with solar activity
More sunspots, more solar energy
Sunspots are the most familiar type of solar activity.

11. SOLAR ACTIVITY
Sunspots are the most familiar type of solar activity.

12. THE SOLAR CYCLE Sunspot numbers increase and decrease
over an 11-year cycle
Observed for centuries.
Individual spots last from a few hours to months.
Studies show the Sun is in fact about
0.1% brighter when solar activity is high.

13. The Seasons The Earth has seasons because the axis is tilted.
Earth rotates on its axis as it orbits the Sun.
Earth’s axis ALWAYS points in the same direction…
but Earth’s location in its orbit around the Sun determines whether the NH or SH is pointed toward the Sun.

14. The Seasons NH Summer Solstice NH Autumnal Equinox NH Winter Solstice
June 20-21
NH Autumnal Equinox
September 22-23
NH Winter Solstice
December 21-22
NH Vernal Equinox
March 20-21

15. Earth’s orbit: an ellipse
Perihelion: place in the orbit closest to the Sun
Aphelion: place in the orbit farthest from the Sun

16. Earth’s orbit: an ellipse
Perihelion: place in the orbit closest to the Sun
Aphelion: place in the orbit farthest from the Sun

17. THE MAUNDER MINIMUM An absence of sunspots was well observed
from 1645 to 1715.
The so-called “Maunder minimum” coincided with a cool climatic period in Europe and North America:
“Little Ice Age”
The Maunder Minimum was not unique.
Increased medieval activity
correlated with climate change.

18. Natural Causes of Climate Change
Variations in Earth’s Orbit
Milankovitch Theories
Eccentricity of Earth’s orbit
Obliquity of Earth’s axis
Precession of Earth’s axis

19. Orbital changes Milankovitch theory:
Serbian astrophysicist in 1920’s who studied effects of solar radiation on the irregularity of ice ages
Variations in the Earth’s orbit
Changes in shape of the earth’s orbit around sun:
Eccentricity (100,000 years)
Wobbling of the earth’s axis of rotation:
Precession (22,000 years)
Changes in the tilt of earth’s axis:
Obliquity (41,000 years)

20. Eccentricity: period ~ 100,000 years

21. Natural Causes of Climate Change
Volcanic eruptions
Volcanic ejecta may block sunlight
Need many eruptions in short time period
Not observed in recent history

22. Natural Causes of Climate Change
Movement of Earth’s Plates
Change ocean circulation
Extremely slow process
Climate change would be very gradual over millions of years
Linked to Pleistocene Ice Age, Little Ice Age, Medieval Warm Period

23. Documenting Human-Caused Climate Change
Intergovernmental Panel on Climate Change (IPCC)
Global group of scientists
Published assessments since 1990
Predict global temperature changes of 1.4–5.8°C (2.5–10.4°F)
Climate change models can mimic modern conditions only if human emissions are taken into account.

24. Atmosphere’s Greenhouse Effect
Global warming – increase in Earth’s global temperatures
Greenhouse effect – keeps Earth’s surface habitable
Incoming heat energy is shorter wavelengths
Longer wavelengths – some trapped, some escape, net warming effect

25. Earth’s Heat Budget Addition to or subtraction from heat on Earth
Incoming radiation from Sun shorter wavelengths
Outgoing radiation from Earth longer wavelengths
Rates of energy absorption and reradiation must be equal

26. Earth’s Heat Budget

27. Greenhouse Gases Water vapor Carbon dioxide Most important
66–85% of greenhouse effect
Carbon dioxide
Natural part of atmosphere
Greatest relative contribution from human activities
Burning of fossil fuels

28. Atmospheric Carbon Dioxide

29. Greenhouse Gases Methane Other trace gases
Second most abundant human-caused greenhouse gas
Great warming power per molecule
Landfill decomposition
Cattle
Other trace gases
Nitrous oxide, CFCs, ozone

30. Human-Caused Greenhouse Gases