1. Natural & anthropogenic causes
Climate change
Natural & anthropogenic
causes

2. Natural causes
All causes referred to as
Drivers
Forcings

3. Milankovitch
Eccentricity: earth’s orbit changes from circle to oval on a 100,000 yr. cycle
Obliquity: angle of tilt varies deg on 41,000 yr cycle
Precession: earth wobbles on its axis over 19-23,000 yrs
RESULT: slight changes in amount of sunlight

4. Evidence shows he was right
Milankovitch predicted ice ages on a cycle of 41,000 and 100,000 years.
Evidence shows he was right
Ocean sediment cores
Fossil coral reefs: reefs form when ice melts, water level rises; reefs die when ice caps grow and water level sinks

5. Natural causes Changes in the Sun’s intensity
1400s-1700s: Little Ice Age
Apparently due to reduction in Sun’s intensity
Sunspots??

6. Natural causes Volcanic emissions
Gas and dust blasted to the stratosphere
Sulfur dioxide, forms haze, scatters incoming solar radiation
Global surface temperature change averaged for 5 volcanoes, including Pinatubo and Tambora

9. Feedbacks As climate changes, it can trigger further changes—feedbacks
Example: warmer temperatures can cause more CO2 to be released from oceans.
Positive or Negative?
Example: changing temperatures can affect ocean currents (global conveyor)

10. Ocean currrents Global conveyor: transports heat around the globe.
Affected by, and affects, climate
Changes in sea icechanges in salinity changes in currents  changes in weather and climate
To global conveyor animation

11. Famous ``hockey stick’’ graph

12. Human causes Do humans influence the climate?
Well, why not?
Our activities produce a lot of CO2

15. Missing on the previous slide
Water vapor
Most abundant greenhouse gas
Its role is quite complex:
Water vapor absorbs thermal radiation emitted from the Earth  warming
Water vapor condenses into clouds, which reflect solar radiation  cooling

17. Is the CO2 being produced from natural or human causes?
Evidence points to human
Carbon from fossil fuels has a different ``signature’’ (C-14) from carbon in modern plants and animals
The increase in the last 100 years is consistent with the calculated releases from fossil fuel burning

18. As much as 95% of CO2 released to the atmosphere would be released even in the absence of humans
Decay of organic material
BUT: natural sources balanced by sinks that remove CO2, such as ocean and forests.

19. Where do greenhouse gases come from?

21. Trend is with respect to the global average from 1961 to 1990
Trend is with respect to the global average from 1961 to In other words: average global temperature from is the 0 line

22. How do scientists know the climate is changing?
Historical records
Writings, phenology (e.g.: flowering times)
Temperature records of last 200 years or so
Proxies
Tree rings
Ice cores
Measurements of its effects
Shrinking ice sheets
Receding glaciers
Ocean acidification

23. Effects Polar ice melting Changes in intensity/duration of droughts
Changes in location/amount of precipitation
Changes in frequency/intensity of storms
Spread of diseases

24. Spread of disease
Malaria mosquito could spread throughout Europe as temperature rise
Also:
Ticks
rats

25. Storm frequency and intensity
Warmer climate means warmer oceans
Warm oceans contribute to hurricanes
Hurricanes get their energy as water evaporates

26. More from warmer oceans
Coral reefs require narrow temperature range
As oceans warm, zooxanthellae, algae, expelled. Corals die, bleach

27. Polar ice melting