Climate change occurs both naturally and as a result of human activities. Various scientific records such as tree rings, pollen, and oxygen isotope ratios found in ice cores provide evidence of climate fluctuations over hundreds of thousands of years. Factors that influence the climate on long timescales include variations in solar energy output, shifts in the positions of continents and opening/closing of ocean gateways, and changes in atmospheric greenhouse gas concentrations from natural processes like volcanism and the carbon cycle. Human activities like burning fossil fuels have recently caused increased levels of greenhouse gases and global warming above natural variability.

1. Chapter 21 – Climate Change
Earth Science and the Environment (4th ed)
Thompson & Turk

2. Fig. 21.1a, p.530

3. Fig. 21.1b, p.530

4. Fig. 21.1c, p.530

5. 21.1 Climate change in Earth’s history
►Earth’s early atmosphere very likely had a
large greenhouse effect
 Sun – back then was 20-30% fainter
 Deep freezes occurred five times at least
►Oceans and all land covered with ice ~700 - 600mya
 Records show many changes over time
 Recent records show mean temperature
increase from the late 1800s

6. Fig. 21.2, p.531

7. Fig. 21.3, p.532

8. Fig. 21.4, p.532

9. 21.2 Measuring climate change
►Historical records – accounts recorded as
records, or in stories
 Vikings’ tales of the Little Ice Age (1450-1850)
 Landscape paintings, other historical &
archeological accountings chronicle changes
over the span of human history

10. 21.2 Measuring climate change
►Tree rings – growth rings of trees hold
climate information
►Plant pollen – the pollen record records
what was able to grow, which is linked to
temperature and precipitation
 i.e; 10,500 years ago pines replaced spruce
indicating warmer temperatures

11. Fig. 21.7a, p.535

12. 21.2 Measuring climate change
►Oxygen isotopes in glacial ice
 18O & 16O (common isotope) both occur
 16O evaporates more readily (lighter), so most
ice is “heavier”
 Ice from greenland and Antarctica show a
record back >100,000 yrs
►Glacial evidence – till, tillites, striations all
give information on climate at that time
 14C dating of logs preserved in till

13. Fig. 21.6, p.534

14. Fig. 21.7b, p.535

15. 21.2 Measuring climate change
►Plankton and isotopes in ocean sediment
 Shells and other “hard parts” preserved in
marine rocks / muds give two lines of
information
►What was alive at the time gives climate information
►16/18O ratios in biogenic carbonate
►Rock and fossil record
 fossils give much information, what lived when
 Rock records its formative environment

16. Fig. 21.5, p.533

17. 21.3 Astronomical causes
of climate change
►Changes in solar radiation
 The sun’s output varies over time
 Local activity such as sunspots and solar storms
has effect on solar output
 Changes in global temperature seem to be
related to sunspot cycles
►Direct effect or unknown feedback mechanism?

18. 21.3 Astronomical causes
of climate change
►Bolide impacts – some think that an event
65mya blasted enough dust and rock into
the atmosphere, that the subsequent
cooling killed of the extinction of the
dinosaurs (among other things)

19. 21.4 Water and climate
►Water is in all Earth’s four spheres
 The most abundant greenhouse gas
 Is the substance of clouds (thus all they do)
 Glaciers and snowfields have very high albedos
 Evaporation of water transfers heat into the
atmosphere
 Freezing & condensation release heat
 Moving water weathers, erodes & transports
Earth materials
 Ocean currents move heat poleward from the
equator

20. 21.5 The natural carbon
cycle and climate
►Carbon is a small part of the atmosphere,
but has large effects
 CO2 & methane (CH4) are both greenhouse
gases and play their role in climate
►Carbon in the biosphere
 Carbon IS the biosphere – or at least the
fundamental building block of life
 When a thing dies, its carbon is either released
(as gas) or preserved (coal swamps, etc)

21. 21.5 The natural carbon
cycle and climate
►Carbon in the hydrosphere
 CO2 dissolves in water
 Found as bicarbonate (HCO3
-) and carbonate
(CO3)2- in seawater
 When water warms, gases are released, which
aids in further heating

22. 21.5 The natural carbon
cycle and climate
►Carbon in the crust and upper mantle
 Contains 1,000x as much carbon as is in the
atmosphere
 Carbonate rocks – moderate-long term storage
of carbon
 Fossil fuels – recoverable fossil fuels contain 5x
as much carbon as is in the atmosphere
 Deeper carbon – during subduction, carbonates
are consumed and remain trapped

23. Fig. 21.9, p.537

24. Fig. 21.10, p.538

25. Fig. 21.11, p.539

26. 21.6 Tectonics and climate change
►Position of the continents
 200 mya, the single continent Pangea was near
the south pole
►Continental interiors tend to have more severe
winters. For a single large landmass, even more so.
►Influences winds an ocean currents
►Movement opens and closes straits, etc.

27. 21.6 Tectonics and climate change
►Mountains and climate
 Global cooling followed the impact on India and
the forming of the Himalayas
 Many large subdction-related mountains contain
carbonate rock
►Carbonate rock erodes and takes CO2 out of the
atmosphere
►Volcanoes and climate
 can emit ash and sulfur compounds that cool, or
CO2 that warms climate

28. 21.6 Tectonics and climate change
►The interaction of these to regulate climate
 When ridges spread slowly, oceans are deeper
and sea level falls
 This exposes carbonate rock which eventually
erodes, taking CO2 out of the atmosphere
►During rapid ridge movement, oceans
become shallower
 Covers up limestone, weathering slows
 Covers land, decreases global albdeo

29. Fig. 21.12, p.540

30. Fig. 21.13, p.540

31. Fig. 21.15, p.543