1. Climate Change

2. Climate Variability vs. Climate Change
Changes over seasons and years;
yearly fluctuations (above or below) long-term average
30 yr average : “climatological normals”
Example Duluth climate normals
There is significant variability around these normals
Example: normal daily max temp for Duluth on Apr 30 is 56.6 but not every Apr 30 in had a max temp of 56.6
This year to year fluctuation around the normal is climate variability

3. In addition to averages, ranges are part of climatological normals.

4. Climate variability is caused by (for example) :
Volcanic eruptions which can have a cooling effect.
El Nino-La Nina , cause snowy/ non-snowy , warm / cold winters in Duluth.
SHORT-TERM!

5. 2. Climate Change
long-term continuous change to normals (averages, ranges).
long term : many decades
slow, gradual
requires scientific (or other) records

6. Causes of Climate Change
“Climate Forcings”
Natural or anthropogenic disturbances to global energy balance.
Positive forcing: induces an increase in global mean surface temperature
Negative forcing: induces a decrease

7. Climate forcing 1. Plate tectonics geologic time scales
Changing continent, ocean sizes & locations, changing atmospheric composition,
changing sizes and locations of mountain ranges
Change atmospheric and oceanic circulation
Examples….

8. 300-360 million years ago current
If there is more land at higher latitudes, ocean currents are affected and heat transport system is altered; more glacial ice at higher latitudes , albedo is higher and temperatures cool. Also when plates are moving there is more volcanic activity which can release more CO2

9. Triassic 200-250 million years ago
Aridity, monsoons, humid regions

10. Over past few million years, Tibetan Plateau and Himalayas have been rising, causing increased aridity in western China and central Asia

11. Climate forcing Milankovitch forcings “Wiggle” “Wobble” “Stretch”
2. Astronomical periodicities
Milankovitch forcings
“Wiggle”
“Wobble”
“Stretch”

12. “Wiggle”: obliquity Tilt of Earth’s axis changes Strength of seasons
22.1° – 24.5°
Strength of seasons
Especially High latitude variation in insolation
41,000 year periods

14. “Wobble”: precession Earth’s axis wobbles
Changes timing of perihelion and aphelion
Timing and intensity of seasons
27,000 yr periods

16. On Jan 4, earth is 3% closer
to sun than on July 4

18. “Stretch”: eccentricity
Shape of earth’s eccentric orbit changes
Changes the intensity of solar radiation received at aphelion and perihelion
100,000 yrs

20. Effect of these three:
Global temperature fluctuations of
± 2 – 5 degrees C per 10,000 yrs
match closely with glacial-interglacials over past 100,000 yrs

22. Animation of Milankovitch cycles

23. Ch 1: pp. 12-24 Ch. 2: pp. 35-50 seasons Ch. 3: pp. 56-69
Book Stuff for Test
Ch 1: pp
Ch. 2: pp seasons
Ch. 3: pp
Ch 4: pp

24. Climate Forcing Sunspot cycle 11 year
3. Solar Variability
Sunspot cycle 11 year
± 1 W/m2 change in solar constant (1372 W/m2)
Effects UV radiation
Example: Maunder Minimum : period of reduced sunspot activity; global temp decrease of 0.5 C
Sunspot activity

26. Climate Forcing
4. Volcanic Eruptions Big, explosive eruptions can inject dust and sulfur dioxide into stratosphere. change into sulfuric acid droplets that reflect (backscatter)solar radiation Causes global average cooling of tenths of a degree C 1-2 years following eruption. Mt Pinatubo 1991 example
Not all volcanoes are explosive enough to reach stratosphere; not all have high SO2

27. Aerosol content around globe before and after June 1991
Pinatubo eruption. (Red is higher aerosol content).

29. Climate forcing
5. Human-Induced changes Atmospheric composition (increased concentration of GG and aerosols) Land use/ Land cover changes (urban surfaces, agricultural practices, deforestation, overgrazing)

30. Timescale Differences of Forcings
Plate tectonics : millions
Astronomical (Milankovitch) : 10s of 1000s
These are irrelevant when looking at past 100 years
Solar, Volcanic, Anthropogenic : relevant to short timescales

31. Radiative Forcing and Radiative Feedback

32. Radiative Forcing
Globally and annually averaged changes in radiation balance at top of atmosphere.
Plate tectonics and Milankovitch are not radiative forcings
Solar, volcanic, anthropogenic are radiative forcings

33. A;BEDO!
Top of the atmosphere
70 IN
70 OUT 12 58
104 23 58 98
116 47

34. GG : positive radiative forcing agent
Sun’s energy : positive radiative forcing agent
Volcanic eruptions : negative radiative forcing agent
Anthropogenic: more longwave is absorbed by atmosphere and less goes out to space

35. Quantifying radiative forcing
How much a forcing factor alters global and annual average radiation balance at top of atmosphere, relative to 1750 (beginning of Industrial Revolution)
In 2011, estimated radiative forcing from anthropogenic
= 2.29 Wm-2
from Fifth IPCC report

36. Mechanism of Greenhouse Warming
1. the simple explanation:

37. Increased green-house gas concentration:
More of the longwave emitted from surface is absorbed by atmosphere and less goes out to space.
Net solar incoming exceeds longwave loss:
Increased temperature