1. Anthropogenic Influences on Climate
Snow/Ice Report
Greenhouse Gases
Aerosols
Land Use and Land Cover Change
For Next Class: Read pp of Snow Booklet

2. Driving Question
How do human activities affect global climate and how significant are those influences compared to natural causes of climate change?
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3. Human Activity and Climate Change
In 2013, the Intergovernmental Panel on Climate Change (IPCC) concluded that global warming since the mid-20th century very likely (estimated probability greater than 90%) was caused mostly (>50%) by human activities
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4. Anthropogenic Forcings on Climate
Greenhouse gases
Aerosols
Land use/land cover change

5. Human Activity and Climate Change
Trends in Greenhouse Gases
“Most of the increase in globally-averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG (greenhouse gas) concentrations.” (IPCC 2007)
Fossil fuel combustion accounts for 75% of the increase in atmospheric carbon dioxide
deforestation is likely responsible for the balance
Rising levels of other infrared-absorbing gases associated with human activity (e.g., methane, nitrous oxide, halocarbons, and ozone) enhance the greenhouse effect
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6. Earth–Atmosphere Radiation Balance
Figure 4.12

7. Atmospheric Absorption in the EM Spectrum

8. Why are Greenhouse Gases Important?
Absorb long-wave terrestrial radiation, heating the atmosphere, and radiating this energy back to the surface.
Critical for life on Earth.
Without greenhouse effect, surface temperatures would be extremely cold at night.
Too much of a good thing, however, is a concern.

9. In Tacoma before the arrival of President Harrison in May, 1891.
A rectangular piece of coal in a wagon is on display in the middle of Pacific Avenue
In Tacoma before the arrival of President Harrison in May, 1891.

10. Life Magazine (1962)

14. CO2 at Mauna Loa and South Pole (Red) and NOAA (Blue)
IPCC AR5

15. CH4 at UCI (Green), AGAGE (Red) and NOAA (Blue)
IPCC AR5

16. N2O at AGAGE (Red) and NOAA (Blue)
IPCC AR5

17. What is Radiative Forcing?
“The change in net (down minus up) irradiance (solar plus longwave; in W m-2) at the tropopause” (IPCC AR5 Ch. 2)
Abbreviated RF
Positive RF implies warming
Negative RF implies cooling

18. +3.0 w m-2
IPCC AR5

19. +3.0 w m-2

20. 1000 Years of CO2 and Temperatures
Figure

21. CO2 and Temperature
Does correlation equate to causation? Why or why not?

22. No denying that the anthropogenic
greenhouse effect is playing
a role: Question is how much?

23. Atmospheric Aerosols
Aerosols: solid or liquid particles suspended in the air
Naturally occurring aerosols: particles from trees, sea salt, dust, and volcanic dust
Anthropogenic aerosols: particles from the burning of fossil fuels and biomass, smoke, and agricultural dust
Aerosols can influence weather and climate by directly and indirectly affecting the amount of solar radiation reaching the earth’s surface, which can lead to warming and cooling in different regions of the world. Overall RF is negative, however.
Aerosol Optical Depth (AOD): variable used by scientists to describe the amount of solar radiation scattered or absorbed by aerosols (Instrument: sun photometer)

24. Human Activity and Climate Change
Aerosols
90% of anthropogenic aerosols are byproducts of fossil fuel burning in the Northern Hemisphere
cause either cooling (sulfurous aerosols) or warming (black carbon) of the atmosphere
Aerosols can alter the number, mean size, and size distribution of cloud droplets
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25. Human Activity and Climate Change
Aerosols
The direct radiative forcing of aerosols is estimated to offset the CO2 warming by almost one-third. (IPCC 2007)
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26. Global Aerosol
Optical Depth

27. Trends in Global Aerosol Optical Depth
IPCC AR5

28. Direct and Indirect Effects of Aerosols
Aerosols scatter and absorb incoming solar radiation and impact cloud microphysics
TAKE OUT! Aerosols are microscopic suspended particulates in earth’s atmosphere that occur naturally or as a result of human activity. Aerosols directly interact with incoming solar radiation by either scattering or absorbing that light, effectively limiting the amount that reaches earth’s surface. Many scientists believe that the SE has remained relatively cool because of the high concentration of aerosols in our region.
Also, aerosols indirectly affect the surface energy balance by impacting the microphysical processes of cloud formation and precipitation development. Raindrops and snowflakes form on a nucleation site, and aerosols can serve as these nucleation sites. But the problem is when you have a surplus of aerosols, cloud droplets will still form, but since that moisture is spread out over such a large concentration of particles, individual cloud droplets can’t grow large enough to precipitate.
Therefore the indirect effects of aerosols lead to increased cloudiness and precipitation suppression, which ultimately cause a net cooling effect at earth’s surface.

29. Direct and Indirect Effects of Aerosols
Small black dots = aerosol particles
Larger open circles = cloud droplets
Straight lines = incident and reflected solar radiation
Fig IPCC AR4

31. The Cloud Albedo
Effect results in
Negative RF.

32. -0.82 w m-2
IPCC AR5

33. Reciprocal Relationship
Climate
Aerosols

34. AppalAIR Appalachian Atmospheric Interdisciplinary Research
an air quality/climate research and public outreach facility for exploring air pollution formation and transport and the relationship of pollution to a changing climate and its effects on regional ecosystems
Participants:
Howie Neufeld – Biology
Brett Taubman – Chemistry
Barkley Sive – Chemistry
Rahman Tashakkori – Computer Science
Baker Perry – Geography
Jim Sherman – Physics
Ryan Emanuel – NC State
Doug Miller – UNCA
Collaborating member of the NOAA-ESRL Global Aerosol Network ( and the NASA AErosol RObotic NETwork (AERONET,

35. Changes in Surface Albedo
What is surface albedo and why is it important in the context of climate change?
How have humans changed surface albedo?

36. Changes in Surface Albedo
Anthropogenic changes to the physical properties of the land surface can perturb the climate
Directly exerting a radiative forcing
Modifying other processes such as latent and sensible heat fluxes
Large-scale character of vegetation can affect surface albedo
Albedo of agricultural land can be very different from that of a natural landscape, especially forest
Particular important when snow is present, as open land can be highly reflective with snow cover, while a forest is not

37. Albedo
Figure 4.5

39. Human Activity and Climate Change
Changes in land use and land cover
Human development has transformed an estimated one-third to one-half of Earth’s land surfaces
Changes can affect the vertical flux of heat and moisture
influences where and when thunderstorms occur
may modify atmospheric and oceanic circulation
At middle latitudes, clearing of forests for agriculture and reforestation of abandoned farm land has caused regional climate change
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40. Changes in Land Cover Since 1750
Cropland area expanded from 1750 to 1950 across Europe, Gangetic Plain, and in North America
Since that time, croplands have been abandoned in Europe, North America and China, with an increase in forested areas
Deforestation is occurring quite rapidly in the tropics
How does deforestation (conversion of forest to grass) affect albedo, the surface energy balance, and RF?

42. Radiative Forcing of Land Cover Change
Land cover change since 1850 has generally led to higher surface albedo and a slight negative radiative forcing
Best estimate is w m-2
However, spatial variability is quite high, with some areas showing no change in RF and other areas more negative than -5 w m-2
With tropical deforestation becoming more significant in recent decades, warming due to reduced evaporation may become more significant globally than increased albedo.

43. Black Carbon on Snow
Presence of soot particles in snow causes a decrease of albedo and can affect snowmelt
Best estimate of RF is w m-2

44. -0.15 w m-2
IPCC AR5

45. Anthropogenic Forcings on Climate
Greenhouse gases
Aerosols
Land use/land cover change

47. No denying that the anthropogenic
activity is playing a role: Question
is how much?