1. Climate Change
Hundreds Gather to Protest Global Warming

2. Weather vs. Climate
What is the difference?
How are they related?

3. Climate Variability vs. Climate Change
Changes over seasons and years;
Climate fluctuations yearly above or below a 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

4. In addition to averages, ranges are part of climatological normals
In addition to averages, ranges are part of climatological normals. Example: average annual temperature for Duluth is 39.7°F, but there is quite a range of temps around that average

5. Climate variability is caused by (for example) :
Volcanic eruptions which can have a cooling effect
El Nino-La Nina , cause snowy or non-snowy winters in Duluth

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

7. Causes of Climate Change
“Climate Forcing”
Disturbances to global system
Can be natural or anthropogenic
Positive forcing: induces an increase in global mean surface temperature
Negative forcing: induces a decrease in global mean surface temperature

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

9. million years ago

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

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

12. Review Weather vs Climate Climate Variability vs Climate Change
Climate Change caused by Climate Forcings:
Plate tectonics

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

14. “Wiggle”: obliquity Tilt of Earth’s axis changes Strength of seasons
21.8° – 24.4°
Strength of seasons
41,000 year periods

15. “Wobble”: precession Earth’s axis wobbles
Changes timing of perihelion and aphelion
21,000 yr periods

17. “Stretch”: eccentricity
Shape of earth’s eccentric orbit changes
Changes the intensity of solar radiation received at aphelion and perihelion
95,000 yrs and 410,000 yrs

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

20. 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

22. Climate Forcing
4. Volcanic Eruptions Big, explosive eruptions can inject dust and sulfur dioxide into stratosphere change into sulfuric acid droplets that reflect solar radiation Causes global average cooling of tenths of a degree C in year following eruption Mt Pinatubo 1991 example

24. Climate forcing
5. Human-Induced changes atmospheric composition and land cover changes

25. Climate Forcings review:
Plate tectonics
Astronomical Forcings
Solar Variability
Volcanic Activity
5. Human-Induced Forcings

26. 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

27. Radiative Forcing
Globally and annually averaged changes in radiation balance at top of atmosphere.
Plate tectonics and Milankovitch are not radiative forcings
E.g., Milankovitch decreased obliquity means less summer radiation in N. hemisphere but is balanced by more S. hemisphere winter radiation.
These seasonal affects cancel one another
Solar, volcanic, anthropogenic are radiative forcings

28. Solar activity as radiative forcing
Increased solar radiation: More solar incoming at top of atmosphere Increased temperature

29. Greenhouse gases as radiative forcing
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

30. CO2 : positive radiative forcing agent
Sun’s energy : positive radiative forcing agent
Volcanic eruptions : negative radiative forcing agent

31. Intergovernmental Panel on Climate Change (IPCC)
Produced reports in 1990, 1995, 2001, 2007, 2013
Consensus view of the climate community
(100s of authors)
IPCC video

32. 3 working groups: Physical Science Basis
Impacts, Adaptation and Vulnerability
Mitigation of Climate Change
(Summary for Policymakers)

33. Quantifying radiative forcing
Amount by which a 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

34. Radiative Feedback Positive feedbacks dominate
Positive feedbacks: enhance effect; initial increase in temp is reinforced
Examples:
1) water vapor- greenhouse feedback:
More evaporation, more water vapor (gg), more absorption and radiation of heat
2) snow-albedo feedback: warming melting snow and ice cover causes decreased albedo, more absorption, increased temperature
Negative feedbacks: decrease effect; initial increase is weakened
Example: warming leads to more cloud cover, increasing albedo, decreasing temperature
Positive feedbacks dominate

35. Understanding current climate change requires backdrop of past climate change

36. Quaternary began 2.6 my BP
Pleistocene Epoch 2.6 my BP – 11, 500 y BP
Holocene Epoch 11, 500 – present?
Anthropocene Epoch ???
8 cycles (100,000 y each) of glacials/interglacials
Most recent Ice Age : 3 my BP
We are in this Ice Age now, in warm part
Last Glacial Maximum : 25-18,000 y BP
Ended 15, ,000 y BP

37. Temps 5-8°C lower; sea level 130 m lower

38. This interglacial that we are in should last another 30,000 yrs
Glacials and interglacials match Milankovitch cycles
Onset of Mil. forcing led to summer cooling over northern land masses.
Positive feedback : more snow cover: higher albedo

39. “Little Ice Age” Extensive Arctic sea ice and glacial advances
Mid16th to late 19th Century
Coldest interval
Extensive Arctic sea ice and glacial advances
Mid-19th Century warming ended the Little Ice Age

40. 1880 – 2007 : 0.7°C increase in temp Most pronounced in N hemisphere
Four periods:
1880 – 1920: no trend; variations within 0.3°C
1920 – mid-40s : warming in N. hemisphere 0.4°C
1940s – early 70s : slight cooling N hemisphere; S. hemisphere constant
(within 0.4°C extremes)
Mid-1970s – present : marked overall warming
With regional variability

41. Top warmest Years (1880 – 2015)
Rank 1 = Warmest Period of Record: 1880–2015
Year 1
2015 2
2014 3
2010 4
2005 5
1998
6 (tie)*
2013
2003 7
2002 8
2006
9 (tie)*
2009
2007
10 (tie)
2004
2012

42. Over past decade: very strong warming over northern high latitudes

43. Anthropogenic Factors of Climate Change
Use data from Fifth IPCC report (2013)
Intergovernmental Panel on Climate Change
Produced reports in 1990, 1995, 2001, 2007, 2013
Consensus view of the climate community
(100s of authors)

44. View anthropogenic factors as radiative forcing agents:
How does each factor change the radiation balance at the top of atmosphere in Wm-2 ?
CO2
Largest single positive radiative forcing agent
Radiative forcing in 2011 compared to 1750:
1.68 Wm-2
(compared to 1750, increase in CO2 by itself would lead to a radiation imbalance of 1.68)
IPCC

45. 2. Methane (CH4)
forcing = 0.97 Wm -2
3. Halocarbons (partially halogenated organic compounds)
forcing = 0.18
4. Nitrous oxide
forcing = 0.17
Total RF from well-mixed gg = 3 Wm-2

46. Short-lived gases
Carbon monoxide (CO) RF = Non-methane volatile organic compounds (NMVOC) (benzene, ethanol, etc) RF = Nitrous oxides (NOx) RF = Total =

47. Aerosols (also short-lived)
Except for black carbon (soot from fossil fuel burning) they are negative forcing agents:
Net negative RF =
Direct and indirect effects:
Direct: aerosols absorb and scatter solar and longwave radiation
Indirect: aerosols act as condensation nuclei for clouds:
Adds additional negative RF of -0.55
Great uncertainty IPCC

48. Review Climate Forcings:
Plate tectonics
Astronomical Forcing
Solar Variability
Volcanic Eruptions
Human-Induced Forcings
Quantify radiative forcing by looking at change at top of atmosphere relative to 1750
In 2011 : Wm-2
Carbon dioxide responsible for 1.68
Positive and negative radiative feedback
radiative

49. Review con’d Quaternary Period began 2.6 myBP
Includes Pleistocene and Holocene Epochs
8 pulses of glacials and interglacials
We have been in an interglacial since 15,000-13,000 years ago
Top 10 warmest years since 1880 in 2000s except 1998
Greatest warming has been in high latitudes of Northern Hemisphere
Aerosols: greatest uncertainty in climate change science
Mostly negative effect except for black soot

50. Carbon dioxide sources

51. Methane Sources:
Lifetime in atmosphere: 12 years

52. Halocarbon sources
propellants in aerosols, as blowing agents in foam manufacture, in air conditioning units and refrigerants
Lifetime in atmosphere:
HFCs: years PFCs: 2,600-50,000 years NF3: 740 years SF6: 3,200 years

53. Nitrous oxide sources
Lifetime in atmosphere : 114 years

54. Aerosols Sources: 90% are natural (not anthropogenic)
Dust storms, vegetation, forest fires, volcanoes, sea salt

55. 10% anthropogenic
Fossil fuel combustion, burning vegetation, incinerators, smelters, power plants

56. Grey: no data
Intense reds : finer pieces like smoke or pollution
Yellow: big pieces, like dust

57. Direct and Indirect Effects of Aerosols
Direct: aerosols reflect solar radiation back to space
BUT depends on color, size composition
Some aerosols (soot) are dark and absorb solar radiation
Sea salt, dust, volcanic ash

58. Indirect: aerosols are necessary for cloud formation
Aerosols from pollution create small cloud droplets and reflect more solar radiation
than natural aerosols

60. Land Use Changes Overgrazing and forest clearance : increase albedo
Deforestation and biomass burning increase CO2
Net negative RF = -0.15

61. Positive forcings are countered by negative forcings
especially due to aerosols.
Lowering total net anthropogenic forcing to Wm -2
Uncertainty is due to uncertainty in aerosol effects

62. IPCC Conclusion re: RF
The total anthropogenic RF for 2011 relative to 1750 is 2.29 [1.13 to 3.33] W m −2
has increased more rapidly since 1970 than during prior decades.
43% higher than that reported in IPCC 4th Report for the year 2005.
caused by a combination of continued growth in most greenhouse gases
concentrations and improved estimates of RF by aerosols indicating a weaker net cooling effect

63. IPCC summary of past Century effects
Page
Black lines: observations
Wide blue lines: climate models using only natural forcings
Wide pink lines: climate models using natural and anthropogenic forcings
Show: ARCTIC AND ANTARCTIC SEA ICE EXTENT
UPPER OCEAN HEAT CONTENT (OHC) IN MAJOR OCEAN BASINS
CONTINENTAL LAND SURFACE TEMPERATURES

64. GCMs General Circulation Models Atmospheric Ocean GCMs (AOGCMs)
Modeling groups worldwide have developed GCMs
IPCC assesses impacts of projected increases in gg and consequences for 21st Century

65. podcast

67. Models have become increasingly sophisticated since first IPCC report in 1990
New models use range of gg emission scenarios (RCPs : Representative Concentration Pathways)
GG concentration trajectories; represent a range of climate outcomes
RCPs used in Fifth report (2013):

68. “Each RCP could result from different combinations of economic, technological, demographic, policy, and institutional futures. For example, the second-to-lowest RCP could be considered as a moderate mitigation scenario. However, it is also consistent with a baseline scenario that assumes a global development that focuses on technological improvements and a shift to service industries but does not aim to reduce greenhouse gas emissions as a goal in itself”.

69. 2100 RF relative to 1750
Mitigation scenario
21st Century climate policies
RCP2.6
2.6
Very low forcing level
RF peaks and declines
RCP4.5
4.5
stabilization
RF stabilizes by 2100
RCP6.0
6.0
RF doesn’t peak by 2100
RCP8.5
8.5
Very high GG forcing

70. What the models tell us:
Temperature
Water Cycle
Ocean
Cryosphere
Sea Level
Carbon Cycle
Climate Change Stabilization, Commitment and Irreversibility

71. Model results: A. Temperature
Global surface temperature change for the end of the 21st century is likely to exceed 1.5°C relative to 1850 to 1900
Warming will continue beyond 2100
Warming will continue to exhibit interannual-to-decadal variability and will not be regionally uniform

72. larger in the tropics and subtropics
4. The global mean surface temperature change for the period –2035 relative to 1986–2005 will likely be in the range
of 0.3°C to 0.7°C
larger in the tropics and subtropics
5. Increase of global mean surface temperatures for 2081–2100 (late 21st Century) relative to 1986–2005 is projected to likely be
0.3°C to 1.7°C
1.1°C to 2.6°C
1.4°C to 3.1°C
2.6°C to 4.8°C
19 year periods
Different RCPs

73. 6. Arctic region will warm more rapidly than the global mean
warming over land will be larger than over the ocean
8. virtually certain that there will be more frequent hot and fewer cold temperature extremes over most land areas
9. very likely that heat waves will occur with a higher frequency and duration. Occasional cold winter extremes will continue to occur IPCC

74. B. Water Cycle
“Changes in the global water cycle in response to the warming over the 21st century will not be uniform. The contrast in precipitation between wet and dry regions and between wet and dry seasons will increase, although there may be regional exceptions”
1. high latitudes and the equatorial Pacific Ocean are likely to experience an increase in annual mean precipitation by the end of 21st century

75. 2. mid-latitude and subtropical dry regions, mean ppt will likely decrease 3. mid-latitude wet regions, mean ppt will likely increase 4. Extreme precipitation events over most of the mid-latitude land masses and wet tropical regions will very likely become more intense and more frequent

76. 5. likely that the area encompassed by monsoon systems will increase over the 21st century. (While monsoon winds are likely to weaken, monsoon precipitation is likely to intensify ) 6. high confidence that the El Niño-Southern Oscillation (ENSO) will remain the dominant mode of interannual variability in the tropical Pacific IPCC

77. C. Ocean
“global ocean will continue to warm during the 21st century. Heat will penetrate from the surface to the deep ocean and affect ocean circulation”.
strongest ocean warming is projected for the surface in tropical and Northern Hemisphere subtropical regions.
warming in the top 100 meters: 0.6°C to 2.0°C
At greater depth the warming will be most pronounced in the Southern Ocean.
1000 m 0.3°C to 0.6°C

78. 3. Atlantic Meridional Overturning Circulation (AMOC) will weaken
over the 21st century.
some decline in the AMOC by about 2050
(It is very unlikely that the AMOC will undergo collapse in the 21st century. However, a collapse beyond the 21st century for large sustained warming cannot be excluded)

79. D. Cryosphere
“very likely that the Arctic sea ice cover will continue to shrink and thin and that Northern Hemisphere spring snow cover will decrease during the 21st century as global mean surface temperature rises. Global glacier volume will further decrease”.
Year-round reductions in Arctic sea ice extent are projected by the end of the 21st century
43% to 94% in September and from 8% to 34% in February

80. 2. a nearly ice-free Arctic Ocean in September before mid-century is likely (in one RCP) 3. In Antarctic, a decrease in sea ice extent and volume is projected with low confidence for the end of the 21st century 4. end of the 21st century: global glacier volume (excluding periphery of Antarctica) decrease by 15 to 55% 35 to 85%

81. 5. Northern Hemisphere spring snow cover is projected to decrease by 7% - 25% 6. permafrost (upper 3.5 m) extent at high northern latitudes will be reduced is projected to decrease by between 37% to 81%

82. E. Sea Level
“Global mean sea level will continue to rise during the 21st century. Under all RCP scenarios, the rate of sea level rise will very likely exceed that observed during 1971 to 2010 due to increased ocean warming and increased loss of mass from glaciers and ice sheets” 1. Global mean sea level rise for 2081–2100 relative to 1986–2005 will likely be in the ranges of 0.26 to 0.55 m 0.32 to 0.63 m 0.33 to 0.63 m 0.45 to 0.82 m

83. 2. thermal expansion accounts for 30 to 55% of 21st century global mean sea level rise, and glaciers for 15 to 35%. (The increase in surface melting of the Greenland ice sheet will exceed the increase in snowfall, leading to a positive contribution to future sea level ) (increase in snowfall on the Antarctic ice sheet is expected resulting in a negative contribution to future sea level ) Changes from both ice sheets combined : 0.03 to 0.20 m by 2081−2100
IPCC

84. 3. Sea level rise will not be uniform
3. Sea level rise will not be uniform. By the end of the 21st century, it is very likely that sea level will rise in more than about 95% of the ocean area. 70% of the coastlines worldwide are projected to experience sea level change

85. F. Carbon Cycle
“Climate change will affect carbon cycle processes in a way that will exacerbate the increase of CO2 in the atmosphere. Further uptake of carbon by the ocean will increase ocean acidification”
feedback between climate and the carbon cycle is positive in the 21st century
climate change will partially offset increases in land and ocean carbon sinks caused by rising atmospheric CO2. More of the emitted anthropogenic CO2 will remain in the atmosphere.

86. 2. global increase in ocean acidification for all RCP scenarios
2. global increase in ocean acidification for all RCP scenarios. decrease in surface ocean pH by end of 21st century :
0.06 to 0.07
0.14 to 0.15
0.20 to 0.21
0.30 to 0.32
IPCC

87. 3. By 2050, annual CO2 emissions (derived from Earth System Models): smaller than 1990 emissions (by 14 to 96%). By the end of 21st century, about half of the models infer emissions slightly above zero, while the other half infer a net removal of CO2 from the atmosphere.

88. G. Climate Stabilization, Climate Change Commitment and Irreversibility
“Most aspects of climate change will persist for many centuries even if emissions of CO2 are stopped. This represents a substantial multi-century climate change commitment created by past, present and future emissions of CO2 “
1. Cumulative total emissions of CO2 and global mean surface temperature response are linearly related.
Limiting the warming caused by anthropogenic CO2 emissions alone to less than 2°C (since 1861–1880) will require cumulative CO2 emissions from all anthropogenic sources to stay between
0 and 1570 GtC
0 and 1210 GtC
0 and 1000 GtC since that period
515 was already emitted by 2011

89. 2. large fraction of anthropogenic climate change resulting from CO2 emissions is irreversible on a multi-century to millennial time scale Surface temperatures will remain approximately constant at elevated levels for many centuries after a complete cessation of net anthropogenic CO2 emissions. Due to the long time scales of heat transfer from the ocean surface to depth, ocean warming will continue for centuries. 15 to 40% of emitted CO2 will remain in the atmosphere longer than 1,000 years. IPCC