1. Global Warming Alan Robock robock@envsci.rutgers.edu
Department of Environmental Sciences
Rutgers University, New Brunswick, New Jersey USA

2. Mann et al.
(1999)

3. Global Warming Fundamental Questions
1. How will climate change in the future?
2. How will change of climate affect us?
3. What should we do about it?
Considerable warming and sea level rise, in all conceivable scenarios
Uncertain, but predominantly adverse environmental and socio-economic effects
Reduce emissions (mitigation), study impacts, adapt

4. Global Warming Fundamental Questions
1. How will climate change in the future?
2. How will change of climate affect us?
3. What should we do about it?
Intergovernmental Panel on Climate Change (IPCC) Working Group I (WG I)
IPCC WG II
IPCC WG III

5. Intergovernmental Panel on Climate Change (IPCC)
3000 scientists from more than 150 nations
First Assessment Report (FAR), 1990
Second Assessment Report (SAR), 1995
Third Assessment Report (TAR), 2000

10. Actual observations

11. 1. How will climate change in the future?
How does climate system work?
How has climate changed in the past?
Validate climate models by simulating past.
Use climate models to predict different future scenarios.
Will people be the main cause of climate change in the next century?
If so, we need to respond.
If not, there is nothing we can do about it.

12. Detection vs. Attribution
Detection: Are the observed trends of climate (e.g., global surface air temperature or Northern Hemisphere sea ice) larger than would be expected due to natural variability of climate? [Yes]
Attribution: Do the observed trends match those predicted by climate models forced by the observed trends in anthropogenic CO2 and tropospheric aerosols? [Yes]

13. Climate Change – The IPCC Scientific Assessment (1990)
“The unequivocal detection of the enhanced greenhouse effect from observations is not likely for a decade or more.”
Climate Change – The IPCC Scientific Assessment (1990)
“The balance of evidence suggests
a discernible human influence on global climate.”
Climate Change 1995 – The Second Assessment of the Intergovernmental Panel on Climate Change (IPCC)
“There is new and stronger evidence that
most of the warming observed over the last 50 years is attributable to human activities.”
Climate Change 2000 – The Third Assessment Report of the IPCC

15. Climate System 1. Atmosphere 2. Hydrosphere (oceans)
3. Cryosphere (snow, ice, glaciers)
4. Biosphere (including people)
5. Lithosphere (soil, volcanoes)

16. The Climate System

17. Atmosphere Time Scale: days
Hydrosphere:
Oceans months-104 years
Lakes and rivers months
Soil moisture 1-2 months
Ground water years
Cryosphere:
Ice sheets years
Sea ice months-years
Seasonal snow months
Lithosphere:
Continents years
Soil years
Volcanic eruptions days-months
Biosphere:
Vegetation (affects gases, albedo, roughness, moisture flux)
Animals (also affect gases directly and interact with vegetation)
Humans

19. on the interannual time scale.
El Niño is the major interchange of energy between the ocean and atmosphere
on the interannual time scale.

20. Temperature Feedbacks
Start with temperature increase, e.g., from more CO2 – + + + – + – – –
External forcing

21. Predictability: How can we predict the climate decades into the future when we can’t even predict the weather for next week?
Predictability of the first kind: Predict the future based on initial conditions, with boundary conditions constant. This is limited by the chaotic nature of the atmosphere, which is a physical system with built-in instabilities, in vertical convection (e.g., thunderstorms) and horizontal motion (e.g., baroclinic instability - development of low pressure systems, such as hurricanes and Nor’Easters).

22. Consider a prediction using the above equation of the future state of the variable X, say the surface air temperature. The subscript n indicates the time, say the day, and a is a constant representing the physics of the climate system. X for any day is a times its value on the previous day minus X squared on the previous day.
With such a simple equation, it should be possible to predict X indefinitely into the future. Right?

23. Let’s assume that a is exactly 3
Let’s assume that a is exactly and that a prediction with three decimal places is the exact solution.
Then let’s consider three types of errors: imprecise knowledge of the physics of the climate system, imprecise initial conditions, and rounding due to limited computer resources.
This example is from Edward Lorenz.

26. Predictability: How can we predict the climate decades into the future when we can’t even predict the weather for next week?
Predictability of the second kind: Predict the future based on boundary conditions, independent of initial conditions. If there are slowly-varying (with respect to the atmospheric predictability limit of 2-3 weeks) boundary conditions (e.g., greenhouse gases, stratospheric aerosols, sea surface temperatures, soil moisture, snow cover) that can be predicted, then the envelope of the weather can be predicted. [The first two examples are external to the climate system, and the last three are internal.]

27. Fundamental Determinants of Climate
1. Input of solar radiation
2. Atmospheric composition (gases and aerosols)
3. Surface characteristics (albedo, roughness, potential evapotranspiration)
Humans can change climate by affecting 2 or 3.

28. Planetary albedo (a) is the average reflectivity of the Earth = 107/342  0.3
Earth’s global, annual mean energy balance

29. Earth’s global, annual mean energy balance
Atmosphere:
Total = ( ) W m‑2 - ( ) W m‑2 = 0 W m‑2
Outer Space:
Total = ( ) W m‑ W m‑2 = 0 W m‑2
Surface:
Total = ( ) W m‑2 - ( ) W m‑2 = 0 W m‑2
Greenhouse effect
Earth’s global, annual mean energy balance

30. Greenhouse Effect A = 4p r2 A = p r2 r a Ts S0 = 1368 W m-2
Emission = sTe4 a
a = planetary albedo (0.30) r
S0 = 1368 W m-2 Ts

31. Greenhouse Effect Global Energy Balance
Incoming Energy = Outgoing Energy
pr2 S0 (1-a) = 4pr2 sTe4
r = radius of Earth
S0 = solar constant (1368 W/m2)
a = planetary albedo (0.30)
s = Stefan-Boltzmann constant
(5.67 x 108 W m-2 K-4)
Te = effective temperature of the Earth
Ts = observed global average surface temperature
Greenhouse Effect
Ts = 288 K
Te = 255 K
33 K (59°F)

32. Sensible and latent heat
S0 = “solar constant” = 1368 W/m2
a = planetary albedo = 0.30
Te = effective temperature
Ts = surface temperature
Greenhouse gases
Greenhouse Effect
sTs4
sTe4
Ts = 288K = 59°F
(Observed)
Sensible and latent heat
esTe4
Greenhouse Effect
sTe4
Ts = Te = 255K = 0°F

33. Causes of Climate Change (Forcings)
Natural: Solar variations
Volcanic eruptions
Chaotic weather variations
El Niño/Southern Oscillation
Other ocean-atmosphere interactions
Anthropogenic: GHG: CO2, CH4, CFCs, N2O
Tropospheric aerosols
Sulfates, black carbon, organics, dust
Direct and indirect effects
Ozone depletion (indirect effect of CFCs)
Land surface modification
Contrails

34. Hansen and Sato (2001)

40. Mauna Loa, February 8, 2002
HOUR W1 W VW1 VW2 RSF V-AIR CO2 SDEV
(Z) (ppm) (ppm) (ppm/v) (ppm) (ppm)

43. Global Carbon Stocks - Most is in the soil, and all is vulnerable to human disturbances.

45. MMTCE = Million Metric Tons Carbon Equivalent
So the numbers here are the average number of tons of greenhouse gases produced per person per year, if all the gases were converted to the same effect on climate as CO2, in units of carbon contained in CO2.

46. Units are tons of CO2 (molecular weight 44 g/mole), as compared to C (12 g/mole) in the previous figure.

47. Units are tons per Terajoule (1012 J).

60. Mountain Glacier Trends
Where does the water go?

62. Change in mean produces more extreme weather
Change in mean and variance produces much more extreme weather
Change in variance produces more extreme weather

63. CO2
CH4
N2O
SO2

70. General Circulation Models (GCMs) 1
Basic Physical Laws:
Conservation of energy (First law of thermodynamics)
Conservation of momentum (Newton’s second law of motion)
Conservation of mass (Continuity equation)
Conservation of moisture
Hydrostatic equilibrium
Gas law

71. General Circulation Models (GCMs) 2
Physical Processes That Must or Can Be Included:
Wind Sea ice
Radiation Snow
Precipitation Glaciers
Soil moisture Vegetation
Ground water Ocean biota
Aerosols
Clouds, convective and large-scale
Air-sea exchanges of moisture, energy, and momentum
Air-land exchanges of moisture, energy, and momentum
Chemistry, particularly O3 and CO2
Ocean temperature, salinity, and currents

72. Real World vs. Model World

73. Theory of Climate Model Development Actual Climate Model Development
How to Construct a Climate Model
Programmatic
objectives
Management
directives
Preconceived
notions
Incorrect interpretation
of observations
Code
errors
Unrealistic
assumptions
Further
misunderstanding
Further refinement of
unimportant details
Publication
Coincidental agreement
between theory
and observations
Confusion
Sophisticated
computer model
Theoretical
Sparse and
infrequent
observations
Actual Climate Model Development

74. Typical grid spacing of a GCM is 4° x 5° latitude-longitude by 2 km in the vertical.
In the near future, we will have global 1° x 1° models and the Japanese are designing an “Earth Simulator” which will have a global 10 km x 10 km grid.
Each time the horizontal resolution is increased by a factor of 2, the time needed to run the model goes up by a factor of 8.
When the vertical resolution is doubled the time required doubles in general, but can go up by more, if winds become faster.

75. To include all the processes in a climate model which are of a scale smaller than is resolved by the model, they must be “parameterized.”
One of the most important and difficult climate elements to parameterize is cloudiness. Clouds have a much smaller spatial and temporal scale than a typical GCM grid box.
Usually, we consider separately 2 types of clouds, layer clouds and convective clouds. There is no fundamental prognostic equation for clouds (no conservation of clouds principle); rather they form when condensation takes place and dissipate due to precipitation and evaporation.

76. Rows and flows of angel hair
And ice cream castles in the air
And feather canyons everywhere;
I’ve looked at clouds that way.
But now they only block the sun.
They rain and they snow on everyone.
So many things I would have done
But clouds got in my way.
I’ve looked at clouds from both sides now.
From up and down, and still somehow
It’s cloud illusions I recall.
I really don't know clouds at all.
— Joni Mitchell
Both Sides Now, 1967

80. Future Sea Level Projections

81. IS92A plus aerosols scenario

82. 4xCO2: same but increase for 140 years
2xCO2 experiment: increase CO2 1%/yr for 70 years-then keep it constant at 2xCO2
4xCO2: same but increase for 140 years
meters
feet
Sea level continues to increase long after temperature increase slows

86. Instrumental observations
Volcanic forcing needed to explain climate change of past 150 years: Energy-balance climate model simulations
Volcanic and Solar Forcing
Volcanic, Solar, and Anthropogenic Forcing
Climate sensitivity
3°C for doubled CO2
1.5°C for doubled CO2
Instrumental observations
xxxxx Proxy observations
Third Assessment Report of the IPCC (2001)
Fig (from Free and Robock, 1999)

87. Third Assessment Report of the IPCC (2001): General circulation model results

88. Third Assessment Report of the IPCC (2001): General circulation model results

89. Third Assessment Report of the IPCC (2001): General circulation model results
Pinatubo

90. Annual mean temperature change
( ) minus ( ), °C

91. Annual mean rainfall rate change
( ) minus ( ), mm/day

93. Claire Parkinson and Donald Cavalieri David A. Robinson
Detection and Attribution of Anthropogenic Global Warming Using Observed Trends in Northern Hemisphere Sea Ice
Konstantin Y. Vinnikov
Department of Meteorology, University of Maryland, College Park
Alan Robock
Department of Environmental Sciences, Rutgers University, New Brunswick, NJ
Ronald J. Stouffer
NOAA/Geophysical Fluid Dynamics Laboratory, Princeton Univ., Princeton, NJ
John Walsh
Department of Atmospheric Sciences, University of Illinois, Champaign-Urbana
Claire Parkinson and Donald Cavalieri
NASA Goddard Space Flight Center, Greenbelt, Maryland
David A. Robinson
Department of Geography, Rutgers University, New Brunswick, New Jersey
Victor Zakharov
Arctic Research Institute, St. Petersburg, Russia
Donald Garrett
NOAA National Centers for Environmental Prediction, Camp Springs, Maryland

103. 2. How will change of climate affect us?

104. What Will Be The Impact on Humans of Climate Change?
Identify areas of human endeavor that will be affected by climate change.
For each activity, determine the future changes of the mean, variability, and extreme values of each important element for that activity, for every region of the earth where it would have an impact, for all times of the year.
If this cannot be done, then at least determine the sensitivity to each element by varying it over a range of possible values.
Evaluate the direct impact of climate change on the activity, taking into consideration future technological, sociological, economic, political, and military responses to each impact, singly, and in all combinations.
Assign probabilities to each choice and result, and determine the net human impact (Robock, 1993).

105. Climate Change and other Environmental Stresses
Algal Blooms
Land Use
Change
Pollution
Loss of
Biodiversity
Invasive
Species
Air
Pollution
Acid
Deposition

106. Areas of Human Endeavor That Could Be Affected by Global Warming
Agriculture Electricity Demand
Water Resources Wind Energy Generation
Fisheries Solar Energy Generation
Air Pollution Hydroelectricity Generation
Human Health Ocean Transportation
Recreation Air Transportation
Insurance Land Transportation
Wetlands Political Systems
Forestry

109. (e.g., drought, early frost)
Weather Stresses
(e.g., drought, early frost)
Climate Change Impacts on the United States (2000)

116. Affects:
Recreation
Water Supply

128. 3. What should we do about it?

129. y
Years in future

130. Mitigation Option: Stabilization of CO2 Concentration

131. Temperature Changes for Stabilization Scenarios

132. Sea Level Changes Because of Greenland Melting for Stabilization Scenarios

133. Adaptation Options

134. For more information, visit these web sites:
IPCC ( reports:
Working Group 1:
Working Group 2:
Working Group 3:
US Global Change Research Program:
National Academy of Sciences report Reconciling Observations of Global Temperature Change:
Global Change Data:
Mauna Loa Observatory Home Page (click Live Data to see latest CO2 observations):
Figures of CO2 and other greenhouse gas trends from NOAA’s Climate Lab: