Climate Climatic Variation Chapter 2 CLIMATE 1 Statistics

Climate & Climatic Variation (Chapter 2)

CLIMATE = 1. Statistics of Weather Daily Precipitation - Iowa/Nebraska

CLIMATE = 1. Statistics of Weather 2. The expected weather + departures from expected weather

CLIMATE Reflects the geophysical processes active at a location…

Northeastern Siberia

Namibia

Amazon Rainforest

CLIMATE = …and how they might change (e. g. , seasonally)… Winter Daily Precipitation - Iowa/Nebraska

CLIMATE = …and how they might change (e. g. , seasonally)… Summer Daily Precipitation - Iowa/Nebraska

… and in the future! (and of course the past)

CLIMATE 1. Implies samples over a period of time. How long? How frequent? 2. WMO standard: 30 years - which 30? - paleoclimate? 3. There is no universal standard, but must define the interval for the topic at hand

CLIMATE 1. Has regular cycles …

Grassland - Net Radiation Cycles FLH FSH Diurnal Dry Lake - Net Radiation FSH FLH

Cycles Annual Soil Temperature at depths marked

CLIMATE 1. Has regular cycles … 2. … with other types of variability superimposed …

Climatic Variation and Change (IPCC TAR, Ch. 2) Note: Trends, Abrupt Change, Stationarity

Climatic Variation and Change (IPCC TAR, Ch. 2) Note: Quasi-periodic Increased range of variability

Climatic Variation and Change Additional Factors 1. Abrupt change - external conditions (e. g. , solar output) - passing a threshold (e. g. ice caps melting) internal feedbacks 2. Multiple climate states from the same external conditions

The Climate System (IPCC TAR, Ch. 1)

The Climate System (IPCC TAR, Ch. 1)

The Climate System Three important controling factors: 1. Latitude 1. - insolation 2. Elevation - temp. decrease with height 3. Closeness to oceans - heat reservoir

The Climate System Water in the climate system: (Peixoto & Oort, 1992)

The Climate System

The Climate System Mean extreme temperatures and differences (˚C) : Northern Hemisphere 8. 0 21. 6 (Jan) (Jul) Southern Hemisphere 10. 6 (Jul) Globe 12. 3 16. 1 (Jan) (Jul) 16. 5 (Jan) 13. 6 6. 5 3. 9

Thermal Inertia of Oceans Annual Temperature Range (Wallace & Hobbs, 1979)

The Climate System (Michael Pidwirny, DLESE, 2004)

The Climate System Subsystems 1. Atmosphere - rapid changes - links other subsystems - greenhouse gases 2. Ocean - slow evolution (“memory”, “flywheel”) - chemical role, esp. CO 2 3. Land - range of time scales - cryosphere & biosphere roles - location of continents

Cryosphere Area (106 km 2) Sea-lev. equiv. (m) Max extent (%) Min extent (%) 24 % (Feb) 4 % (Aug) 13 % (Oct) 7 % (Feb) N. H. Land snow & ice Sea ice 2. 2 (Grnl: 1. 7) 7. 8 8. 9 Total 11. 0 S. H. Land snow & ice Sea ice Total Note: 13. 0 (Antr: 13) 73. 5 4. 2 17. 2 Time scales, albedo effects

Biosphere Note: albedo, evapotranspiration, surface roughness, gas exchanges (esp. CO 2)

Feedbacks Internal couplings through linking processes Amplify or diminish initial induced climate change

Negative Feedback: Example How does Earth’s temperature get established and maintained?

Solar Constant At photosphere surface, solar flux ~ 6. 2. 107 W-m-2

Solar Constant At photosphere surface, solar flux ~ 6. 2. 107 W-m-2 At Earth’s orbit, solar flux ~ 1360 W-m-2

Planetary Albedo Scattering: air molecules, aerosols Reflection: clouds Surface albedo

What is Earth’s temperature? Balance: Radiation in = Radiation out a Incoming = 1360 W-m-2 x (1 -albedo) x (area facing sun) = 1360 x (1 -0. 3) x pa 2 = 1. 2. 10+17 W

What is Earth’s temperature? Balance: Radiation in = Radiation out a Incoming = 1360 W-m-2 x (1 -albedo) x (area facing sun) = 1360 x (1 -0. 3) x pa 2 = 1. 2. 10+17 W Outgoing = s. T 4 x (area emitting) ; i. e. , black body = s. T 4 x 4 pa 2

What is Earth’s temperature? Balance: Radiation in = Radiation out a Incoming = 1360 W-m-2 x (1 -albedo) x (area facing sun) = 1360 x (1 -0. 3) x pa 2 = 1. 2. 10+17 W Outgoing = s. T 4 x (area emitting) ; (i. e. , black body) = s. T 4 x 4 pa 2 Balance implies T = {0. 7(1360 W-m-2)/4 s}1/4 = 255 K = -18 o. C

What is Earth’s temperature? Balance: Radiation in = Radiation out a Balance implies T = -18 o. C Observed surface T = +15 o. C Difference? Must account for atmosphere (greenhouse effect).

What if temperature decreases? a The same: Incoming = 1. 2. 10+17 W Outgoing = s. T 4 x (area emitting) = s. T 4 x 4 pa 2

What if temperature decreases? a These are the same: Incoming = 1. 2. 10+17 W Outgoing = s. T 4 x (area emitting) = s. T 4 x 4 pa 2 But for T < 255 K: Þ imbalance Þ Incoming solar exceeds outgoing IR Þ net energy input Þ T increases ~ Negative Feedback ~

Negative Feedback 1. Perturb climate system 2. Negative feedback moves climate back toward starting point 3. A stabilizing factor

Positive Feedback: Example How does Earth’s temperature get established and maintained?

Greenhouse Effect IR radiation absorbed & re-emitted, partially toward surface Solar radiation penetrates

Greenhouse Effect IR radiation absorbed & re-emitted, partially toward surface Net IR: ~25 -100 W-m Emitted IR: ~200 -500 W-m

Greenhouse Effect Cooler atmosphere: - Less water vapor - Less IR radiation absorbed & re-emitted Solar radiation penetrates

Greenhouse Effect Cooler atmosphere: - thus less surface warming - cooler surface temperature Solar radiation penetrates

Positive Feedback 1. Perturb climate system 2. Positive feedback moves climate away from starting point 3. A destabilizing factor Other examples (textbook): - ice-albedo feedback - CO 2 -ocean temperature feedback

Feedbacks Distinguish between: 1. external forcing change - e. g. , insolation, volcanism - often predictable 2. Internal feedback mechanisms - nonlinear, coupled interactions - generally less predictable (stochastic)

Radiation Spectrum Emission Black Body Curves 255 K 6, 000 K Wavelength [m] Solar (shortwave, visible) Terrestrial (longwave, infrared)

Daily Solar Radiation at Top of Atmos. [106 J-m-2]

Earth’s mean annual radiation and energy balance

Absorbed Solar Radiation

Outgoing Terrestrial Radiation

Key Energy Fluxes at Surface Sensible Heat FSH ≈ - r Cp. CH(Tair-Ts) FSH = r Cp(w. T)s Tair Ts CH = CH(V, zo, dq/dz)

Surface Sensible Heat Flux (Peixoto & Oort, 1992)

Key Energy Fluxes at Surface Latent Heat CW = CW(V, zo, dq/dz) but also CW = CW(physiology) soil moisture CW µ leaf temp. sunlight CO 2 level FLH ~ - r. Cp. CW{eair-esat(Ts)}

Surface Evaporation (Peixoto & Oort, 1992)

Grassland - Net Radiation Cycles FLH FSH Diurnal Dry Lake - Net Radiation t Less cooling by evaporation FSH t Ts increases t FSH larger FLH

Role of Albedo Scattering: air molecules, aerosols Reflection: clouds Surface albedo Ocean Snow Crop Forest Cities 2 -6% 40 -95% 15 -25% 5 -10% 14 -18%

Role of Albedo changes with latitude - changing land surface - changes in incidence angle Albedo changes with time - land changes (e. g. , ice sheets) - cloud cover

Role of Albedo changes with latitude

Role of Greenhouse Gases Primary gases: water vapor, CO 2, methane (CH 4), nitrous oxide (N 2 O), ozone (O 3)

Time Scales of Climatic Variation (IPCC TAR, Ch. 2) Note: Magnitude of changes Reduced “detectability” farther back in time

Time Scales of Climatic Variation (IPCC TAR, Ch. 2) Different size of changes

Time Scales of Climatic Variation

Earth’s Orbital Parameters Vernal Equinox (~ March 21) Aphelion (~ July 5) Perihelion (~ Jan 3)

Earth’s Orbital Parameters b a Eccentricity = SQRT(a 2 - b 2)/a ; for circle, = 0 Longitude of perihelion (one choice: angle from NH vernal equinox) Tilt of rotation axis (obliquity)

Variability of Earth’s Orbital Parameters

Earth’s Orbital Parameters b a Periodic variations Current Range ~ Period (yr. ) ~ 0. 02 [0. 0 - 0. 05] 95, 800 Longitude of perihelion ~ 270˚ [0˚ - 360˚] 21, 700 Obliquity [21. 8˚ - 24. 4˚] 41, 000 Eccentricity: 23. 4˚

Earth’s Orbital Parameters b a Seasonal efffect of variations (little annual effect) Eccentricity: intensity of seasons Longitude of perihelion NH-SH differences in summer insolation Obliquity extratropical summer-winter differences

Variability of Earth’s Orbital Parameters

Changes in Earth’s Orbit Some paleo-records can resolve different frequencies in an orbital element’s variability (e. g. , 19, 000 and 23, 000 yr periods in precession). Some can detect “beat” frequencies. Relative importance of frequencies changes with time - and may not correspond to dominant frequencies in climatic response. Shorter, lower amplitude frequencies might be important for decadal-millenial climate changes.

Changes in Earth’s Orbit Changes in Earth’s orbit affect - annual insolation cycle - past glacial-interglacial variability Croll (late 1800 s) Milankovitch (1941) Berger (1970 s)

Changes in Earth’s Orbit Changes in Earth’s orbit affect - annual insolation cycle - past glacial-interglacial variability Optimum conditions: minimum obliquity, high eccentricity, aphelion during NH summer - allow snow to persist through summer - allow relatively warm winter (increased subtropical evap. & increased snowfall) - transition seasons may also be important for snow-cover expansion

Variability of Earth’s Orbital Parameters

Milankovitch Theory

Scales of Climate Global Regional Microscale Microscale Microclimate B Plant B Soil Pathogen D Chemicals itus Management Insect B Chemicals Human Influences Erosion Plant A Soil Pathogen B Insect A ls ica Detr ls ica em Ch Soil A Soil C Soil B H 2 O, temperature, nutrients, microbes, soil carbon, trace chemicals H 2 O, temperature, nutrients, microbes, soil carbon, trace chemicals Particulate Deposition, Precipitation, Solar Radiation, IR Crop B em Ch Management trace gases, shading, particulate matter Air-Transported Pathogen B Solar, IR, wind, CO 2, CO, NOx, SO 2, H 2 O, temperature, trace gases, shading, particulate matter Air-Transported Pathogen A Microclimate C Crop A Surface slope, IR Radiation, Evaporation, Biogeochemicals Microscale Solar, IR, wind, CO 2, CO, NOx, SO 2, H 2 O, temperature, Microclimate A Microscale Hydrology, Soil Microbiology, Soil Biochemistry Field Field Regional Continental Scales of Landforms Field Regional Field

Climate & Climatic Variation (Chapter 2) END