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

… 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 …

Cycles - Net Radiation F SH F LH - Net Radiation F SH Grassland Dry Lake Diurnal

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) -internal feedbacks -passing a threshold (e.g. ice caps melting) 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 - insolation - insolation 2.Elevation - temp. decrease with height 3.Closeness to oceans - heat reservoir

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

The Climate System

Mean extreme temperatures and differences (˚C) : Northern Hemisphere 8.0 (Jan) 21.6 (Jul) 13.6 Southern Hemisphere 10.6 (Jul) 16.5 (Jan) 6.5 Globe 12.3 (Jan) 16.1 (Jul) 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 (10 6 km 2) Sea-lev. equiv. (m) Max extent (%) Min extent (%) N.H. Land snow & ice 2.2 (Grnl: 1.7) 7.8 Sea ice 8.9 Total % (Feb)4 % (Aug) S.H. Land snow & ice 13.0 (Antr: 13) 73.5 Sea ice 4.2 Total % (Oct)7 % (Feb) Note: 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 ~ W-m -2

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

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

What is Earth’s temperature? Balance: Radiation in = Radiation out Incoming = 1360 W-m -2 x (1-albedo) x (area facing sun) = 1360 x (1-0.3) x  a 2 = W a

What is Earth’s temperature? Balance: Radiation in = Radiation out Incoming = 1360 W-m -2 x (1-albedo) x (area facing sun) = 1360 x (1-0.3) x  a 2 = W a Outgoing =  T 4 x (area emitting) ; i.e., black body =  T 4 x 4  a 2

What is Earth’s temperature? Balance: Radiation in = Radiation out Incoming = 1360 W-m -2 x (1-albedo) x (area facing sun) = 1360 x (1-0.3) x  a 2 = W a Balance implies T = {0.7  1360 W-m -2 )/4  } 1/4 = 255 K = -18 o C Outgoing =  T 4 x (area emitting) ; (i.e., black body) =  T 4 x 4  a 2

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

What if temperature decreases? The same: Incoming = W Outgoing =  T 4 x (area emitting) =  T 4 x 4  a 2 a

What if temperature decreases? ~ Negative Feedback ~ These are the same: Incoming = W Outgoing =  T 4 x (area emitting) =  T 4 x 4  a 2 a But for T < 255 K:  imbalance  Incoming solar exceeds outgoing IR  net energy input  T increases

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 Emitted IR: ~ W-m Net IR: ~ 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)

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

Daily Solar Radiation at Top of Atmos. [10 6 J-m -2 ]

Earth’s mean annual radiation and energy balance

Absorbed Solar Radiation

Outgoing Terrestrial Radiation

Key Energy Fluxes at Surface Sensible Heat T air F SH =  C p (wT) s F SH ≈ -  C p C H (T air -T s ) C H = C H (V, z o, d  /dz) TsTs

Surface Sensible Heat Flux (Peixoto & Oort, 1992)

Latent Heat F LH ~ -  C p C W {e air -e sat (Ts)} C W = C W (V, z o, d  /dz) but also C W = C W (physiology) soil moisture C W  leaf temp. sunlight CO 2 level Key Energy Fluxes at Surface

Surface Evaporation (Peixoto & Oort, 1992)

Cycles - Net Radiation F SH F LH - Net Radiation F SH Grassland Dry Lake Diurnal  Less cooling by evaporation  T s increases  F SH larger

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

Role of Albedo 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 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

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

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

Earth’s Orbital Parameters 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) b a

Variability of Earth’s Orbital Parameters

Earth’s Orbital Parameters Periodic variations CurrentRange~ Period (yr.) Eccentricity: ~ 0.02[ ]95,800 Longitude of perihelion ~ 270˚[0˚ - 360˚]21,700 Obliquity 23.4˚[21.8˚ ˚]41,000 b a

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

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 1800s) Milankovitch (1941) Berger (1970s)

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

Global RegionalRegionalRegionalRegional MicroscaleMicroscaleMicroscaleMicroscaleMicroscaleMicroscaleMicroscaleMicroscaleMicroscale Plant A Crop BCrop A Insect A Soil Pathogen B Air-Transported Pathogen A FieldFieldFieldFieldFieldFieldFieldFieldFieldField RegionalRegionalRegionalRegional Continental Hydrology, Soil Microbiology, Soil Biochemistry Soil A H 2 O, temperature, nutrients, microbes, soil carbon, trace chemicals Soil A H 2 O, temperature, nutrients, microbes, soil carbon, trace chemicals Soil B H 2 O, temperature, nutrients, microbes, soil carbon, trace chemicals Soil B H 2 O, temperature, nutrients, microbes, soil carbon, trace chemicals Soil C H 2 O, temperature, nutrients, microbes, soil carbon, trace chemicals Scales of Climate Scales of Landforms Soil Pathogen D Plant B Insect B Air-Transported Pathogen B Human Influences Management Chemical s Erosion Chemical s Surface slope, IR Radiation, Evaporation, Biogeochemicals Detritus Particulate Deposition, Precipitation, Solar Radiation, IR Microclimate A Solar, IR, wind, CO 2, CO, NO x,SO 2, H 2 O, temperature, trace gases, shading, particulate matter Solar, IR, wind, CO 2, CO, NO x,SO 2, H 2 O, temperature, trace gases, shading, particulate matter Solar, IR, wind, CO 2, CO, NO x,SO 2, H 2 O, temperature, trace gases, shading, particulate matter Microclimate CMicroclimate B Chemical s

Climate & Climatic Variation (Chapter 2) END