Recent Climate, Energy Balance and the Greenhouse Effect David B. Reusch Penn State/New Mexico Tech CVEEN 7920/Geol 571

~4 x W W = watts = power = energy/sec

~4 x W W = watts = power = energy/sec

~4 x W W = watts = power = energy/sec

Basic Balance  342 W/m 2 of shortwave radiation input from the Sun is balanced by…  Earth outputs totaling 342 W/m 2 of  Reflected/scattered shortwave  Absorbed/re-emitted longwave  So what temperature is that?  342 W/m 2 of shortwave radiation input from the Sun is balanced by…  Earth outputs totaling 342 W/m 2 of  Reflected/scattered shortwave  Absorbed/re-emitted longwave  So what temperature is that?

Earth’s Average Temperature  An input of 342 W/m 2 translates to a mean surface temperature of -18 °C  We know that T A is actually 15 °C so what’s missing?  The short answer: an atmosphere which provides the natural greenhouse effect  An input of 342 W/m 2 translates to a mean surface temperature of -18 °C  We know that T A is actually 15 °C so what’s missing?  The short answer: an atmosphere which provides the natural greenhouse effect E =  T 4

~4 x W W = watts = power = energy/sec

Natural Greenhouse Effect

What Wavelength?  Sun ~6000 K, Earth ~288 K  Dominant Wavelength  Inversely related to temperature (Wien’s)  Hotter -> shorter wavelength  0.48  m (480 nm; visible)  10  m (infrared or IR)  Radiation emitted over a range of wavelengths  Sun ~6000 K, Earth ~288 K  Dominant Wavelength  Inversely related to temperature (Wien’s)  Hotter -> shorter wavelength  0.48  m (480 nm; visible)  10  m (infrared or IR)  Radiation emitted over a range of wavelengths

Note: shape of Earth’s spectrum. It’s modified by the atmosphere! Solar Peak Terrestrial Peak

What Happens To Insolation?  Reflection  Scattering  Absorption  Transmission  Reflection  Scattering  Absorption  Transmission

ReflectionReflection  Change in direction of a wave on encountering an interface  Atmosphere, clouds and surface  Measured by albedo  Change in direction of a wave on encountering an interface  Atmosphere, clouds and surface  Measured by albedo

Reflection (and albedo)  5-85%  = 35-75%

ScatteringScattering  Random redirection of light by the atmosphere  Wavelength and particle concentration dependence  Rayleigh (blue skies) and Mie (white clouds) are main processes  Random redirection of light by the atmosphere  Wavelength and particle concentration dependence  Rayleigh (blue skies) and Mie (white clouds) are main processes

ScatteringScattering

AbsorptionAbsorption  Energy taken up by object (photon is absorbed and destroyed)  Anything absorbed must be re-emitted to maintain equilibrium  At Earth temperatures, this converts shortwave into longwave when energy is re-emitted  Energy taken up by object (photon is absorbed and destroyed)  Anything absorbed must be re-emitted to maintain equilibrium  At Earth temperatures, this converts shortwave into longwave when energy is re-emitted

AbsorptionAbsorption

AbsorptionAbsorption  Atmosphere absorbs selectively (only some wavelengths)  Mostly transparent in visible range  Broad range of longwave absorbed by various greenhouse gases  Stratospheric O 2 & O 3 absorb UV  Atmosphere absorbs selectively (only some wavelengths)  Mostly transparent in visible range  Broad range of longwave absorbed by various greenhouse gases  Stratospheric O 2 & O 3 absorb UV

IR or longwaveUV & Visible

Shortwave 31% reflected directly 49% absorbed by surface 20% absorbed by atmosphere

Longwave 390 W/m 2 is energy from a body at 15 °C

Longwave

Longwave

Balance incoming

Outgoing Longwave Radiation

Additional complexity  Earth is a rough sphere  Slope, aspect  Latitude  Time/space varying albedo (reflectivity)  Vegetation, snow/ice, soils, moisture  Human land use change  Atmospheric composition/structure, clouds  Ocean, ice  Earth is a rough sphere  Slope, aspect  Latitude  Time/space varying albedo (reflectivity)  Vegetation, snow/ice, soils, moisture  Human land use change  Atmospheric composition/structure, clouds  Ocean, ice

Composition: Stable  Main components of dry atmosphere are pretty stable (~99%)  78% N 2, 21% O 2  Long-term (geologic) rise in oxygen  Changes in stable isotope ratios  Main components of dry atmosphere are pretty stable (~99%)  78% N 2, 21% O 2  Long-term (geologic) rise in oxygen  Changes in stable isotope ratios

Composition: Variable  Minor by volume (< 1%) but major by climate effect in many cases (GHGs)  Reactive (S, N, Cl cycles)  Non-reactive (CO 2, CFCs)  Water vapor (up to 4% by volume)  Particulates (aerosols)  Variation exists over many time and space scales  Minor by volume (< 1%) but major by climate effect in many cases (GHGs)  Reactive (S, N, Cl cycles)  Non-reactive (CO 2, CFCs)  Water vapor (up to 4% by volume)  Particulates (aerosols)  Variation exists over many time and space scales

Greenhouse gases  Certain naturally occurring trace gases change the atmosphere’s energy balance  Carbon dioxide (CO 2 ), Methane (CH 4 )  Water vapor and others…  Contribution to warming varies  By concentration  By “radiative efficiency”  By lifetime in the atmosphere  Certain naturally occurring trace gases change the atmosphere’s energy balance  Carbon dioxide (CO 2 ), Methane (CH 4 )  Water vapor and others…  Contribution to warming varies  By concentration  By “radiative efficiency”  By lifetime in the atmosphere

Leading Greenhouse Gases GasConcentration Carbon Dioxide (CO 2 ) 380 ppm Methane (CH 4 ) 1700 ppb Nitrous oxide (N 2 O) 500 ppb Ozone (O 3 ) 70 ppb Note: concentrations are approximate! Mexico ~one million people Mexico ~one million people India ~one billion people India ~one billion people

Climate Change 2007: Summary for Policymakers

33 Seasonal Cycle in NH Biota Anthropogenic Influence

Solar Base = 342 W m -2

Recent Change and Variability

-- Climate Change 2007: The Physical Science Basis (Chapter 3) Recent Climate Variations: Surface Air Temperature

Ranked Global Temperatures Tied

-- Climate Change 2007: The Physical Science Basis (Chapter 3) Spatial Changes in Temperature

Muir Glacier, Alaska, August 13, 1941, photo by W.O. Field

Muir Glacier, Alaska, August 31, 2004, photo by B.F. Molnia, USGS

Grinnell Glacier Glacier National Park 2005

-- Climate Change 2007: The Physical Science Basis (Chapter 3) Spatial Changes in Precipitation

-- Climate Change 2007: The Physical Science Basis (Chapter 5) Recent Climate Variations: Sea Level

Arctic Sea Ice Trends

Sept 2007 All-time Minimum

500 Million Years of Change

500 Million Years of Change

500 Million Years of Change

Today is Different  Rates of change not seen in geologic record  World did not have nearly 7 billion people  Rates of change not seen in geologic record  World did not have nearly 7 billion people