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Earth’s Environment, Climate Change, and Human Impacts. The Earth’s Energy Budget. Return to Physics. Energy is transferred by: Conduction. Faster molecules bump into slower molecules. Heating a skillet on the stove.
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Return to Physics Energy is transferred by: • Conduction. Faster molecules bump into slower molecules. Heating a skillet on the stove. • Convection. Energy is transferred with the material. Boiling pot of soup. • Latent heat. Energy is lost or absorbed when changing states (e.g., energy required to evaporate water). • Radiation. Heat from Sun reaching Earth.
Radiation: Basic Concepts • All matter radiates energy. • Radiant energy travels in the form of electromagnetic waves. • These waves do not require molecules to propagate. • Different types of radiation are characterized by different wavelengths: • AM radio waves ~100 meters • Microwaves ~ 1 mm • Infrared ~ 10-6 meters (1 micrometer (µm) = 10-6 meters) • Visible light ~ 5 x 10-7 meters • UV ~ 1 x 10-7 meters
Radiation: Basic Law • Stefan Boltzman law: • E = T4 • E is energy in Watts/m2 • T is temperature. • is a constant. • As T increases, E increases by a power of 4. • If T doubles, E increases by 16 times!
Spectrum of the Sun vs. Spectrum of the Earth
If the Earth always radiates energy, why doesn’t it cool? • It is in a state of radiative equilibrium. Incoming radiation is balanced by outgoing radiation. • Radiative equilibrium predicts surface temperature of approximately 255 K (approximately -18°C). • But, the Earth’s observed average surface temperature is 288 K (approximately 15°C). • Why the difference? The answer lies in an understanding of absorption, reflection, transmission of radiation.
Absorption Day • Objects that are good absorbers are also good emitters. • Consider an asphalt road. • During the day the asphalt absorbs solar radiation and warms. • At night the asphalt emits infrared radiation and cools relative to its surroundings. Warm Asphalt Road (warms due to solar radiation) Night Cool Asphalt Road (cools by IR radiation)
Albedo • Albedo: the ratio of reflected radiation to incident radiation. • Surface albedo varies • Spatially • Temporally • Earth’s average albedo is 31%.
With Greenhouse Effect Fig. 23.6
The Greenhouse Effect • A global warming effect in which the atmosphere of a planet traps heat and maintains the surface of the planet at a higher temperature than if there were no atmosphere. • Has existed throughout Earth’s history. • TMJ.
Composition of the Atmosphere • Atmosphere: • Nitrogen (78%) • Oxygen (21%) • Minor constituents: Argon, carbon dioxide, water vapor, ozone • Major greenhouse gases: • Water vapor • Carbon dioxide
The future of climate change is difficult to predict. What do we know?
What do we know? • Temperature and carbon dioxide are highly correlated. Fig. 23.7
What do we know? • Temperature and carbon dioxide have been increasing since the Industrial Revolution. Fig. 23.8
What do we know? • Compared to the last 1000 years, temperatures and carbon dioxide levels have been higher in the last century. Fig. 23.8
What do we think we know? • We think we know how carbon is cycled through various Earth reservoirs. Fig. 23.11
How do we figure out what’s going to happen? • Computer models. • Supercomputers. • General Circulation Models (GCMs) encompass various parts of the Earth system (atmosphere, oceans, etc.). • Very complex. Fig. 23.2
Why do we have difficulties with predictions? • Positive and negative feedbacks complicate climate change predictions. • Positive feedback: A change in one component is enhanced by changes in another component. • Negative feedback: Change in one component counteracts a change in another component.
Feedbacks • Water vapor feedback: Positive. Increasing temperature increases amount of water vapor in atmosphere. Water is a greenhouse gas, so this increases surface temperature, which in turn increases evaporation, etc.
Feedbacks • Albedo feedback: Positive. Increasing temperature decreases snow and ice, which decreases albedo. Decreased albedo means more absorbed energy, which means increasing temperature.
Feedbacks • Radiation feedback: Negative. An increase in energy reaching the Earth’s surface causes an increase in the temperature of the Earth, and therefore the amount of heat the Earth reradiates back out.
Feedbacks • Plant growth feedback: Negative. More carbon dioxide means more plant growth, which means more use of carbon dioxide in photosynthesis.
So, could we add Fe to “fertilize” ocean & thus ameliorate greenhouse CO2 build-up? 1. Will it work? 2. What are the ecological consequences? Just Add Iron ABCnews.com, Amanda Onion 10/11/00 How algae may slow warming By Gareth Cook, Boston Globe Staff, 10/12/2000 Helping ocean algae could beat greenhouse effect LONDON (Reuters), WIRE:10/11/2000 Global Warming NPR Morning Edition- John Nielsen, 10/11/00 Iron-Fed Plankton Absorbs Greenhouse Gases By ANDREW C. REVKIN, NY Times, 0/12/00 Iron May Increase Gas - Eating Algae By THE ASSOCIATED PRESS, 10/11/00 Oct. 2000
Why else do we have trouble predicting climate change? • Systems are COMPLEX!
