What Goes Around Comes Around: Humankind, the Environmental Crisis, and the Future of Life on Earth Again Earth As A Closed System Reminder: Earth Sciences 088F Final Exam Saturday, December 9, 2006 7:00 pm Room: Natural Sciences Rm. 1 Closed system: exchange of energy but negligible exchange of mass with surroundings Again The Earth s Four Spheres The state of the Earth at any given time are the sum of the interactions between Earth s processes of the four spheres. Significance: If we have any hope in gaining a representative view of the global system, we must appreciate the individual components as well as their interactions. Unfortunately, the systems approach is at odds with the traditional reductionist approach and therefore is slow to become a focus in practical research.
Global Warming: Should we care about it? Obvious effects: Increase aridity of already arid lands Flooding of coastal areas where humans live in high densities An Example of Feedback in the Earth System: Plate Tectonics and Anchovies At first glance, these appear to be trivial matters Just increase irrigation and stop building close to shore, right? Direct effects are the least of our worries. What can be learn from looking at the Earth as a system? Plate Tectonic Environments: Note Trench Offshore of Peru (Deep Water) Stratification of Water Masses in Ocean Surface water Boundary Layer (Thermo-/Halo-/Pycnocline) Deep water Surface Water: warm, low salinity, but nutrient poor (high oxygen) Boundary Layer: rapid cooling, increase in salinity, moderate nutrients Deep Water: cold, saline, high nutrients (lower oxygen)
Nutrient levels highest in deep, cold water Prevailing winds in Peru associated with rising of air at equator. But winds veer westward due to Coriolis force as they approach equator Nutrient poor surface water Nutrient rich deep water Coriolis effect, in turn, due to Earth s spin Westward-blowing winds generate westward-flowing currents in Surface water Nazca Plate Peru Prevailing winds blow westward Nutrient levels very high in very deep waters of Peru-Chile trench (trench produced by subduction) El Niño: A disruption of the ocean-atmosphere system in the tropical Pacific Having important consequences for weather around the globe. Among these consequences are: 1. Increased rainfall across the southern tier of the US and in Peru, which has caused destructive flooding, and drought in the West Pacific 2. Devastating brush fires in Australia. Observations of conditions in the tropical Pacific are considered essential for the prediction of short term (a few months to 1 year) climate variations, so such events can be disasterous to the economy. Warm, nutrient-poor surface waters pushed westward Thermocline Warm water Normal Conditions wind High primary productivity in low P area Upwelling of cold, nutrient-rich deep water (to relieve pressure deficit) Cold water Under normal conditions, surface water is pushed westward, creating low pressure area off coast of Peru Upwelling of cold, nutrient rich waters amplifies primary productivity
Major contributor to economy of Peru: The Anchovy Fishery Thermocline El Niño Conditions Wind decreases in intensity Warm, nutrient-poor surface waters slosh back eastward Primary productivity crashes due to nutrient loss Upwelling of cold, nutrient-rich deep water shut off or reduced due to loss of pressure gradient Under El Niño conditions, wind dies down. Warm, nutrientpoor surface water sloshes eastward because wind is not longer pushing it westward Schooling Anchovies! Warm water Cold water Cold, nutrient rich waters no longer reach surface due to loss of pressure gradient Normal Winter Weather System Weather System During El Niño Event Low pressure system usually sits over Southeast Asia/Australia since warm water is pushed westward During El Niño event, low pressure system shifts westward, making normally warm, wet weather in Southeast Asia unseasonably dry, and normally cold, dry weather in South America unseasonably warm and wet
Increased rainfall, floods in South America. Consequences of El Niño Drought in Southeast Asia and Australia Unseasonably wet conditions felt as far afield as northern U.S and Canada in 1997. Crash in Anchovy fishery in Peru Economic Losses Due to El Niño An apparent increase in the frequency of El Niño events through time Economic Losses attributed to 1997-98 El Niño event Note: these disturbances are focused in tropical regions where most countries are of third world economic rank. Global warming decreases wind gradients and therefore makes the sloshing eastward of warm, surface waters more likely
O.k., So let s just count on higher frequencies of El Niño and prepare for them. Big Deal, right? How bad can it be? Anthropogenic greenhouse gas emissions Deforestation (reduce consumption of carbon dioxide) Cattle Ranching (producer of methane) Increase in human population Global warming Melting of permafrost, release of methane from methane hydrates Anaerobic decomposition of organic wastes (release methane and carbon dioxide) Another factor: Carbonate Solubility CO 2 + H 2 O + CaCO 3 = 2HCO 3- + Ca 2+ Remember how this equilibrium controls carbonate production in oceans? Cold water contains more CO 2 so tends to dissolve CaCO 3 Warm water has less CO 2 so tends to make more CaCO 3 But what if atmospheric CO 2 increases? Increase atmospheric CO 2, dissolve more CaCO 3 in oceans? CO 2 + H 2 O + CaCO 3 = 2HCO 3- + Ca 2+ How temperature offsets this effect is not yet clear BUT reef growth has been reduced, so less CO 2 is being taken up By reef photosynthesis (remember that corals have algal symbionts) Bottom line: positive feedback makes slight changes BIG CHANGES Yet another scenario What if coral reefs and other carbonate producers are killed off? Reefs form natural breakwaters in tropical coastal countries, so remove them and be prepared for more destruction from tropical storms. Decrease CO 2 uptake, augment CO 2 content of atmosphere Further warming Another climatic effect on global warming climate becomes more erratic, more tropical storms etc. So another possible feedback loop Further increases in fossil fuel combustion It is obvious that fossil fuel use contributes CO 2 to the atmosphere But it also increases content of SO x and NO x concentrations SO x and NO x react with H 2 O in the atmosphere, producing sulphuric and nitric acids and increasing acidity of precipitation And we all know what happens when carbonates come in contact with acid, right?
Carbonates react with acid to produce CO 2 So, increase acid precipitation, increase CO 2 input to atmosphere Warms atmosphere further END OF LECTURE Bottom Line: Global warming is not a simple matter to clear up But life goes on.