208_Lect07_color - Chemical Cycles: •Greenhouse Effect:...

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Unformatted text preview: Chemical Cycles: •Greenhouse Effect: Cause and effect •Chemical Cycles: CO2 and O2 •Chemical Fluxes: CO2 and O2 •Proxies for climate change: Isotopes Greenhouse Effect & Global Warming • Global Warming • • World wide increase in avg. Temp. World avg Cause = greenhouse effect What is climate change 1 Greenhouse Effect: Greenhouse Effect: Simply put … • Anomalous heating of atmosphere • • • E from surface absorbed by GH gas GH gas re-radiate the E, heating atm. & surface Natural process! W/out it, 30 ºC cooler Goldie Locks Effect • • If Earth was 17% closer to sun, then liquid water would not form on surface. Thus no CO 2 dissolved in oceans and E would be hot enough to melt Lead … .Like Venus is. If Earth was further from sun, then solar radiation would be lower and E would be and ice house like Mars. Observed increase in GH gases Direct measurement Mona Loa Ice core data 2 Observed Effects of GH Global Warming by 0.3-0.6 ºC! Receading Glaciers & Ice caps - past 100 yr Receading Glaciers Rising Sealevel - 18 cm in 100 yrs (greatest rate in E history)! Rising • • • Some would argue the Global Warming trend is natural - not forced by human activity. • • Some argue that solar activity is linked to global warming. In the geologic past this is true: Global trends in temperature proxies sometimes correlate with solar activity and cosmogenic nuclide abundances cosmogenic nuclide (e.g. 36Cl) (e.g. 36 • • • E.g. E.g. Midieval Warm period Warm (900-1400 A.D.) and the Little Ice Age (1500-1800 A.D.) However, this is not true of today ’s warming trend: there is 36 no no measurable increase in 36 Cl abundance over the past century. Measurable variability in solar activity after 1978 accounts for ~0.01% of total irradiance. 3 Some would argue the Global Warming trend is natural - not forced by human activity. • Long-term trends in temperature proxies sometimes correlate with Earth orbital cycles called Milankovitch cycles (e.g. the last ice age) • The cause of today ’s climate change is the greenhouse effect! However, this is not true of today ’s warming trend - it is much to rapid to correlate with variations in Earth ’s orbit • • This is the overwhelming consensus of the scientific community. AGU ’s position Observed Results of GH • • • Global Warming by 0.3-0.6 ºC (avg surface T)! avg surface Receding Glaciers & Ice caps - past 100 yr Rising Sea level - >20 cm in 100 yrs (greatest rate in E history)! • • • Averaging ~1.8 mm/y from 1950 to 2000 Rising faster today Mostly from thermal expansion of ocean, not added melt water Observed results of GH: Loss of Sea Ice • Effects polar bears: 2006 study showed predation and cannibalism within Beaufort Effects Sea population. In past 5 years, 43% of cubs survive compared to 65% between 19801990 •Barnes Ice Cap on Baffin Island is thinning (0.12 m/y ‘70-’84) accelerating (1.0 m/y Barnes ‘04- ’06). Correlates with increases in number of positive degree days (warming). 4 Observed results of GH: Increased hydrologic cycle Cyclone activity • Increase in number of category 4 and 5 cyclones over past 35 yrs. Increase in the duration of cyclones over past 35 yrs. Extreme rain events during Indian Monsoon between 1951-2001 • 10% Increase in frequency of intense rain events (>10 cm/day) • Increasing magnitude of intense rain events • Total amount of precipitation not increasing • • • Global Dimming - may have muted global warming • Aerosols in atmosphere increase Earth ’s albedo • • Carbon aerosol Particles reflect sunlight Between 1960 and ~1985, increase in aerosols caused ‘dimming ’ of ~3 to 6% S-dioxide aerosol •~1985 to early ‘90s Earth began to brighten again ~1985 Total aerosol –Decreasing aerosol emissions –Improved air-quality regulations –Reduced Pinatubo (volcanic) aerosols - 1991 eruption Brightening and Global Warming • ~1985 to early ‘90s Earth began to brighten again ~1985 Decreasing aerosol emissions Improved air-quality regulations • Reduced Pinatubo (volcanic) aerosols - 1991 eruption • • • This correlates with the rapid increase in temperature during the 1990s 5 Predicted Effects of Global Warming • • Increasing Global Temperatures Stabilizing our climate will require near-zero emissions (GRL, 2008) Model result GH gasses remain in atm for centuries • Must stop emissions to prevent warming beyond today ’s temperatures • Not possible given energy needs and sources • • Predicted Effects: Shifts in climate zones Predicted Effects: Continued rise in sea level • • Consider how this will effect coastal communities. Bangladesh: 1000 people/km 2 6 Predicted Effects: Extreme Weather Heightened hydrologic cycle (greater rainfall and snowfall) Recall Current Observations of Cyclones and Monsoon events above. • • Predicted Effects: Negative impact on marine ecosystems Increasing CO 2atm increases amount of CO 2 in oceans. This decreases pH of oceans (making them more acidic) Harmful to Plankton and Coral • • • • These form the base of the marine food web! Prediction - Harmful conditions will develop first in southern ocean within decades. • Nature, 2005 Predicted Effects: Negative impact on marine ecosystems • Measured decline in productivity in all oceans Area of low productivity (<0.07 mg chlorophyll/m 3). Area is expanding in all oceans. • Area expanding fastest in North Atlantic. • • 7 Predicted Effects: Negative impact on marine ecosystems • Observed change in phytoplankton productivity with latitude in both N. Atlantic and E. Pacific • Productivity migrating to high latitude. Direct effect on food webs, especially large mammals and fish who feed on zooplankton Predicted Effects: Negative impact on marine ecosystems • • • • • Global warming and resulting changes in ocean chemistry (increasing acidity) lead to negative effects on Coral Coral is a symbiotic relationship between the coral polyp and algae Coral Bleaching - coral expel their algae due to change in environment. This negatively impacts the vitality of the reef community. Recent results suggest this may not lead to to the ‘death’ of coral. It is suggested that this, in-fact, opens a niche for another algae more capable of surviving. Predicted Effects: Negative impact on terrestrial ecosystems • • • • Alpine Frogs - as climate warms, they must migrate up-mountain to reach cooler climate. Thus, the available habitat is decreasing. Tropical frogs - fungus growing on skin is killing them. Increased humidity is favoring the growth of fungus. Polar Bears in competition with Grizzly Bears around Hudson Bay - Polar Bears don’t hibernate. Will they eat sleeping grizzly cubs? Polar bears eat seals, will they adapt? These are just a few examples of many - we are currently experiencing the greatest rate of extinction on Earth (i.e., we are in the midst of the most rapid mass extinction in Earth history). 8 9 Negative feedback - Hot-house increases weathering (of silicates) consumption of CO2 - Hot-house causes anoxic bottom water & inhibits decomposition CO2 (from proxies) over Time 1. High CO 2 in Early Phanerozoic •few primary producers •(no forest beyond coasts, few phytoplankton) •Was it hot? Likely not •low solar output. So warm not hot. 2. CO2 Decline in Devonian •Land plants evolve to forest higher elevation •more plants - less CO 2 3. Carboniferous: CO2 Decline Continues •Coal swamps •Increased weathering from increased mountain building during assembly of Pangaea •ICE HOUSE 10 4. CO2 rise in Mesozoic •mountain building slows •weathering rates slow •Evolution of coccolithophores and foraminifera •increased calcareous ooze •increased CO 2 flux from subduction as these sediments subduct Infer Oxygen rich Carboniferous from Heavy C isotopes 11 Moderate Temp. vs . Warm Poles - no deep circulation 12 ...
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