GEOL 1060 (Exam 3)

CONCEPTS:

10/31/13 ->

*Clicker Questions

a. "The IPCC (UN's Intergovernmental Panel on Climate Change) is a political body." -Scientists who participate in the IPCC assessment process do so without any compensation other than the normal salaries they receive from their home institutions b. "Climate scientists need there to be a problem in order to get money" Is there more money for climate science now? -No c. The movie presents a global temperature chart showing that the Medieval Warm Period was significantly warmer than the present. -Deliberate omission of half of the 20th century data on the plot -Ends in 1910; so it is not current d. "Climate variation in the past is clearly natural...so why do we think it's any different today?" Do we know why summers were warmer in the early Holocene (9,000-6,000 years ago)? -Yes, the Northern Hemisphere was closer to the Sun e. The movie states: "Most of the rise in [20th century] temperature occurred before 1940." -They fabricated the plot f. "CO2 is a relatively minor greenhouse gas." -False g. The movie claims: "We can't say thatCO2 will drive climate, it certainly never did in the past." a. Much of the early Earth warm times can only be explained by increases in GHG -Early Faint Sun Paradox h. The movie claims that the track of the 20th century warming follows solar activity precisely. Their plot looks pretty good, because... -It fails to include most of the recent warming j. "Global sea level rise is controlled only by the ocean's temperature, not melting ice, and thermal expansion would take more than your or -This guy's loony

*Costa Rica Deforestation

a. 1940 (67%) → 1983 (17%) -However, provides an income source for the locals

*Ozone Hole Example

a. A global atmospheric problem caused by specific emissions b. Has a potential to be dangerous c. Science provides strong evidence why (but never absolute proof) d. Global community agreed (first time?) to stop CFC production (Montreal Protocol and amendments) -This led to important preventative actions

*Little Ice Age

a. Abrupt onset of Little Ice Age in the late 1200s -HIgh probability that a bunch of sites got hit with this in ~1250 -Fluctuations: Irregular cooling (1300-1450 AD); ice melt and ice growth b. Two-step trend during this period c. Why? -In the very first peak of ice growth, there is a correlation to volcanic aerosols (1258 AD) d. Volcanic forcing of climate over the past 1,500 years -Certainly not random e. If Arctic Ocean sea ice thickens and expands, it eventually exports ice along the East coast of Greenland and into the North Atlantic, where it melts in the warm Gulf Stream waters

*Discovery

a. Antarctic Ozone Hole -Satellites have been monitoring the total amount of ozone since the 1970s -Mostly in the stratosphere -Starting in the late 1970s, satellites recorded the sudden disappearance of half of all the ozone in one region, but the computer rejected the results -The ozone levels were so low that they were outside the range allowed by its programs b. In 1984, scientists at the British Antarctic Survey finally realized that for six years, ozone data was missing for September and October -The computer glitch was exposed -The ozone hole was thus discovered

*Deserts

a. Areas of low precipitation -Arid: < 10 cm/yr (4 inches) -Semi-arid: < 25 cm/yr (10 inches) -Hyper-arid: -Dry sub-humid -Humid -Drylands: What life cares about; effective moisture b. Effective moisture: -The ratio of precipitation to potential evapotranspiration -PPT : PET

*Boulder Flood vs. Global Warming

a. Argument: -As the planet warms, the Arctic warms the fastest -This decreases the pole-to-equator temperature gradient -The strength of the polar vortex is determined by that gradient, so the polar vortex in the Northern Hemisphere weakens -A weaker polar vortex wobbles more and has more loops in it, increasing the probability of blocking high pressure zones -Stationary highs can block the normally westerly circulation at Northern Hemisphere mid latitudes -It was a stationary high that blocked super-storm Sandy from heading out into the North Atlantic like it normally would have done b. However, neither the Boulder floods nor Sandy are direct results of recent global warming -It is likely that the pattern of warming increased the probability of both events happening -Likely that the chance of extreme weather events will be more probable the planet continues to warm -Weaker polar vortex and more frequent blocking highs disrupting normal airflow -Warmer oceans, more evaporation, and increased atmospheric moisture → more energy in the atmosphere (→ latent heat of evaporation) -Sun warms the ocean -Convects up into the atmosphere

*Evolution of Global Temperatures Over the Past 70 Ma

a. Best representation is the bottom of the ocean -Changes the slowest b. First order trend: -Temperature has cooled on average for the last 70 Ma -Embedded in this trend is warming periods

*Review

a. CO2 in the atmosphere is a chemically unreactive gas; but, when dissolved in seawater, becomes more reactive and takes part in several chemical, physical, biological, and geological reactions b. When CO2 dissolves in seawater, it forms a weak acid: carbonic acid - This can change the pH of the ocean waters -This change is greatest at the surface waters -Current and future changes in ocean pH due to fossil fuel CO2 dissolving in sea water c. Change in ocean pH since 1850 AD: -Dissolved CO2 in the ocean is increasing -pH of the ocean is decreasing -More acidity

Warm Times / Cold Times

a. Clicker Questions b. Cenozoic Cooling c. Past Warm Times d. Explanation e. Holocene Case Study f. Iceland Case Study (1) g. Arctic Canada Case Study (2)

Deserts and Desertification

a. Clicker Questions b. Deserts c. Distribution d. Desertification e. Driving Monsoonal Circulation f. Boulder Flood vs. Global Warming

The Ozone Hole(s)

a. Clicker Questions b. Discovery c. What is Ozone? d. How is Ozone Created? e. Where Does Ozone Come From? f. Ozone in the Atmosphere g. UV Radiation h. Ozone Shield (Dr. Jekyll) i. Tropospheric Ozone (Mr. Hyde) j. Measuring Ozone Concentrations k. Ozone Destruction l. Polar Stratospheric Clouds m. Why Does the Ozone Hole Occur in October? n. Solar Radiation and CFCs o. Chlorine Ozone Destruction Take-Homes p. Mitigation: A Success Story q. Ozone Hole Example

Past Warm Times

a. Clicker Questions b. Evolution of Global Temperatures Over the Past 70 Ma c. Evolution of Global Temperatures Over the Past 5 Ma d. First Order Trend e. Explain f. Last Glacial Cycle g. Primary Explanation of Ice Age Cycles h. Holocene i. Review j. Little Ice Age k. Conclusions l. Take Homes

Forests, Deforestation, and the Role of Forests in the Climate System

a. Clicker Questions b. History of Forests c. Forest Types d. Rainforest Biodiversity e. Review f. Costa Rica Deforestation g. Deforestation: Why We Should be Concerned h. The Role of Forests in the Climate System i. Forest Take-Homes

The Great Global Warming Swindle

a. Clicker Questions b. Movie Illustrations

Ocean Acidification

a. Clicker Questions b. Predicting the Future c. Present Day Sea-Surface d. Review e. The Ocean as a Reservoir of CO2 f. Ridding the Ocean of CO2 g. Carbonate Buffer h. Conclusions and Mitigations i. Final Thoughts (For a High CO2 World)

Catastrophe Through Earth's History

a. Clicker Questions b. The Early Faint Sun Paradox c. The Birth of Oxygen d. K/T Extinction Event

*Take Homes

a. Climate perturbation caused by explosive volcanism, apparently crossed a threshold condition, after which positive snow-albedo and sea-ice feedbacks attained permanent snow/ice cover until late 20th century b. Illustrates how short-lived perturbations can lead to system-level change

*Past Warm Times

a. Cooling for 70 Ma -But, some sudden jumps -Shift to an ice-house world 2.6 Ma -Present warm times: Holocene (last ~10,000 years) b. The last Ice Age -2.4 Ma to ~10,000 years ago -Primary explanation of ice age cycles: Solar radiation forcing (changes in solar energy received by Earth due to irregularities in Earth's orbit); irregularities that themselves are regular

*Explain

a. Cooling for 70 Ma -With some sudden jumps b. Shift to an ice-house world 2.6 Ma ago c. Present warm times

*Desertification

a. Degradation of dryland areas -Degradation: Effective moisture is being diminished -Loss of biological or economic productivity -Reduced complexity in croplands, pastures, and woodlands -Major global environmental issue largely because of the link between dryland degradation and food production b. Make effective moisture even worse: → -Arid -Semi-arid (mostly) -Dry sub-humid areas (mostly) c. Causes of desertification: -May be caused by: Unsustainable human activity; climate change; or, may be caused by a combination of human activity and climate change -Drought: Rainfall significantly below normal for an extended period (~ several years; > 25% less than normal) -Drought and desertification need not be correlated, but they often are d. Sensitive regions -Dryland regions of the world are sensitive to desertification e. Example: -Following a brief period of excess rainfall, agriculture extends into drylands ("rain follows the plow") -Return to normal -Disrupted soils lead to desertification -Over-irrigation in closed drainages leads to salinization (vegetation dies; leads to desertification) -Groundwater depletion f. Case study: Sahel -Region between Sahara Desert and equatorial regions -Eastern Sahara has been wetter and drier in the past due to natural climate cycles Semi-arid/dry sub-humid -Barely enough rain to grow crops -Causes: Climate; climate change; agricultural practices; political process; population growth and migration -Sahel precipitation climatology (cm): Monsoonal system -Sahel lies in the Northern Hemisphere -Differential heating of summer monsoons -Sahel rainfall index shows drought persisting, though weaker, to present -Sub-Saharan drought from 1970-2000 --As drought sets in, cropping area begins to double -Fuel wood gathering impacts vegetation -Lowered groundwater; waterholes dry up -Water shortages concentrate livestock; trample vegetation -Without vegetation, sand is mobilized -Large-scale dust storms are more frequent -Saharan dust reaches Caribbean and weaken coral reefs -Impacts on human activity in the Sahel -Explanations: Natural climate variability; changes in sea-surface temperatures, related to ENSO variability; aerosols produced by industrialization in Europe cool Sahel, reducing the strength of the African Summer Monsoon; inappropriate technology/misguided foreign aid encouraged migration into the Sahara g. Desertification in the U.S. -The Dust Bowl of the 1930s -Causes: 10-fold increase in population between 1860-1920; deep plowing; monoculture destroyed soil structure; increased sensitivity to erosion -Final straw: Great Depression (no money for prairie farmers); natural, true drought at this time -Changed farming practices: Shallow plowing, along contours; planted windbreaks; crop rotation (fallow sometimes); irrigation

*Clicker Questions

a. Deserts are defined as those regions that are: -Dry -Relates to the amount of precipitation that comes in b. Could the South Pole, Antarctica, sitting on frozen water, be a desert? -Yes, a polar desert -It gets so little precipitation c. Deserts are most commonly located: -30º N and S of the equator -Also in the Polar Regions where it is dry d. Boulder is situated: -Mostly rain shadow, and sometimes rain window -Mostly semi-arid zone e. The great Boulder flood this fall was an example of: -An extreme rain window event f. Is there any link between the Boulder flood and global warming? -Strong, first-principled argument that the probability of extreme events has increased due to global warming -Suggests a link between a warmer planet and probability of these extreme events taking place g. Coastal deserts (like the Namib and Atacama) exist because: -They are next to persistent upwelling areas h. Which of the following things that might change is the least important variable in determining the strength of the African monsoon? -Least: Net primary productivity in adjacent oceans -Most: Temperature of the adjacent oceans; heating of the land by the summer Sun; latent heat of condensation; amount of vegetation cover i. If sea surface temperatures (SST) decreases in the Atlantic, that reduces the monsoon rains, which reduces vegetation cover. In this case, does vegetation change result in a feedback? -Yes, positive feedback j. If fuel wood gathering and livestock overgrazing reduce vegetation cover, what two consequent factors will tend to promote desertification? -Less evapotranspiration and higher albedo -Less water recycling and less of the Sun's energy absorbed k. Who was Woody Guthrie? -A folk singer from the last century -Present in one of the greatest U.S. desertification events -Wrote a song about it

*Predicting the Future

a. Difficult, yes b. But, some predictions are pretty secure -CO2 fossil fuel emissions will continue -Atmospheric CO2 levels (our greenhouse effect) will keep rising -The planet will continue to warm, albeit irregularly c. Because CO2 fossil fuel emissions will continue, the planet will continue to warm, glaciers will melt, sea level must rise, and the global ocean will become more acidic d. How do we measure acidity? -pH -pH is the measure of the hydrogen ion (H+) concentration of a liquid -Logarithmic scale -Every unit changes by a factor of 10 -pH of 7 = neutral -pH > 7 = "basic" -pH < 7 = "acidic" -If the pH solution is decreasing, the solution is becoming more acidic -If the pH of a solution is increasing, the solution is become more basic, or less acidic

*Mitigation: A Success Story

a. During the 1980s, the scientific community (atmospheric chemists) build a solid case that the catalytic interaction between chlorine atoms, released from CFCs, and ozone, was responsible for the observed destruction of ozone over Antarctica b. Many of the current climate contrarians used the same arguments against the evidence that Cl from CFCs was causing ozone depletion as they do against greenhouse gases causing global warming c. Despite contrarian complaints, in 1987, world leaders got together in Montreal and for the first time, agreed as a world goal to stop using CFCs -Not easy -Montreal Protocol in 1987 -Copenhagen in 1992 was the strongest amendment

*Clicker Questions

a. Earth has always been getting colder and warmer without any influence from human activity... -Agree b. Earth has always been getting colder and warmer without any influence from human activity, so why is the present warming any different? -There are natural explanations for past warmings, but only greenhouse gases explain the current warming c. Earth has been generally cooling since the end of the dinosaurs, 70 Ma. Why might that be? -There must have been a reduction in the greenhouse effect -This is a forcing -It is not: A really big volcanic eruption killed them and cold persisted (short-term); the Sun has been getting colder (the Sun has been getting hotter); Earth has moved farther from the Sun (the Earth's orbit on average can't change); Earth's albedo must have increased (the only way for the albedo to change is for the climate to change, and then you're back to square one) d. If the early Holocene summers in Iceland were 3 ºC warmer than present... -This is much more than 20th century warming -This shows that natural variability exceeds anthropogenic caused changes -There must be a strong forcing other than GHGs -The Sun must have been brighter then

*First Order Trend

a. Earth has been cooling, in general, but with notable exceptions, for most of the past 70 Ma (since the end of the age of dinosaurs) b. The most recent ice age began around 2.5 Ma -Through most of that time, Earth has been mostly in a "glacial cycle" c. For about the past Ma, Earth has experienced long (100,000 year) "glacials" separated by brief (10,000 year) "interglacials" -We call the present interglacial the Holocene, which began ~10,000 years ago

*Cenozoic Cooling

a. Earth has been cooling, in general, but with notable exceptions, for most of the past 70 Ma, since the end of the dinosaurs -First order trend is toward cooling

*Rainforest Biodiversity

a. Educator: No bigger than Minnesota -20,000 different species of plants -More than 20% are endemic -Minnesota has only 2,000 plant species, and only one (a dogtooth violet) is endemic -In all of North America, there are only 17,000 plant species

*Review

a. Evolution of global temperatures over the past 70 Ma: -Record from the bottom of the ocean -First order trend: Structured, but on average the planet has cooled -~2.5 Ma we see stones (icebergs); shift to an ice-house world -However, interesting hiccups throughout trend b. Most recent 40,000 years from Greenland ice cores -Warm is up again -~10-15,000 years ago enter modern time, out of ice age c. Holocene temperatures records from high Northern latitudes d. "Little Ice Age" throughout Europe -Before this time (1300-1900 AD), things were warmer -Tiger Ice Cap: Grew on an unglaciated plateau ca. 550 years ago, and was continuously present from 1450-1992 -Dead plants in growth position preserved under ice -Ice caps are single best proxy for past temperatures -Serpens Ice Complex (1958 AD) e. "Medieval Warm Period" (900-1300 AD) -This was not everywhere f. Medieval times -Vikings establish colonies on Greenland -Inuit from Alaska hunting bowhead whales in skin boats colonize Arctic Canada and Greenland -Ice-free seas

*The Role of Forests in the Climate System

a. Example 1: Amazonia -30% of the rainfall over the Amazon Basin is recycled water -During a rainfall event, leaves intercept the rainwater -Organic -rich soil absorbs rainfall -Evaporation off leaves and leaf transpiration return water vapor to the atmosphere -Two effects: Land water migration of rainfall; water vapor fuels more storms (latent heat of condensation) -Paradox: Requires heavy rainfall to exist, but 30% of the rainfall is itself dependent on the rainforest being present b. Example 2: Clear-cutting -Two adjacent catchments: one clear cut, the other left forested -Stream runoff and erosion in the deforested catchment was 4-10x the forested catchment c. Example 3: Ivory Coast -Replacement of rainforest by cropland over last 5 decades -Runoff increased 8-fold -Areas formerly suitable for cocoa now abandoned due to lower rainfall, less humidity, and more extreme summer temperatures -Similar in India where rice production fell after deforestation d. Tropical Rainforest moisture recycling -Evaporation cools lower troposphere (latent heat of evaporation) -Condensation (rain) heats upper troposphere (fuels monsoon flow) -Converting grasslands to Savannah or forest: increases surface roughness, leading to increased turbulence and convection (→ rain) -Patchwork deforestation may enhance rain by created heat islands (convection)

*Evolution of Global Temperatures Over the Past 5 Ma

a. First order trend: -Temperature has cooled on average for the last 5 Ma -Wiggling warmer -> colder -> warmer -> colder -> warmer -> -The last ice age: 2.4 Ma to ~10,000 years ago

*Iceland Case Study (1)

a. Goal: Recover a complete sediment core from the center of the lake in front of these outlet glaciers and use the records preserved in the mud to tell whether we could capture the entire Holocene out of it b. How can we tell if Langjokull is present? -If glaciers are calving, then stones are present -Ice-rafted debris (IRD) -If glacial erosion is occurring, then high sedimentation rates, silt dominates in summer, and thin clay caps in winter (varves) -Glacier flour attenuates light, few tiny plants in deep water; no glacier flour, light reaches bottom and little plants flourish -Diatoms: Water clarity and environmental quality c. Only in the Little Ice Age was the ice big enough to deliver stony sediment to the lake d. During the peak warmth of the early Holocene, Iceland was so warm that Langjokull melted completely -Ice cap modeling suggests the early Holocene summers must have been at least 3 ºC (5.5 ºF) warmer than present

*Holocene Case Study

a. How do we know the planet was warmer and/or colder in the past, and can we explain why? b. Iceland during the warm early Holocene: How much warmer?

*Final Thoughts (For a High CO2 World)

a. Life is tenacious and adaptable b. There will be many losers c. There will probably be some winners (i.e., extra CO2) d. We hope there will be some unexpected adaptations e. But, acidification will happen

*Deforestation: Why We Should be Concerned

a. Loss of biodiversity -Biodiversity: the degree of variation of life -Ecosystem service b. Global warming -Burning releases CO2 -Less photosynthesis (less NPP) leaves more CO2 in troposphere -Which is a positive feedback on warming? Both; both lead to increased CO2 in the atmosphere c. Climate impacts -What are ways incoming solar energy is transformed when it strikes a leaf? Sensible heat (transpiration, evaporation); latent heat; reflected (0.2 albedo) -Key variables: Leaf area index (how many leaves/unit area); rooting (depth; soil moisture content); water-holding capacity of the soil -Trees are atmosphere heaters and water recyclers -Biosphere becomes active player in the climate system

*Ozone Destruction

a. Natural cycle (absorption of UVC) b. Problem: Total amount of ozone in the stratosphere (everywhere) is 30% less than predicted if photodissociation is the only loss c. Catalytic reactions: -Trace elements that occur in the stratosphere can also destroy ozone d. Catalyst: -A substance that increases the rate of a reaction, but is itself unchanged by the reaction -Chlorine (Cl) is a catalyst for ozone destruction -Chlorine is free to repeat the cycle of ozone destruction again and again (~50,000 times) before Cl is removed -Chlorine comes from CFCs (chloro-fluoro-carbons - compounds containing chlorine, fluorine, and carbon) -Developed in the 1930s by DuPont and General Motors as a new refrigerant to replace highly toxic and flammable refrigerants in use (ammonia) -Inert gases; ~100 year residence time (long) -They break through the tropopause and into the stratosphere during rare, large convective storms in the tropics -Antarctica surrounded by ocean with no disruption to airflow by land, so the tropospheric winds thermally isolate Antarctica -Nitrogen

*Review

a. Net Primary Productivity (NPP) -The net annual production of organic matter by a particular ecosystem -Net means the total fixed minus the total amount respired -gC/km2/yr is the (net) grams of carbon fixed over each square kilometer in an average year

*How is Ozone Created?

a. O2 + photon → O + O -Slow b. O + O2 → O3 -Fast c. O3 + photon → O2 + O -Fast d. O + O3 → 2 O2 -Rare e. O + O2 → O3 -Common f. Cl + O3 → ClO + O2 -Fast g. ClO + O → Cl + O2 -Fast h. Cl + O3 → ClO + O2 -Fast

*Ozone Shield (Dr. Jekyll)

a. O3 absorbs very efficiently at UVC, and moderately well at UVB, but not much at UVA b. Sunglasses, sunscreens, etc. are designed to protect you from UVA and UVB, but not UVC c. Skin cancer is the most common of all cancer types d. UVA: -Rays cause skin cells to age and can cause some damage to cells' DNA -Mainly linked to long-term skin damage such as wrinkles, but are also thought to play a role in some skin cancers e. UVB: -Rays are mainly responsible for direct damage to the DNA -Cause sunburn -Thought to cause most skin cancers f. UVC: -Rays don't penetrate our atmosphere and therefore are not present in sunlight -Not normally a risk factor for skin cancer

*Conclusions and Mitigations

a. Ocean acidification is a predictable response to human activities that increase atmospheric CO2 b. There appears to be no practical way to remove this additional CO2 from the oceans after it has been absorbed, nor any realistic ways to reverse its widespread chemical and probable biological effects -Make seashells and send it to the ocean floor c. Reducing CO2 emissions would make a difference, and some have suggested adding something to the ocean to consume H+ ions (acidity) d. But, wasn't there a lot more CO2 in the atmosphere back in dinosaur times and lots of marine seashells living at the same time? -As we look into the future and watch CO2 go up to 1,000, we had a time in the past with 1,000 ppm CO2 with lots of seashells -Current rates of CO2 increase are unprecedented e. Solution: -Rates of atmospheric CO2 increase, and slow negative feedbacks -Dissolution of carbonate in marine sediments can counteract acidity increases if they occur slowly -The ocean can keep up with a slow rise of CO2, but the rates CO2 are rising at now are faster than anything we've seen before -Magnitude of change vs. speed change takes place at f. Presently, NOAA is monitoring CO2 concentration -Looking at changing acidity (warning system) -Predominantly at coral reefs

*Clicker Questions

a. Oceans cover about: -70% of the globe b. The global ocean is the largest reservoir in the active carbon cycle -True -The ocean contains 95% of all carbon in the active carbon cycle -1/3 of fossil fuel CO2 emitted is taken up by the ocean -1/3 of fossil fuel CO2 emitted is taken up by the vegetation c. If plants and oceans each take up the same amount of the extra fossil fuel CO2, we should be equally worried about the impact of CO2 on plants as on the ocean -No, because plants just convert CO2 to cellulose -Plants convert CO2 to cellulose through photosynthesis -Extra CO2 in atmosphere on its own makes it easier for plants to grow because they don't need to "breath" (lose water) as often d. What happens when CO2 dissolves in seawater? -It forms a weak acid, called a carbonic acid, which can change the pH of the ocean waters -It makes seawater more acidic (or, less basic) -As the ocean concentration of CO2 increases, so does acidity, causing pH to decline e. From what we have learned about the ocean, we would expect the greatest changes in pH due to anthropogenic CO2 emissions to the atmosphere be found in what part of the ocean? -Surface waters because they exchange quickly f. Based on what you know about ocean circulation, do you expect the higher acidity to remain restricted to the surface waters? -No, because slow vertical circulation mixes surface water into the deep ocean -Takes ~1,000 years for the ocean to turn over (~1,000-~3,000 years) g. Why does surface water pH decrease with time? -We run out of fossil fuels h. How do we get rid of CO2 from the ocean? -Make limestone i. As the oceans become more acidic, which form changes the most? -CO2-/3 (carbonate ion - thing that seashells need to make shells)

*History of Forests

a. Only last 100 Ma would look familiar -<2% of Earth history b. Earth 4.6 billion years old (Ba) -Handsome creatures in the sea, 500 Ma ago c. Life -> 3 Ba -Multicellular life, 600 Ma d. Plants -Green algae on land, 400 Ma ago -Short plants no more than 0.5 m tall for first 100 Ma emerged -As competition for light increased, taller plants had an advantage (required support - trunks) -Tall forests for last 300 Ma -Flowering plants, 100 Ma ago

*The Birth of Oxygen

a. Oxygen (O2) is a reactive gas, unlike N2 and Ar, the other two common gases in our atmosphere -Because it oxidizes most things, it is a great destroyer b. Because it's reactive, it is always getting used up in reactions, and lost from the atmosphere -Plants keep the O2 concentrations up to where it is in the atmosphere c. The emergence of carbon based photosynthesis by plants, which convert CO2 and water to organic matter wit the help of sunlight, releasing oxygen -Early life used hydrogen sulfide, which doesn't produce oxygen d. When life learned how to photosynthesize, free oxygen was released -Life in the oceans, full of dissolved iron stars tot photosynthesize and release O2 f. Banded Iron Formations -Almost all BIF older than 2 billion years -Time when photosynthesis evolved and oxygen was consistently being produced g. Once all the iron in the oceans was rusted, O2 could escape to the atmosphere -The planet's first, and one of its greatest, mass extinction events -Live, unprotected from the ravages of O2, had 3 choices: Extinction (most life forms perished); retreat to pockets of anoxia; evolve oxygen protection h. Stromatolites: Living fossils -First tings to give rise to photosynthesis -Pioneered plant lineage i. With free oxygen in the atmosphere came the first ozone layer j. Oxygen: Currently 21% -Too little and we couldn't absorb enough oxygen when we breath to cover the energy expended in breathing -Minimum: 10-15% -Too much and everything would burn up because oxygen is so reactive; global wildfire k. Lessons: -Catastrophes are bad for the status quo -Provide opportunities for new stuff -Species are vulnerable, but life is resilient

*What is Ozone?

a. Ozone is a gaseous molecule that contains three oxygen atoms (O3) -Rather than the normal two atoms (O2) b. Nasty stuff: -Extremely reactive -Strongly oxidizing c. Formation and destruction of ozone is going on all the time in a natural cycle -Mostly in the stratosphere -Interaction of specific wavelengths of solar radiation and oxygen -This natural cycle is also being impacted by human activity d. A small amount of ozone is being created on the troposphere, by both human industrial activity and some natural causes (e.g., lightening)

*Tropospheric Ozone (Mr. Hyde)

a. Ozone shields us from harmful solar radiation b. Its reactive nature cleans the troposphere of pollutants, but at ground level it is a major eye and lung irritant and kills plants c. Ozone damages living tissue and makes rubber bands brittle d. L.A. and Denver photochemical smog e. Ozone is present in the air that surrounds us f. Formed when hydrocarbons and nitrogen oxides (NOx) from forests (natural), industries, and automobile exhaust and volatile organic compounds react with heat and sunlight g. Ozone gives off the acrid smell after lightening discharge (natural) h. Ground-level, "bad," ozone: -The harmful effects can include throat and lung irritation or aggravation of asthma or emphysema -Ozone is also a greenhouse gas in the troposphere (it does absorb Earth's back radiation)

*Last Glacial Cycle

a. Peak warmth of the last interglacial (130,000 - 120,000 years ago) followed by return to glacial conditions b. Extensive continental ice-sheets start to develop about 120,000 years ago c. Ice sheets start to melt ~15,000 years ago, and were mostly gone by ~10,000 years ago -Start of the present interglacial (Holocene) d. Peak glacial: 25,000 - 15,000 years ago e. -> Glacial melting

*Where Does Ozone Come From?

a. Photodissociation of O3 consumes (blocks) the most energetic energy (shortest wavelengths) from the Sun, and in the process heats the stratosphere b. Most O3 production is in the tropical stratosphere -The solar flux is highest there (perpendicular to Sun's energy) -Stratospheric winds move O3 to higher latitudes

*Explanation

a. Plate tectonics -About the time of the dinosaur demise, but unrelated to it, continental collisions increased, causing the formation of new mountain ranges -New mountains expose a lot of fresh rock -Plant acids and slightly acid rain (all rain is) "weather" rock minerals, forming soil -Rock weathering consumes atmospheric CO2, turning it into a new mineral -Periods of mountain building typically reduce the greenhouse effect on tectonic timescales (millions of years)

*Why Does the Ozone Hole Occur in October?

a. Polar vortex isolates Antarctica in winter -Keeps heat and new O3 from entering Antarctic stratosphere -At - 80 ºC, polar stratospheric clouds form CFCs b. When the Sun returns, it releases reactive Cl from polar stratospheric cloud droplets and they destroy O3, which cannot be replaced efficiently until polar vortex breaks down as summer warms the system (November) -With summer, and loss of polar vortex, O3 arrives from tropics and new O3 is created

*Driving Monsoonal Circulation

a. Positive feedbacks -Impacts on fuel wood gathering and stock overgrazing (both reduce vegetation cover) -Vegetation-free land raises albedo

*Solar Radiation and CFCs

a. Short-wave UV radiation breaks CFC bonds, releasing atomic Cl, which is then free to participate in the chlorine catalytic cycle, where each Cl atom destroys tens of thousands of O3 molecules b. The chlorine cycle is eventually broken when Cl combines with CH4 or H2 to form HCl, which is scrubbed out by precipitation (acid rain)

*Conclusions

a. Simple, long term cooling -Northern Hemisphere summer is getting farther from the Sun -Nailed by explosive volcanic explosions b. Decreasing Northern Hemisphere summer insolation and decadally-paced explosive tropical volcanism produced self-sustaining expanded Arctic sea ice c. In Arctic Canada, Little Ice Age began abruptly ~1250 AD, intensified in ~1450 AD

*Primary Explanation of Ice Age Cycles

a. Solar radiation forcings: -Changes in solar energy received by Earth due to irregularities in Earth's orbit -Procession of the equinoxes (mild vs. hot summer; mild vs cold summer) -Changes in tilt of spin axes: When Earth is tilted more toward the Sun, the summers will be...warmer; when we tilt, each hemisphere has increased seasonally (hotter summers, colder winters)

*Ridding the Ocean of CO2

a. Steps: -Make the ocean more acidic -Makes the oceans even more acidic and produces carbonate ions (or, stuff that allows the formation of seashells (limestone)) b. Biological and physical pumps of CO2 -The ultimate CO2 sink: bury CO3 quick enough and it will be removed from the system c. The pH of seawater determines the proportions of CO2, bicarbonate, and carbonate ions d. The process of carbonate ions becoming bicarbonate ions means it takes a hydrogen ion (negative feedback) -Carbonate buffer

*Distribution

a. Sunbelt -Abundant sunshine and lack of moisture at the descending limbs of the Hadley Cells -Arid zone b. Rain shadow -Windward side/rain window (moist air) -→ Leeward side/rain shadow (dry side) -Much of the western U.S. arid zone is due to the rain shadow effect c. Continental interior -So far from the ocean that not a lot of precipitation comes in -There are deserts in the middle of continents that don't fall into any of these particular categories d. Coastal strips -Cold upwelling water cools the atmosphere -Dense = high pressure plus little evaporation e. Polar deserts -Antarctica and parts of the Arctic

*Carbonate Buffer

a. Term is used to describe how the dissolved inorganic carbon system in seawater acts to diminish changes in ocean H+ concentration, and thus pH b. If the ocean has a natural buffer (carbonate ions) that provides a negative feedback on acidification, can we breathe easy? -Not really -The carbonate buffer only slows down acidification; it does not stop it -We need those carbonate ions -Without, we cannot create limestone -Or limestone will be created less effectively c. Calcification is the process by which marine organisms build their shells -Calcium + carbonate ion + calcium carbonate (limestone) -For marine organisms with carbonate shells to live, requires carbonate ions -As carbonate ions become less, these organisms have a harder time making their shells -Calcium carbonate dissolves in acid, so as the ocean becomes more acidic, carbonate shells start to dissolve, endangering organisms counting of their protective shells -Ex: Coral reefs (may start dissolving when atmospheric CO2 doubles)

*Clicker Questions

a. The Earth has always been getting warmer rand colder in the past. There have been far warmer times than the present in the past. So why is today considered unusual? -There are probably good explanations for other warm times, too -The Earth really can't on its own alternate between extreme hots/colds -Must be plausible explanations for why Earth would have been hotter/colder in the past b. Which of the following is least likely to be a significant contributor to the climate change of the Little Ice Age? -Least: Changes in CFC concentrations in the atmosphere -Most: Explosive volcanism; changes in sea ice area; changes in solar irradiance; changes in GHG concentrations c. Would Arctic amplifications (positive feedbacks inherent to the Arctic) make the Arctic regions colder than the Northern Hemisphere average during the Little Ice Age? -Yes d. Explosive volcanism can cool the planet, but why might it be a poor explanation for the Little Ice Age? -Volcanic sulfate aerosols are removed in ~3 years -However, decadally-paced volcanism produces a larger cumulative cooling than even very large single eruptions because recurrence interval shorter than ocean recovery time -Much longer for ocean temperatures to recover -10-15 year recover vs. 3 year recovery -With the long recovery time of the ocean's surface waters, it is possible to get a greater cumulative impact with multiple, closely spaced eruptions e. What would you suggest we use as a proxy for explosive volcanism prior to the historical record? -Volcanic ash in ice cores -Volcanic ash in ocean sediment -*Sulfuric acid in ice cores -Evidence that glaciers grew due to cold -Pollen f. If sea ice exported along East Greenland and eventually melts in the North Atlantic Ocean, it both cools and freshens surface water. Would this impact the strength of Thermohaline currents? How and why? -Yes, weakens, because the water is less salty

*Ozone in the Atmosphere

a. The distribution of ozone in the atmosphere is controlled by the balance of formation and destruction, and atmospheric motion b. The very short wave energy (< 200 nm) required to split O2 molecules and that required to split O3 molecules (200 - 300 nm = UVC) is consumed in the stratosphere and is not found below 20 km height c. Formation and destruction involve the absorption of specific wavelengths of solar radiation -So, they heat the atmosphere -This is why the stratosphere is stratified

*Movie Illustrations

a. The movie presents a global temperature chart showing that the Medieval Warm period was significantly warmer than the present -Credit: IPCC -However, if we include the present of the 20th century, the current temperatures (2013) is significantly higher than anytime during the Medieval Warm Period b. Although water vapor is indeed the dominant GHG in the atmosphere, CO2 is the next most important -Perhaps more importantly, as we learned in our Ocean Acidification section, the weakening of removal processes (sea shells to the sea floor) as the ocean absorbs more CO2, means that the residence time of the new CO2 we add to the atmosphere is ~100,000 years c. Warming should be faster in the upper troposphere, but the move claims the troposphere is warming more slowly, disproving GHG warming d. Temperature changes from satellites a. Early reports of tropospheric temperatures determined from satellites did not agree with surface thermometer measurements e. Ice Age CO2 and temperature -CO2 and temperature change together, but temperature "leads" CO2 over Antarctic -Recent studies show Antarctica temperatures change later than global temperatures, and that CO2 and global temperatures are aligned f. Sunspots increased in the early 1900s, but have decreased since the 1960s, just when temperatures increased the most

*Present Day Sea-Surface

a. The ocean is slightly alkaline (basic b. Carbon dioxide in the atmosphere is a chemically unreactive gas, but when dissolved in seawater, it becomes more reactive and takes part in several chemical, physical, biological, and geological reactions c. A decrease of ocean surface waters by a tenth of a pH unit (8.16 to 8.06) doesn't sound like much, but... -Because pH is a log scale (every unit smaller is ten times more H+ than the next higher unit), a drop in 0.1 pH units = 30% increase in hydrogen ion concentration

*Holocene

a. The past 10,000 years b. Within the Holocene, solar energy in the Northern Hemisphere was at a maximum at the beginning of the Holocene, and has been decreasing ever since c. Evidence: -We expect current Northern Hemisphere to be coolest of the Holocene d. Northern Hemisphere's climate over the past millennium (the past 1,000 years of climate history): -Medieval Warm Period -Little Ice Age -20th century warming e. Medieval Warm Period: -~900 AD - ~1200 AD -Explorers (Vikings) exploration -Vikings establish colonies on Greenland -Inuit from Alaska hunting bowhead whales from ice-free seas in ski boats colonize Arctic Canada and Greenland -Wine grown in England -Beginning ~1300 AD, sea ice in the North Atlantic increased; Inuit houses no longer have whale bones, only seal bones, and travel to Greenland colonies became difficult -By ~1400 AD, the sea was so heavy that ships were unable to bring supplies and Greenland colonies were lost f. Little Ice Age: -~1300 AD - ~1900 AD -Arctic glaciers and explosive volcanism -Despite being the coldest centuries in the past 8,000 years, no one has satisfactorily explained why it happened -Arctic amplification: If global temperatures change, Arctic temperatures will change even more -Tiger Ice Cap grew on an unglaiated plateau ca. 550 years ago -Glaciers and ice caps are the most reliable monitors of past summer temperature changes at high northern latitudes -Hypothesis: Rooted plants might be common where there is recent ice-cap recession on flat group where the ice did not erode

*Forest Take-Homes

a. Tropical Rainforests: -World's highest biodiversity -Highest NPP, important for drawdown of atmospheric CO2 -Major role in recycling atmospheric water vapor through evapotranspiration -Most exist on impoverished soil; harvesting or slash/burn agriculture not sustainable -They are sensitive to disturbances b. Boreal Forests: -Low biodiversity -Relatively low NPP -Most on young soil; harvesting can be sustainable

*Forest Types

a. Types: -Boreal -Temperate -Tropical b. Boreal Forests -Conifers -Slow growing -Cold -Half-year low light -Shallow -Immature - Mineral-rich soils -Low plant and animal diversity -Capable of sustained harvest, but low yield (slow growth) c. Temperate Forests -Mixed deciduous hardwoods -Fertile soils -Resistant to disturbance: if cleared, rapid recolonization -Sustained yield is "okay" in most regions -Eastern U.S. and European examples -Total area is so small -Insignificant in the global picture d. Tropical Rainforests -Conifers -Hardwoods -Very high biodiversity -Very high NPP -Closed canopy -High rainfall -Where are rainforests most common? Close to the equator -Why would we expect rainforests commonly close to the equator? ITZC (Inter-Tropical Converge Zone); main feature in tropical regions; moisture rises up and produces rain -Tropical rainforests occur wherever it is warm and dependably wet -High standing biomass (40% of total global biomass; but, only 3% of total global area) -Lungs of the world -Inhale CO2 (through photosynthesis) and exhale O2 -The risky bit: Soils (ancient, little rock left, leached of nutrients (long time and high rainfall), few sources of nutrients - aluminum and iron; almost all nutrients are recycled - incapable of sustained high harvest -30% of tropical rainforest is in the Amazon Basin -40% of the global production of O2 comes from Amazon -Ecosystem service

*UV Radiation

a. UV radiation is between 200 - 400 nm b. We divide the UV portion into three segments: -UVA -UVB -UVC c. UVA -Longer wavelength -Solar flux increases for longer wavelength -Least energetic -320 - 400 nm -Relatively harmless -Causes tanning, but not burning -Little UVA is absorbed by ozone d. UVB -Middle wavelength -290 - 320 nm -Harmful -Causes sunburn, skin cancer, and other disorders -BCC (most will get), squamous, melanoma (bad), etc. -Beneficial with inducing production of Vitamin D -Half of UVB flux is absorbed by ozone e. UVC -Shortest wavelength -Most energetic -200 - 290 nm -Extremely harmful -Destroys DNA -Cannot repair UVC damage -Almost completely absorbed by ozone

*Measuring Ozone Concentrations

a. Units of measure: Dobson units (DU) -A measure of the total number of ozone molecules in the atmosphere above a specific spot on Earth -1 DU = a layer of pure ozone 0.001 cm thick at 1 atmosphere -Typical ozone concentration is 300 DU (3 mm)

*Arctic Canada Case Study (2)

a. Unprecedented recent ice cap retreat b. Earth does not warm or cool for no reason -Orbital irregularities are the primary driver of ice age warm/cold cycles, with strong positive feedbacks required to explain the full magnitude of change c. Limitations of historical record -How do we know the observed trend is not part of a longer cycle? -Atlantic Multidecadal Oscillation (low frequency, unforced climate variability) d. Natural modes of variability -Do unforced, multidecadal cycles of temperature change explain some or all of the observed recent Arctic warming? -The instrumental temperature record is too short and spatially limited to resolve -Is recent warming outside the range of natural variability? -Paleoclimate record -High northern latitude ice caps are the most reliable monitors of past summer temperature changes -Cold ice caps on flat terrain do not erode; they preserve ancient vegetation -Tell us when snowline dropped below and remained below (on average) until the current decade (1235 +/1 20 years ago) -Regrowth (mosses) or colonization occurs within 3 years, rapidly resetting the radiocarbon clock; dead plants are eroded by meltwater or wind e. Newly exposed vegetation rates tell us: -Current summer temperatures are at least as warm as any century in the past 5,000 years -But, five sites do not fit this plot -Rooted tundra plants exposed by recent melt at five sites gave dates between 41,000 and 47,000 years f. Consequently, we can say with considerable confidence that summers of the past century were warmer on average than any century in at least 40,000 years -We speculate that the true age of our old vegetation is ~120,000 years, at the end of the last interglaciation g. Conclusions: -5,000 years of summertime cooling has now been reversed by a 4 ºC rise in recent decades -Despite the fact that the energy from the Sun is less -Our data from Arctic Canada cannot be explained by changes in solar forcing

*Polar Stratospheric Clouds

a. Very strong polar vortex in the winter that thermally isolates Antarctica b. In the winter (June - August), there is no Sun, so the atmosphere gets bitter cold (-80 ºC) -At such low temperatures, stuff in the atmosphere freezes to form polar stratospheric clouds (mostly water and nitric acid) -Chlorine attaches to polar atmospheric cloud droplets

*The Early Faint Sun Paradox

a. We can't visit the Sun, but we are pretty sure we know what makes it emit energy: -Nuclear fusion: Specifically, the joining of 4 hydrogen atoms to make 1 helium atom, with the release of much energy -1 helium atom is smaller than four hydrogen atoms (more dense) b. The Sun's density increases, the rate of fusion increases and so solar luminosity increases c. The Sun has been getting steadily hotter in the past 5 million years -Currently 15 ºC (60 ºC) d. The Earth's temperature varies only as the ¼ power of the solar output -Stefan's Law -Less impact on the temperature e. Planetary energy balance: -Earth's albedo -Heat from sources within the Earth -The Sun's temperature -Earth's greenhouse effect -The distance Earth is from the Sun f. Impact: Ocean surface water of the world should have been frozen -Yet we find shallow ocean sediments g. Not necessarily a catastrophe, because GHGs kept the Earth warm when the Sun was too weak h. How can we resolve this paradox? -More greenhouse gases -With present GHGs, the ocean should have been frozen -Requires 1,000x as much CO2 that presently exists in the atmosphere to thaw the ocean -Sounds like a lot, but carbonate rocks hold so much carbon -Only 2% of carbonate rocks that exist that you would need to put in the atmosphere -More methane likely because no oxygen present -Gaia Hypothesis -Lower albedo -Early Earth may have no clouds -Even albedo of 0, temperature is below -20 ºC -Other heat sources -100 w/m2 less energy

*Chlorine Ozone Destruction Take-Homes

a. When the Sun returns, complex chemistry occurs on the surfaces of polar stratospheric clouds releasing reactive chlorine b. Chlorine catalytic reactions destroy ozone c. No new ozone can be created until summer and none imported until polar vortex breaks down d. With summer, polar stratospheric clouds dissipate and ozone arrives from lower latitudes

*Clicker Questions

a. Where are rainforests most common? -Close to the equator b. Why would we expect rainforests commonly close to the equator? -ITZC (Inter-Tropical Converge Zone) -Main feature in tropical regions -Moisture rises up and produces rain

*Clicker Questions

a. Where is the main ozone hole? -Antarctica -Why not in the Arctic spring as well?: Mountains around the Arctic set up standing waves in the atmosphere that preclude a strong polar vortex in the Arctic; some open water in the Arctic Ocean keeps the temperatures from getting so cold; but there has been some reduction of Arctic ozone in recent years b. Is the ozone hole always there? -Only specific months Early "spring": September, October, November -Not present before 1979 c. There is indeed an ozone hole. Is it getting bigger or smaller? -Smaller d. There is indeed an ozone hole, and we know it exists because of human activity. Has the world collectively acted to eliminate the cause of the ozone hole? -Yes e. Because oxygen absorbs a portion of the Sun's radiation (energetic UV), this warms the stratosphere -True -And, because most of the absorption is where the Sun's energy enters the stratosphere (the top), the stratosphere is hottest at the top and coldest at the bottom (hence, it is stable) f. Why is the formation and destruction of ozone mostly in the stratosphere and not in the troposphere? -There is no solar energy of the necessary wavelengths in the troposphere g. Because ozone absorbs solar radiation in a specific portion of the electromagnetic spectrum and heats the surrounding atmosphere, it is a greenhouse gas -False -Greenhouse gases are transparent to the Sun's radiation but absorb in a portion of Earth's radiation h. Does more ozone in the stratosphere mean less UVB at Earth's surface? -Yes i. Are high levels of UVB related to the frequency of skin cancer? -Yes j. If the thickness of fall the ozone in the atmosphere (300 DU) is about 2 pennies, what is the thickness of all the other gases in the atmosphere compressed to the same standards (0 ºC; 1 atm)? -About the height of Mount Everest k. The mid-latitude winds (40 - 60 ºS) that isolate Antarctica must be ______ winds -Westerlies

*Clicker Questions

a. Which is the most likely to have been difference in Earth's infancy with the biggest impact on its energy balance? -Earth's greenhouse effect b. Because the Sun was much cooler in Earth's history, the oceans must have been frozen. Geological evidence confirms this. -False c. How do we know Earth was not frozen? -Maybe there are shallow ocean sediments showing wave action d. The Sun was much cooler in early Earth's history, but the oceans never froze. Which of the following is least likely to help explain our paradox? -Large ice sheets back then e. Early Earth would have needed 1,000x as much CO2 in the atmosphere to keep the oceans from freezing. Where could that much CO2 come from? (Current atm.: 760 ppm; baby Earth: 760,000 ppm) -Rocks f. The Gaia Hypothesis postulates that Earth maintains a near constant temperature by regulating things despite large changes in forcings. These mechanisms would be? -Negative feedbacks g. Lets think about this gas, oxygen. What best describes atmospheric oxygen molecules? -Can't live with it; can't live without it h. Because O2 is reactive it is always getting used up in reactions, and lost from the atmosphere; therefore... -New O2 must be always being created j. With free oxygen in the troposphere and in the stratosphere came the first... -Ozone

*The Ocean as a Reservoir of CO2

a. Why does the addition of CO2 to the ocean concern us, and how do you get rid of it? b. The ocean can serve both as a sink or a source for CO2 depending on the relative abundance of CO2 in the atmosphere and biosphere reservoirs -The ocean can be thought of as an additional source -Is out of equilibrium and becomes a source of CO2 for the atmosphere c. CO2 that enters the ocean has a much longer residence time, and as the atmospheric CO2 levels decrease, there is a net flux of CO2 from the ocean to the atmosphere d. Rule of thumb: -Atmospheric CO2 increasing → Ocean = Sink -Atmospheric CO2 decreasing → Ocean = Source -Consequently, the "effective" residence time of CO2 in the atmosphere is thousands of years