Earth, Wind & Fire Exam 1
Volcanoes at mid-ocean ridges
As solid mantle rises due to mantle convection, the decrease in pressure causes the ultramafic mantle to partially melt, forming basaltic (mafic)
Volcanic Forcing of Short-Term Climate Change Example
- 1816: The Year Without Summer ---- motivated a lot of scientific research in Europe and lead to better understanding of volcanoes ---- Snow in New England in summer ---- Dark, cold in Europe ---- Crop failures across Europe and North America ---- Worse famine of 19th century ---- Cause: Mt. Tambora eruption (Indonesia) ---- Still the largest eruption in historical records ---- Killed 70,000-100,000 people ---- Substantial volcanic ash into the upper atmosphere
Greenhouse gases
- A gas that preferentially traps heat more than other gases - Infrared radiation vibrates water molecules and other molecules efficiently and makes them hot (infrared radiation - used interchangeably with heat). Greenhouse gases are efficient at absorbing that infrared radiation
Caldera
- A large volcanic crater created by the collapse of land following an eruption, due to all the empty volume previously taken up by magma - Only occurs in really big eruptions because of that collapse down in the middle - Ex. Yellowstone (from reading) Caldera Eruptions can be huge - Mount St. Helens (1980): ~1-2km^3 - Krakatoa (1883): ~18km^3 ---- The year without summer - global cooling due to dust cloud blocking the sun - Santorini (~1830 BC): ~35m^3 ---- Downfall of Minoan civilization? - Lava Creek Tuff eruption, Yellowstone caldera (640,000): 1000km^3 ---- Blanketed much of North America in ash ---- multiple huge eruptions - Crater Lake Caldera: ~50km^3
Earth's Energy Balance
- A lot of energy comes in from the Sun - Everything that comes in goes back out ---- Some sunlight is bounced back into space ---- Some heat is released into space ---- Some heat is naturally kept in by gases in the air like water vapor ---- Less heat is able to be released into space ---- Extra heat is kept in the air by "greenhouse gases" produced from human activity - Key word is balance: when the climate is warming, a small about of the total energy becomes trapped (rest on slide)
Atmospheric Circulation
- Actual pattern is a combination of north-south transport of heat from equatorial region to poles, but with strong east-west winds due to the Coriolis Effect - Key Point: moving heat from equator to poles is fundamentally what drives atmospheric circulation (and ocean circulation as well)
Partial melting: add water
- Add water to a hot rock will melt the rock - Adding water to dry, hot rock lowers the melting point - Subducting slab pulls water down with it - Subducting slab is cooler than crust above - The water percolates up to warmer rocks above. Water lowers the melting point, enabling melting of rock above, causing volcanoes above subduction zones
Sunspots
- Amount of energy from sun can vary enough over time to affect climate - Fewer sunspots correspond to a little less energy from sun - **graph of amount of energy from sun and sunspots by year** - An 11-year cycle of peaks in sunspots cycle - Climate deniers use existence of this control on climate to say humans aren't influencing climate. Solar intensity and greenhouse gases both affect climate
iClicker question: Why was a tsunami warning initially sounded and then canceled? (For 7.9 earthquake that recently happened off the coast of Alaska)
- Answer: Whether or not a tsunami forms depends on how shallow the earthquake is, and the initial automatic hypocenter estimates aren't as accurate as subsequent refinement - If the earthquake is shallow enough to possibly trigger a tsunami, they will issue a tsunami warning - Magnitudes and positions of earthquakes will change some after an earthquake after initial estimates are refined
Three ways to melt rock: increase temperature, decrease pressure, add water Clicker question: Which is most common?
- Answer: decrease pressure - Method of melting when hot mantle rock comes up during convection (at mid-ocean ridges and hot spots) - More volcanism and ridges and hot spots
iClicker question: Which happens (partial melting) at mid-ocean ridges?
- Answer: decrease pressure - water does matter but not as much as the large scale decrease in pressure - you get mid-ocean ridge because of convection - where you get melted material being squished up to form new crust
Three ways to melt rock: increase temperature, decrease pressure, add water Clicker question: Which is the least common?
- Answer: increase temperature - Adding water is common (close to 40% of volcanism on Earth happens around subduction zones)
Benefits of volcanism: geothermal energy
- Iceland: clean, renewable - Geothermal plants provide ~26% of electricity in Iceland
Clicker question: When partial melting occurs, the melt composition contains _______ the un-melted portion of the rock.
- Answer: more SiO2 than - Silica is one of the lowest melting point components of rock - it is the part that melts out first - The more SiO2 in the mineral - the lower the melting point - Most rocks contain multiple types of minerals - When partial melting occurs, melt composition is more SiO2 rich
iClicker question: Knowing what you know about dissolved gases, are viscous magmas more or less explosive?
- Answer: more viscous magmas are more explosive - Gas bubbles cause the explosion - Gas bubbles form suddenly in a viscous fluid - meaning they can't just bubble up and escape - In lower viscosity magmas you get less trapped gas because gases can more easily escape. When there's a lot of dissolved gas that can't escape - bigger explosion
iClicker question: What percentage of climatologists believe in anthropogenic climate change?
- Answer: ranging from 91%-100% - Scientific consensus is very high
iClicker question: What is an isotope?
- Answer: same atomic number (meaning same element), but different atomic weight - This causes the overall atom to be slightly heavier or lighter than other atoms of that element - Effects how they move through Earth's system
Shield Volcano
- Broad, very wide, low slope - Much larger than stratavolcanoes) - ex. Mauna Loa, Hawaii - have less explosive eruptions
CO2 and Weathering Feedbacks
- Climate changes over the last few hundred million years are driven in part by changes in the CO2 input of the atmosphere by plate tectonic processes - Changes in seafloor spreading control delivery of CO2: more spreading = more volcanism = more C02 - If there was no NEGATIVE feedback to reduce or increase CO2, temperature would have varied much more than it has over geologic time.
What controls chemical composition of magma
- Composition of rock being partially melted - Degree of partial melting
Glaciations and tectonic scale of climate change
- Cretaceous configuration: less land near poles, hotter in part because having oceans near poles inhibits ice growth - Today's configuration: more land near poles, cooler Earth because land in cold areas enables ice sheet growth - More land at higher latitudes (near poles) allows for more ice cover to develop, which reflects more sunlight (so less solar energy absorbed) and creates a positive feed back to cause greater cooling.
Proxy record: ice cores
- Dated with volcanic ash, ice flow models, and by counting layers - Located at high latitudes, altitudes - H2O in ice ---- Oxygen isotopes - temp, precipitation - Dust amounts ---- Global dryness, wind - Air bubbles ---- Actual samples of trapped air, determine past concentrations of different gases, i.e. CO2, CH4
What makes volcanic eruption explosive?
- Decreasing pressure allows gas to come out of solution and form bubbles - the sudden change in volume from the addition of bubbles can be explosive - Shield volcanoes have less explosive eruptions
Climate Forcing
- Defined as an imposed perturbation of the Earth's energy balance - Causes (external forcing): changes in plate tectonics; changes in Earth's orbit; changes in Sun strength - Climate Variations (internal responses): changes in atmosphere; changes in ice; changes in vegetation; changes in ocean; changes in land surface - **graphic on slide showing this**
Direct Measurement vs. Proxy Records
- Direct measurements have limited time frame - Historical records often qualitative, incomplete - Proxies = natural archives of climate information
Gas content
- Dissolved gas content, including water content - Wetter magma, more gases = more explosive - At high pressure in the earth, gases (including water) are dissolved in magma, but as magma rises, pressure decreases and gases form bubbles. Low viscosity magmas/lavas release the gas pressure, and are less explosive. In contrast, gas bubbles rise slowly in high viscosity magmas, trapping the high pressures and making them more explosive.
Two main factors controlling explosiveness
- Dissolved gas content, including water content (Wetter magma, more gases = more explosive) - Viscosity of magma/lava (More viscous, more SiO2 = more explosive)
Summary of Causes of Climate Change on Earth
- Earth-Based causes best account for long-term climatic change over million year + timescales. - Milankovitch Cycles explain shorter term climate change (10-100 ka). - Very short climate cycles (decades- centuries) seem to result from Earth-based causes and solar cycles. - And now, human influence on atmosphere, greenhouse gases.
El Niño/La Niña
- El Niño ---- Anomalously warm conditions in the eastern equatorial Pacific are known as El Niño. These typically last 9-12 months and are strongest during December to April, when they have the biggest impact on the atmosphere. ---- Less overturning of the water, which leaves warmer waters at the surface - La Niña ---- Anomalously cold conditions ---- More overturning water, which brings up colder water to the surface - El Niño occurs every 2-7 years (average period of 4 years but irregular)
Ocean Circulation and Climate Variability in the Past
- Evidence for a past shutdown of the heat conveyor (change in warm ocean current near Europe) ---- Due to melting ice sheet, dumping lots of cold but fresh water into ocean, disrupting circulation pattern ---- Warming led to ice sheet melting, which changed circulation patterns and stopped heat from coming north - resulted in a cooling period ---- **graph of temperature change on slide**
Volcanic hazards
- Flowing Lava--the least hazardous of these hazards - Explosive blast (e.g. Mount St. Helens) - Volcanic ash in atmosphere - Landslides (Mount St. Helens) - Volcanic Gases (suffocation, acid rain) - Pyroclastic flows (ash and gases). - Lahars (volcanic debris flows to ash-laden flood, a mixture of ash and water)
Proxy record: glacial deposits
- Geological Evidence of long term climate change - Glacial deposits in places that no longer have glaciers indicate that climate was different in the past - Moraine - name for glacial deposit
IPCC2 (2014) climate report
- Greenhouse gas levels continue to increase - most recent report - **graphs from report on slide** - process of making cement gives off CO2 - global increase in sea level since 1900: 20cm
Solar Energy Budget
- Incoming solar radiation 100% ---- 6% reflected by atmosphere ---- 20% reflected by clouds ---- 4% reflected from earth's surface ---- **rest of these numbers on graphic on slide** - ~30% reflected directly back to space - ~50% of solar energy absorbed by land and oceans - ~20% absorbed by atmosphere/clouds
Continent locations and ice
- Locations of continents influences amount of ice, influences climate: more land near poles allows ice to be more stable and to be thicker and grow compared to ice sheet over open ocean - Antarctica and Greenland are land masses - covered by 2-4km thick ice sheets - North Pole is ocean and has much thinner, intermittent ice cover
Radiation Wavelength
- Longer wavelengths - infrared radiation - Graph shows greenhouse gases and wavelengths at which they are absorbed the most - also depending on incoming solar radiation and outgoing earth radiation - Different gas molecules absorb different frequencies of radiation CO2 absorbs lots of energy - that is what makes it a greenhouse gas
Possible Cause of the Little Ice Age
- Low solar activity (1645-1715): 50 sunspots over a 30-year period compared to normally 40,000-50,000 spots - Note: has been a bit of a trend of increasing sunspot recently (why people denying climate will use this to say climate change isn't real)
Milankovitch Cycles
- Milankovitch (1941) proposed that changes in the geometry of Earth's orbit around the Sun are responsible for ice ages and warmer periods - Identified 3 specific types of orbital variations ---- Eccentricity: 100,000-year cycle ---- Obliquity (tilt): 41,000-year cycle ---- Precession: 23,000-year cycle ------ As the tilt changes, the axis wiggles around itself on a 23,000 year time scale
Impact of Ice on Energy Budget
- More ice, absorbing less - lower amount absorbed by land and oceans - Also affects amount reflected from earth's surface - lower absorbed would mean more being reflected
Partial melting
- Most rocks contain multiple types of minerals - Rocks melt gradually, over a range of temperatures - SiO2-rich minerals usually melt first (e.g. at lower temperatures) - When partial melting occurs, the melt composition is more SiO2 rich than the un-melted portion of the rock - If you completely melt a rock - you don't change the composition. When you partially melt a rock (and the melted and non-melted separate) - you change the composition of the rock
Unequal Radiation on a Sphere
- North Pole: radiation spread over a large area - Equal-area beams of incoming solar radiation between poles and equator - Equator: radiation focused on a small area - South Pole: radiation spread over a large area - **graphic of this on slide** - Equator is so much warmer because you get more energy per unit area - that makes it warm ---- Sunlight at equator is more direct ---- Same amount of incoming energy is spread over a much larger surface area when light reaches the poles
Ocean Circulation
- Oceans serve as one of the main mechanisms for redistributing heat. Heat in general moves from equator to poles. Heat (energy) from ocean also affects atmosphere. For example, St. Johns, Newfoundland, is colder than London, because ocean currents move heat north to Europe ---- Ocean circulation brings a substantial amount of heat into Europe ---- Climate is complex: there are other reasons related to oceanic and atmospheric circulation why Europe is warmer as well - Flow of the ocean is driven by difference in heat between equator and poles. Continents are in the way of a typical circulating pattern. With the current configuration of continents, ocean has developed a pattern depicted on slide - **graphic on slide showing ocean circulation**
Volcanic Locations
- On tectonic plate borders: divergent margins (mid-ocean ridges) and convergent margins (subduction zones) - hot spots (mantle plumes) - these locations are determined by how rock melts
Proxy record: 18O/16O ratio
- Oxygen isotopes ---- 16O lighter than 18O - distribution changes over time ---- evaporation - lighter 16O more likely to evaporate ----- Precipitation - heavier 18O more likely to fall as rain ---- Proxy for temperature, rainfall in water/carbonate (CaCO3). Also ice volumes - More 18O rains out near coast - More 16O at high altitudes - In general, 18O concentration is observed to decrease toward the pole, and also is lower in dry regions (**map is per thousand, not per hundred** - numbers are negative because it is depleted in 18O) ---- Warmer wetter areas are not as depleted in 18O as dry areas
Proxy record: Tree rings
- Predominantly temperate (mid-latitudes) - Dated using radiocarbon - Tick bands during growing season, thin bands during cold/dry months - Varying widths of growth bands reflect temperature or precipitation ---- Need stress to vary growth rates ---- US Southwest - desert ---- Can also reflect wildfires (because they can harm a tree, not kill it)
Chemical composition of mafic magma
- Rich in Mg and Fe - low in SiO2 - low viscosity (runny) -> gasses able to escape -> effusive (non-explosive) eruptions (ex. shield volcanoes like Hawaii; mid-ocean ridge volcanism) - typically comes from partially melting ultramafic mantle rock
Partial melting: decrease pressure
- Rock that is already hot and under a lot of pressure will stay solid - when you lower the pressure and maintain the heat the rock will melt - Mantle convection brings already hot mantle up. Temperature decreases slightly but pressure decreases greatly. Mantle rock melts, forms magma below mid-ocean ridges - most common way of partial melting
the 'missing heat' of global warming
- Scientists find the 'missing heat' of global warming 700 meters below the sea - key point: ocean water between 300-700 meters has been warming more than scientists realized, which may explain why some climate models have predicted warmer atmospheric temperatures over the last ~15 years than have been observed: the global warming is there, just in the oceans -vertical colored bars on graph indicate volcanic eruptions which caused short-tern cooing - the discrepancy between models and measured temperature - explained by putting measured amounts of energy into the oceans. Climate change isn't just surface temperatures
Volcanic hazards: climate change
- Short term: cooling from ash, SO2 and H2SO4 reflecting sunlight. - Long term: Increased CO2, other greenhouse gases released -> Warming
How do explosive volcanic eruptions affect climate?
- Short-term cooling caused by large explosive eruptions, due to ash and sulfur dioxide in the air, reflecting sunlight ---- These affects last: (need to know!!) - Long term climate effect: increases CO2, causes warming - Ex. Mt. Pinatubo eruption, 1991, Philippines ---- 2nd largest eruption in the 20th century ---- Image of world on this slide ---- Stratospheric aerosols (ash, sulfur dioxide) ejected high into atmosphere by eruption = more solar radiation reflected back to space ---- Decrease in global temperature .5 degrees Celsius for ~2-4 years
Stable Isotope Fractionation
- Stable isotope: isotopes that don't radioactively decay - Which evaporates more easily, 16O or 18O, Why? ---- 16O - lighter by 2 neutrons, so it evaporates more easily - various climatic processes such as evaporation will fractionate (separate) isotopes, based on their different weights. The relative amounts of various isotopes in samples of water, ice, rock, plant, human, etc. can therefore tell us about past climate
Stratovolcano
- Stereotypical volcano shape - Smaller than shield volcanoes - Also called composite volcano - An explosion will compress the air around it and that is what does a lot of damage (the shock wave of compressed air moves very quickly) - ex. Arenal, Costa Rica
Predictions for the future
- Surface temperature is projected to rise over the 21st century under all assessed emission scenarios. It is very likely that heat waves will occur more often and last longer, and that extreme precipitation events will become more intense and frequent in many regions. The ocean will continue to warm and acidify, and global mean sea level rise - **graph of the assessed scenarios on slide** - **maps with average change in surface temperature AND change in average precipitation depending on CO2 emissions on slide**
Oxygen Isotopes are a Measure of Global Ice Volume: process with ice sheets
- Taking water out of the ocean, putting it at poles, and not returning it to ocean - Time with glaciers, ocean is enriched in 18O - Times with glaciers cause increase in 18O in oceans, because more 16O is stored in ice sheets
Oxygen Isotopes are a Measure of Global Ice Volume: based on rainfall
- The ratio of isotopes is expressed as "per mil" - More 16O than 18O evaporates from oceans because it is lighter - **photo on slide showing where more or less 18O and 16O can be found based on Earth's natural precipitation and evaporation process** - More 18O falls as rain because it is heavier - Progressive decrease in 18O inland and toward poles - If there aren't ice sheets, rainfall flows back into the ocean
Orbital Forcing - effects
- Tilt (obliquity): controls intensity of seasons (warmer summer + colder winter) - Precession + eccentricity: control length of seasons and small changes in amount of solar energy reaching surface - Total changes in energy budget are small, but enough to change global climate - Climate impacts through continental ice sheets: ---- Longer, more intense summers lead to enhanced melting of ice sheets ---- Colder winters don't tend to grow enough ice to compensate (already cold in winter)
Rock weathering
- Weathering of continental rocks removes CO2 from atmosphere,"stores" the carbon in oceans as limestone: - When increased seafloor volcanism increases CO2 levels in atmosphere, global temperature warms, which increases rates of rock weathering, which pulls more CO2 from atmosphere, cooling global climate. - When decreased seafloor spreading reduces CO2 levels, global temperature drops, which decreases rates of rock weathering, allowing CO2 to increase in atmosphere, warming global climate. - CO2 in the atmosphere combines with the rock and that ends up taking CO2 out of the atmosphere, putting those carbons and oxygens in the oceans and organisms use parts of those reactions to make their shells
Ocean Circulation and Climate Variability (Greenland example)
- What could happen if the Greenland ice sheet melted? ---- It could change the temperatures and salinity. Melting a lot of fresh water, might change part of the ocean circulation pattern ---- Changing ocean circulation pattern - would change distribution of heat (could get more cooling in the northern hemisphere) - Scientific study from 2015: presents evidence that Atlantic Ocean overturning (essentially the warming ocean current) has slowed down in the later 20th century due to increase melting of the Greenland Ice Sheet. ~99.5% likelihood that human-influenced warming is the cause ---- Anomaly - cooling in location indicated on map because of melting ice (most other places have gotten warmer) ---- Speck of blue south of Greenland - sea surface has gotten colder on average ---- Low salinity of the fresh water - means it is less dense and stays close to the surface
Proxy
- When you are using one thing to do or tell you about something else - Using a direct measurement of something to indirectly measure something else ---- Ex. of climate proxies: tree rings, glacial deposits, oxygen isotopes, deep ocean cores, ice cores
CO2 Concentration Impacts
- Where/how does CO2 concentration in atmosphere directly affect this energy budget?: When the solar energy is radiating back (the infrared radiation going back up is absorbed) And absorbed in the atmosphere - Without greenhouse gases, the average temperature of Earth's surface would be about -18 degrees C (0 degrees F), rather than the present average of 15 degrees C (59 degrees F)
Historical Records of Climate Change
- Written accounts ---- El Niño events recorded from late 1500s ---- Crop harvest, migrations, spring blooms (can infer climate changes and variations from plant blooms) ----- Hurricane landfall - Artwork ---- Snow/ice temperate locations during Little Ice Age (where we don't have snow/ice now) - Repeat photographs quantify changes
Pyroclastic flows
- a density flow consisting of a hot (up to 800 degrees C) poisonous mixture of gas (erupted from volcano) and volcanic ash moving downslope sometimes at speeds in excess of 200km/hr - Ex. Mt. Merapi, Indonesia
Intergovernmental Panel on Climate Change (IPCC)
- a group of scientists all from different countries - a United Nations scientific intergovernmental body - thousands of scientists and other experts contribute (on a voluntary basis, without payment from the IPCC) to writing and reviewing reports - provides an internationally accepted authority on climate change, producing reports which have the agreement of all leading climate scientists and the participating governments - 2007 Nobel Peace Prize was shared between IPCC and Al Gore - published four comprehensive assessment reports reviewing the latest climate science; these represent the scientific consensus on climate at the time of each report (1990, 1995, 2001, 2007, 2014) Mission: Its mission is to provide comprehensive scientific assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and socio-economic consequences, and possible options for adapting to these consequences or mitigating the effects.
Numerical climate models
- allow scientists to isolate the effects of different factors on past and present climate, and predict future climate - these are mathematical summaries of what we know about the mechanisms of the climate system - one of the major tests of these models is to reproduce the main features of modern climate - another is to capture the dynamic changes of the recent Ice Ages, in time and geographically - any numerical model is just a set of equations. Usually the hard part is coming up with the equations
Proxy record: ocean deposits
- deep drill cores - Shells of plankton are CaCO3, contain oxygen ---- 18O/16O ratio of sea water = ratio in organisms ---- when glaciers are growing - 18O/16O ratio high - Foraminifera - CaCO3 skeleton can be analyzed for 18O/16O
Continental crust
- felsic rock, granite - when partially melted = felsic magma
The "Hockey Stick"
- geological temperature records - from 1998 - original plot went back to 1400 - showing that at least from 1400-1900, relatively lower temperatures. At that point a big increase in temperature. - **graph on slide**
Viscosity
- how easy it is for something to flow (mantle has higher viscosity) - magma viscosity is controlled by SiO2 content - More SiO2 = more viscous lava - Easy to flow - low viscosity, hard to flow - high viscosity
Chemical composition of intermediate magma
- in between felsic and mafic - Typically comes from partially melting basalt (oceanic crust). Still makes stratovolcanoes, still explosive.
3 ways to melt rock
- increase temperature - decrease temperature - add water
Partial melting: increase temperature
- least common way to melt rock
Instrumental Records of Climate Change
- longest instrumental temperature record is from central England, which begins in the 17th century (Manley 1974) ---- **shown on slide** ---- plot shows summer temperature record from a single location in England ---- degrees C anomaly - difference from the average of all the data - most instrument records over land only start as early as the middle of the 1800s - good data from over the oceans start much later than that - graphs on slide titled Instrumental Record of Climate change ---- measurements show a clear trend ---- they show a clear trend (not visible in England data) because of spatial averaging. Regional and global average show trends much more clearly than records at individual locations
Oceanic crust
- mafic rock, basalt - partially melted = intermediate magma
Earth's Climate History (last 550 million years)
- mostly hotter than today - No global ice sheets for most of Earth's history - Multiple periods of glaciation, but mostly it's been hotter
Importance of Climate History
- past variability can show climatic extremes that have not been experienced during recorded history - in order to understand the effects of human activity on climate, we must establish what the planet, the atmosphere, and climate change was like before human perturbations - constructing and interpreting long-term records of climate are the only means to determine how periodic climate change is (all in all, we are just a blip)
Chemical composition of felsic magma
- rich in SiO2, AI - high SiO2 causes high viscosity - high viscosity -> trapped gas bubbles at high pressure -> explosive eruptions (ex. Mount St. Helens, stratovolcano) - comes from partial melting of continental crust
Benefits of volcanism: mineral deposits
- sulfur, gold, copper - Hydrothermal fluids (hot water with abundant dissolved minerals) in volcanic areas are a major source of ore deposits
1000-year comparison of temperature and model predictions
- there is variability and uncertainty, but the anthropogenic effect on climate is larger than this variability - models without greenhouse gases: lower - with: increase
Obliquity
- tilt of the Earth's rotational axis -- cycle of ~41,000 years -- varies from 22.2-24.5 (current tile is 23.5) -- greater tilt = more intense seasons -- if Earth's orbit were circular ---- no tilt = no seasons ---- 90 degree tile = largest seasonal differences at the poles (6 months darkness, 6 months overhead sun)
Mantle rock
- ultramafic rock - partially melted = mafic magma
Models, based on data, used to isolate natural (volcanoes, solar intensity) and anthropogenic (greenhouse gases) climate change
- volcanic forcing line: lots of variation but no trend - solar irradiance forcing (sunspots) line: there is a long term trend of increasing sunspot activity (not out of the bounds of previous times though) - all other forcing (primarily greenhouse gases): where meaningful change and trend can see. In 1800, start to see increase that continues to today
Climate
- weather averaged over longer periods/areas of time - "average weather" - the statistical description in terms of the mean and variability of relevant quantities over a period ranging from months to thousands or millions of years (defined by Intergovernmental Panel on Climate Change) - the classical period is 30 years (as defined by the World Meteorological Organization)
Climate Change and Syrian Civil War
2015 study suggests that anthropogenic climate change likely contributed to the Syrian Civil War. 2007-2010 drought was the worst drought in instrumental record, causing widespread crop failure and a mass migration of farming families to urban centers. Climate change makes it 2-3 times more likely to have severe and persistent droughts. (This was peer-reviewed science; link is there but we cannot say definitely)
Ash hazards
Abrasion of plane engines, other sandblasting, water pollution, respiratory problems, kills plants, livestock, aquatic ecosystems, pyroclastic flows, lahars
iClicker question: What is the classic duration of time that weather is averaged over to define climate?
Answer: 30 years - 30 years came about because of popularity of 30 year fixed rate mortgages
iClicker question: Which happens (partial melting) at/above subduction zones?
Answer: add water
iClicker question: How do explosive volcanic eruptions influence climate?
Answer: cause global cooling and global warming
During an ice age, the 18O/16O ratio will be ______ in glacial ice and _____ in ocean sediments compared to interglacial times
Answer: lower; higher - 18O is heavier than 16O, so when you have evaporation you leave more 18 behind - During glacial times, what you have is evaporating water from the oceans and some precipitates out close to the poles and that ends up being the glacial ice. You leave more of the 18O in the oceans and your amount of 18O is going to be higher in the oceans - Precipitation has less 18O - and that is what makes the poles - Right now we are in an interglacial time. Glaciers have less 18O than ocean - Ocean sediment from 30,000 years ago would have a higher ratio than sediment today. When you've taken out more water from the ocean and put it in ice on land, ocean will be more enriched in 18O and glaciers will be more enriched with 16O - Most evaporation near the equator and clouds are moved from equator to poles
iClicker question: The Earth's climate over the last 550 million years has mostly been warmer and wetter than today.
Answer: true
Effect of Climate Change on Humans
Climate change increases the probability of: devastating hurricanes, droughts, floods, disease, famine and civil unrest - all increase human suffering. All of these things would happen regardless of climate change, but climate change just makes them occur more often
Solar intensity variations: decades to centuries
Ex. The Little Ice Age (~1400-1850) -- In Europe: colder winters and shorter growing seasons -- **graph of sea ice on the coast of Iceland on slide** -- evidence: ---- lakes, rivers and ports in Europe froze ---- the European population seriously affected ---- mountain glaciers in the Alps of Switzerland and Austria advances The Little Ice Age was not a true ice age -- Major ice sheets did not develop. -- Small (<1°C) drop in global temperature Much of the world was colder than today
Coriolis Effect
Has to do with the planet's rotation (what causes hurricanes to spin in one direction in northern hemisphere and a different direction in the southern) an effect whereby a mass moving in a rotating system experiences a force (the Coriolis force ) acting perpendicular to the direction of motion and to the axis of rotation. On the earth, the effect tends to deflect moving objects to the right in the northern hemisphere and to the left in the southern and is important in the formation of cyclonic weather systems.
3 Observations of Climate Change
Observation 1 of recent climate warming: annual trends in maximum temperature anomalies (1950-2003) **graph of this on slide** -- shows places that have had an increasing trend of temperature highs -- highs are winning in polar regions (poles are heating even faster) Observation 2: annual trends in minimum temperature anomalies (**graph on slide**) -- lows are increasing (getting warmer) Observation 3: change in frost-free length days per decade 1948-1999 (**graph on slide** -- how long the season is between freezes -- duration of time without freezing temperatures has been getting shorter -- across most of the US, confident that there has been a meaningful change in the length of frost free days (getting shorter winters)
Ejected material
Obsidian, volcanic ash, pumice, bombs (can be small or large - molten blobs of lava that are launched so high into the atmosphere that they are cooled by the time they come down)
Benefits of volcanism: ocean chemistry
Ocean-floor hotsprings (black and white smokers) provide many nutrients to the ocean. "Crucible of life"?
Random facts about climate/climate change
There is no scientific controversy over whether global warming is occurring. Science operates by consensus, there is overwhelming scientific consensus. 97% of climate researchers agree that humans are causing warming. Majority of the 3% don't discredit human influence, they just aren't sure. Population density: many people along coastlines. Climate change is causing measureable sea level rise, and increases in the intensity and frequency of hurricanes/typhoons/cyclones. As of 1998 over half the population of the planet live within 200km of the ocean. By the year 2025, nearly 75% of Americans are expected to live in coastal counties. If all ice melts (global ice sheets of Greenland and Antarctica), sea level rises roughly 216 feet. Probably would take 5000 years.
Benefits of volcanism: agriculture
Volcanic soils are rich in mineral nutrients
Volcanic ash
microscopic jagged pieces of rock and glass (silica), explosively erupted into atmosphere
Pyroclastic rocks
result of explosive volcanic ejecta, typically travel through air, deposited as layers of ash, glassy shards
Weather
systematic variations in the atmosphere