GEL010 Final
What is the Anthropocene and why is it significant for humans to understand (hint: think human activity leaving a global signature in the geological record)?
relating to or denoting the current geological age, viewed as the period during which human activity has been the dominant influence on climate and the environment.
What is a feedback loop?
Feedback occurs when effect of 1 action triggers change in a 2nd action, which in turn, feeds back to trigger a change in the original action
What is the fuel (pump) that keeps atmospheric circulation going and works to redistribute heat energy on Earth from places of high heat to those that are cooler?
- Latent heat of evaporation and condensation - Release of latent heat high in the troposphere when the air cools acts to pump the air around the atmospheric circulation cells and to redistribute heat
How does a GHG differ from other gas molecules
GHG are not diatomic molecules; Could be structures unsymmetrical and is not neutral (has a charge)
What are megadroughts and why is drought related to global warming?
- Megadroughts: severe drought lasting for two or more decades - Increased global warming leads to change in the atmospheric circulation patterns over our region → leads to more droughts that are longer, drier and have shorter rainy seasons
What is the thermohaline (oceanic) conveyor belt?
- Thermohaline conveyor belt: the lower limb (deep ocean) of the ocean conveyor belt that has a significant vertical component as high density water masses sink at the poles - The thermohaline conveyor belt redistributes heat globally (about the same amount of heat energy as does atmospheric circulation) - Has three modes of operation (slow, fast or off)
What is a threshold?
- Threshold can be reached at which point any further change could be permanent (impossible to return to original condition)
How are gyres set up and how do they relate to atmosphere subtropical highs?
- Western boundary currents initiate formation of subtropical gyre - Circulation of subtropical gyres is clockwise in Northern Hemisphere and counterclockwise in Southern Hemisphere - End product is large gyres situated beneath subtropical highs
Why did the oceans go anoxic during the super greenhouse (warm) times of the Mesozoic?
- When ocean waters warm due to global warming, they lose oxygen (O2) and become anoxic (toxic water for life) - During this time, oceans were devoid of O2 other than at the very surface
Could methane-gas hydrates play a role in our future climate? How?
- Today, we have 2500 to 5000 billion tons of methane gas hydrates buried (equivalent to ALL fossil fuels we have on Earth) → if we do not constrain the amount of CO2 in our atmosphere, deep ocean waters will warm enough to melt these methane gas hydrates which would release the GHG CH4 to the atmosphere
In what type of 'climate condition' do we currently live
- We are entering a paleo-world - Currently at CO2 levels that have not been witnessed by Earth in over 3 million years
What is albedo?
- Albedo: expressed as a % of the sun's light that is reflected from various surfaces back to outer space
What relevance does ocean anoxia have to future global warming?
- Anoxia events are simulated by global warming, so with greater temperatures, this event is more likely to occur - Anoxic events coincide with several mass extinction events
Where on Earth does the maximum Sun's heat reach in winter and in summer?
- In the summer, the northern hemisphere receives more solar energy than the southern hemisphere. Vice versa - Winter Solstice: Sun highest over Tropics of Capricorn - Summer solstice: Sun is highest over Tropics of Cancer - Hottest place on earth is at equator only during spring and autumn equinox
What is meant by 'energy is empowerment'.
- Because there is a direct correlation between gross national product of a country and its energy use - Energy translates to CO2 emissions
What impact does global warming have on the conveyor belt?
- Buildup of GHG appears to be triggering a slowing of the present-day thermohaline conveyor belt - Rate of deep-water formation will slow by 10 (best case scenario) to 35% (business a usual) by 2100
What is carbon capture (through direct air capture or at power plant stacks) and human-driven sequestration of Co2 from the air through mineral weathering
- Carbon capture: process that captures carbon dioxide emissions from sources like coal-fired power plants and either reuses it or stores it so it will not enter the atmosphere - Rocks exposed on land undergo chemical weathering when exposed to water and CO2 → the dissolved molecules from the rock produced by weathering is carried by rivers to the ocean and used by living plants/animals in ocean to build their shells - In this way, CO2 is removed from atmosphere during rock weathering and buried as a new type of rock/ Humans are accelerating this cycle by burning organic matter contained within sedimentary rocks
What is meant by the 6th largest extinction?
- Climate change altering ecosystem productivity = invasive species and reconfiguring ecosystems in unprecedented way (low diversity ecosystems) - Extinctions occur when climate change outpaces capacity of species to adapt - Current rate of extinctions 1000 times faster than historical rates - 2 degree warming could double or triple extinction rate
Does climate change typically occur gradually? Or can it accelerate after a while? Why?
- Climate change is an exponential process - Climate change accelerates and can intensify quickly (in years or decades) even if the cause driving it doesn't accelerate
Overall, how do clouds control our surface temperature? More specifically, do high vs low clouds warm or cool our surface temperature?
- Clouds cool the Earth's surface by increasing its albedo - Low clouds: generally cools the surface because they reflect more incoming solar radiation than they absorb --> Low lying position keeps them warm so they radiate equivalent amount of energy as absorb - High clouds: generally warm the surface because elongated ice crystals allow much of the incoming solar radiation to pass through --> Because formed higher in troposphere, they are colder and radiate less infrared radiation back to space, they absorb it which makes them a source of heat
What is maritime vs continentality in terms of climate?
- Distribution of land masses and oceans on Earth's surface also controls surface temperatures - Because water can absorb and retain far more heat than rock/land materials - Climate variability is much greater on continents than over ocean = CONTINENTALITY - Less variable climate over the oceans is referred to as MARITIME climate - Continental temperatures are more sensitive to climate change and can change the most
What is the ENSO (El Niño)?
- ENSO: climate phenomenon that affects the tropical Pacific on an inter-annual to decade-scale by creating periods of very wet winters in the eastern Pacific and dry western Pacific regions oscillating with the opposite scenario - Occurs due to changes in both atmospheric circulation and oceanic circulation
What have we learned from the PETM about how our future climate may respond to continued burning of fossil fuels and about the time needed to recover from high CO2 levels.
- Earth has always recovered from past atmospheric CO2 perturbations, but the time scale of the recovery is geologic and not on human-time scales - Recovery from PETM global warming event -- by Earth's natural sweepers of CO2 -- took over 80,000 years
Where does upwelling of nutrient-rich water occur primarily?
- Equatorial upwelling: water to the immediate NORTH of the equator (Northern Equatorial Current) and water to the immediate SOUTH (Southern Equatorial Current) are moving wested → they are being deflected to the right in the northern hemisphere and to the left in the southern hemisphere due to the combined actions of the Coriolis effect and Ekman transport - Causes divergence of water at the equator → in zones of divergence, the water has to rise from below to replace the water that was diverted N and S of the area → this is called upwelling
How does the atmosphere work to distribute heat (and water) over the Earth's surface?
- Evaporation: heat energy from atmosphere is absorbed by some H2O molecules at water surface - higher energy of vibration and rotation allow them to overcome the molecular attractive forces that hold the molecules together - Condensation: as water molecules in the air vapor rise and cool they lose energy - results in their condensing to water droplets (forming of clouds0 - Precipitation: rain occurs when droplets grow too large and gravity works to send them down to land/ocean surface as rain or snow
What are we doing to change the rate at which C is being transferred from the largest carbon reservoir to the atmosphere (think fossil fuel burning)
- Fossil fuel burning (from largest reservoir of rocks) makes the CO2 in the atmosphere 35% more abundant than it was 150 years ago
Could the Earth return to a cool greenhouse or ice-free greenhouse in the future?
- If we continue to burn our fossil fuels at the current rate, it is feasible that we transition from an 'icehouse' to a 'cool greenhouse' with smaller ice sheets on the precipice of melting or into a full ice-free greenhouse
Where is atmosphere circulation initiated and by what process?
- Initiated in the tropics --> Redistributes heat energy around the globe - Latent heat of evaporation and condensation is used as fuel - Also affected by the position of land masses on the Earth's and the Coriolis phenomenon
What are the marine methane-gas hydrates (methane ice) and what role did they play in past global warming?
- Methane hydrates: a natural reservoir of methane 'ice' is buried a few 10s of meters below the sea-floor in the oceans adjacent to many continents - When ocean water 100s of meters deep warms, the ice melts and methane gas is released to the ocean → ultimately this is the atmosphere creating a greenhouse-gas forced global warming
What are the main impacts of global warming observed in the past several decades (hint: look at the subheading list in the 1st lecture set)
- Monster storms (cyclones, hurricanes, etc) - Extreme and increased wildfires (hotter weathers, dry lightning, windy) - Rising sea levels due to melting of ice (Artic, Polar Ice Sheets) - Marine Heat Waves (areas of extreme warm sea surface temps for days to months) - Extinction
What is the role of sea ice formation in deep-water circulation
- Newly generated deep-water forms when sea-ice forms in the winter --> The ocean is salty, and when sea ice forms, much of this salt is pushed into the ocean water below the ice → water below sea has ice a higher concentration of salt and is denser than the surrounding ocean water → this water sinks and moves to the bottom of the ocean basin → circulates along the ocean bottom toward the equator - This happens with Antarctic Bottom Water
In what direction are winds and ocean currents deflected in the Northern Hemisphere? In the Southern hemisphere?
- Northeasterly & Southeasterly Trade Winds: the air that moves equatorward from the subtropical high pressure region from the trade winds - they are deflected right of the paths of initial motion thus setting up easterly trade winds in the tropics - Westerlies: the air that moves poleward from the descending air column of the subtropical high is deflected to the right or towards the east = westerly winds
Where and why do we have subtropical highs and what does this have to do with deserts?
- Occurs in Intertropical Convergence Zone - Descending air mass creates high pressure region = subtropical high pressure - Air in this high-pressure zone is dry because it warms as it sinks preventing clouds from forming
What are the main processes that have controlled atmospheric CO2 and O2 levels through Earth's history?
- Ocean sweeping - Photosynthesis: process by which CO2 in atmosphere is used by plants - Respiration: respiration process releases CO2 from organic matter and sends it back to the atmosphere
What is the ocean's natural alka-seltzer? How common is it?
- Once atmospheric CO2 dissolves in ocean water, it rapidly breaks down into other forms of carbon molecules through a chemical chain reactions - One of these molecules is CO23 (carbonate) and it is nature's 'Alka Seltzer' - Alka Seltzer is limited
Why has the Paleocene-Eocene Thermal Maximum (PETM) been considered important for understanding the current fossil-fuel burning driven global warming?
- PETM: a climate aberration (short-lived climate even) occurred 56 Mya; During this period, global temperatures rose by an average of 5 degrees; Culprit behind this warming was a massive injection of heat-trapping GHG into the atmosphere and oceans - These rapid departures from a background climate state provide us with the most relevant insight into the rates at which global climate can change
Why is the ocean stratified and operate as 2 independent layers?
- Pattern of surface ocean circulation mirrors atmospheric wind pattern - forms the upper limb of the oceanic conveyor belt - Deep ocean circulation - the lower limb of the conveyor belt - is density driven. Transport of heat energy along the belt controls climate on timescales of 10s to 1000s years - and is big player in helping the Earth to recover after major climate change - Warmer less dense water seats on top
What is the evidence that megadroughts occurred in CA during the Medieval Warming?
- Ponderosa Pine forests → developed in what are now deep-water alpine lakes and very active rivers (but trees do not grow in standing water 10s of meters deep) - Stands of trees rooted up to 60 meters below the present-day water level in lakes in the Tahoe region, Yosemite and on the eastern side of the Sierra
How do negative and positive feedback loops differ in terms of controlling how much change will take place with continued forcing?
- Positive feedback reinforces initial change - Negative feedback restores conditions back to stable and equilibrium conditions
Why in northern California, do we care about the jet stream?
- Pushes weather patterns from west to east - Increased wildfire
How does all of this relate to ocean acidification?
- Seawater is naturally maintained at a pH of ~8 because it uses the intermediate and most abundant form of C (bicarbonate) to buffer → the process of buffering uses up some of ocean's natural Alka Seltzer (this is a natural process) - Problem: for the ocean to keep "sweeping" CO2 (which is rapidly rising from human activities), it need even more of the natural alta seltzer in the seawater to buffer - The ocean has a very small amount of alka seltzer → when the ocean's ability to buffer seawater is outpaced by the rate of anthropogenic CO2 being absorbed, ocean acidification happens
What is meant by convective air circulation?
- Temperature and pressure differences in atmosphere create air movement - Changes in buoyancy of air by heating at the Earth's surface and by cooling in the troposphere as it rises
What are positive feedbacks in the Carbon cycle doing already to ensure continued warming of Earth's surface over the next few decades?
- The climate-carbon cycle feedback is positive, both for land and ocean systems; global warming induces a reduction of land and ocean carbon uptake, enhancing the atmospheric growth rate of CO2. Over the historical period, the CO2-induced feedbacks are by far dominant; land and ocean act as strong carbon sinks
What is the role of this oceanic conveyor belt in transporting heat from the lower latitudes to higher latitudes (hint: the Gulf Stream the western boundary current in the N. Atlantic)
- When the warm waters (less dense and remains on the surface) in the Gulf Stream reach the region around Iceland, they are cooled by the cold winter air that streams off Canada and Greenland → cool/salty water = dense, which allows it to sink to the bottom → this forms a southward-moving mass called the North Atlantic Deep Water - This sunken water flows southward around Africa, where it joins the circumpolar current around Antarctica (Raceway)
Oceanic circulation → how do winds control the surface ocean?
- Wind blowing on the surface of ocean causes wind stress or friction - results in ocean currents deflected to the right of the path of the blowing winds (Coriolis effect) - Because of Coriolis effect and positioning of continental land masses, currents develop narrow rapid flows that move away from equator as warm western boundary currents - Western boundary currents move warm water polewards
How did the Medieval warming impact the northern Europeans (Vikings) and indigenous americans (e.g., the Ancient Puebloans, the Mayans, early Californians)?
0 Europeans (vikings) → warmer temperatures in the North atlantic made Greenland ice sheets begin to melt → led to their prosperity → those who established settlements on coastal Greenland, Iceland and Newfoundland → river systems of eastern Europe prospered for nearly 400 years - Indigenous americans → brought mega-droughts and led to the collapse of Native American cultures in the Americas
What is the current level of CO2 in the atmosphere? And is this level unprecedented in the past?
414.5 ppm and levels have not been seen since 3 million years ago
How high could CO2 levels go if we continue burning fossil fuels as 'business as usual?'
600 to > 1000 ppm
What are atmospheric rivers (extreme precipitation events)? Why are they relevant to CA? How much do they change global warming?
A type of extreme precipitation event that we experience in CA - Intense rainstorms that follow megadroughts - These rain events dump lots of water in a short period of time and often lead to flooding
How does variability in sunspot abundance translate to climate change on Earth?
An increase in abundance of sunspots on the Sun's surface = increase in the amount of solar radiation to Earth
Why is the maximum sun's heat point not always on the geographic equator?
Angle of sun ray's hitting earth: Tilt of axis = sun rays striking ground at lower angle at the poles than equator
What are the main reservoirs/components of the Earth system?
Atmosphere Hydrosphere Biosphere Geosphere Anthroposphere
Why did the slowdown in sea-level rise ~ 6,000 years ago lead to the emergence of permanent settlements and city-states?
Because when the sea level was rising rapidly, it was flooding areas at rates too quickly for permanent settlements to develop
Coriolis phenomenon → what is it and how does it affect atmospheric and oceanic circulation?
Brought on by the rotation of the Earth, that to an observer on the surface of the Earth causes an apparent deflection from the straight-line oath of motion of an object
How does the ocean absorb atmospheric CO2?
CO2 gas from the atmosphere dissolves in surface ocean water → the warmer the seawater, the more CO2 gas can dissolve into it
What 2 processes keep gyres circulating?
Coriolis effect: Controls wind deflection and in turn circulation in surface ocean currents - Ekman spiraling: When surface water molecules move by the force of the wind, they, in turn, drag deeper layers of water molecules below them. As a result, each successively deeper layer of water moves more slowly to the right or left, creating a spiral effect.
Which layer is larger?
Deep ocean
What characteristics of seawater primarily drives this thermohaline circulation system?
Density drives this circulation system → density varies due to differences in the salinity and temperature of water masses
What creates latitudinal temp gradients on Earth and why are they important as part of the climate system?
Differences in air temperature between different locations are critical in weather forecasting and climate. The absorption of solar light at or near the planetary surface increases the temperature gradient and may result in convection (a major process of cloud formation, often associated with precipitation
What is the overall albedo of Earth? And what primarily controls that?
Earth's albedo: about 0.3 - Controlled by changes in ice cover, cloudiness, airborne pollution, or land cover
What are the primary types of electromagnetic radiation? Which enter into, cycle in, and ultimately escape Earth's atmosphere?
Gamma rays, x-rays, ultraviolet rays, visible light, infrared, microwaves, radio waves - Incoming: shortwave radiation in the form of ultraviolent rays (UV) - Outgoing: In lower atmosphere, energy that is absorbed ends up as heat which is re-radiated back into space as longwave infrared radiation
What is an ice-albedo feedback (increased and decreased growth?)
Ice-albedo feedback (Increased Growth): Bright white surfaces of ice reflect 60-90% of sunlight that strikes it. Atmosphere above sheets cool and promotes more formation of ice - Ice-albedo feedback (Decreased Growth): melting of arctic ice = more sunlight absorbed in dark oceans. Causes further warming and melting of ice
What makes a gas a greenhouse gas, and which one is the primary GHG on Earth?
If it can absorb infrared radiation
Why do we have a latitudinal temperature gradient?
Imbalance of net radiation across the globe sets up a latitudinal (equator-to-pole) temperature gradient
How does El Nino affect Californians?
In California, these periods are warming temperatures overall and the Jet Stream is usually displaced well north of its normal position → this translates to typically less snow in CA
Which intervals of the electromagnetic radiation spectrum are primarily absorbed by GHG molecules?
Infrared radiation
What provides the ceiling to these convection cells in Earth's atmosphere?
Major temperature change at the top of the troposphere acts as a ceiling to deflect air currents horizontally
How does climate respond when a threshold is reached
Massive anthropogenically driven changes in Earth system and climate
What defines this temperature threshold?
Need to get to time prior to fossil-fuel burning (pre industrial time)
Is this climate 'typical' throughout Earth history?
No! By the end of this century, the rate of C emissions to the atmosphere will be at levels that we have not seen on Earth since 34 million years ago (when polar regions were ice-free)
Is the term 'natural greenhouse effect' interchangeable with 'global warming?' Why or why not?
No, Although the greenhouse effect tends to be associated with the negative effects of global warming and climate change, the natural greenhouse effect is actually necessary for life on Earth
Can variability in sunspot abundance directly cause large changes (~1°C) in Earth surface temperature?
No, an increase in sunspots translates to a very small (0.1%) change in solar radiation
Where on Earth does deep-water formation primarily occur?
North Atlantic deep water (powered by Gulf Stream) and Antarctic Bottom Water
How long does it take for the ocean water to go through one cycle?
Over 1000 to 1500 years for ocean to completely turn over
What are marine deserts and how do they relate to subtropical highs?
Oxygen starved or hypoxic zones in ocean
What are 3 natural C "sinks" on Earth's surface for storing (sequestering) atmospheric CO2?
Plants, the ocean and soil
What role did this climate change play in evolution?
Promoted evolution --> ungulates (odd toed) including horses, zebras, tapirs and rhinos, and ruminants evolved, and primates and rodents appeared for the 1st time (rapidly migrating around the world)
How can we ensure that we follow the best scenario?
Requires deep reductions in CO2 and other greenhouse gases emissions to occur before 2030 and decrease to net zero emissions by 2050
What are the smallest and largest carbon reservoirs on Earth?
Smallest: atmosphere Largest: rocks (includes fossil fuels)
What are sunspots?
Sunspots are darker cooler spots on the surface of the sun (but the areas around them are the source of most of the sun's solar flares) and heat radiation to space and Earth
What would Earth's surface be if there was no greenhouse effect?
Surface temperature would be -18 degrees, cannot support life
Which is the environmental indicator that indicates when the Earth's carbon cycle is 'out of whack'?
The atmosphere → most sensitive reservoir to changes in C given its relative size to other reservoirs → it is an environmental monitor of changes in global C cycling and health of the planet
In what part of the atmosphere does climate change occur?
The troposphere
Why do we have seasons on Earth?
Tilt of the earth's axis and orbit
What is a tipping point?
Tipping point = point of no return, that is when threshold is crossed
Why is the threshold for total maximum warming = 1.5 degrees c (2 c max) important?
To avoid worst climate change consequences (sea level rise, flooding, fires, hurricanes, drought, major ecosystem loss)
What is whiplash climate?
Type of extreme weather event that includes rapid shifts between two conditions
How might El Nino change in its frequency and/or intensity with continued global warming?
Warmer ocean temperatures resulting from global warming may lead to more frequent and intense super El Ninos (maybe twice as frequent)
How is the Jet Stream affected by global warming?
Waves in the jet stream can also make extreme weather events worse, sometimes causing storm systems or heat waves to move more slowly or get stuck in place.
How to determine negative vs positive feedback loop
When looking at feedback map, if there are an odd number of negatives, then it is negative feedback vice versa
How did El Nino contribute to the fall of the Mayan empire?
With Medieval warming came a shift in intensity and frequency of El Nino → Mayan empire was heavily reliant on water supplies, and when El Ninos became more frequent, they were hit extremely hard by the drought
Is there a natural greenhouse effect on Earth?
Yes
Are the geographic and climatic equator the same thing?
Yes they are
Has climate change played a role in impacting the sustainability of early human civilizations?
Yes → rising sea levels encouraged more temporary settlements (less stabilization)
Are levels of atmospheric CO2 and temperature always coupled (i.e., change in the same direction together)?
Yes! There is a robust link between CO2 and temperature (when one goes up, so does the other and vice versa)
Could the current 20-yr drought in the American Southwest, including California, be related to global warming?
Yes. Global warming affects the frequency, intensity and duration of drought in the western Americas
Positive loop
a change in one component leads to a change in the same direction in the linked component, which amplifies 1st component
Negative loop
a change in one component leads to change in opp direction in the linked component, which reduces change in initial component
Jet streams
a current of air 10 km high in the atmosphere that drags cold air southward or warm air northword - creating fronts --> Sinking air in the subtropical high pressure region moves poleward along the Earth's surface --> At 40 to 60 degree N and S, it mixes with cold, near surface air coming from polar regions --> Mixing of cold and warm air causes very stormy weather
What is the best scenario for the trend in CO2 over this century (to 2100)? Why?
we can probably keep temperatures below 1.5°C (possibly 2°C) of total warming since 1860s — with near 1.5°C total warming by mid-century but then declining through to 2100.