lecture 1 - 15 Flashcards
Difference between climate and weather
Climate is the average weather - extended period of time
Weather is the state of the atmosphere at a given time
Example of annectodal climate change
Hurricane dorian is ghe worst hurricane ever recorded in the bahamas
What does the surface weather station stevenson screen measure?
Temperature, humidity, pressure. Wind
What are weather balloons used for?
Profile lowest 30 km of the atmos twice a day around the world
Climate change evidence #1 is the global mean surface temp - how is this evidence of climate change
Global average is increasing, hottest period since 1980
What are the four strong evidence for climate change
Mean surface temp increasing
Global mean sea level rising
Arctic sea ice extent - declining
Increasing atmospheric carbon dioxide + ocean acidification
Explain hydrostatic balance in the atmosphere
Atmo pressure and air density decrease exponentially with height
Decreasing air pressure w height makes an upward pressure force the balance the downward force of gravity
Where do clouds and precipitation occur in the atmosphere?
Troposphere
What are the greenhouse gases
Water vapour CO2 Methane Nitrous oxide Ozone CFCs
99.9% of the dry atmosphere consists of what gases?
Nitrogen
Oxygen
Argon
Where is the ozone layer found in the atmosphere
Stratosphere
What is tropospheric ozone?
Air pollution
Made from nitrous oxide emitted from fossil fuel burning
What is residence time
Average lifetime of a molecule in armosphere
What is a steady state
Inflow rate (sources) equal the outflow rate (sinks)
Explain the bathtub analogy for residence time
Resevior is like a bathtub
If the atmos gas concentration stay the same, then the source and sinks must equal each other
Water flow into tub must equal water flow out of tub
Which gases have the longer residence time in the atmosphere?
Nitrogen and oxygen
Why are the oceans a key factor in determining climate and climate change
Ability to store and transoprt huge amounts of energy and delay the temperature response because of its heat capacity
What is the thermocline?
Layer where the ocean temp decreases rapidly with depth
Why is the deep ocean cold?
Because the water comes from the polar sea surface
Densest surfa e waters are near the poles —> denser water sinks —> this supplies cold eater in the deep ocean
What is the eath’s energy balance
Incoming solar energy absorbed = terrestrial infrared radiation emitted to space
What are the properties of an electromagnetic wave
Wavelength, frequency, amplitude
The analysis of radiation by wavelength or frequency is called
Spectroscopy
What is thermal radiation
Radiation emitted by substance because of its temp
As a substance gets hotter, the emitted thermal radiation wavelength gets longer or shorter
Shorter
A materials ability to emit radiation is the same as it’s ability to…
Absorb radiation
What is black body radiaiton
Efficiency is 100% to absorb and emit radiation
What is infrared radiation
Invisible radiaiton
Wavelengths that are longer thsn the visible red wavelengths
What are the two types of radiation important for climate change
- Solar infrared radiation - shortwave, emitted by sun, makes up 1/2 solar radiation
- Terrestrial infrared radiation- longwave, emitted by earth and atmosphere, STRONGLY ABSORBED AND EMITTED BY GREENHOUSE GASES AND CLOUDS
Which electromagnetic waves can transmit through the earth’s cloudless atmosphere
Some UV, most visible light, some infrared, some microwave and some radio
What causes the greenhouse gas effect
Complete of partial blocking of some of the infrared wavelengths
The fraction of incoming radiation that id reflected by an object is called the … of the object
Albedo
What does an albedo of 1 mean? How about 0?
1 = 100% reflected 0 = 0% reflected, all is absorbed
The average planetary albedo is 0.3, what does this mean?
30% of incoming radiation is reflected, 70% is absorbed
What reflects most of the sunlight and what absorbs most of it?
Relfects = clouds, ice, desertd
Absorbs = trees/forest, oceans
What is the effective planetary temperature
Temp earth appears to emit from space
Teff must be big enough to make enough outgoing thermal radiation to balance the net incoming solar radiation
Increases if more solar radiation
Decreases if earth gets higher albedo
Why is the effective planetary temperature lower/colder than the actual observed average surface temp?
Teff does not take into account the greenhouse gas effect which raises the surface temp
What 3 factors determine the globally averaged surface temperature
Amount of incoming solar
Albedo of earth
Greenhouse gas effect
The terrestrial infrared radiation gets progressively more blocked as the greenhouse gas concentration increases. Why?
Greenhouse gases absorb and emit at certain terrestrial infrared wavelengths
Increasing amount of g gases reduce the penetration depth of the terrestrial infrared radiation at the specific wavelengths that interact with the g gases
What happens if the atmosphere becomes more opaque at cetain wavelengths?
The radiation at those wavelengths can’t penetrate as far
Radiation that escapes to space starts from colder, higher up regions of the atmosphere where radiation reaching the ground starts from lower down. How does the increasing opaqueness of the atmosphere effect the greenhouse gas effect?
More opaque, radiation can’t penetrate as far into the atmosphere
More radiation reaches the ground + g gas effect is larger
How does adding g gases warm the earth
G gas concentrations increase - atmos more opaque
Penetration depth of infrared radiation is reduced - can’t travel as far
outgoing terrestrial radiation escaling to space comes from higher up in the atmos where it is colder
Colder atmos release less thermal radiation
Results - earth releasing less terrestrial bc of g gases but the net incoming solar is staying the same
Why is global warming happening (essentially)
The extra g gases are making the atmosphere less transparent in the infrared
Net incoming solar radiation energy is larger than the outgoing terrestrial
Where does the accumulated energy from the imbalance of solar snd terrestrial radiation go?
94% to ocean warming and 3% to melting ice sheets, 3% to heating land
Will the energy imbalance between solar and terrestrial persist forever?
No - it will eventually reach a new steady state
Ocean, land and air temp sill increase gradually and gradually increase the amount of terrestrial infrared escaping to space
But new steady state will have higher surface temp
How is the current energy surplus that the earth is experiencing being used up?
Heating ocean
Melting ice sheets and glaciers
Heating land and sub-surface
Explain the difference between a maritime climate and a continental climate
The heat capacity of the oceans imposes a time delay In the climate system
Takes longer to heat oceans
What are some consequences of the high heat capacity of the oceans
Warmest summer temp occur month of two after max solar energy on june 21
Annual temp extremes are smaller nearest ocean
Full impact of global warming is delayed while oceans warm up
Tropical oceans are heat sources to drive tropical cyclones
Why are the poles cold?
Earths angle, solar radiation near pole is spread out over a larger area, so less energy per unit area
Why do we experience seasons?
Earth’s tilt
What are the two types of local radiative energy imblanaces
- Net radiative surplus (positive) over the tropics and net radiative deficit over the poles
- Locally earth;s surface has a surplus whereas local atmos above has a deficit
What motion does the energy imbalance of the poles and equator drive?
What about the local imbalance of the surface and the atmos?
Pole-equator - drives the meridional dynamics / motion of the atmosphere and the oceans
Locally - drives the vertical dynamics the lower atmos (troposphere)
The latitudinal imbalance in radiative energy get balanced in total by what..
The internal dynamical motions of the at atmos and oceans
Transfers sensible and latent heat from thd tropics to the poles
What internal dynamical processes transfer sensible and latent heat from the tropics to the poles?
Had;ey cells, tropical cyclones, extratropical cyclones snd ocean circulstion
Explain the net radiative imbalance between the atmosphere and the surface?
Surface has net radiative heating
Atmos has net radiative cooling
*turbulence, convection, thunderstorms - transfers surface heating to atmosphere so that total energy balance occurs everywhere
What is the earth’s general circulation?
Transfers sensible and latent heat from regions of net radiative heating to regions of net radiative cooling
Dynamical motions set in place to achieve local energy balance everywhere
What are the two main climate regimes?
- Tropical and sub-tropical
(30 deg n and s) - Extra-tropical
(Poleward of 30 deg latitude)
Explain the tropical and subtropics climate regime
30 deg n and s Horizontally uniform temp Active weather (thunderstorms, tropical cyclones Weak seasonality Monsoons, hadley cells Easterly trade winds
Monsoons are a heat capacity effect. Explain
Air over land is warmer than ocean air in the summer —> oceans have large heat capacity, don’t warm up as fast
Sets up a circulation of air - warm rises over land and cool sinks down over ocean
This cycle reverses in the winter - seasonal varying rainfall is called monsoon
What drives the thermohaline ocean circulation
Local net radiation imbalance
What is the thermohaline ocean circulation
Deep circulation
Transfers heat, water and salt
Caused by ocean water density differences
Densities determined by temp and salinitydifferences
Where does the oceans deep water come from?
Greenland and the antarctic seas
Consider an atmosphere with no greenhouse gases and no clouds. How would this effect the energy of the earth?
It would be in a steady state / balanced
Atmos transparent to long-wave terrestrial and not emit any longwave
Surface temp would be the effective planetsry temp (-18 deg)
No consider an atmos with greenhouse gases and clouds creating a “blanket” in the atmos. Explain the blanket analogy
G gases emit more terrestrial infrared back to the ground than to space because its warmer in the atmos closer to the ground
Top of blanket is colder - less emitted
Bottom of blanket warmer - more emitted
Amount of infrared emitted depends in temp
Why does the planet need the greenhouse gas effect
Without it, surface temp would be teff (-18 deg) and freeze all water and life as we know it - greenhouse gas effect helps keep the planet warm and liveable
What is radiative forcing
Chg in net total radiation at the top of the atmos which occurs bc of a chg in climstr system (i.e increasing co2, changing solar input, adding volcanic aerosols)
The net total radition is the difference between what
Between downward and upward solar shortwave and terrestrial infrared radiation
What happens to the terrestrial infrared radiation if we instantly double the amount of carbon dioxide
The surface temp is still at 15 deg
The blanket is thicker
Penetration depth of long-wave ir is reduced
Stronger absorption of long-wave ir
Top of the blanket is now colder because the long-wave being emitted to space is at a higher altitude
What happens to the terrestrial infrared radiation if we double the amount of carbon dioxide and a new steady state is established
The warming of the atmos and surface continues until teff emitting level of terrestrial IR to space is back at -18
The surface temp will warm by 3 deg to 18 deg
This change takes time because of the oceans time delay
What causes the greenhouse gas effect
Emission of terrestrial infrared radiation by g gases and clouds downward to the earth’s surface
Is venus’ surface warmer because it’s closer to the sun?
No
It has a stronger greenhouse gas effect
What is a greenhouse gas
Molecule that can absorb terrestrial infrared radiation with wavelengths in the 4-100 um
How many atoms does a greenhouse gas have
3 atoms or more
Greenhouse gases are… or… atomic molecules
Tri or polyatomic
Greenhouse gases are tri or polyatmoic molecules giving them different vibrational modes. How does this effect their ability to absorb and emit in the infrared?
If vibrational mode matches the infrared radiation wave frequency, the molecule can emit or absorb
What are the 5 greenhouse gases
Methane CO2 Water vapour Nitrous oxide Ozone Halocarbons
What are the two vibrational modes of carbon dioxide? Explain them
Bond stretching and bond bending
The two frequencies correspond to specific wavelengths in the terrestrial infrared where they can emit and absorb
What contributed to the natural greenhouse effect
Water vapour
Clouds
Other gases (mostly CO2)
What is the natural greenhouse gas effect?
Warms the earth surface from the teff of -18 deg to the actual surface temp of 15 deg
What accounts for 70% of the natural greenhouse gas effect
Water vapour and clouds
Why does the concentration of CO2 oscillate annually?
Global photosynthesis and respiration
When do the co2 concentrations show a minimum globally? What about an increase?
Minimum during nothern hemispheric autumn after summer’s new biomass growth removes co2 through photosynthesis
How do we know the pre-industrial co2 concentrations of about 280ppm?
Air bubbles trapped in ice cores drilled from the Greenland and antarctic ice sheets
What are the main anthropogenic sources of methane
Rice paddies Cattle Biomass burning Fossil fuels Landfills
What are some natural sources of methane?
Wetlands
Lakes, termites, oceans, permsfrost
What is a natural sink of methane
Chemical reactions in atmos
Sink in soils
What is most of the increase in nitrous oxide emissions from?
Agricultural sctivites
Fertilizer
Animal production
What is the global warming potential
By definition the gwp of co2 is always..
Radiative forcing of a gas averaged over the given time period compared to same mass of co2
Gwp is always 1
The extent to which a greenhouse gas directly contributes to climate change depends on what 3 things
Quantity of gas
Time before its removed from atmos
Infrared energy absorption propreties
The global warming potential is usually averaged over what length of a time period
100 year time period
Methane is 23 times more potent as a greenhouse gas than co2 but co2 still exerts more radiative forcing than methane in the atmosphere… why?
Because there’s more co2 in the atmos
The gwp potential of nitrous oxide is much larger than methane because…
Nitrous oxide has a longer lifetime than methane
Why does water vapour not have a global warming potential
Because it’s a natural greenhouse gas nad only has a lifetime of 1 week
What is equivalent co2
Concentration of co2 that would result the same level of radiative forcing for a given type and concentration of another greenhouse gas
Is equivalent co2 larger of smaller than actual co2 ppm
Larger
Usually by 25-30%
If we eliminated all anthropogenic aerosols, how would it affect to co2 concentrations?
It would increase them almost instsntly
Believed that snthroopgenic aerosol cooling effect is offset by non-co2 g gases
Why do they recommend reducing blsck soot?
Its the only aerosol that significantly warms the climate by directly absorbing solar energh
Removing soot reduces radiative forcing directly
What are the two bad properties of halocsrbons (hfcs)
Destroys atmospheric ozone by releasing chlorine
Strong greenhuose gas - 5000 times stronger than co2, long lifetime,
Ground level ozone pollution is formed by what
Oxygen + volatile organic compounds + nitrous oxide (traffic exhaust + indutries) = react with sunlight = makes smog
Harmful to humans and plants
Where does the carbon being released via fossil fuels go
Oceans and land + most into the atmosphere
What are three forms of carbon storage?
Inorganic carbon (co2 in oceans, atmos, valcanic vents) Organic carbon (photosynthesis) Carbon in rocks
What is co2 residence time in the atmosphere/
4 years
CO2 is nesrly uniformly mixed in the atmos since global atmos mixing occurs on a time scale of less than year… however the anthropogenic carbon pulse lifetime in the total climate system is much longer… why?
Because its determined by the final burial rste of carbon into the ocean bottom, which is very small
What is the difference between emissions and concentrations
Emissions is what were adding
Concdntrations is how much there is total
What are two anthropogenic carbon dioxide sinks
Land biomass and oceans
What are the sources and sinks of anthropogenic co2
Sources
Fossil fuels and land use (deforestation)
Sinks
Oceans, land biomass, stays in atmosphere
What is gross primary productivity?
Photosynthesis removign atmospheric co2 — creating new biomass
What does deforestation do to the csrbon budget?
Appears as a source because it reduces the removal of co2 from the atmos
Explain the ocean biological carbon pump
Photosynthesis in surface waters - stores carbon as organic matter, reduces partisl pressure of surface ocean co2
Helps draw down carbon dioxide from atmosphere
What is happening to the ph of the oceans as more co2 is drawn in
Becoming more acidic, affecting ecosystems
Fresh water makes up 3% of all water on earth. 70% of thst fresh water is icecaps and glaciers and 30 % is ground water… what makes up that last 0.3% of fresh water?
Lakes and swamps and rivers
What is runoff?
Precipitation - evapotranspiration
In the global annual average the total amount of evaporation of water and ice from the earth’s surfacd must equal the total what?
Precipitation
What makes the oceans locally saltier? What makes them locally fresher?
Saltier - evaporation greater than precipitation - drought can occur and ocean becomes saltier
Fresher - evaporation less than precipitation - excess water runoff returns to oceans
What is the residency time of water vapour in the atmos? How does the effect tropospheric aerosols and pollution?
One week
Pollution and tropospheric aerosols wash out with rain - so their residency time is also about a week
Why does you skin feel cold after coming out from swimming in a lake? How would a windy day affect this?
Cold water on skin evaporates
This requires energy/latent heat
Latent heat is extracted from your body/skin
Wind = low humidity = evaporation rate is faster and cooling is faster
In the phases of water, what processes require latent heat input? What processes release latent heat?
Require - evaporation and sublimation of ice (from ice to vapour)
Release - condensation and deposition (vapour to ice)
What drives the hydrological cycle?
The atmosphere has a net radiation deficit and the surface has a net radiation surplus
When does the latent heat get released back into the atmosphere as sensible hest in the hydrological cycle?
When it rains, the latent heat gets released as sensible heat
In the atmosphere how is the latent hest being transferred?
Going from evaporation to condensation sites
Energy from surface up to the higher latitude in the atmosphere
What is the saturation water vapour
Max amount of water vapour at equilibrium
It increases with temperature
What is the relative humidity?
Ratio of actual amount of water vapour to the saturation amount of water vapour
What happens when the relative humidity is 100%
The air parcel is being cooled when its being lifted into the atmosphere and forms a cloud
What happens to the relative humidity as the air parcel cools? (Hint; air that goes up is make]ing rainy clouds, sir thst going down is cloud-free and sunny)
When it coolsmas it moves upward, the amount of water vapour stays the same
As temp decreases the saturated amount lg water vapour decreases
As a result, the relative humidity increases, and once it reaches 100% the water vapour condenses and makes a CLOUD
What causes rain?
Air parcel rises, expands to match air pressure which gets smaller w height
Volume increases and parcel does work against surrounding sir which uses internal energy - parcel starts to cool
Relative humidity increases as parcel cools - at 100% makes a cloud because parcel is saturated with water vapour
Eventually gets cold enough, ice crystals forms and grow and fall out of the cloud, melt and rain to the ground!!!
What 2 things is the rainfall rate proportional to?
Amount of water vapour being lifted
Strength of the upward motion in the cloud
Most desert are located under what
The descending branch of the hadley cells
Warms air and evaporates the clouds
High precipitation occurs where
Near equator with the ascending branch of the hadley cell
Warm moist air being lifted upwards
What are some climate vegetation interactions
Vegetation and albedo
- dense forest = dark = absorb sun
- pasture = light = reflects
Transpiration increases water vapour in atmos
What are aerosols
Tiny particles
0.01-10 um
What are primary aerosols? What are secondary aerosols?
Primary = crested st earth’s surface and lofted by wind
Secondary = made by gas to particle chemical reactions in atmosphere
What is the lifetime of aerosols?
Only about a week in troposphere
By burning fossil fuels, how are aerosols created?
Incomplete combustion
Why are aerosols important?
Reflect sunlight back to space(cooling)
Act as nuclei centre for cloud droplets and ice crystals
Health concern + air quality
Acid rain
Volcanic eruptions - aerosols in strato
Reduce visibility (planes can’t see shit)
What is the direct aerosol effect?
Aerosols reflect sunlight to space
Exception - soot absorbs sunlight
More aerosols mean more cloud droplets because they can act at nuclei for them. How does this affect the cloud properties and the climate?
Clouds are brighter and reflect more sun
What is the indirect aerosol effect (cooling effect)
Aerosols make clouds brighter so they reflect more sun back to space
They have smaller droplets making it harder for the cloud to rain and therefore they last longer in the atmosphere
How long can volcanic aerosols that reach the stratosphere reside there? Why?
1-2 years
Lacks clouds and rainfall to remove them
What is a positive feedback?
Amplifies the original change, can be negative or positive amplification / increase or decrease
What is a negative feedback
Reduces the magnitude lf the original change, regardless of whether the change was an increase or a decrease
Why is the water vapour feedback large and positive?
Global air temp increases bc co2 concentrations increase, water vapour increases in atmos, increased greenhouse gas warming from water vapour
Amplified
Why do the nighttime temps in a desert get very cold even though it was very hot during the day
Amount of atmos water vapour in desert is low
The blanket is thinner, penetration depth is longer, more terrestrial radiation from the ground going upward and cooling at the ground
Do high clouds warm or cool the earth?
Warm the earth
Transmit most solar but block warm infrared from the surface and emits cold infrared to space
Do low clouds warm or cool the earth?
Cool the earth
Reflect most solar back to space and emit warm thermal infrared radiation
What type of cirrus clouds show a positive feedback? What type show a negative feedback?
more thin cirrus clouds - warming (thin wispy clouds)
Less thin cirrus clouds - negative feedback
Cumulus clouds - positive and negative feedback
More cumulus clouds - cooling - negative feedback
Less cumulus clouds - warming
Positive feedback
What is an uncertainty with clouds and climate change?
Whether it will be a positive or negative feedback
If its cirrus clouds (more infrared blocked) or less total clouds (more solar reaching surface) then it will be positive feedback — more warming
If its low clouds (increase solar albedo) and less thin cirrus clouds - negative feedback, cooling
The ice albedo and temperature feedback - positive or negative? Explain
Positive
Warming - increased open water in summer, thinner ice, less snowmcover - more shortwave solar absorbed into system - more warming
Large areas in arctic ocean are currently dark… this means
Absorbing solar radiation - positive feedback
Vegetation has some positive and negative feedbacks. Give examples or each
Positive
Albedo; higher temp - more veg - darker surfsce - more absorption- higher temp
Moisture supply; more veg - more evapotranspiration - more water vapour - more rain - more veg
Negative
Carbon budget; more co2 - more veg - more photosynthesis - removal of co2
About 1/3 of all land has been converted to what… how does the effect climate
Cropland or pasture
Surface albedo, soil moisture and carbon fluxes
What are some possible feedback in the biosphere that we need to know to predict future co2?
Plankton multiplier Soil microbial activity Biosphere dieback Release of stored methane (All positive)
Carbon dioxide fertilization (negative)
Methane temperature feedback - positive or negative? Explain
Positive
Temperature goes up - permafrost thaws - co2 and methane release into atmosphere - temp warms
The climate consists of 5 interacting components… what are they
Atmosphere Hydrosphere Cryosphere Land surface Biosphere
What is the main difference between weather and climate forecasting?
Weather forecast = predict future atmosphere state at a particular time and location, minimizing difference between predicted and actual weather at that place and time
Climate = we don’t care about weather at a particular time, but care about the average predictions and the extended time period
How is weather forecasting done?
Computers numerically solve atmospheric equations or motion
What are the 3 equations that have to be solved to predict weather? What equation predicts what?
Momentum - predict winds
Energy - predict temp
Continuity - density of air and water
Why aren’t the weather forecasts perfect?
Gaps and errors in measurement
Limited spatial resolution of computer model
- need faster computers to improve models
Non linearity of system - limits range of weather predictions to weeks, not an issue for climate models though
How do we model complex sub-grid processes like clouds?
Approximate the small scale effects, measure on a small scale
What are the steps in running a global climate model (global circulation model - GMC)
- Specify input - choose boundary based on known changes of solar, co2, ice sheets, mountains, continent position
- Run model simulation of ocean and atmos - physical laws or radiation + circulation
- Analyze climate output
- Compare - data from earth’s history
What are some main difference in climate vs weather models in terms of resolution, simulation time, vegetation, oceans
Climate Resolution = 100km Oceans = full air-sea interaction. Ocean dynamics Time - >30 years Veg = highly interactive
Weather Resolution = 10km Oceans = fixed sea surface temp Time = 2-14 days Vegetation = fixed or ignored
Climate models are now so sophisticated that they are now called…
Earth systems models
Testing the climate models ability to predict 20th century temps is part of the validation procedure. Models tend to do a good job of predicting 20th century climate but it can be right for the wrong reasons… what are some future improvements for climate models
Faster computers higher spatial resolution Improve parameters around some processes More observational data More inter-model comparisons from groups around the world
How were climate models used to understand current climate change
Cooling of sea surface temp in North Atlantic may be caused by anthropogenic aerosols from europe, helped weaken African monsoon
Also weakened monsoon circulation and shifted inter-tropical convergencezone
What equilibrium climate sensitivity?
Equilibrium / final steady state change in the global mean surface temp following doubling of pre-industrial co2
What is the transient climate response
20 year global mean surface temp chg after 70 years of carbon dioxide increasing at 1% per year compounded
- results in a doubling of co2 in 70 years
What are some positive feedbacks in the earth’s climate system
Water vapour
Ice albedo
Clouds
the equilibrium climate sensitivity would only be about 1.2 deg if we just consider the effects of a doubling co2 concentration. Why is actually 3 deg?
Because of the positive feedbacks
What does a low sensitivity mean/ what about a high sensitivity?
Low = low change, climate change will be much easier to deal with
High = climate change will be detrimental and cost to adapt is high
Whatis the precautionary principle
Principle in environmental law
Dictates that we should plan for a higher value, don’t ignore the high value rven though you have an average
Insurance policy
Why do we still have some uncertainty in the model derived equilibrium climate sensitivity?
Because the feedbacks have significant uncertsinties
Especially clouds and oceans
What is the transient climate response
Amount of warming expected in 70 years for a doubling of co2
What is the range for the transient climate reponse
1-2.5 deg in the next 70 years
Climate sensitivity is designed to look at graudal average trends in climate induced by gradual change in radiative forcing. It does not account for…
Rapid changes
Unstable tipping points
Who makes assessment reports roughly every 6-8 years to update climate forecasts, using w0 global climate models from various centres around the world and creates model predictions to project climate change in the next 100 years…
Ipcc
Intergovernmental panel on climate change
What are representative concentration pathways
Four future radiative forcing pathways developed for the climate odeling cmomunity as a basis for modelling experiments
I.e models for climate scientists to follow so that the reports are comparable
How are rcp’s set up?
Final radiative forcing values of 2.6-8.5 With co2 concentrations and the effects/pathway of each value
What is our current radiative forcing value (2011)? What is the value is co2 doubles?
- 3 W / m2
3. 8 W / m2
Which rcp pathway are we currently following?
Rcp 8.5 - this is the worst one :)
The last 542 million years was the..
Phanerozoic
What was the main controller of temperature in the phanerozoic?
Co2
The earth’s crust is divided into…
Plates that move in response to convection in the mantle
Explaine the relationship between volcanism and rock weathering
If rock weathering sink of co2 exceeds volcanism’s supply/source of co2
Atmos co2 decreases, climate cools, vice versa
What 3 things do tectonics control
Volcanism
Continental drift
Orogenesis (mountain making, continental plates collide)
Is weathering a negative or positive feedback on tectonic forcing
Negative feedback
Prevents extreme temps by stabilizing amount of co2
System adjust to reduce initial change
What ended after an asteroid hit 65 million years ago near the yucatan peninsula
Cretaceous period
What are the 6 major extinction events that happened during the Phanerozoic in order
Often-sit down, perhaps their-joints creak, agonizingly
Ordovician - silurian (glaciation)
Late Devonian (dust, volcanoes)
Permian (largest mass extinction)
Triassic/jurassic (floods)
Cretaceous/ palocene (k-t event - asteroid)
Anthropocene - current day, caused by humans
Earth has been gradually cooling over the last 50 million years, how do we know this?
Temps derived from oxygen isotope analysis of marine organisms buried in the sea floor
Why did the global climate cool over the last 50 million years? (3 things)
Sea floor spreading rate decreased, slowing the rate of co2 input
Weathering caused faster removal of co2, formation of Himalayas
Poleward ocean heat transport reduced and deep water formation shifts to high latitudes
What formed the Himalayas? Effect on climate?
Collision of indian subcontinent with asia
Exposed rock for chemical weathering
Removed co2 and cooled climate
What allowed Antarctica to cool and start growing ice sheets?
Opening of drake’s passage helped isolate Antarctica from meridional (north-south) heat transport
We are in a long glaciation epoch although currently we are in an interglacial period called the..
Holocene
How do we deduce recent psst climates?
Tree rings
Ice core drilling
Lake sediment
Atmospheric co2 lowered from the pre-industrial holocene concentration of 280 ppm to 190ppm during the glacial maximum about 20,000 years ago…mwhere did this 90 ppm of co2 go?
Deep ocean
Glaciation is initiated by the earth’s orbit which is controlled by attractions between the earth, moon, sun and other planets (mostly Jupiter). What are the three orbital variations
- Earth’s tilt varies over 41,000 year - solar input varies in high latitude
- Orbit around sun varies every 100,000 years - seasons
- Position of solstices
What are milankovitch cycles? (3 variations do to with earth’s orbit)
Earth’s orbit around the sun
Tilt of earth
Soltices
How can glaciation start
Summer solar energy needs to be weak enough to not melt all the previous winter’s snow
Ice sheets need to form on land
SUMMER SOLAR ENERGY AT 65 DEG NORTH LATITUDE
What is the key variable to predict the growing ice sheets
SUMMER SOLAR ENERGY AT 65 DEG NORTH LATITUDE
What was the period of deglaciation cooling that happened over 12,000-10,700 years ago
Younger dryas
What is some evidence for the younger dryas cold period
Southward re-advancement of polar water in the north atlantic to 45 deg north
Scotland reverted to arctic vegetation
Insect fossil in Britain indicated cooler temps
What caused the younger dryas
Change in melt-water flow in north america during deglaciation
Drainage direction of north American ice sheet changed from southward to gulf of Mexico to northward into the hudson bay + arctic ocean
Brought pulse of fresh water, cutting off deep water formation and cooling the region
Why were the monsoons much stronger 10,000 years ago?
Because sun was much closer to earth
When did the transition for hunsting-gathering to farming start? Why?
About 10,000 yesrs ago
Monsoons much stronger because Northern hem summers much warmer and wetter
About 5000 years ago, many civilizations started to collapse (china, indus, nile, peru, maya, and some others)… why?
Drought
During a little ice age, about 1400-190p in europe, what sun spots occured?
Maunder sunspot minimum
Sporer sunspot minimum
What are some possible explanations for the little ice age that happened in europe and destroyed many villages and farmhouses in the alps
Change in ocean circulation- thermohaline circulation may have slowed down
Strong volcanoes putting aerosols in stratosphere, reducing solar radiation reaching surface
What interglacial period happened about 120,000 yesrs ago, had sea levels about 4-6 m higher than today’s and a smaller greenland ice sheet? Its also a potential indicator for what our future may look like in the next hundreds of years
Eemian
The eemian is believed to have been only 1 deg warmer than today and sea level was 4 m higher at its maximum. Why?
May be because the collapse if west Antarctica ice sheet caused rapid sea level rise without an accompanying warming
What period is an analog for our future in next 1000 years
Mid-pliocene warm period, 3.3 million years ago
What period had temps 2-3 deg highter, sea level 25 m higher, Greenland ice sheets much smaller
Mid pliocene
The global cooling that occurred towards the end of the pliocene may be responsible for what shift in vegetation
Forests to grasslands and savannas
Why is the pliocene s]a useful period to use as an analog
Continental positions were basically the same
Ocean circulation and biota were similar
Give us an idea what to expect with a warmer equilibrium established on earth with co2 over 400 ppm
What were the pliocene biomes like
Northward shift to temperate and boreal vegetation zones, expansion of tropical savannahs
High arctic covered in boreal forests, glaciation in canada not happening yet
The mid pliocene was around 400 ppm, 2-3 deg warmer, sea level was 25 m higher suggesting reductions in contniental ice sheets and warmer ocean temps… why is this important to us now
Its a window into out future, what to expect in the long-term
What period is an analog for rapid warming?
Paleocene-eocene thermal maximum (PETM)
In which period did global temp rise by 6-8 deg over a 20,000 year period , where many benthic forminifera a d terrestrial mammals wen’t extinct, but numerous modern mammalian order emerged?
Petm
What were the 2 observations that indicated a massive release of carbon at the petm?
Large global negative carbon isotope excursion
Dissolution of deep ocean carbonates
What was it likely that the negative shift in carbon isotope was likely organic carbon
Organisms discriminate againt carbon 13 during photosynthesis
What limits the petm analog?
Ice sheets and ocean circulation quite different as well as continental positions
