Lecture 13-16 Flashcards
The greenhouse effect
Retention of solar energy in the form of heat
The result of GHG
Greenhous gas GHG
Atmospheric gas which can absorb infrared radiation
Major elemental composition of Earth’s atmosphere
Methane, carbon dioxide, water vapour
What type of light energy is involved in greenhouse effect
Shortwave radiation: visible light, has very short wavelength
- comes from the sun (some of this energy is absorbed and then reflected by the Earth
- process changes wavelengths from shorter visible light to longer infrared radiation
Infrared radiation: has longer wavelengths
What kind of movements do two-atom gas molecules make?
Stretching
example: oxygen, nitrogen
What kind of movements do >2 atom molecules make?
Stretching and bending
Why does solar radiation pass through atmospheric gasses without interacting?
Neither bending or stretching vibrations fall within the same wavelength range as visible light
How do molecules interact with infrared radiation?
Bending vibrations are slower than strethcing vibrations
For some molecules, the rate of movement for bending vibrations can fall within the wavelength range of infrared radiation, hence interacting with infrared radiation.
How do GHG absorb and radiate heat?
Infrared radiation interaction causes bending vibrations to move more vigorously
Some energy from infrared radiation is captured and then radiated outward
- Some to space, where it is lost
- Some back to the planet –> heat
Examples of GHG
Water vapour
Carbon dioxide
Methane
Nitrous oxide
Chlorofluorocarbons (CFCs)
ozone
Who utilizes photosynthesis?
Autotrophs who acquire energy from sunlight
Who utilizes cellular respiration?
Heterotrophs to derive energy from sugars
Autotrophs to use sugar energy fixed through photosynthesis
All large multicellular life requires aerobic cellular respiration in order to produce enough energy to support metabolism and growth (oxygen as an electron donor to produce energy)
How can species thrive in niches without the presence of oxygen and/or carbon?
Some forms of life can produce energy using different electron donors and acceptors
These alternative reactions produce less ATP than aerobic cellular respiration
Generally these types of energy acquisition are believed to have evolved before photosynthesis
- persist in environments devoid of sunlight and/or oxygen.
Chemoautotrophs
Life that uses inorganic substances as electron donors or acceptors other (exclude either carbon, oxygen or both)
Although chemoautotrophs are single-celled organisms, their impact on the global cycle of elements is significant
- Bacteria are the main driver of the global nitrogen cycle
What are some reactions where molecules other than carbon are the electron donor (O2 is the electron acceptor)
Nitrification (nitrifying bacteria, e.g. in well-aerated soils)
Sulphur oxidation (sulphur-oxidizing bacteria)
Iron reduction
Methanogenesis
How do species near deep sea hydrothermal vents get their energy?
Far from sunlight –> primary producers can’t use photosynthesis
Food chains for some persist mainly from the energy produced by sulfur oxidizing bacteria
How do cows produce GHG
Enteric fermentation –> burps out methane
How do we compare GHG?
Two main metrics to compare the relative impact of a gas on the greenhouse effect:
1) Residence time (also called atmospheric time)
2) Global Warming Potential GWP (also called relative radiative forcing)
Residence time in relation to GHG
The amount of time a greenhouse gas remains in the atmosphere reservoir
Global warming potential (GWP)
Measure the contribuation of a gas on global warming, using CO2 as a standard
For a given time period: how much infrared energy 1 ton of gas will absorb, compared to 1 ton of CO2 (often measured out of 100 years)
Why do we say that time period used to measure GWP can be deceiving depending on the residence time?
Divided over a longer time period, GWP seems smaller
Example methane:
- 25 to 28 GWP over 100 years
But residence time is only 10-12 years
Methane does most of its damage quickly then leaves
If measured on a 20 year time scale, GWP of methane=80.
What are the most impactful gases based on GWP, residence time, current atmospheric concentration and human influence?
Carbon dioxide: GHG with the higher concentration in the atmosphere presently
Methane: traps 25x more heat than CO2. Has the greatest future potential to impact global temperatures.
Nitrous oxide: has high GWP and residence time, and is released as a part of agriculture. Difficult to stop.
What are the natural sources of methane?
Methanogens
- Bacterial species (found in areas lacking oxygen)
- Animals which ferment their food during digestion
What are some anthropogenic sources of methane?
Agriculture: animal husbandry (cows) and crops (rice in particular)
Energy: natural gas is mainly methane, processing of petroleum releases methane
Is atmospheric CH4 mainly antropogenic or natural?
60% anthropogenic
Rates of methane release have increased twice as fast as CO2 in the 20th century
Does methane have a cycle?
Since methane is produce through biological processes it fluctuates seasonally similarly to CO2
When bacteria freezes, there is a drastic production in methane –> seasonal fluctuations
Depending on location, there is variation (how near to the equator –> less fluctuation)
Methane leaves the atmosphere mainly through reactions with OH- ions in the atmosphere
- Through a long series of reactions –> converts CH4 to CO2
How does the cattle industry participate in methane production?
Major source
Methanogenesis takes place during the digestion of foods in ruminant mammals
High biomass of cows globally results in high impact
Permafrost
Soil water which has remained frozen for a minimum of 2 continuous years
Decomposition in the absence of O2 –> methanogenesis (whereas in the presence of O2 –> respiration)
Every season, when a bit of the top layer defrosts, plants and soil microbes spring to life. Some of the permafrost melts
During the warm period, organic matter can build up (does not have the time to decompose fully)
Decomposing matter builds up over time
Complete melting of deep permafrost
- Rapid decomposition of stored organic matter (in absence of O2 in the soil –> produce methane and carbon dioxide)
What kind of feedback does melting permafrost engender with increasing atmospheric temperature?
Positive feedback between melting permaforst and increasing atmospheric temperature
Melting permafrost –> atmospheric GHG –> increasing temperatures
Estimated 1500 Gt methane and CO2 held in permafrost globally
Tipping point: we will not be able to stop the melting on permafrost
Natural nitrous oxide
Natural part of the nitrogen cycle
- produced by bacteria in the soil
- Lightning breaking N3 bonds in the atmosphere
Anthropogenic contributions nitrous oxide
Produced as a byproduct of agriculture
- Nitrogen fertilizer used for crops feed bacteria, which produce more nitrous oxide
Less contributor to GHG, but increasing
How is nitrous oxide removed from the atmosphere?
Removed by bacteria
breakdown by UV radiation
How to calculate residence time for excess CO2
R.T. (yrs)= excess C (GtC)/Net C(sink) (GtC/year)
This assumes a well mixed reservoir with a simple removal process
Why does taking out excess CO2 from the atmosphere happen very slowly?
Because of the multiple layers of different sinks and linkages involved in taking out CO2 from the atmosphere
What is the relative impact of a specific gas on the greenhouse effect a result of?
- The atmospheric concentration
- The relative ability to absorb infrared radiation
- The estimated residence time of a molecule in the atmosphere
Climate trends definition
global temperature change over a set period of time (generally over long geological time periods)
Climate rhythms definition
Repeating cycles of climate (generally shorter on a geological timescale)
What is Earth’s climate defined by?
Global temperature averages (not weather patterns)
Climate vaires between hot and cold global averages
Climate rhythms in recent history
Rapidly repeating rhythms of mild temperature changes
Ice Age
Persistent glaciers present
Glacial period
Glaciers are growing
Interglacial period
Glaciers are receding
Currently in a warm interglacial period that began approx.11 000 years ago
Hot House Earth
not persisten glaciers present
Last time planet was in this state was 50 million years ago
Name three reasons that explain how Earth’s climate can move between extremes
Climate forcing
Feedbacks
Tipping points
Climate forcings
Factors which have been shown to influence global climate
Feedbacks
A process(es) which can amplify or dampen a climate forcing
Positive vs. negative
Lasting changes to global climate (change in a single process alone is NOT enough)
Most climate feedbacks are positive (easy for a small change in global temperatures to lead to a much greater global change)
Tipping point
The physical or ecological state of an area (or the planet) crosses an “irreversible” threshold of climate forcings
Irreversible on a human timescale
On a geological timescale, all climatic changes on Earth to date have been shown to be reversible
Does solar radiation change? If so, what are the processes driving this change?
Yes, the sun has a natural life span and has changed since it was formed, and will change in the future.
Processes driving change:
- Availability of hydrogen fuel
- Rate of burning for hydrogen fuel
How does solar radiation work?
Hydrogen atoms in the sun forced together through intense pressure from gravity (fuse into helium, release energy)
Helium is heavier than hydrogen.
Increases pressure at the core. This increase in pressure increases the rate of hydrogen fusion –> more energy it will release
Has solar luminosity increased or decreased since the sun formed?
33% increase in solar luminosity since the sun formed over 4 GYA
Increased in fuel consumption –> greater release of energy
Has an increase in solar luminosity increased global temperatures?
Not a factor in modern rapid temperature increases
A major factor influencing global climate in the distant past (since there was considerably less energy reaching the surface of Earth. Less energy available to heat the planet)
Has Earth’s atmosphere changed over time?
Major changes to types of gases found in the atmosphere since planetary formation. First atmosphere likely formed as gases released from cooling planetary rocks.
More recently, smaller scale fluctuations between concentrations of current gases
How did the planet stay warm even if the sun was only producing 80% of the lumonisity it produces today?
SIgnificantly higher levels of atmospheric CO2 helped the planet stay warm, even with a lower solar radiation budget.
What levels of O2, CH4, and CO2 were there in the early atmosphere (4 GYA)?
Lack of O2 (and O3)
High levels of CH4
High levels of CO2
What was the birth of the organic carbon cycle?
Methanogens
How did photosynthesis evolve?
Decreasing atmospheric CO2
Increasing atmospheric O2 (and O3)
Methane levels high
First photosynthesizers are bacteria (plants have not evolved yet)
- Cyanobacteria produce so much O2 as a waste product
Why did methane suddenly decrease when oxygen became more prevalent in the atmosphere?
Methanogens can only live in oxygen-free environments
Methane reacts with oxygen and converts to CO2
What happened to global temperatures when oxygen replaced methane and carbon dioxide in the atmosphere?
Significant decrease in temperature
Huronian Glaciation
lasted over 300 million years
cycles of glacier and interglaical periods
possible snowball earth
Ice-albedo feedback
Positive feedback between ice formation and increasing albedo lowering temperatures
Specific feedback system important to glacial growth and decline
Continental drift
Tectonic plates move over geological time
Driven by geological processes producing new crust and recycling old crust
What can the location of landmasses on the planet surface influence?
Temperature
- ocean currents
- solar radiation budget
- precipitation
What impact does the movement of continents have on oceanic currents?
Redirect oceanic currents
Changing the direction of heat transfer
Eliminate heat transfer in a region
Example: 45 MYA South America connected to Antarctica
- 41-35 MYA Drake’s passage opened, isolating Antarctica current from nearby relatively warm current
- Glaciation of continent started 35 MYA
Why is the albedo of Earth’s surface not equal?
Land reflects much more thermal energy than oceans
Angle of insolation
Higher latitude: same solar luminosity spread out over larger area –> less energy per area of planet surface
Lower latitude: greater concentration of solar thermal energy per area of the Earth’s surface
Why was there less energy available to transfer to areas of energy deficit in early Earth?
Mostly continents around the equator (as opposed to oceans). Greater reflection of thermal energy from within the critical zone of energy surplus
How do plate tectonics produce new rocks?
Mountain-building events
Volcanic events
Brand new rocks: much greater amount of carbonate, calcium, and other minerals to weather in a (relatively) short time period
Mountain-building events
Formation of new elevated regions of rock
- Can from at the convergent boundary of two different tectonic plates during continental drift (when two usually continental plates converge, rocsk at the collision zone are forced upwards
- Previously buried rocks now exposed to chemical weathering from rainfall
Can form from volcanic activity
- Flow of lava resulting in a new mountain formation
- Completely new minerals form from dyring lava (new rock exposed to the surface for chemical weathering)
Is the location of mountain building events important?
Yes, greater impact on global climate if occurs within the equatorial region
More rainfall –> faster chemical weathering
Cenozoic period
66 MY to today
Several mountain building events (increased chemical weathering transporting atmospheric CO2 to oceanic calcium carbonate)
Formation of Antarctic circumpolar current (formation of antarctic glaciers, increasing albedo)
Isthmus of Panama linked 2 MY
- creation of the gulf stream led to grater snowfall in Northern Europe and North America (increasing albedo) –> long term positive feedback
Orbital processes and types of movement
Earth’s movement in space varies over time
Eccentricity
Obliquity (tilt angle)
Precession (tilt direction)
Eccentricity
Changing distance between the sun and the Earth, as the Earth orbits the sun
Earth’s orbit is an ellipse
- Shape of ellipse changes between being more circular to more elliptical over 100 000 years (currently near mot circular)
What does orbit path influences?
Length of seasons –> greater difference in length with eccentricity
Solar radiation on Earth –> at greater eccentricity, 23% difference between closest and farthest Earth orbit location
Obliquity (tilt angle)
Earth roates on an angle which varies
Earth’s tilt creates differences in solar insolation seasonally (produces seasons)
Greater tilt –> grater extreme between seasons
Precession (tilt direction)
Direction of the Earth’s tilt
- Points in one direction or the opposite direction
- Flips on a regular cycle of 23 000 years
Current direction of tilt
- Why seasonal extremes are milder in the winter Northern hemisphere, but more extreme during summer in the Southern hemisphere
Milankovic Cycles
Obliquity, precession, eccentricity
All changes in Earth’s movement influence climate on predictable short geological time scales
Changes in amount and location of solar radiation on planet (solar radiation falling between 30-60 can differ by 25%)
Have acted as major climate forcings for 2 MY (during the Pleistocene)
- Pleistocene features a series of glacial and interglaical periods
Evidence: comparing the variation in insolation at 65% north in July as a baseline (variations coincide with periods of glaciation and interglacial periods)
Changes in insolation can cause changes in temperature –> need feedbacks to amplify small changes in temperature into climate change
Low or high insolation during interglaical periods?
very high
Low or high insolation during glacial periods
preceded by a period of excessively low insolation
Proxy data
Data derived from sources that are not direct measurements of the variable of interest, but can be used to infer the measurements of the variable of interest
Long time scales (geological record)
Short time scalres (ice cores)
Geological data
Evidence for past glaciation written in the landscape
- Glaciers carve out characteristic valleys in landscapes as they form
- Deposits left at the melting end of a glacier are characteristic
Glacial evidence persist over long time scales
- Knowledge of plate tectonic movement over geological time can be used to infer glacier extent over geological time
How are glaciers formed?
By snowfall compressing over time and pressure
Atmospheric gases trapped in air pockets at the time of glacier formation
Ice cores
Can be removed from old glaciers
Can provide a continuous snapshot of atmospheric gases as well as other events that leave atmospheric traces (such as volcanic eruptions)
Can also indicate global temperatures
Most common oxygen isotope is O16
- 1/1000 oxygen atoms has two extra neutrons (O18)
- Climate influences global temperatures as a reference, can be correlated to past global temperatures
(Going to lose O18 much more readily as oxygen moves north. What remains is composed mainly of O16).
Is it harder for O18 or O16 to evaporate? What about precipitate as rainfall?
O18 harder to evaporate
O16 harder to precipitate
Name some sources of information on past climates
Meteorological instrumented records: thermometer and barometer invented around the 17th century (most instrumental records date back to the 19th century)
Records intended for other purposes:
- private diaries, annals, chronicles with weather information.
- Shipping logs (documenting winds), tax records (e.g. explanations due to bad=good crops), newspaper records
- Crops production, pricing records (wheat, grapes), dates of natural phenomena
Clues in the natural worlds:
- ice cores, coral cores, sediments from oceans or lakes, fossil remains
- tree rings (darker and lighter bands; one is spring growth and the other is summer growth gives clues to humidity at the time)
- pollen (look in sediments to see what kind of pollen was around –> indicates what type of species was present)
Carbon dating
Most isotopes tend to be unstable (decays over time) –> half life
C14 forms high up in the atmosphere, decays into C12 –> measure the ratio, you can estimate the age
Is oxygen useful for dating?
No, O16 and O18 is stable isotopes, and stay as such forever (relative concentration does not change with time)
Not useful for dating, but rather used to analyze (since different isotopes behave or react differently)
Ice-preserved clues of temperature
Evaporation requires energy
Heavier water is harder to evaporate
If it is colder (less energy available), evaporating lighter water is preferred
O18 and O16 in ice is a function of ocean temperature and global ice amount. Therefore, we have a paleo thermometer
Ratio of O18 and O16 gives you clues to the temperature at the time
- Snow that is particularly poor in O18 –> evaporated in cool conditions
- Higher concentration of O18 –> higher temperature
- O16 evaporates easier (and precipitates) (less O16 in the water), which leads to O18 remaining in the water and O16 in glaciers
Ice preserved gas concentrations
Gases are trapped in the ice and can be quantified
How can we use corals to measure temperature?
Corals have O18 and O16 changes due to water temperatures
When was the last glacial maximum
18 000 years ago
A lot of ice –> sea levels decreased
How did we get out of the last ice age?
After nearly 100 000 years of an ice age that peaked 18 000 years ago, a boost in solar illumination in the Northern latitudes helped melt all ice
More sunlight –> warmer summers, snowline makes it to the North, ice albedo feedback –> ice recedes
What has changed since the last ice age?
+5 degrees celcius
Warming temperatures (Earth was colder and drier before) and changing precipitation patterns (as ice starts to melt, more water availability)
Appearance and disappearnace of many great lakes in temperature and lower latitudes
Changing vegetation
Changing sea levels (ice melts, sea rises)
Flooding of low-level areas (Mediterranean basin, Black Sea)
What have ice records revealed about temperature since the last ice age?
Temperatures have risen irregularly
Temperatures have remained relatively stead for the past 10 000 years, maybe decreasing slightly in the past 2000 years
Some suggest that ancient farming followed by the industrial age have delayed the impensing glaciation
There are evidences of accasional rapid climatic transitions in the past 15 000 years (because of positive feedbacks, the climate system can change very rapidly)
What is the 8.2 ka event?
Drained of Lake Agassiz
Lake drained into bay –> drop in temperature
How do we build forecast tools?
Process called system modeling:
1) We must determine all the factors that influence what one is trying to forecast
2) We need to quantify how the interactions occur (interaction/behaviour equations). These interactions are then expressed as mathematical equations describing how each quantity varies with time.
3) We often must estimate the initial conditions (or starting values) of the different relevant factors.
4) We then solve these mathematical equations
How do we model systems with feedbacks?
Systems with feedbacks often have time-dependent behaviour
Modeling requires solving for time-depending interactions
COmplex systems that are irregularly perturbed externally (no stead state) are extremely difficult to predict
What are some forcings that currently change climate?
Changes in GHG (such as those recorded in ice cores)
Fluctuations in solar energy: the 11 year cycle and longer-term variations
- Magnetic poles flip every 11 years. This is associated with change of activities. Monitor this by the observations of sun spots (more sunspots=sun is more active=sends more energy)
Eruptions, sending aerosols in the stratosphere that scatter solar radiation, change atmospheric chemisry (reflects radiation, changes the chemistry by bringing sulfate)
- Dust spreading
- Temperatures can diminish (ex. after Pinatubo)
Sea salts: waves crash, salt it lifted in the atmosphere
Strong winds in deserts: brings dust in the atmosphere, brought very long distances, settles in oceans and brings minerals to phytoplankton
Smoke from fire (deforestation, agricultural practices): dust stays in lower atmosphere, gets flushed by rain. When the dust reaches the stratosphere, it has an effect on climate for a longer time
What is responsible for a 5-10% of the warming observed in the 20th century?
Solar illumination
What does a change in aerosol and cloudiness do to climate?
Competing reflectance vs. greenhouse effect:
- If you add more aerosols, more light scatters (cooling effects)
- More aerosols means more cloud droplets –> smaller clouds –> more surface area –> reflects more (cooling effect)
- Smaller droplets –> longer to rain, cloud lasts longer and grows taller (both warming and cooling effect)
- Warmer air –> less relative humidity –> less clouds
Global climate models (GMC)
Large computer program which mathematically represents complex interactive processes of climate systems
- Components including atmosphere, ocean, land surface, sea-ice, etc.
- Based on physical laws (e.g. Newton’s equation of motion)
- Most sophisticated models available to study climate variability and climate change
Based on a series of equations based on the laws of physics, motion and chemistry.
The Earth is divided into a 3D grid with each grid containing a set of initial conditions (T, pressure, wind speed and direction chemical composition)
Equations try to predict the changes in the conditions within and between the grids when external inputs are introduced into the model. Feedbacks have to be included
What is the difference in forecasting climate vs. weather?
Atmosphere is either unstble or at the brink of instability (where positive feedbacks dominate)
- Small air flow pertubations grow to become planet-wide (chaos theory, butterfly effect)
Climate deals with averages and is more stable thanks to some strong negative feedback processes or processes with limited feedbacks
- Radiative cooling feedback
- Chemical weathering (long-term inorganic C cycle)
Climate is less unpredictable than weather
Validation of GCMS
Ability to reproduce past/present-day patterns of temperature, precipitation and their seasonality and recent changes
Cooling effect of aerosols (through scattering of solar radiation) is important to capture recent temperature variability
Climate change experiments with GCMs
After validation, numerical experiments can be performed (example: by increasing concentrations of GHG, etc. for the new century)
Scenario of future human activity –> future emissions of GHG –> Earth system models –> climate change preditictions –> impact models –> ecosystem, economical, and sociological consequences
What is a climate change prediction in 2100?
3 degrees celcius increase globally
But more over land than over water
More at high latitudes and in winter than at low latitudes or in summer
More at night than during the day
Why do we use global climate models?
Given all the interactions in the cliamte system, the question is approached by computer modeling
Despite their limitations (computer power, knowledge), these physically-based models have been reasonably successful at modeling the present; most researchers believe they are satisfactory tools
They confirm man’s present influence on climate
They make predictions of significant warming before the end of the century
