Unit 9 ONLY

Montreal Protocol

International treaty to gradually replace CFCs with HFCS

• replaced CFCs with HCFCs (CFCs with hydrogen added)

• replaced HCFCs with HFCs (which still deplete O₃ and act as GHGs, but to a lesser degree)

• want to replace HFCs wit HFOs (HFCs with C-C double bonds that shorten atm. lifespan and global warming potential)

Why were CFCs replaced by HFCs?

They have no chlorine to catalyze transformation of ozone into atmospheric oxygen

• BUT HFCs are a powerful greenhouse gas (so they're not perfect and are only a temporary solution)

Why is it important to know that CFCs are persistent?

It will take decades for CFCs currently in atmosphere to completely dissipate, allowing ozone layer to fu

Why is stratospheric ozone important?

It absorbs UV-C and much of UV-B radiation

• without it, life wouldn’t be possible because UV-B/C radiation causes tissue damage and mutates DNA

• helps prevent skin cancer and cataracts

Tropospheric ozone =

= Respiratory irritant, damaging to plant tissue and photochemical smog

How does the formation/combination of O in the stratosphere absorb all UV-C and much UV-B? (protecting org. on Earth)

UV-C breaks O₂ into two free oxygen atoms (2O)

• when a free oxygen atom from this rxn combines with an O₂ molecule, ozone (O₃) is formed

• UV-C also reverses the rxn by breaking ozone into O₂ and O, which can then bond with another free O to form O₂

Chlorofluorocarbons (CFCs)

Primary anthropogenic cause of O₃ breakdown

• used as refrigerant chemicals and propellants in aerosol containers

How do CFCs deplete/destroy ozone?

UV radiation causes free chlorine atom to sperate from CFCs

• highly electronegative chlorine bonds to one of the oxygen atoms of ozone, converting it into oxygen

• free O atom then bonds to O from chlorine monoxide to form O₂ and free Cl atom to go break down more O₃

Polar Stratospheric Clouds (PSC)

Clouds made of water and nitric acid (HNO₃) that can only form in consistent -100F temperature range found above Antartica

• in presence of PSCs, chlorine nitrate (ClONO₂) and hydrochloric acid (HCl) react and give off Cl₂

  • Cl₂ is photosynthesized (broken by sun) into 2 free Cl atoms

26% of solar radiation…

Is reflected back into space by clouds and the atmosphere

19% of solar radiation…

Is absorbed by the atmosphere and clouds and is radiated out into space and down to Earth

55% of solar radiation…

Reaches Earth’s surface where it can be absorbed or reflected (depending on the albedo of the surface it strikes)

• low albedo: darker, lower albedo surfaces absorb sunlight and release infared radiation (which we feel as warmth)

• high albedo: lighter, higher albedo surfaces reflect sunlight directly back out into space, or into clouds/GHGs that absorb it

Greenhouse effect

Gases in Earth’s atmosphere trap heat from the sun and radiate it back down to earth

• without it, Earth would be too cold to support life

• how it works:

  • solar radiation strikes Earth’s surface, heating it

  • Earth’s surface releases infared radiation

  • GHGs absorb infared radiation and radiate it both out into space and back toward Earth

  • portion coming back to Earth is the “greenhouse effect“

• occurs in the troposphere

CO₂ GWP and RT (residence time)

FF comb, decomposition, deforestation

• GWP: 1 (baseline)

• RT: 300-1000 years

• high atmospheric concentration

  • so even though it has a low GWP, it still has the biggest impact because of its atmospheric concentration

CH₄ (methane) GWP and RT (residence time)

Natural gas extraction and combustion, animal agriculture, anaerobic decomposition (especially permafrost thaw)

• GWP: 28

• RT: 12 years

N₂O (nitrous oxide) GWP and RT (residence time)

Agricultural soils (denitrification of nitrate, especially in overwatered, overfertilized soils)

• GWP: >270

• RT: 115 years

CFCs/HCFCs/HFCs GWP and RT (residence time)

Refrigerants, blowing agents in aerosol products

• GWP: >4750

• RT: 50-500 years

• low atmospheric concentration

  • so even though they have a high GWP, their impact is not the largest because of the low atmospheric concentration

H₂O (water vapor)

Evaporation and transportation from plants

• doesn’t drive atmospheric temperature change (temperature controls atmospheric H₂O vapor level)

• doesn’t have a huge impact on atmosphere because of its short RT

GWP (global warming potential)

Measure of how much a given molecule of gas can contribute to the warming of the atmosphere over a 100 year period

• relative to CO₂

• based on residence time and infared absorption

Residence time

How long a molecule stays in the atmosphere

Infared absorption

How well the gas absorbs and radiates infared radiation (IR)

Thermal expansion

Water molecules move slightly further apart when they’re heated

• all the water molecules of ocean moving slightly apart leads to sea level rise

How does an increase in GHGs lead to increased sea level?

• Warmer climate and more melting of ice sheets (at poles and glaciers) from thermal expansion

  • this melted water flows into ocean and leads to sea level rise

Environmental impact of sea level rise

Flooding of coastal ecosystems like estuaries, mangroves, salt marshes, etc…

• loss of species that depend on arctic and tundra ecosystems (polar bears, penguins, reindeer, etc…)

• loss of thaw-freeze cycle that glaciers go through, depriving surrounding ecosystems and human communities of water source

Human impacts of sea level rise

Relocation of human populations

• increase in flood frequency = higher insurance and repair costs, lost property

• saltwater intrusion (saltwater pushing into ground water and contaminating wells)

• refugees forced to move inland

Disease vectors

Living organisms that can transmit diseases from human to human/animal to human

• usually mosquitoes, ticks, fleas

• ex. malaria, Zika, west Nile, dengue fever, cholera, etc…

Expanded range for disease vectors

Warmer temperatures allow insect-transmitted diseases to spread to parts of the world previously too cold

• as the insect vectors expand their range further from equators toward poles, new human populations are at risk

Why has Earth’s climate varied over geological time?

Variations in Earth’s orbit around the sun— variations in eccentricity and obliquity

Variations in eccentricity

Bringing the Earth closer to and further form the sun at different times

• more eccentric = further from the sun

Variations in obliquity

Exposing northern latitudes to higher insolation at different times

Milankovitch Cycles

Predictable variations in Earth’s climate

What main pieces of evidence have scientists used to measure and estimate Earth’s historical temperature and CO₂ levels?

• Foraminifera shells in ocean sediments— different species have different temperature tolerances

• Air bubbles in in ice cores that contain ancient atmospheric gas (CO₂)

• ¹⁶O vs. ¹⁸O (oxygen isotopes) concentrations in ancient ice (more ¹⁸O = higher temp)

Effects of historic climate change

• Rising temperatures

  • habitat/species loss, drought, soil destruction, heat waves, increased precipitation in some regions

• Rising sea level

  • due to glacial, polar ice melt and thermal expansion

• Melting of the permafrost

  • permanently frozen tundra soils that begin to thaw and release methane and CO₂ from anaerobic decomposition

Impacts of historic climate change on coastal communities

• Property loss

  • seawalls can be built higher, but this just delays eventual flooding

• Damage

• Potential relocation

• Loss of barrier islands → islands that buffer coastal communities/ecosystems from wind and waves may be lost as sea level rises

Widening and weakening of Hadley cell (impact of historic climate change on atmospheric currents)

As temperature difference between equator and poles decreases, air ascending and expanding from equator travels further before sinking

• this shifts subtropical zones (dry, desert biomes) toward poles and expands the tropics

• regions between 30 degrees and 60 degrees may experience drier climate as cool, dry, descending air from Hadley cell shifts north and south

Weakened, destabilized jet stream (impact of historic climate change on atmospheric currents)

As arctic warms faster than other areas of earth, temperature difference between equator and poles weakens

• because temperature and pressure difference between polar and subtropical regions is what drives the poler jet stream, less difference between them means weaker, wobblier jet stream

• stronger temp contrast = faster jet stream

  • more stable jet stream and consistent weather

• weaker temp contrast = slower jet stream

  • less stable jet stream and more erratic weather

Impact of climate change on marine ecosystems

• Altered range of marine ecosystems

  • some areas of ocean will become too deep to receive sunlight and photic zone will shift up, further from ocean floor

• Altered ranges for organisms: warm water holds less O₂, so many fish populations have declined, or migrated to cooler waters

Suppression of thermohaline circulation

Normally, redistributes heat from the equator, salt, and nutrients by mixing ocean waters

• now, ice melt from Greenland → especially cold, freshwater buildup in north Atlantic… freshwater is less dense than salt, preventing it from sinking

• expected impacts: slowing warmer Gulf Stream waters, cooling Europe and slowing global thermohaline circulation

Polar amplification

Polar regions of Earth are warming faster than other regions

• especially in the arctic (N pole) because there is more land and less water to absorb heat

Albedo of sea ice vs albedo of ocean water

Open ocean absorbs more heat (as ice melts, more open ocean/water is exposed, which absorbs more heat) (positive feedback loop)

Effect of thermohaline circulation (on polar amplification)

Distribution of tropical heat to poles by thermohaline circulation also warms poles

Effect of melting of permafrost on unequal global warming

Thaws and releases methane and CO₂ from anaerobic decomposition

• ** air pollution adds soot and other PM to atmosphere, distributed to poles by atmospheric circulation

  • darker soot/PM covered in ice absorbs more heat due to lower albedo

Permafrost

Permanently frozen tundra soils in N hemisphere

Impacts of climate change on polar ecosystems

Arctic sea ice loss = habitat loss

• seals use it for resting and find holes for breathing

• algae grow on ice, forming base of arctic food web

• polar bears use ice for hunting seals at breathing holes

Cimate change and soil

Warmer temperatures dry out soil, making plant growth more difficult and decreasing primary productivity

What happens to ocean heat as the atmosphere warms?

Heat is transferred to the ocean

• ocean absorbs heat radiated back to earth by GHGs

• it is estimated that 90% of earth’s warming from the past 50 years occurred in oceans

• thermohaline circulation distributes heat absorbed at surface to depths and other areas of earth

  • heat absorbed by ocean can transfer back to atmosphere for decades

Effects of atmospheric warming on marine species

Warmer water holds less O₂, causing respiration stress or suffocation

• migratory routes and mating seasons altered

• reproductive timing disrupted

• habitat loss

• toxic algae blooms (can also be Harmful Algae Blooms (HAB))

  • blue-green algae release

Climate change impacts on coral bleaching

Coral reef = mutualistic relationship between coral and photosynthetic algae (zooxanthellae); algae sugar and coral supply CO₂ and detritus (nutrient containing organic matter)

• algae have narrow temperature tolerance and leave the reef when temperature rises

  • pollutants from runoff (sediment, pesticides, sunscreen) can also force algae from reef

• coral lose color and become stressed and venerable to disease without algae (main food source)

Increased CO₂ in atmosphere =

= Increased ocean CO₂

• CO₂ combines with ocean water to form carbonic acid (H₂CO₂), which dissociates into Bicarbonate (HCO₃^-) ion and H⁺ ion

Calcification (importance)

Marine organisms that make shells use calcium (Ca⁺) and carbonate (CO₃^2-) ions to build their calcium carbonate shells

Increased ocean acidification and calcification

Increased CO₂ + ocean acidification make carbonate ions less available (carbonate ions bond with excessive hydrogen, leaving fewer carbonate ions available for calcification)

• carbonic acid → increased H⁺ ions which bond with carbonate to form Bicarbonate (HCO₃^-)

• marine shells breakdown as pH decreases and carbonate ions are less soluble in ocean water

• less calcification because fewer carbonate ions; weaker shells of coral mollusks, and urchins

Anthropogenic causes for ocean acidification

Fossil fuel combustion (CO₂), deforestation (CO₂), and coal/gas combustion (NO_x/SO_x → acid precipitation)

Relationship between CO₂ and ocean acidification

Direct

• more CO₂ = more ocean acidification

Relationship between atmospheric CO₂ and pH

Inverse

• lower pH = more acidic

In the past 150 years, ocean pH has decreased from 8.2 to

8.1

• *pH = log scale, so 8.2 to 8.1 = 30% decrease

• by 2100, ocean pH could decrease to 7.8

Ocean acidification

Decrease in pH of ocean waters