5. Global Climate Change PDF

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5a. 1 Climate Change: Introduction Definitions: ● ● ● ●

Weather: state of the atmosphere as we experience it instantaneously Climate: average weather over an extended period of time in a specific region Global climate: globally averaged weather over an extended period of time Global average temperature: stable parameter for climate

5a. 2 (THIS VIDEO IS FKING LONG) How do we know the temperatures and CO2 thousands of years ago? ● Scientists look at Ice Cores which contain preserved air bubbles ○ Access to old snow ○ Reading Ice Cores ■ Ice accumulated over time, snow layers are accumulated storm after storm ■ Stored chemical indicators of past temperatures ■ Can clearly see the layers of ice like tree rings ○ Firn: snow that is more than one year old ■ Snow doesn’t melt from year to year (Greenland) ■ 60cm of snow ■ Look at the temperature, accumulation rate through air bubbles (gases) ○ In order to predict the future climate accurately it is important to understand the climate of the past Air Bubbles in Ice ● Snow contains a lot of air within its snow crystals ● Wait of new snow presses old snow together ○ Snow crystals slowly change shape ○ At one point, so much new snow is on top that it compresses the snow tightly and closes all the air pores, forming air bubbles ■ Air can no longer escape from the ice Climate History ● Composition of snow water changes between winter and summer ● Large events can also be seen through ice ● Can go back more than 100,000 years Atmospheric CO2 and Climate ● Our climate has gone through long cold periods (glacial / ice ages) and short warm periods (inter-glacial periods) ○ Cold periods: low CO2 mixing ratio of around 200ppm ○ Warm periods: CO2 mixing ratio of around 800ppm

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Over 100,000 years between warm periods ○ Warm periods last around 10,000-20,000 years Holocene ○ Increase of CO2 took around 5000 years ○ Humans have added CO2 to the atmosphere for the past 100 years ■ 400ppm current CO2 concentration increased exponentially after 1800s ○ Timing of CO2 increase coincides with industrial revolution and use of fossil fuels ○ After 1900, temperature has been increasing of around 0.8 degrees celsius warmer

5a. 3 Review: Environmental Impact of Humans ● Human impact on a local scale began thousands of years ago ● Atmospheric change has proceeded on a global scale in an increasingly faster rate since the start of industrialization ● Anthropogenic change occurs on time scales of decades to centuries, compared to the thousands/hundred thousand years for our atmosphere to change naturally ● Increasing population make this a challenge for the future ○ Increasing population leads to increasing CO2 pollution 5b.1 Climate Change: Radiation and the Greenhouse Effect Energy and the Greenhouse Effect ● Energy ○ E= the capacity of a physical system to do work ■ Describes the state of a certain system ■ Potential Energy: mass * height *gravity ■ Kinetic E: mass * speed^2 ● Energy is always converted from one type of energy to another, not made or destroyed ○ Thermal E: a warm body has more thermal energy than cold body (depends on temperature ■ Gas: molecules in gas permanently move around, average speed determine their thermal energy ■ Higher the speed of the gas, higher the energy ○ Radiative E: light carries energy ○ Chemical E: molecules can store energy ● Electromagnetic radiation (light) ● The atmospheric greenhouse effect 5b. 2 Conservation of Energy

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Most important thing we need to know about energy: energy can neither be created nor destroyed; BUT they can be converted from one form to another

The Sun as an Energy source ● Energy generation: nuclear fusion ○ 2H -> He + Thermal energy ○ Temperature at the Sun’s surface (photosphere): ~6000k ● Transport of energy to earth through space: mostly via light -> electromagnetic radiation Electromagnetic waves ● Waves travel with the speed of light, c = 3* 10^8 m/s ○ Lambda = wavelength ○ Amplitude ○ f= c/ lambda ○ Unit: Hertz = 1/s (vibrations per second) ● Energy of an EM wave is inversely proportional to wavelength ○ E = h(Planck’s constant) c(speed of light) / lambda ● Photons ○ Packets of energy, often also thought of as quantum particles that move with the speed of light ○ Packet of EM wave ○ Useful to describe interaction with molecules such as absorption and emission** ● Waves and photons are equivalent descriptions of EM radiation ● Different wavelengths ○ Most interested with visible and infrared wavelength in this section

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Visible light: Blue / Green / Yellow / Red Ultraviolet (100-400nm) infrared (beyond red) (0.7100micro m)

5b. 3 Absorption. Emission. Radiative Equilibrium ● Absorption: Standing in the sun in dark shirt -> heat up

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Everything in our environment that is exposed to the sun will reach a max temperature Body will have lose energy ○ Body will emitted EM radiation and thus lose some of the thermal energy ○ If we keep the incoming radiation constant, body will reach steady state Radiative Equilibrium ○ Energy absorbed = energy emitted Like steady state box model ○ Temperature (concentration, radiation absorbed (source), radiation emitted (sink)

5c.1 Blackbody Radiation: a perfect blackbody absorbs all wavelengths of EM radiation that fall on it ● Doesn’t really exist ● By Kirchoff's Law: a blackbody also emits all wavelengths of EM radiation ○ Emission intensity is controlled by the blackbody’s temperature, Planck’s law, Wien’s Law, and the Stefan-Boltzmann Law ● Planck Curve ○ Planck’s Law: describes the emission intensity for different wavelengths ○ At lower temperature, less radiation is emitted ■ Color of the light becomes more reddish (longer wavelengths) ■ “Dimmer” feature on lamps ○ Higher temperature: ■ Peaks at shorter wavelengths ■ More energy emitted overall ○ Wien’s Law: smaller the temp. The higher the peak wavelength ○

5c. 2 Reflection / Albedo: incoming radiation bounces off the surface of an object -- the radiation energy is not absorbed. The extend of this reflection is the “surface albedo” ● Earth emits radiation of around 255k

5c. 3 What happens to EM radiation in Earth’s atmosphere ? ● Sunlight entering the Earth’s atmosphere undergoes: ○ Reflection (from the ground, snow, cloud) ○ Absorption (by gases, such as ozone, and by the ground) ○ Scattering (by gas molecules, aerosol particles and cloud droplets) ● Infrared radiation emitted by the Earth is partially absorbed by greenhouse gases in the atmosphere, rest transmitted to space ● Earth emits infrared radiation and sun emits visible light Absorption of EM radiation in the atmosphere ● Molecules absorb (weaken) EMR at specific wavelengths ○ More molecules -> more absorption -> less light goes through ○ Longer path -> more absorption -> less light goes through ● Certain gases absorb at specific wavelength Emission of EMR in the Atmosphere ● Air emits EMR according to its temperature ○ Air behaves like a blackbody ● Because temp. Are low, wavelength of the emitted radiation is in the infrared ● EMR is emitted in all directions The Atmospheric Greenhouse effect

5c.4: Climate Change: Radiation and the Greenhouse Effect What else happens to visible radiation? ● Blue skies vs. red sunsets Scattering of EMR by Air Molecules ● Light hits a molecule and is deflected towards another direction ● Scattering by molecules is stronger in the shorter, bluish wavelengths of visible light than in the longer, reddish wavelengths ● Favors blue wavelength ○ Blue part of the light is reduced compared to red slightly before sunset ○ When sun is closed to the horizon, the reduction of the blue is substantial ■ Sunset Influence of Clouds on Radiation and Climate ● At any one time, half of the Earth’s surface is covered by clouds ● Average albedo of clouds is 50% ● Clouds consist of small water droplets ○ Multiple scattering bodies diffuse incident light White Clouds ● Light is scattered by water droplets

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All colors of visible light are scattered the same way, resulting in scattered “white” light Much of the light gets reflected more on the top, and the bottom is dark (little light exits the bottom)

High Clouds (Cirrus): mostly made out of ice crystals, thin and cold ● Small albedo ○ Solar radiation is only weakly reflected ● Greenhouse effect ○ Larger effect than albedo ● Overall, surface is warming Low Clouds (Cumulus): water droplets and very thick, good at absorbing infrared radiation ● HIGH ALBEDO ○ Blocks solar radiation ● Greenhouse effect ○ Warming not as strong as cooling effect from albedo ● Overall, planetary cooling Net Role of clouds ● Without cloud cooling, the earth would be warmer by ~12 degrees C ● Greenhouse effect of clouds warms Earth’s surface by ~7 degrees C ● Net effect of clouds: Cooling by ~5 degrees C Influence of Aerosol/Haze ● Increase in albedo, causing higher reflectance back to space ○ Ex. Mount PInatubo Eruption 5d. 1 Climate Change: Causes Climate Change ● Temperature change ● Change in cloudiness and rainfall ○ Changes ecosystems, and human agriculture ● Change of arctic sea ice, ice caps and glaciers ● Variation of sea level ○ Vary when climate changes ● Others ● These can happen naturally, but recent changes are unprecedented Climate Change from Natural Causes ● Sunspot cycle ○ Causes sun’s radiation to vary slightly ○ Change in solar radiation reach earth and number of sunspots vary together ○ Intensity of sun fluctuations (0.1%) in an 11 year cycle -> too weak to be noticed ● Milankovitch Cycles

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Variation in earth’s orbit with the periods of 22,000. 41,000, and 100,000 years could have been triggers for ice ages ○ Earth’s tilt is currently 23.5 degrees ○ Seasons by shift over time due to this cycle Volcanic Eruptions ○ Ash and other particles block sunlight -> surface cools down ○ High albedo, reflects sunlight back out ■ Ex. 1860 “year without a summer” due to eruption of Mount Tambora in Indonesia ○ Only lasted for a few years

5d.2 Greenhouse gases ● Global warming potential (GWP): amount of warming per unit increase in greenhouse gas concentration ● Gases together with clouds are responsible with absorbing infrared radiation and reemitting it back to the Earth, keep the earth warmer than it would be without atmosphere ● Humans did not cause greenhouse effect, but we have been messing with it ● Well known Greenhouse gases ○ Water Vapor: humans have no direct impact ○ Carbon Dioxide: most well known, residence time of more than 100 years ○ Methane: residence time of 10 years, 20 times more efficient as greenhouse gas than CO2 ■ Much less methane in the atmosphere ○ Nitrous oxide: residence time of 150 years, 310 GWP ○ Chlorofluorocarbons (CFC): residence time of ~100 years, GWP can go up to 12,000 ○ Tropospheric Ozone (O3): residence time of ~1 month ● How have humans changed the concentration of greenhouse gases in the atmosphere? ○ Since 1700, CO2 concentration has increased from 270-400 ppm ● CO2 ○ Source ■ Aerobic respiration ■ Outgassing by land and ocean ■ Fossil fuel combustion (introduced by human) ● Electricity generation ○ Most of electricity is produced by burning fossil fuels ● Transportation ● Industry ○ Fossil fuel combustion ● Agriculture ● Commercial ● Residencial

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We keep adding CO2 into the atmosphere Emissions have been increasing till around 2007, and started to decrease due to economic downturn in 2008

Sinks ■ Green plant photosynthesis ■ Dissolution in ocean (dissolves)

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Methane (CH4) ● Source ○ Wetlands: Bacteria living under these conditions ○ Ruminants (beef): considerable increase due to increasing desire for beef ○ Natural gas Coal mines ○ Rice Agriculture: rice is grown in flooded fields, same bacteria as wetlands ○ Landfill waste: US tries to capture the methane here as biogas ■ Electricity production ○ Biomass burning ● Sink ○ Oxidation reaction CH4 + OH reaction ● Around 1800, methane concentration has been increasing exponentially

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Nitrous Oxide (N2O) ○ Sources ■ Ocean ■ Atmosphere NH3 oxidation ■ Tropical soils ■ Agricultural soils ■ Biomass burning ■ Industrial sources ■ Cattle and the feedlots ○ Sink ■ Transport to and chemistry in stratosphere ○ The concentration has increased similar to that of methane Chlorofluorocarbons ○ Purely man-made gases ○ Sources ■ Contributed to ozone hole, contribution to climate change is substantial ■ Refrigerant fluid in air conditions and refrigeration units ■ Leakage and direct emission from industry and consumers ○ Concentration has increased until 1995, and since been decreasing slowly ■ People discovered the ozone hole in 1995 Tropospheric Ozone (O3)

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Source ■ Formed chemically from other pollutants ○ Sinks ■ Chemical reactions ■ Deposition to surface ○ Not stable in ice cores ■ No archives of its levels Aerosol Particles ○ Haze ○ Their effect is much more complex ○ Certain particles absorb radiation, thus heating the atmosphere ○ Soot and brown particles ■ Absorb solar radiation -> warming ■ Source: incomplete combustion ○ White particles ■ Reflect solar radiation (high albedo) -> cooling ■ Source: chemistry of air pollutants ○ Short lifetime ■ Particulate sinks ● Deposition ● Washout ○ These particles have overall cooling effect ■ But since we want to remove them, these reduction will lead to overall warming of the atmosphere lolz

5e.1 Climate Change Predictions Global Change: fact or Scare? ● Rise in temperature ● Rise in sea level ● Retreat of glaciers all over the world ● Retreat of sea ice in the arctic 5e.2 The future climate change depends on ● Future greenhouse gas emissions ○ Political ○ Economic ○ Technological ○ Societal issues ● Fraction of greenhouse gas emissions staying in the atmosphere ○ Scientific issues related to carbon cycle and atmospheric research ● Sensitivity of climate system of atmospheric greenhouse gas changes ○ Scientific issues related to greenhouse effect, feedback effect, etc.

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Changes in ocean acidity Icecaps might be completely gone Sea level rise -> some cities might be underwater Temperatures in the arctic will increase by 5 degrees by 2100 if we do nothing about greenhouse gases Predictions of up to 1m average sea level rise

Why is climate prediction so difficult? ○ Uncertainty of emissions ○ These factors of climate change are not independent of each other ■ Greenhouse gases ■ Clouds -> albedo ■ Atmospheric oceanic temperature ■ Snow and ice cover ○ Ex. more CO2 -> higher temp. -> more atmospheric water vapor -> stronger greenhouse effect from water vapor Negative feedback ○ Cause -> effect -> suppress -> cause ○ Climate: warmer temperatures -> more water vapor -> more clouds/higher albedo -> cooling (counteracts initial warming) Positive feedback ○ Cause -> effect -> enhancement -> cause ○ Leads to runaway system ○ Climate: warmer temperatures -> less snow and ice -> more sunlight absorbed by land and sea -> warmer temperatures -> less snow and ice

Effects of Oceans ● The oceans take up and release carbon dioxide ● Ocean currents redistribute heat/thermal energy 5f.1 Climate Change: Remediation Mitigating Anthropogenic Forcing of the Greenhouse effect ● Reduce greenhouse gas emissions by using less energy, or use of non-fossil energy sources ● Geoengineering ○ Remove atmospheric carbon dioxide or reduce emissions via carbon sequestration ○ Manage solar radiation reach earth surface World Energy Consumption ● Coal, natural gas, oil will dominate even till 2040 ● Increase in energy consumption is mostly in developing countries such as China and

India Alternative Energy Sources ● Geothermal energy: pumping cold water thousands of meters in the ground, water heats up and pumps up to the surface ○ Hot water or steam is used for electrical energy ○ Generate up to 5% of our demand ● Hydroelectric Power: falling water turns generator turbine ○ Kinetic energy of flowing water -> electric power ○ Advantages ■ Renewable ■ No air pollution ○ Disadvantages ■ Landscape gets lost ■ Impacts aquatic environment ■ Very few region suitable for generation ○ Not going to expand ● Nuclear Energy: via fission, radioactive decay of compounds such as uranium is used to produce heat and turns into energy ○ Fission: no air pollution ○ But: ■ Expensive ■ Risk of accident or disaster ■ Nuclear waste storage remains a problem ○ Fusion: does not work yet ● Bio fuels: plant respiration takes up CO2, which is released to the atmosphere when energy is gained ○ Corn -> ethanol -> use as fuel or fuel additive ○ Problem ■ Increased fertilization for growing fuel crops, increase emission of N2O ● Cancels out CO2 saving ■ Increased food prices if crops, such as corn and sugarcane are converted from food to fuels ■ Requires massive change to agriculture ■ Worsens air quality, since combustion of organic material occurs ○ Best bio-fuels are those obtained without fertilization and are based on non-food crops ■ Perennial grasses ■ Waste biomass ■ Wheat chaff ■ Cornstalks ■ Wood mill waste ● Wind energy ○ Turns a propeller connected to a generator

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Kinetic energy of wind -> electric power Problem ■ They don’t look pretty lol ■ Energy has to be stored ○ Can’t solve all our problems ○ Can produce 20-30% of our energy ○ Advantages ■ No heat produced ■ No gas emitted ○ Disadvantages ■ Not very attractive ■ Need energy storage device for windless periods Solar radiation ○ Solar energy -> heat -> energy ○ Rooftop heat collectors ■ Inexpensive ■ Limited in use ○ Solar power plants ■ Large number of mirrors focus sunlight onto one target ■ Can be stored for later use ■ Easy and quick to build ● Take up lots of space ■ Focus solar light on a tank with molten salt, which heats up. Heat is then converted to electricity with turbines Photovoltaics (Solar Cells) ○ Convert solar energy directly into power using semiconductor cells ○ Easy to maintain ○ Efficiency 12-40% ○ Getting much cheaper ○ Need energy storage device for nights and cloudy days

Stats: ● Solar energy falling on one square meter in US is Sol = 5kWh / day ● Total amount of energy the US consumes is around Eus= 3*1013kWh per year ● Area (in km2) = [EUS / (EF × Sol × 365 days/year)] × (1 km2/106 m2) 5f. 2 Geoengineering: manipulation of the Earth’s climate system to counteract the effects of climate change caused by greenhouse gas emissions (Last resort) ● Solar radiation management (SRM) ○ Increase surface reflectivity of the planet, brightening human structures (painting them white), planting crops with high reflectivity, covering deserts with reflective material

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■ White roofs in human settlements ■ Albedo increase in desert ■ White or silver floating plastic disks on oceans ○ Enhancement of marine cloud reflectivity ■ Make sea salt particles to increase cloud droplet population -> lower to medium efficiency, medium cost, technical challenges ○ Place reflectors in space to reduce amount of solar energy reaching earth ■ Highly effective but very expensive ■ Reduces energy available for electric power generation ○ Mimicking the effects of volcanic eruptions by injecting sulfate aerosols into the power stratosphere ■ Highly effective, low cost ■ Impact on rain and stratospheric ozone depletion Carbon dioxide Removal (CDR) ○ Land use management to protect or enhance land carbon sinks ■ Re-forestation -> limited potential for CO2 removal ■ BioChar (biomass converted to charcoal) -> limited ○ Enhancement of natural weathering processes to remove CO2 from the atmosphere ■ Turn silicate rocks to carbonate: CaSiO3 + CO2 -> CaCO3 + SiO2 ■ High potential for CO2 storage, but expensive due to required large mining operations ○ The enhancement of oceanic uptake of CO2 ■ Fertilization of the oceans with naturally scarce nutrients, or by increasing upwelling ○ Direct engineered capture of CO2 from ambient air ■ High potential but expensive ...