Climate Change: The Physical Science Basis

Extent of human activities that have had a significant global impact on the Earth's ecosystems Considered to start with Industrial Revolution Anthropogenic net emissions of CO2 increased from 280ppm to 395ppm

Anthropocene

AAAS --> IPCC Working Group I Assessment Reports (FAR, SAR, TAR, AR4)

Nine of the ten warmest years are in the 21st century (except 1998, warmed by strongest ENSO) Rose by 0.74+0.18 degrees C over the 20th century Over last half, rate was almost double --> 13 degrees C 2005 & 2010 tied for the warmest year since measurement Skeptics say that it's due to "urban heat island effect"

Air temperatures

Reduced vegetation in urban areas alters the degree of shading & evapotranspiration Surface materials --> lower albedo Urban geometry influences wind flow, energy absorption & ability to emit long-wave radiation

back into space Anthropogenic heat emissions

Urban heat island effect

Changes in Arctic T & sea ice Changes in precipitation amounts, ocean salinity & wind patterns Changes in extreme weather (heat waves, droughts, intensity of tropical cyclones, etc.) Urban heat island effect very small (less than 0.002 C of warming per decade)

Other direct observations of climate change

Land surface temperatures rising faster than SSTsWarming in the Arctic is double that for the globe (late 1960s to present)

Snow/sea ice/glaciers reflect as much as 80 to 90 percent of incoming solar energy, whereassnow-free surface reflects 10-20 percent

Warming trend --> decrease snow/sea ice/glaciers --> absorption of solar radiation increases -->adds more heat

Positive feedback

Feedbacks

Precip. Increased in eastern parts of NA & SA, Northern Europe & N & C Asia Drying in Med. S. Africa & S.E. Asia

Changes in Precipitation & Increased Drought

Proxy data: data gathered from natural recorders of climate variability Medieval warm period Trees record past climates --> thickness of rings Michael Mann's temperature Hockey Stick (Observations, Northern Hemisphere, proxy data from

1000 - 1860; Global instrumental observations, 1860 to 1990; Projections until 2100) --> y axis isdepartures in temp in C

Paleoclimate Perspective

Climate Change: The Mechanisms

Flow of energy from sun to earth and from earth back to space Albedo: percentage of shortwave radiation scattered upwards by a surface Snow/ice have high albedo (45-85%) Black pavement has low albedo (3%)

Global Energy System

Climate Forcing

GEOL 130 Final NotesThursday, May 02, 2013 1:58 AM

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Glaciation-deglaciation cycles w/ periodicity of 1000kyr w/ superimposed cycles ofabout 41 to 21kyr

Precession: axis of rotation wobbles --> changes the time when earth reachesperihelion, at ~22,000yrs

Obliquity: axial tilt varies at periods of 41,000 yrs Eccentricity

Orbital forcing/Milankovitch hypothesis

How the sunspot # is related to solar output is unclear Solar activity

External causes

Mount Pinatubo (2nd largest volcanic eruption in 20th century) Eruptions inject material into the tropical stratosphere & distributed worldwide within

1-3 yrs Spread out toward closer pole --> decay time of 2 yrs

Volcanic eruptions

Deep currents move ocean water in slow circuit across floors of worlds' oceans Responsible for rapid cyclic climate change Below the pycnocline, slow velocity In cold regions the highest surface water densities are reached (salty & cold);

this causes sinking of water --> drives circulation Salinity is involved in a positive feedback: higher salinity --> enhances

circulation, circulation in turn transports higher salinity waters into deep waterformation regions

Shutting it off would cool N.H. & warm S.H. because cross-equatorial heattransport in oceans is reduced

Thermohaline Circulation Ocean circulation changes

Internal factors: Natural changes

Water vapor, carbon dioxide, methane, nitrous oxide, ozone Greenhouse gases

Tropospheric aerosols & clouds Stratospheric ozone Land-surface changes

Internal factors: human-induced factors

Climate Forcing

Tsunamis ITsunami: covers all forms of impulsive wave generation (earthquake, volcanic eruption, submarinelandslide, etc.)

Sudden rise or fall of the seafloor displaces large volume of water Generates waves with large wavelengths that travel very fast in the deep ocean Become compressed & move slower as they travel closer to coastline Primary cause of tsunamis Mw: moment of magnitude measures the energy released during an earthquake Logarithmic --> one increase in unit --> 30 times energy Mw > 7.5 to create a destructive tsunami

Earthquake-generated tsunamis

Volcanic eruption or slope failure can cause sudden displacement of water & subsequent tsunamiVolcano-generated tsunamis

Generated by sudden failure of submarine slopes Waves often lose their energy very quickly Often caused by earthquakes so both can be simultaneous

Landslide-generated tsunamis

Meteorite-generated tsunamis

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Not as common & scientific evidence lackingMeteorite-generated tsunamis

Run-up height: maximum height a tsunami reaches on shore (vertical distance between max.height reached by the wave & normal sea level) --> over 1m is dangerous

Inundation distance: maximum horizontal distance water travels in land

Wave Mechanics

Most tsunamis occur along the "Pacific Ring of Fire" --> borders the northern edge of the Pacific Plate

Offshore (bathymetric) & coastal features can change how energy is focused & path of travel Amplify by funneling wave energy: bays, harbors, restricted lagoons Dissipate: reefs, mangroves/saltmarshes

Influence of coastlines

Deposits from older paleo-tsunami --> how often, how destructive

Overwash: transport of offshore marine material inland

Contain marine shells, coarse sand, pebbles Oriented convex-up; angular shell fragments; forams

Tsunami deposits

Larger sample sizeUseful for recent events & lateral trends

Larger shells useful

Trench studies

Smaller sample size Useful for older events Forams important

Core studies

Marine "microfossil" Single-celled organism Produces a test or a shell of CaCO3 By provenance & taphonomic character can tell forams that originated in sea v. along

coast Lagoon sediments (high abundances of lagoon species, low fragmentation) Tsunami deposit (high abundnances of fossil & fragmented forams, many offshore

species) Lagoon sediments (high abundances of lagoon species, low fragmentation

Foramnifera

Proxies (grain size, foraminifera, shells, geochemistry, sediment composition, etc.)

Ground-truthed modeling

Orphan Tsunami of 17000AD

At great depth, hot & ductile, at shallow depth, cool & brittle --> gets stuck Overriding plate thickens & bulges up until the leading edge becomes unstuck & breaks free

seaward & upward. Land falls --> subsidence

Subducting plate & overriding plate --> as subducting plate descends, it does so in stick-slipfashion

Making a tsunami

Subsidence --> buried soil --> soil & silt deposited by tide

Land subsides --> sand-laden tsunami overruns subsided landscape lays down a sand sheet Sand sheets

Earthquake Deformation Cycle

In Cascadia, earthquake on Jan. 26 1700 9PM Parent --> tree rings, computer simulations & written accounts Cascadia --> earthquakes in intervals of every 500 years (range from 200 - 1000 years)

"Orphan tsunami"

Climate Change: Modeling

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Climate Change: ModelingCan be viewed as three domains: time, space & human perceptionClimate system: Interactions b/w atmosphere, hydrosphere, cryosphere, biosphere, chemistry

Ice-albedo feedback --> positive Water-vapor "greenhouse" feedback --> positive Cloud feedback --> negative (more moisture convection --> greater cloud cover --> less surface

radiation --> less evaporation --> less convection

Climate feedbacks

Balancing the planetary radiation budget Parameters: albedo, incoming solar radiation, outgoing infrared radiation, heat transport EBMs & glacial cycles

Energy Balance Models (EBMs)

1-D refers to altitude Balance between shortwave & longwave radiative fluxes Atmospheric composition & influence of external & internal forces

One-dimensional radiative-convective (RC) models

Two-dimensional statistical dynamical (SD) models

Radiation Dynamics Surface processes Chemistry

Conservation of energy Conservation of momentum Conservation of mass Ideal gas law

Fundamental equation solved by GCMs

General circulation models (GCMs)

Computational power

Continued greenhouse gas emissions at or above current rates would cause further warming &induce changes very likely to be larger than those of 20th century

For next two decades, a warming of about 0.2 deg C per decade is projected Even if greenhouse gases & aerosols stayed at 2000 levels, warming of about 0.1 deg C per decade Near terms projections insensitive of choice of scenario; longer term projections depend on

scenario & climate model sensitivities Projected warming greatest over land & at most high northern altitudes / least over the Southern

Ocean & parts of the North Atlantic Ocean Precipitation increases very likely in high latitudes Decrease likely in most subtropical land regions

Projects of future changes in climate

Snow cover is projected to contract Widespread increases in thaw depth most permafrost regions Sea ice is projected to shrink in both the Arctic & the Antarctic Arctic late-summer sea ice may disappear almost entirely by end of 21st century Very likely that hot extremes, heat waves & heavy precipitation events become more frequent Likely that future tropical cyclones will become more intense Less confidence in decrease of total number Temperatures in excess of 1.9 to 4.6 C warmer than pre-industrial level --> eventually melt

Greenland & raise sea level by 7m

Projections of future changes in climate

Is Sea Level Rising?1992-2010 --> trend = +3.26mm/year

Thermal expansion (40% --> 20%)Contributing factors

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Thermal expansion (40% --> 20%) Glaciers & ice caps (35% --> 40%) Continental ice sheets (25 --> 40%)

Ice melting Land rising Ocean-atmosphere interaction Changes in density of ocean Ocean circulation Terrestrial water storage SLR = Oceans + Land

Complex causes of sea-level rise

Sea-level cycles of ~100,000 years Maximum amplitudes of 120-140m

Previous interglacial

Sudden rise of 6.5 feet to 10 feet occurred within 50-100 years about 121,000 yrs agoPotential sudden jump in sea levels

Record of post-glacial SLR from peak of the glacial until apparent cessation 6000 yrs agoPost-glacial SLR

RSL = E - RWL (elevation of the dated sample - tide level)No ocean-level change in the last 4000 yearsSea level rise due to land subsidence20th century --> SLR from ocean level plus land subsidence (2x to 3x increase) --> 1.8+0.2 mm/yr

Climate Change: Paleo-perspective from the ice coresLong term (10^4 - 10^6) rhythmic changes in climate with predictable variations --> driven largely byastronomical influencesSuperimposed are oscillations, chaotic, often abrupt

Cyclical variations in the amount of solar radiation received at the surface of Earth induces majorclimate changes

Evidence from stable oxygen isotope signal in deep-sea marine sediments & ice cores Precession of the equinoxes (19-23 ka) Obliquity of the ecliptic (ca. 41 ka) Eccentricity of the orbit (ca. 100 ka)

Astronomical rhythm of climate change

Frequency of the climate cycle changed during the Quarternary Rates of warming at the start of interglacial stages are more rapid than gradual cooling trends

leading to glacial stages Amplitude of climate oscillation increased Interglaciations have been short (15-17 ka)

External stimulus of insolation at the 10^5 may be predictable

Shorter frequencies cannot be explained by astronomical cycles aloneShort-term (sub-Milankovitch) climatic variations

Very high accumulation rates Preservation of multiple proxies Small samples of ancient atmospheres

Unique because:

Impacts of humans Glacial-interglacial conditions over last 800,000yrs Stability of the last 10,000yrs

Results:

Tight link b/w concentration of CO2 & surface temperatureLarge climate changes can occur in periods of less than a few decades

Two main findings:

Ice cores as archives of past climates

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Large climate changes can occur in periods of less than a few decades

CO2, O, NOx in air bubbles trapped in the ice Concentrations of major ions Cosmogenic isotopes Stable isotopes Dust Electrical conductivity Physical properties

42 types of measurements

Transition from last glacial epoch to Holocene was accompanied by increase in atm. CO2 of 40%Last glacial to the Holocene

No steady state Uptake by terrestrial biosphere Release of CO2 from the ocean due to increase of SST

Holocene

Climate Change: Paleo-perspective: the oceans

Cesare Emiliani Deep-sea sediment records --> continuous & contain a mixture of lithogenous sediment &

biogenous microfossils Accumulate @ rates 1-5cm/1000yr

Can thoroughly mix 10cm of sediment Milankovitch cycles (100-23 kyr period) are readily preserved at deep-sea sedimentation

rates Millennial-scale & sub-millennial cycles are attenuated

Bioturbation

Paleoceanography

Delta-value: 18O/16O given in o/ooOxygen-isotope ratios

Marine organisms from cold water contained higher proportion of heavier 18O isotope than thosein warmer water

Estimate past temperatures from fossilized biologic carbonate remains Water molecules w/ lighter 16O preferentially enriched in the vapor phase Remaining water vapor even more depleted in 18O in the clouds

Water vapor that ultimately precipitates at low temperature to form ice caps is extremelydepleted in 18O, relative to ocean water

Carbonate fractionation

During glaciation periods, light 16O atoms of oxygen were preferentially extracted from the sea &stored in ice sheets, leaving seawater enriched in the heaver 18O isotope

Oxygen-isotope ratios: ice sheets

Climatic changes on timescales of decades to centuries Attributed to large-scale iceberg melting & sedimentation of ice-rafted detritus (IRD) Massive discharge of icebergs stop THC b/c of freshwater influx, cooling North Atlantic region. As

circulation starts again, the rapid start leads to abrupt warming Part of succession of warm & cold episodes known as Dansgaard-Oeschger events

Sub-Milankovitch: Heinrich Events (HE)

Marine Life and the EnvironmentMore land species than marine --> ocean relatively uniform conditions --> less adaption required meantless speciationOverwhelmingly benthic rather than pelagic

Cold - fewer appendages, warm - more Physical support

Adaptations of marine organisms

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Cold - fewer appendages, warm - more Buoyancy Organism size

Flattened body & tapering back end Streamlining

Deep ocean is nearly isothermal

Cold --> smaller More appendages in warm Warm -- > grow faster & live shorter & reproduce more often More species in warm More biomass in cool (upwelling)

Cold v. warm-water species

Stenothermal: withstand only small variation in temperature Eurythermal: withstand large variation in temperature

Temperature

Stenohaline: withstand only small variation in salinity Euryhaline: withstand large variation in salinity

Salinity

Amount of dissolve increases as temperature decreases Dissolved gases

Camouflage through color patterns Countershading Disruptive coloring

Avoid predation

Increases 1 atm w/ every 10m deeper Do not have inner air pockets or have collapsible rib cages (eg. Sperm whale)

Water pressure

EpipelagicMesopelagic

Bathypelagic Abyssopelagic Dissolved O2 minimum layer about 700-1000m & nutrient maximum O2 content increases with depth below

Pelagic (open sea)

Gas containers (shells or swim bladder) Increase buoyancy

Float (zooplankton have shells/tests eg. Krills or forams) Active swimming

Avoid sinking

Paired vertical fins as stabilizersPaired pelvic fins & pectoral fins for steering & balance

Rounded: maneuver at slow speeds Truncate & forked: maneuvering & thrust Lunate: rigid & lots of thrust (swordfish) Heterocercal: asymmetrical & lift for buoyancy (shark)

Tail fin (caudal) for thrust

Fin design

Lungers: wait for prey & pounce (grouper) --> white muscle Cruisers: actively seek prey (tuna) --> red muscle

Finding prey

Schooling Speed/transparency/camouflage/countershading/etc.

Avoid predation

Marine mammals in PelagicGEOL130 Page 7

Whales, dolphins, porpoises Use oxygen efficiently

CetaceaMarine mammals in Pelagic

Large, sensitive eyes

Photophores: light-producing cells Attract prey Staking out territory Seeking a mate Escaping from predators

Bioluminescence

Large, sharp teeth Expandable bodies Hinged jaws

Adaptations of deep-water nektonThe Deep

Bathyal, abyssal & hadal zones Little to no sunlight Same temperature & salinity O2 levels high

Low supply High species diversity

Chemosynthesis (also occurs at low temperature seeps) Archaea use sea floor chemicals to make organic matter Tube worms/crabs/giant clams & mussels

Hydrothermal vent biocommunities

Most food from surface waters

Attached to substrate & move over seafloor Epifauna

Animal diversity @ tropical and algae diversity & mid-latitudes Moderate diversity of species

Spray zone High tide zone Middle tide zone Low tide zone Move downward --> more species of marine algae & hard shells --> soft bodied &

crabs abundant in all zones

Intertidal zonation

Rocky shores

Less species diversity but greater number of organisms Similar intertidal zones Mostly infauna (burrow into sediment)

Continental shelf Mainly sediment covered Kelp forest associated w/ rocky seafloor Lobsters & oysters

Shallow ocean floor

Sediment shores

Most coral polyps live in large colonies Hard CaCO3 structures

Warm seawater Limited to:

Coral reefs

Benthic (sea floor)

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Warm seawater Sunlight (for symbiotic algae) Strong waves or currents Clear seawater Normal salinity Hard substrate

Made of algae, mollusks, foramnifers & corals Algae provide food & corals provide nutrients

Internal or external fertilization Hermaphroditic Synchronous Tides

Sexual reproduction

Asexual reproduction

Reproduction

Great diversity of species Tourist locales Fisheries Protect shorelines

Importance

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