Global Climate Change Chapter 7

Introduction

ocean contributes operating for long time from local to global, 71% of surface, 8% albedo, solar radiation absorbed at surface, influences radiation heating and cooling, contributes to non-radiative latent heat and sensible heat fluxes at air-sea interface (10x more heat is transferred from ocean surface to atmosphere with latent heating than sensible heating), water vapor main source, major regulator of concentration of CO2, ocean and atmosphere work together in governing climate

Air-sea interactions

ocean absorbs 92% of solar radiation with snow-covered only 15%, most water vapor principal greenhouse gas enters atmosphere with evaporation of seawater, ocean cycling CO2 dependent on sea temperature, circulation pattern, salinity, and biological activity in surface waters (chilled surface waters at higher latitudes absorb CO2, warmer lower latitudes upwellings brings cold water to the surface, releasing CO2 to the atmosphere, exchange gases, energy, heat, water, and other materials, atmospheric conditions impact, thermohaline circulation takes time, cold surface are heat sinks with stabilizing overlying air with increasing sea fogs and reducing thunderstorms, warm currents are heat sources with supplying latent and sensible heat and moisture to overlying air, destabilizing air and energizing storm systems, SST influences atmosphere circulation

Mean state of the ocean circulation

surface ocean currents are wind-driven so ocean surface waters mirror long-term atmospheric circulation, subtropical gyres driven by trade winds and westerlies, sub-polar gyres driven by counterclockwise surface winds in the aleutian and icelandic sub-polar low pressure systems

Western boundary current

currents that are warm, deep, and fast flowing on west side of ocean basins and carry water from tropics poleward faster than the eastern counterpart

Gyres

large-scale systems of rotating currents

Ekman spiral

model of the direction and speed of 3D current pattern caused by a steady horizontal surface wind (steady wind causes surface waters to move 45 degrees right of wind in north hemisphere, successively lower layer moves more toward right at slower speed, depth of 100-150 m, net water movement at 90 degrees to the right of wind direction)

Ekman transport

piles up and removes surface waters, produces variations in height of surface to cause slope gradually, sloping ocean surface generates horizontal gradients in water pressure, pressure gradients give rise to geostrophic flow, horizontal movement of surface water arises from a balance between pressure gradient force and coriolis force, diverging waters from the central region of subpolar gyres, converging waters form region of subtropical gyre

Indonesian throughflow (ITF)

one of the few areas of the world ocean where inter-basin water transport takes place, warm and lower salinity water from Pacific is transported into Indian ocean around 1000s of indonesian islands

Retroflection

where current turns back on itself so only a portion of the current enters and mixes with other waters

Coastal upwelling

occurs where ekman transport moves surface waters away from the coast and surface waters are replaced by water that wells up from below

Coastal downwelling

occurs where ekman transport moves surface waters toward the coast, water piles up and sinks

Upwelling and downwelling

relatively cold upwelling waters along coast of central and northern CA in response to the ekman transport caused by winds predominantly blowing from the north, northern hemisphere upwelling occurs along west coasts by blowing equatorward causing ekman transport of surface water away from the shore, relatively cold surface waters chill the overlying humid marine air to saturation so that dense fog develops in summer, below the pycnocline the water layer where the density gradient is greatest and brings colder water to the surface, coastal upwelling transports dissolved nutrients from ocean depths into photic zone (growth of phytoplankton), world’s most productive fisheries with upwelling about half the world’s total fish catch comes from upwelling zones, zones of coastal downwelling the surface layer of warm with nutrient deficient water thickens as water sinks, reduces biological productivity, transports heat, dissolved materials, and dissolved oxygen to greater depths

Equatorial upwelling

westward-flowing, wind driven surface currents near the equator turn northward on the north side of the equator but southward on the southside so surface waters are moved away from the equator and replaced by upwelling waters

Thermohaline circulation

deep-ocean circulation driven by variations in density, currents are weak but the volume of deep waters is much greater so the magnitude transported is similar to surface water, stratification of ocean controlled by temperature difference between warm surface waters and cold deep waters with high latitudes the salinity is controlled, deep circulation contributes to poleward heat transport (years to millennia modulating climate), deep water forms in greenland-norwegian sea and labrador sea in late winter when the surface water reaches its lowest temperature and greatest density, some winters lack any deep convection whereas other winters have vigorous overturning, southern hemisphere with deep waters forming at several locations around antarctic continent in the weddell sea, deep water formation occurs underneath floating sea ice, water cooled by cold winds acting on openings in sea ice cover and becomes denser during formation of sea ice, water made denser by cooling and brine rejection sinks along the continental slope of Antarctica into the deep ocean, weddell sea with cold dense bottom waters are created in ross sea as well as scattered locations along the continental shelf of Antarctica

Open ocean convection

primary mechanism of deep water formation in the north hemisphere where cold winds chill the surface water to the extent that its density becomes greater than that of the water beneath it, creating an unstable water column and driving overturning

Brine rejection

salt left behind during the freezing of seawater increases the salinity of water immediately below the freezing interface

El nino, la nina, and the southern oscillation

more than a century scientists have been aware of short-term variations in climate at many locations, el nino and la nina readily apparent in the tropical pacific ocean with variations on quasi-periodic basis, weather extremes in many other parts of the world

Southern oscillation

seesaw variation in air pressure across the tropical indian and pacific oceans (low air pressure over the indian ocean and western tropical pacific, opposite high air pressure over the international dateline, plentiful monsoons in india while the reverse means monsoons are lighter in india)

Southern oscillation index (SOI)

based on difference in anomalous air pressure between darwin and tahiti

Historical prespective

local fisherman in peru and ecuador named annual wind-driven warm ocean current accompanied by poor fishing, el nino because it coincided with christmas with 12-18 months every 3-7 years, enso coupled with changes in ocean in the atmosphere that then feedback and further alter the ocean

ENSO

relationship between el nino and the southern oscillation, begins when the air pressure gradient across the tropical pacific starts to weaken, heralds the slackening of trade winds

Neutral conditions in the tropical pacific

prevailing winds blow from the S/SE along W coast of S america with most of the time ekman transport drives warm surface waters W, upwelling of cold, nutrient-rich waters along the W coast replace the warm, nutrient-poor surface waters that are transported offshore supporting a diverse marine ecosystem and highly productive fishery, equatorial upwelling produces a strip of relatively low SST along equator (cold tongue), trade winds drive warm surface waters W toward Indonesia and N Australia (increases depth of thermocline from 50 m in E tropical pacific and 150 m W, raises sea level in W tropical pacific about 60 cm higher than in E), contrast SST between W/E tropical pacific about 8 degrees celsius (colder surface waters in central and eastern tropical pacific chill overlying air, suppress convection, so rainfall is light in region and adjacent W coastal plain of S america, W tropical pacific, warm surface waters heat overlying air, strengthening convection currents that produce heavy rainfall), contrast between higher air pressure over central and E tropical pacific and lower air pressure over W tropical pacific drives trade winds (greater horizontal air pressure gradient stronger the winds, high SST in W tropical pacific lower surface air pressure whereas low SST in E tropical raise surface air pressure), coriolis force deflects winds to the right in N hemisphere blow NE (trade winds deflected to left in S hemisphere trade winds blow SE), flowing over ocean surface trade winds become warmer and more humid so in W tropical pacific warm humid air rises, expands, and cools (water vapor condenses in towering cumulonimbus clouds producing heavy rainfall), air flows back E and sinks over cooler waters of E tropical pacific (sink air compresses, warms, so that clouds vaporize/fail to develop)

El nino

air pressure gradient across the tropical pacific weakens (W pacific the trade winds slacken, SST drop, sea level falls, thermocline rise, E tropical pacific, SST rise, sea level climbs and thermocline deepens, relaxing trade winds weaken the W flow of equatorial currents with reversing direction, thick layer of warm surface waters drifts E until deflected toward the N/S by continental landmasses (may take several months for higher SST to reach W of N/S america, warm surface waters in E tropical pacific reduces upwelling of nutrient-rich waters along coast of Ecuador and Peru (phytoplankton population decline and the commercial fish harvest plummets), warm surface waters stress coral reefs living in shallow tropical waters (coral depends on symbiotic zooxanthellae that photosynthesizes nutrients, unusually high SSTs, coral bleaching, extended bleaching can kill coral polyps and corals destroying habitats for organisms), change in the trade wind circulation give rise to anomalous weather patterns in tropics and subtropics, intensity and frequency and spatial distribution of tropical cyclones (stronger winds aloft inhibit development/weaken tropical cyclones over atlantic basin, because of extensive area of warmer water over E tropical pacific, hurricanes travel farther N/W

Coral bleaching

unusually high SST, coral expel their colorful zooxanthellae and appear white

Teleconnection

linkage between changes in atmospheric circulation occurring in widely separated regions of globe, over 1000s of km (higher than usual SST over central and E tropical pacific heats and destabilizes the troposphere, deep convection generates towering thunderstorms that help drive atmospheric circulation governing course of jet streams storm tracks and moisture transport by winds at higher latitudes)

La nina

unusually strong trade winds (colder than usual surface waters over the central and E tropical pacific with exceptionally vigorous upwelling, somewhat warmer than usual surface waters over W tropical pacific, SST anomalies are essentially opposite those observed during el nino), 9 to 12 months, persist as long as 2 years, across mid latitudes of N hemisphere winds more meridional (steering cold air masses toward the SE and warm air masses toward NE), extreme meridional flow pattern forms from a broad pool of rotating air separate from the main current the persists over the same area (long as a cutoff persists over the same area the weather remains dry and the probability of drought increases, caused the severe summer drought in central US in 1988)

ENSO index/multivariate ENSO index

based on 6 variables measured in the tropical pacific with sea-level air pressure, zonal component of surface wind, meridional component of surface wind, surface air temperature, sky cloud cover, and sea-surface temperatures, SST drawn from area of tropical pacific includes equatorial cold tongue with bounded longitude values, el nino is positive SST departure from normal greater than or equal to 0.5 degrees celsius, averaged over 3 consecutive months, la nina negative SST departure from normal

ENSO alert system

launched by NOAA climate prediction center, during the second half of the 20th century, el nino conditions prevailed 31% of the time and la nina occur 23%

Watch

conditions in equatorial pacific are favorable for the development of el nino/la nina within the next 3 months

Advisory

el nino/la nina conditions have developed are expected to continue

ENSO observing system

fully operational as of december 1994, consists of island and coastal tide gauges, ship-based measurements, satellites and TAO, array of moored buoys in tropical pacific, all to improve understanding, detection and prediction of ENSO variability

Monitoring ENSO

TAO/TRITON measure with atmospheric variables (air temperature, wind, RH), oceanic parameters (sea surface and subsurface temperatures) at 10 depths in upper 500 m as well as salinity in newer moorings, 5 moorings along equator measure ocean current velocity, observational data are transmitted to NOAA PMEL, TRMM uses active radar and passive microwave energy sensors to monitor clouds, precipitation and radiation over the sea of pacific between 40 N/S, NASA GPM begins march 2014 and will advance understanding of global water and energy cycles, more accurate predictions of el nino/la nina allows better forecasts for informed planning in agriculture, fisheries, and water resource management

Other oscillations between the atmosphere-ocean

other regular climate-impacting oscillation involve the interaction of the atmosphere and ocean, NAO, AO, PDO, affected more restricted geographical areas and operate over longer time periods

North atlantic oscillation (NAO)

seesaw variation in air pressure between iceland and azores that influences precipitation and temperatures primarily in winter over E N america and much of europe and N africa

NAO Index

directly proportional to the strength of the N atlantic air pressure gradient, difference in sea level air pressure between Azores high and Icelandic low

Arctic oscillation (AO)

seesaw variation in air pressure between N pole and middle latitude that changes the horizontal air pressure gradient, altering the speed of the polar vortex that impacts winter weather in middle latitudes, shits frequently between it ± extended periods occur when ± dominates a winter season, 2009-2013 with - phase of NE chilly winter and E coast snowstorms in 2010

AO positive phase

air pressure lower over arctic and higher at middle latitudes, air pressure gradient is greater, stronger winds act as a dam that impedes teh SE flow of arctic air

AO negative phase

air pressure is higher over arctic and low at middle latitudes, polar vortex circulation is not as strong as usual, allows butterfly cold arctic air masses to more frequently move S

Pacific decadal oscillation (PDO)

long-lived variation in climate over the N pacific ocean and N america with sea-surface temperature fluctuations between the N central pacific ocean and W coast of N america

PDO warm phase

aleutian low is well developed with strong counterclockwise winds sterring mild and drier air masses into the pacific NW (winter mild and dry, water supplt suffer from reduced mountain snow pack)

PDO cold phase

aleutian cyclone is weaker so that cold, moist air masses more frequently invade the pacific NW (winters are colder and wetter, snowpack thicker)

Madden-julian oscillation (MJO)

areas of convection (ascent) and subsidence (suppressed convection) develop in indian and tropical pacific oceans and migrate E with influences outside tropical regions (connection in tropical latitudes where deep convection occurs, rising air parcels extend from the lower troposphere well above 500 mb, driven by converging warm air at the ocean surface with an unstable layer allowing air parcels to rise unabated, affected by changing SST as it’s most prevalent in warmer tropical pacific and indian oceans), surrounding areas of deep rising air currents are regions of subsidence characterized by fewer clouds with convection is suppressed

Pineapple express

consistent flow of atmospheric moisture originating in the vicinity of Hawaiian Islands which have a long history of pineaplle production and blows NE along with wind

Atmospheric river (AR)

narrow corridors in the atmosphere that convey moisture from the tropics to the mid-latitudes with the potential to cause devastating floods

Monsoon climate

regions where seasonal reversals in prevailing winds typically cause wet summers and dry winters, much of india with monsoon rains fall between june and september accounting for 80%+ of total annual precipitation

Asian and african monsoon

spring with cooler air over the ocean and warmer air over the land create a horizontal air pressure gradient directed from sea to land generating onshore flow of humid air, over land intense solar heating triggers convections (hot, humid air rises and consequent expansional cooling leads to condensation, cloud development and rain, aloft the air spreads seaward and subsides over the relatively cool ocean surface this completing the monsoon circulation), early autumn with radiational cooling chills the land more than the ocean, higher surface air pressures over land and creating a horizontal air pressure gradient directed from land toward sea (air subsides over land and dry surface winds sweep, air rises over relatively warm ocean surface and aloft drifts landward completing the winter monsoon circulation), over land the summer monsoon is wet whereas the winter monsoon is dry, solar radiation with land and water distribution and topography impose some regularity on the monsoon circulation and monsoon climates so that summers are wet and winters are dry, intensity and duration of monsoon rains are not the same from 1 year to the next (monsoon failure and drought are always possible in monsoon climates)

Monsoon active phase

weather is mostly cloudt with frequent deluges of rain

Monsoon dormant phase

weather is sunny and hot

North american monsoon system (NAMS)/southwest monsoon

prominent feature of the climate of the american SW bringing dramatic increases in rainfall, extension of mexican monsoon accounting for 70& of annual precipitation in parts of mexico, not as strong/persistent as S asian monsoon

Ocean warming

warming of ocean accounts for 93% of increase in energy inventory between 1971 and 2010, year to year basis more of this energy translated to atmosphere than other depths of the ocean, average temperature of the upper layer has increased more than 3x as the lower, water vapor surpluses from mid-latitude condenses into liquid that precipitate in nearly equal amounts elsewhere (salinity increases with evaporation of ocean water and development of sea ice, fresh water from rivers, precipitation, and melting ice decrease salinity), IPCC with evaporation minus precipitation

Ocean as a carbon sink

biological component of the carbon cycle in the ocean, anoxia, through photosynthesis algae fix carbon in the ocean from CO2 and produce oxygen, other organisms construct shells and exoskeletons from carbon then die and shells precipitate to the ocean bottom and form sedimentary rock

Anoxia

devoid of oxygen

Ocean acidifcation

change in the ocean’s chemistry due to absorption of excessive amounts of anthropogenic CO2, 300 million years with ocean pH marginally basic about 8.2 (25% to 30%, removes essential building blocks for shell formation and organisms suffer

pH

measure of the hydrogen and hydroxyl ion concentration ranging from 0-14 with 7 as neutral

Paleocene-eocene thermal maximum (PETM)

roughly 55 million years ago the atmosphere warmed dramatically on the order of 6 degrees celsius linked with changes in the carbon cycle similar to today (fossil records indicate that there were major deaths and replacement in marine species at the onset of the PETM)

Sea-level rise

water contracts when its temperature drops and expands when temperature rises, waxing and waning of land based glaciers plus ocean temperature fluctuation are two factors that govern eustasy, tectonic processes alter the size of the ocean basins also contribute to sea-level change, global warming trend causes sea level rise in response to melting of land based polar ice sheets and mountain glaciers coupled with thermal expansion of seawater, risen since mid-19th century has been larger than the mean rate during the previous 2 millennia

Eustasy

global variation in sea level brought about by changes in volume of water occupying the ocean basins

Is carbon increasing?

yes