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Terms in this set (60)

-Overview:
a. Surface currents driven by winds through the frictional coupling between atmosphere and sea surface (this will set the ocean currents in motion)
b. Surface currents are restricted to top 100 m
c. How deep is the ocean (on average)? - 4,000 m = 13,000 ft.
d. Layering (surface layer (top) -> thermocline (transition) -> deep water (bottom))

-Do ocean surface currents follow the same path as surface winds?
a. No, Coriolis causes water to flow differently
b. No, gravity causes the water to sink
c. No, because the continents get in the way

-Coriolis surface currents are deflected to the right (Northern Hemisphere) or left (Southern Hemisphere) of prevailing winds
a. This process is complicated by:
-Continents
-Ekman Spiral (Transfer of Coriolis Effect down through the water volume; responsible for the net motion of surface water)
-Ekman Transport (Net effect is that the surface water moves at right angles to the wind; right of the wind in NH, left in SH; we can expect simple gyres)

-What two factors control primary productivity? - Sun and nutrients

-Why are there so few nutrients at the center of ocean gyres? - Something used them all up; they were transported to the seafloor; there is such a long transport time; there is no source of nutrients
a. Nutrients consumed by primary production (photosynthesis) in the photic (sunlight) zone
b. Primary producers are eaten by larger things that sink when they die, removing nutrients from the surface water
c. Sinking dead things decompose in the deep ocean and most of their nutrients are returned to the water at depth (upwelling = vertical)

-At the equator, there is equatorial upwelling
-Divergence = upwelling
-Upwelling brings nutrients to the surface

-Coastal upwelling: Coastal winds can create upwelling along the coast
-Offshore winds = upwelling
-Onshore winds = downwelling
-Because the absolute temperature varies greatly across the planet, the most effective way to monitor temperature change is to compare the various records as differences from their own averages
-The magnitude of the departure of recent decades from the long-term average temperature
-A departure from a reference value or a long-term average
-A positive anomaly indicates that the observed temperature was warmer
-A negative anomaly indicates that the observed temperature was cooler

-First-order trend:
a. 1900-2012
b~1.6 ºF

-Second-order trend:
a. Warming has structure
b. We need to explain the warming trend
c. But, you should always be skeptical
-What are the assumptions over the warming in the past century?

-What are some possible problems with direct measurements?
a. Density of recording sights
b. Natural climate cycles (fluctuations)
c. Faulty thermometers (equipment)
d. Seasonal contrasts
e. Developing countries have shorter records
f. Oceans cover 70% of Earth
g. Heat Island Effect
h. Spotty/moderate coverage

-The temperature record of the past 100 or so years may be flawed because:
a. Most of the Earth is ocean where there are no thermometers
b. Towns are hotter, and most thermometers are in towns
c. Not all countries have long thermometer records

-Heat Island Effect: Which answer does not help explain why cities are hotter than their surroundings?
a. Latent heat is released more often over cities
b. Explanation of the Heat Island Effect:
-Cities have lower albedos
-Inversions in the lower atmosphere
-Heat generated by cities can be trapped there
-Not uncommon for cities to be 3 ºC (6 ºF) warmer than surroundings
-Most stations are now outside of the city

-Inequalities of warming:
a. Land has warmed more than oceans
-Is the land is warming more than the ocean because it has a lower albedo?
a. No, the ocean has a lower albedo
-The land has warmed more than the oceans because of conduction
a. Land can only transfer energy by conduction
b. Ocean transfers energy by convection
c. Cooling by evaporation
d. Higher heat capacity
e. Even though the ocean absorbs more of the Sun than the land, the land still warms more than the ocean
-The heat capacity of water is greater than land, and the ocean's mixed layer distributes heat over a much greater mass (convection) than conduction on land
-The heat storage of the ocean is greater than for the land, and will eventually warm the entire ocean, but very slowly
-Northern Hemisphere exceeds the Southern Hemisphere in warming
a. North Hemisphere has much more land than the Southern Hemisphere
b. Latent inequality
-The Arctic has warmed the most
a. The Arctic is warming more than anywhere else on the planet. This must be because it has strong positive feedbacks
b. Warming is greatest in the Arctic despite less land there
-Mostly due to sea ice loss and albedo feedbacks
-Retreating glaciers
a. Almost everywhere, but in the tropics/high latitudes in Southern Hemisphere? - Yes
-Are tropical glaciers receding?
a. Probably
-What about the big ice sheets in Greenland and Antarctica?
a. Loss of ice is by both direct melting and calving from outlet glaciers
b. Ice shelves are breaking up
c. As ice shelves break up, the glaciers behind them are free to flow more rapidly, delivering more ice to the ocean
d. There is still negligible ice melt
e. Greenland is melting more and more rapidly
f. Antarctica is changing less rapidly
g. Ironically, more snow is falling at the South Pole

-If glaciers are retreating, sea level should be rising. Is it?
a. Yes, of course
b. How do we know?
-Satellites
a. Measure sea level
-Tide gauges
a. What controls tide gauges (relative sea level)?
-The volume of water in the ocean
- The volume of the ocean basin
-Vertical motion of the continents
-Average air pressure changes (currents)
c. To capture true sea level changes, we need to analyze lots of tide gauges around the world and use satellites

-Sea level rise
a. Tide gauges: 1.8 cm/decade (100 years)
b. Satellites: 2.5 cm/decade (20 years)
-Sea level rising over the past century
-Faster in most recent 30 years than past 100 years
-Not obviously accelerating in recent decades

-Where is the ice melt coming from?
a. Some of the observed sea level rise must be from melting ice. The largest contributor is probably:
b. Small glaciers and ice caps
c. Melting the quickest

-Why is sea level rising?
a. Glaciers melting (50%)
b. Calculating all of the glacier ice that has melted in the past century adds up to only about 9 cm of sea level, half the total observed sea level rise
-What could explain the other half?
a. Only half of the observed rise in sea level over the past century can be explained by melting glaciers. The rest of the rise might be best explained by:
b. Global warming
-The ocean is warming (50%)
-Uplift under former ice sheets

-Thermal expansion
a. The ocean is warming
b. Rule of thumb:
-20 cm of sea level rise for every 1º C rise in temperature of the top 100 m

-Sea ice
a. The change in sea ice and land snow cover has a dramatic impact on the planetary energy balance
-The most powerful feedback system
b. Sea ice changes are difficult to predict because there are both thermal (freeze-melt) and dynamic (large-scale motion) components
c. Why does the sea ice move north and disappear along western Svalbard?
-This is the Gulf Stream
d. How does loss of sea ice impact sea level?
-Sea level will not change
-With glaciers melting, sea levels must be rising
a. Tide gauge records (100 yr.)
b. Satellites (30 yr.)
-Loss of fresh water sources
a. Especially in the summer
-Negative impact on tourism
-Geologic records of past climates
a. Losing ice-core records
-Because the planet is warming, Arctic Ocean sea ice is shrinking; this will result in:
a. Strong positive feedbacks
b. Sea ice feedbacks (ice-albedo feedback)
-Summer:
a. As the planet warms, sea ice cover is reduced, greatly reducing albedo
b. The ice free ocean (low albedo) now absorbs a much larger proportion of the solar energy in summer than when sea ice was present
c. Although the ice-free ocean stores much of the solar radiation, it is distributed through the surface layer, so the air temperature warms only slightly
-As the planet warms, sea ice cover is reduced, more energy is stored in the ocean
a. The warmer ocean delays autumn freeze up, so the winter ice area decreases, and ice is thinner
-Winter:
a. Without sea ice, the atmosphere is no longer insulated from the ocean, which returns its stored heat to the atmosphere until freeze-up
b. Because the polar atmosphere in winter is currently about -40 ºC and the ocean can't get below -1.5 ºC, the winter atmosphere warms greatly without sea ice insulation
-Both summer and winter are very strong positive feedbacks

-If the planet warms in the summer, snow cover over Arctic lands will melt earlier. The impact will be:
a. Summer temperatures over land will warm more
b. Temperature change over the land with snow change (rather than over the ocean with sea ice change) because the land energy is transferred only by conduction (whereas the ocean is convection)

-Decreasing snow cover warms the land in summer more than sea ice loss warms the ocean in summer. Why?
a. Conduction vs. convection
b. Feedback from snow melt in a warming climate?
c. If snow cover is less, continental albedo is lower, and more short-wave solar energy is converted to long-wave (heat) energy
d. Absorbed energy only transferred into land by conduction so surface warms a lot (and so warms the atmosphere)
e. Positive feedback in summer

-If snow cover over land is less in summer because of warming, is there a positive feedback in winter?
a. Yes, small positive feedback
b. Feedback from snow melt in a warming climate?
c. Stored extra heat in land surface from snow-free summer will warm the atmosphere for a while in the fall, but once new snow accumulates, this effect is very small
d. Small positive feedback
e. Positive feedbacks from snow and sea ice in both summer and winter
f. → Polar amplification of global warming:
-If the planet warms, because of strong positive feedbacks in the polar regions (especially the Arctic), should warm considerably more

-When permafrost melts, CH4 (methane) and CO2 (carbon dioxide) are released - greenhouse gases
a. Consequently, as the plane warms and permafrost melts, the release of CH4 and CO2 will produce:
a. A positive feedback
b. Arctic warming has resulted in permafrost thawing
c. On land, carbon from plants preserved in permafrost is then released as CO2 or CH4, both GHGs, producing positive feedbacks on warming
d. Vast amounts of methane clathrates frozen in sea floor permafrost have not yet started to be released, but are a potential larger feedback
-Carbon dioxide has been increasing in the troposphere for at least the past 50 years. This is a...
a. Fact

-Why might we be concerned that carbon dioxide is increasing in the atmosphere?
a. CO2 is a greenhouse gas

-Greenhouse gases are transparent to solar radiation and absorb Earth's radiation
a. Strong influence on planetary temperature

-There has been concern about increasing CO2 in the troposphere since the 1800s

-In 1896, Swedish chemist calculated that doubling CO2 in the atmosphere would raise the Earth's temperature 5-6 ºC
a. Did not see this as a problem
b. He figured that if industry continued to burn fuel at the 1896 rate, it would take 3,000 years for the CO2 level to double
c. Now we except the atmospheric CO2 to double by 2050

-50 year record of CO2 (100 year residence time) shows:
a. Steady increase from 315 to 400 ppmv
b. Biosphere annual impacts on C-cycle

-Trapped atm in ice cores tell us current CO2 levels unprecedented in >800,000 years

-Only 1/3 of anthropogenic CO2 added each year remains in the atmosphere; oceans and vegetation are transient

-Methane (10 year residence time) is a less important GHG; currently 2 times pre-industrial; increasing slowly, irregularly

-GHGs increasing steadily since 1900 AD, but planetary temperature does not rise steadily

-Consequently, GHGs alone cannot explain all the observed 20th century warming

-1st order trend:

a. Regular increase
b. Rate of increase is itself increasing

-What is the main reason that the concentration of CO2 in the atmosphere is increasing?
a. Fossil fuel combustion

-2000 AD = 368 ppm
a. Mauna Loa, Hawaii
-Wiggle = 8 ppm
b. Niwot Ridge, Colorado
c. Point Barrow, Alaska
-Wiggle = 17 ppm
d. American Samoa, Tropical Pacific
e. South Pole / Tasmania, Australia = 366 ppm

-The wiggles that are the second order CO2 trend must be related to...
a. The annual cycle of plant grown and decay

-2nd order trend:

a. Biosphere breathing
b. Primary productivity (plant photosynthesis) consuming CO2 during the summer months, and decomposing (oxidizing), releasing stored carbon as CO2 in the winter months
c. Largest variation is where season contrasts are largest (high latitudes) and a large terrestrial biosphere (Northern Hemisphere)

-Based on what we have seen, I expect the amplitude of the yearly cycle at Tutuila, American Samoa, Tropical Pacific, to be __________ than/as Hawaii
a. Smaller

-Based on what we have seen, we can explain the low amplitude of the yearly cycle at American Samoa to be a result of...
a. Low seasonality at American Samoa
b. Not much biosphere around American Samoa
c. Year-round sunlight and warmth at American Samoa

-Despite very large differences in the season amplitude of the CO2 levels, all our Northern Hemisphere sites had 368 ppmv, CO2 in the year 2000 AD. From this, we can conclude that...
a. The Northern Hemisphere troposphere is very well mixed
b. Southern Hemisphere?

-Based on what we have seen, I expect the amplitude of the yearly cycle at the South Pole to be ___________ than as Hawaii because ____________?
a. Smaller, because so little vegetation on Antarctica

-Based on what we have seen, I expect the magnitude of the yearly cycle at the South Pole to be ___________ than as Hawaii
a. Smaller

-The South Pole has slightly less CO2 than any of the Northern Hemisphere sites. This suggests that...
a. It takes a couple of years for CO2 to mix between the Northern and Southern Hemisphere

-The entire Southern Hemisphere is well mixed, and primary productivity of the terrestrial biosphere must be much larger than the ocean biosphere
a. Southern Hemisphere amplitude is smaller and opposite phase relative to Northern Hemisphere

-3rd order trend:

-Looks at a lot like ENSO, volcanism, and chaos
a. Natural variability

-Take homes from instrumental record (1957-2013):
a. CO2 steadily increasing
b. Troposphere is very well mixed
-NH vs. SH
-Weeks within; 1-2 year between
c. Biosphere explains 2nd order trend wiggles
d. Terrestrial NPP much bigger than ocean NPP
e. Global Carbon Cycle
-Active C-cycle
-Explain steady climb in CO2?
-Biggest reservoir of carbon is in carbonate rocks (40 m)
-System is not in equilibrium
-Visible changes
-Atmosphere is gaining carbon
-Source: Extra amount of carbon we are putting in the atmosphere from fossil fuel combustion
-Sink: Biosphere and ocean are each extracting and storing 2 of these
-Ocean is by far the largest active carbon reservoir
-Increasing CO2 due mostly to fossil fuel combustion + some deforestation (burning)
-2/3 fossil fuel CO2 emitted by fossil fuel combustion is taken up by ocean and vegetation, but these are a finite carbon sink
-CO2 residence time in atmosphere is 100 years
-Long-term changes in luminosity

-Systematic variations in the "solar constant" on decadal to centennial timescales

-Why is it so hard to measure changes in the Sun's strength in real time?
a. There isn't much change on these timescales
b. Clouds influence measurements
c. The Sun is only visible half the time

-The long wish is to measure precisely subtle changes in solar irradiance were realized with satellites

When the Sun has many sunspots, it is ___________ than when there are no sunspots...
a. Hotter

-Sunspots are dark areas on the Sun, cooler than elsewhere
a. But, these dark spots are surrounded by larger, brighter areas
b. So the Sun is actually brighter when there are lots of sunspots
c. There is a link between solar irradiance and the number of sunspots visible on the Sun
d. Sunspots follow the same 11 year cycle as solar irradiance
-There is an 11 year cycle in solar irradiance; this is in some way related to the 22 year cycle in the Sun's magnetic field reversals
e. Over the 11 year cycle, solar irradiance varies by about 0.1% (maximum is about 0.15%)
f. The 11 year cycle is tracked by the Sunspot Number, with most sunspots linked to higher irradiance

-Sunspot proxies for solar irradiance allow us to evaluate changes in the Sun's output before satellites could monitor directly

-Based on what we know about the instrumental record of global temperature, could changes in solar luminosity help to explain some of the observed changes?
a. Yes
b. If the Sun is brighter, the planet should be warmer
-#1 determinant

-Collaborative Quiz: Based on what we know about the instrumental record of global temperature and now what we know about changes in sunspots (and therefore solar luminosity) over the past century,
a. Describe in what way changes in the Sun's luminosity helps to explain some of the observed temperature changes
b. First order trend:
-The planet has warmed over the past century
c. Second order trend:
-Initial warming up until ~40s, ~50s; then is flat for a couple of decades
-Second warming around ~60s, ~70s until 2010
d. Third order trend:
-Wiggles
e. Describe in what ways in the Sun's luminosity fails to explain some of the observed temperature change

-Based on changes in solar luminosity reconstructed from sunspot numbers, the Sun might explain some of the observed early 20th century warming
a. But, it not only cannot explain the late 20th century warming, changes in solar luminosity along predict global cooling, in opposition to the observed global warming

-Solar variability take homes:
a. Solar irradiance varies on an 11 year cycle, with the greatest irradiance when there are the most sunspots
b. But, total variability is only 0.1% to 0.15%
c. This is relatively small
d. Observed spot numbers suggest that solar irradiance increased in the first half of the 20th century, at the same time that Earth's temperatures were rising
e. But, observed sunspot numbers have been decreasing since 1950s (weaker Sun) at a time when Earth's temperatures were rising
f. The Sun cannot contribute to late 20th century warming
g. Future sunspot numbers projections show continued decline - may reduce future warming

-Changes due to irregularities in Earth's orbital parameters (Earth-Sun distance)
a. Precession of the equinoxes
b. Tilt of the spin axis
c. Elliptical orbit
d. These three influence the Earth-Sun distance and amount of energy we get in different seasons
e. All of these changes occur on timescales too slow to significantly influence planetary temperature over the past century
f. Milankovich Effect
g. Also not significant over the last 100 years
h. We're left with sunspot cycles as the biggest effect

-Solar irradiance gives us a decent match for early 20th century warming
a. Magnitude
b. 11 year cycle: +/- 0.1%
c. Most current estimates are that maximum solar variability are no more than 0.15%
d. Climate forcing
e. Recall: annual average solar flux at the top of the atmosphere is 340 W/m2 (annual average across the sphere of Earth)
f. 0.15% of 340 translates to a forcing of 0.5 W/m2
g. How does this compare to GHG Radiative forcing?
-Injects stuff into the stratosphere

-Example: Pinatubo
a. Shortly after Pinatubo erupted, climate modelers predicted how Earth's temperatures would change over the subsequent 5 years
b. .5ºC
c. Bold prediction because we would soon know if they were correct
d. Impact was about 0.5ºC (1ºF) cooling across the entire planet for 3 years
e. What do you think the climate models would predict would happen to Earth's temperature after a major explosive eruption?
f. Troposphere would cool and the stratosphere would warm

-Injects ash into the stratosphere, where gravity removes ash in weeks to moths
a. No precipitation in the stratosphere

-What do we know now about sulfate aerosols from explosive volcanism?
a. Aerosols should be in the troposphere and stratosphere
b. Short residence time in the troposphere, and longer in the stratosphere
c. They are going to reflect and scatter the Sun's energy, and absorb Earth's

-From the climate impacts of sulfate aerosols (shade and GHGs), and our estimates of residence times in the stratosphere and troposphere, what do you predict would be the climate impacts of a major explosive eruption injecting lots of sulfur gas into the troposphere and stratosphere on
a. Temperature at Earth's surface: -Cools
b. Temperature in the troposphere: -Cools
c. Temperature in the stratosphere:
-Warms

-After a large explosive eruption injecting SO2 into the stratosphere and troposphere, Earth's surface would:
a. Cool

-After a large explosive eruption injecting SO2 into the stratosphere and troposphere, Earth's stratosphere would:
a. Warm

-After a large explosive eruption injecting SO2 into the stratosphere and troposphere, Earth's troposphere would:
a. Cool
b. Because Earth's surface is cooling, the troposphere has to cool