Chapter 14 Atmo 102 – Flashcards
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When was the last time North America was covered with ice sheets?
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18,000-22,000 years ago
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What is another name for ice sheets?
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continental glaciers
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What percentage of Earth's land surface is covered by glaciers?
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10%
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What are some methods of examining past climate events (geology)?
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- core samples from ocean floor sediments - ice cores from glaciers in Greenland and Antarctica
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What evidence does geology tell us about past changes in climate?
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suggests global climate has undergone slow but continuous changes
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What are some chemistry methods of examining past composition of the atmosphere?
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looking at bubbles of ancient air trapped in ice - help determine CO2 concentrations
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What role do isotopes play in climate event studies?
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reconstructing past climate events - use isotopic ratios
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What are isotopes?
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- same chemical element (same # protons and electrons but different # of neutrons) - small differences in physical properties
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Which two isotopes are important for climate studies?
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O-16 (8 neutrons) and O-18 (10 neutrons)
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O-18 and O-16 evaporation/condensation rates
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O-18 evaporates more slowly and condenses more readily than O-16
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Ratio of O-18 to O-16 during cold periods
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increases
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Ratio of O-16 to O-18 in the atmospheric water vapor during cold periods
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increases
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During cold periods isotopic ratios in ice vs. oceanic shells/sediments
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- ice has higher O-16 - ocean has higher O-18
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How much below normal does a T have to fall for an ice age to occur?
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~8 degrees
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GHG (CO2, methane, H2O vapor) levels during the last ice age compared to now
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CO2: ~30% lower methane: ~50% lower H2O: lower
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Sea level during last ice age compared to now
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100-125m lower
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What is the Younger Dryas?
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period of rapid decrease in T
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Positive feedback mechanism (assume Earth is warming) of water vapor
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1) more evaporation from oceans 2) increase in water vapor in atm. 3) increase in IR absorption = strengthens GHE 4) T rises
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If the positive feedback mechanism is not controlled what will happen?
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Runaway GHE
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Negative feedback (assume Earth is warming) moisture in the air
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1) atmosphere warms/moistens 2) more low clouds 3) more reflection of solar radiation 4) decrease in solar heating of surface 5) slows warming
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Milankovitch theory
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describes climatic changes to variation in Earth's orbit
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First cycle of Milankovitch theory
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*eccentricity* - deals w/ changes in shape of orbit
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Greater eccentricity means what?
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more elliptical = greater variation in solar E received at the top of the atmosphere
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What is our current eccentricity characterized as?
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low
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Second cycle of Milankovitch theory
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*"wobble"* -takes into account the Earth rotates on an axis
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What is "wobble" defined as?
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known as the precession of the Earth's axis - occurs in a cycle of about 23000 years
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Third cycle of Milankovitch theory
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*obliquity* - changes in the tilt of the Earth as it orbits the sun
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Current obliquity and variation range
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current: 23.5 tilt range: 22-24.5 degrees
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If there is a low tilt what does that mean for seasonal changes?
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less seasonal variation and less likely for glaciers to form
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On top of the changes in Earth's orbit what other factors contribute to climate change?
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- amount of dust in the atm. - reflectivity of ice sheets - concentration of GHG's - changing characteristics of clouds - ocean circulation - glaciers melting
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CLIMAP project
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able to reconstruct the Earth's ocean surface T in the past by examining sediments at the bottom of the ocean
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Aerosols
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tiny liquid and solid particles that enter the atmosphere
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Effect of aerosols
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complex; depends on particles size, shape, color and vertical distribution
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How do aerosols enter the lower atmosphere?
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via oceanic emissions of organic sulfur or anthropogenic sources
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Direct forcing of aerosols
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sulfate aerosols reflect incoming sunlight *lowers Earth's surface T during the day* - cooling effect may be equal to warming induced by CO2
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Indirect forcing of aerosols
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sulfate aerosols may also modify clouds by increasing their reflectivity
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Result of volcanic ash/particles being ejected into the stratosphere
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- warming of stratosphere - cooling of global surface air T
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What are volcanic eruptions rich in sulfur result in?
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warm the lower stratosphere
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What role does CO2 play in the warming of the earth?
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- strongly absorbs IR radiation - major role in warming of the lower atmosphere
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What impact will rising ocean T's result in?
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- increase in evaporation rates - increase in atmospheric water vapor
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What is a speculation of why the Younger Dryas occurred?
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cutting off the Gulf Stream from the global ocean circulation "belt"
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Possible consequences of doubling of CO2 from its present value
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globe will warm between 1.5 and 4.5 degrees C
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Since the beginning of this century the avg. global surface air has risen by?
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0.3 and 0.6 degrees
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Evidence that the warming is due to the GHG's
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- stratosphere cooled - high latitudes warm more - night warms more
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Dendrochronology
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study of annual growth rings of trees
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desertification
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an increase in the desert conditions of a region
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Maunder minimum
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refers to a time when there were few sunspots
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Little Ice Age
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cooling trend that occurred from 1550-1850
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water vapor
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most potent greenhouse gas
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Ice Age
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another name for the Pleistocene epoch
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carbon dioxide
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this GHG has doubled in concentration over the past 100 years are so
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year without summer
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another name for the year 1816
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Volcanoes that have the greatest impact on global climate appear to be those rich in this gas:
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sulfur
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Climate models predict that in order for increasing levels of CO2 to raise air T's between 2 and 5 degrees C, this gas must also increase in concentration:
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water vapor
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Overall, clouds have a net ____ effect on climate
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cooling
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If the Earth were in the warming trend, increasing the amount of water vapor in the atmosphere (but not clouds) would most likely produce a ____ feedback mechanisms
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positive
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A negative feedback mechanism:
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weakens an initial change in an atmospheric process
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Most climate models predict that a gradual increase in global CO2 over the next 100 years will most likely bring about:
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an increase in surface air T
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The theory that explains how glacial material can be observed today near sea level at the equator, even though sea level glaciers probably never existed at the equator, is the:
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theory of plate tectonics
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During the period when the earth's orbital tilt is at a minimum, which would probably be true?
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Less seasonal variation between summer and winter
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The wobble of the earth on its axis refers to:
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precession of the equinox
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If the earth were in a cooling trend, what is an example of a positive feedback process?
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Increasing the amount of cloud cover around the Earth
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What are the possible consequences of global warming?
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1) reduction in avg. precipitation over certain areas 2) cooling of upper atmosphere 3) drop in rate of ozone destruction 4) accumulations of additional snow in Antarctica
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The warming trend in the NH could be the result of:
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increasing levels of CO2 and other GHG's
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Climate models predict that the greatest warming due to increasing levels of GHG's will most likely occur in
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polar latitudes
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The planet with the so-called runaway GHE is ?
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Venus
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It appears that throughout much of the Earth's history, the climate was much cooler than it is today (T/F)
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F
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The Milankovich cycles, in association w/ other natural factors, explain how glaciers may advance and retreat over periods of ten thousand years to one hundred thousand years (T/F)
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T
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Most climate predict that if average global T's rise by about 5 degrees F or more, the avg. global precipitation will increase (T/F)
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T
