Ch 12- Earth’s Changing Climate

Glaciers cover less than ___% of the earth’s land surface
10%
Most of this ice is in the ______ & _____ ice sheets, and its accumulation over time has allowed scientists to measure past climatic changes
Greenland and Antarctic
2 Catastrophic results of ice melting?
-Inundated (Flooding)
-Rise in Global T (:. rise sea levels)
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The study of geological evidence left behind by _____ & _____ glaciers is one factor suggesting that global climate has undergone slow but continuous changes
advancing and retreating
What is another form of evidence of global climatic changes?
Samples from ocean floor sediments and ice from Greenland and Antarctica (CLIMAP)
What is CLIMAP?
Climate: long-range investigation mapping and prediction…observed the ocean floor and remains of Cá2+ carbonate shells of organisms (their life indicates the T of surface water)…and Ó2-isotopes
How does the Ó2-isotope ratio of those organisms’ shells tell us about the sequence of glacier advances?
When ocean water evaporates, the heavy Ó2-18 tends to be left behind…
:. during glacier advancement, the oceans have less water & have more Ó2-18
Does comparing the ratio of Ó2-18 to Ó2-16 give info about climate change in past?
Yes, a higher ratio of 18:16 in the sediment suggests a colder climate, whereas a lower ratio = warmer climate
Do vertical ice cores extracted from ice sheets in Antarctica and Greenland provide additional info on past T patterns?
Yes, by examining the Ó2-isotope ratio in ancient cores provides a past record of T trends…the colder the air when the snow fell, the richer the [Ó2-16] in core
Do ice cores record the CAUSE of climate change? (2)
Yes, by 1. deducing from layers of sulfuric acid in the ice (how much came from volcanoes/humans)
2. Checked for chemicals that provide records of biological and physical changes in the climate system, such as Be that indicates solar activity
What is Dendrochronology?
Study of annual growth rings of trees to see climate change
How does dendrochronology work?
As the tree grows, it produces a layer of wood cells under its barks…each year’s growth appears as a ring,,,the change in thickness of rings indicates climatic changes
Other data used to reconstruct past climate changes:
1. Records of natural lake-bottom sediment and soil deposits
2. Study of pollen in deep ice caves, soil deposits, and sea sediments
3. Certain geological evidence and the change in the water level of closed basin lakes
4. Documents concerning droughts, floods, crop yields, rain, snow, and dates of lakes freezing and trees blossoming
5. Study of Ó2-isotope ratio fo corals
6. Dating Cá2+-carbonate layers of stalactites in caves
7. Borehole T profiles, which can be inverted to give records of past T change at the surface
8. Deuterium (heavy H), ratios in ice cores, which indicate T changes
Throughout much of the earth’s history, the global climate was probably much ______ than it is today?
Warmer B/c the polar regions were free of ice
What caused T’s to be colder?
ICE AGE- one glacial period occurred about 700 million years ago and another about 300 million yrs ago
What is the most recent Ice Age?
Pleistocene epoch
How did Pleistocene Epoch appear?
Polar ice appeared when cold era occurred….then Ts dropped and ice grew thicker…snow and ice began to accumulate in high mountains of N. Hem., and alpine glaciers soon appeared
-2.5 Ma, glaciers appeared in N. Hem, marking the beginning of the Pleistocene epoch
Was the Pleistocene a period of continuous glaciation?
NO…it was a time when glaciers alternatively advanced and retreated (melted back) over large portions of NA and Europe
What caused the glaciers to melt/warmer period was called?
Interglacial periods…btw glacial advances, it was a warmer period
Describe the current T change from 1900-45, 45-70, & 1990+?
1900-45: increased
1945-70: decreased
1990+: increased
Is the current global warming continuing?
Yes, but also increasing about 2C/century…significant compared to history
*The earth’s climate is constantly undergoing change. Evidence suggests that throughout much of the earth’s history, the earth’s climate was much WARMER than it is today*
*The most recent glacial period (Ice Age) began about 2.5 Ma. During this time, glacial advances were interrupted by warmer periods called interglacial periods. In NA, continental glaciers reached their max thickness and extent about 18,000-22,000 Ya and disappeared completed from NA about 6,000 Ya*
*The Younger Dryas event represents a time about 12,000 Ya when northeastern NA and Northern Europe reverted back to glacier conditions*
*During the 20th century, the earth’s surface T increased by about 0.6C. This global warming has NOT only continued, but over the last several decades has increased*
3 External causes of climate change?
Changes in:
1. Incoming solar radiation
2. Composition of atmosphere
3. Earth’s surface
Natural phenomena cause cause climate to change by which of the 3 mechanisms? Human actions?
-all 3
-2/3
Are there also internal causes of climate change? (i.e.)
Yes, such as changes in the circulation patterns of the ocean and the atm, which redistribute E within the climate system, rather than altering the total amount of E it holds
Explain how a warming trend increases the greenhouse effect?
T rises, and water from oceans evaporates into air…the increased quantity of water vapor absorbs more of the earth’s IR energy
What does the increased greenhouse effect raise? (Water vapor-Greenhouse feedback)
T’s even more, which allows for more water vapor to evaporate…etc. etc.
Is the water vapor greenhouse feedback a (+/-) feedback?
(+) b/c the initial increase in T (stimulus) is reinforced by other stuff
What is the snow-albedo feedback?
another (+) feedback case, in which an increase in global surface air T might cause snow and ice to melt…which reduces the albedo (reflectivity) of the surface, allowing more solar E to reach the surface, which further raises the T
What are (-) feedback mechanisms?
those that tend to weaken the interactions among the variables rather than reinforce them
Ex of one
-Chemical weathering-CÓ2 feedback:
…as chemical weathering increases, the amt of CÓ2 in atm. decreases …as Ts dip, less water evaporates from oceans, chemical weathing decreases, and the removal of CÓ2 from atm Dimishes
Point being: earth-atmosphere has a number of checks and balances called feedback mechanisms that help it counteract tendencies of climate change
ya
So, we see that one of the causes of climate change is the change in the surface of the earth….what is the theory where the slow shifting of the continents and the ocean floors called?
Theory of plate tectonics
What is the theory of plate tectonics?
According to this theory, the earth’s outer shell is composed of huge plates that fit together like pieces of a jigsaw puzzle…the plates, which slide over a partially molten zone below them, move in relation to one another. Continents are embedded in the plates and move along like luggage riding piggyback on a conveyor belt…the rate of motion is extremely slow, only a few cm/year
According to the theory, the now existing continents were at one time joined together in a single huge continent, which broke apart…how does this explain climate change?
Its pieces slowly moved across the face of the earth…when landmasses are concentrated in middle & high latitudes (as of today), ice sheets are more likely to form…greater chance of more sunlight to reflect back into space from the snow…less sunlight absorbed by surface lowers air T, which allows for a greater snow cover, and the formation of continental glaciers
Is the theory also related to CÓ2 levels?
Yep
How can mountains change climate?
chain of volcanic mountains forming perpendicular to the mean wind flow may disrupt the airflow over them, altering the climate both upwind and downwind…also mountains built on continental plates (Himalayan) can have marked influence on global circulation patterns and on the climate
Name of theory that describes the climatic changes to variations in the earth’s orbit (amount of solar radiation that reaches the earth)
Milankovitch theory
What is the basis of the theory>? PAPER!!!
as the earth travels through space, 3 separate cyclic movements combine to produce variations in the amount of solar energy that falls on the earth
1st cycle deals w/ changes in the ______
-Eccentricity…shape of the earth’s orbit as the earth revolves about the sun
-earth’s orbit changes from being elliptical to being nearly circular, which alters the amount of sun the earth gets
2nd cycle takes into account the fact that, as the earth rotates on its axis, it ______ like a _____
Wobbles like a spinning top
The wobble is know as the ____ of the earth’s axis
Precission
Milankovitch cycles summary:
1. Changes in the shape (eccentricity) of the earth’s orbit about the sun
2.Precession of the earth’s axis of rotation, or wobbling
3. changes in the tilt (obliquity) of the earth’s axis
Are these orbital changes the only thing responsible for ice buildup and retreat?
No…evidence of air bubbles in glaciers show that lower Có2 levels may have had the effect of amplifying the cooling initiated by the orbital changes
-Likewise, increasing Có2 levels at the end of the glacial period may have accounted for the rapid melting of the ice sheets
Are CÓ2 levels changing the primary reason for glacial period?
No, b/c something caused a change in Có2 levels, but it may be due to shifts in the oceans circulation patterns
List of other factors that work in conjunction with the M. Theory to explain the T variations between glacial and interglacial periods:
1. Amt of dust and other aerosols in atm
2. Reflectivity of the ice sheets
3. [other greenhouse gases]
4. Changing characteristics of clouds
5. Rebounding of land, having been depressed by ice
Do Variation in solar output affect climate change?
Yes!!! they occur in cycles, with the # and size reaching a maximum about every 11 yrs …they account for small climatic changes over time scales of decades and centuries
Do microscopic and solid particles (aerosols) affect climate?
Yes
What are some natural ways for particles to enter near the surface?
wildfires, dust storms, volcanoes, oceans
What is the overall effect they have?
They cool the surface by preventing sunlight from reaching the surface
During volcanic eruptions, fine ____ & ____ are ejected into the atm
Ash/dust
Scientists agree that the volcanic eruptions having the greatest impact on climate are those rich in ____ gases?
Sulfur
When sulfur is in the atmosphere, what does it combine with to make haze? Effects of haze?
Wate vapor + sunlight = haze
-Reflection of haze tends to cool the air at the earth’s surface, especially in the hemisphere where the eruption occurs
In an attempt to correlate sulfure-rich volcanic eruptions with long-term trends in global climate, scientists are measuring the acidity of annual ice layers in Greenland and Antarctica. Generally, the greater the [sulfuric acid] the greater the acidity of the ice layer…what do these finding suggest?
That volcanoes played an important role in triggering this comparatively cool period in the past
What is the theory for how particles ended up in the upper atmosphere and led to the mass extinction of dinosaurs?
GIANT CRATER…crashed into earth, and could have sent billions of dust/debris into the upper atm, where they circled the globe and reduced the sunlight to the earth…cutting off photosynthesis, and led to destruction of food chain
*The external causes of climate include: 1. Changes in incoming solar radiation; 2. Changes in the composition of the atm, & 3. Changes in the surface of the earth*
*The shifting of continents, along w/ volcanic activity and mountain building, are possible causes of natural climate change*
*The Milankovitch theory (along with other natural forces) proposes that alternating glacial and interglacial episodes during the past 2.5 million years are the results of small variations in the tilt of the earth’s axis and in the geometry of the earth’s orbit around the sun*
*Trapped air bubbles in the ice sheets of Greenland and Antarctica reveal that Có2 levels and methane levels were lower during colder glacial periods and higher during warmer interglacial periods. But even when the high, they still were much lower than they are today*
*Fluctuations in solar output (brightness) may account for periods of climatic changes*
*Volcanic eruptions, rich in sulfur, may be responsible for cooler periods in the geologic past*

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