long term climate change

causes of longterm climate change

Many processes can cause climate to change. These include changes: In the amount of energy the Sun produces over years. In the positions of the continents over millions of years. In the tilt of Earths axis and orbit over thousands of years. That are sudden and dramatic because of random catastrophic events, such as a large asteroid impact. In greenhouse gases in the atmosphere, caused naturally or by human activities.

plate tectonics

Plate tectonic movements can alter climate. Over millions of years as seas open and close, ocean currents may distribute heat differently. For example, when all the continents are joined into one supercontinent (such as Pangaea), nearly all locations experience a continental climate. When the continents separate, heat is more evenly distributed. Plate tectonic movements may help start an ice age. When continents are located near the poles, ice can accumulate, which may increase albedo and lower global temperature. Low enough temperatures may start a global ice age. Plate motions trigger volcanic eruptions, which release dust and CO2 into the atmosphere. Ordinary eruptions, even large ones, have only a short-term effect on weather (Figure 1.2). Massive eruptions of the fluid lavas that create lava plateaus release much more gas and dust, and can change climate for many years. This type of eruption is exceedingly rare; none has occurred since humans have lived on Earth.

solar variation

The amount of energy the Sun radiates is variable. Sunspots are magnetic storms on the Suns surface that increase and decrease over an 11-year cycle (Figure 1.1). When the number of sunspots is high, solar radiation is also relatively high. But the entire variation in solar radiation is tiny relative to the total amount of solar radiation that there is, and there is no known 11-year cycle in climate variability. The Little Ice Age corresponded to a time when there were no sunspots on the Sun. Sunspots on the face of the Sun.


milankovitch cycles

The most extreme climate of recent Earth history was the Pleistocene. Scientists attribute a series of ice ages to variation in the Earths position relative to the Sun, known as Milankovitch cycles. The Earth goes through regular variations in its position relative to the Sun: 1. The shape of the Earths orbit changes slightly as it goes around the Sun. The orbit varies from more circular to more elliptical in a cycle lasting between 90,000 and 100,000 years. When the orbit is more elliptical, there is a greater difference in solar radiation between winter and summer. 2. The planet wobbles on its axis of rotation. At one extreme of this 27,000 year cycle, the Northern Hemisphere points toward the Sun when the Earth is closest to the Sun. Summers are much warmer and winters are much colder than now. At the opposite extreme, the Northern Hemisphere points toward the Sun when it is farthest from the Sun. An eruption like Sarychev Volcano (Kuril Islands, northeast of Japan) in 2009 would have very little impact on weather. This results in chilly summers and warmer winters. 3. The planets tilt on its axis varies between 22.1o and 24.5o . Seasons are caused by the tilt of Earths axis of rotation, which is at a 23.5o angle now. When the tilt angle is smaller, summers and winters differ less in temperature. This cycle lasts 41,000 years. When these three variations are charted out, a climate pattern of about 100,000 years emerges. Ice ages correspond closely with Milankovitch cycles. Since glaciers can form only over land, ice ages only occur when landmasses cover the polar regions. Therefore, Milankovitch cycles are also connected to plate tectonics.


changes in atmospheric greenhouse gas levels

Since greenhouse gases trap the heat that radiates off the planets surfaces, what would happen to global temperatures if atmospheric greenhouse gas levels decreased? What if greenhouse gases increased? A decrease in greenhouse gas levels decreases global temperature and an increase raises global temperature. Greenhouse gas levels have varied throughout Earth history. For example, CO2 has been present at concentrations less than 200 parts per million (ppm) and more than 5,000 ppm. But for at least 650,000 years, CO2 has never risen above 300 ppm, during either glacial or interglacial periods (Figure 1.3). Natural processes add and remove CO2 from the atmosphere. Processes that add CO2 : volcanic eruptions decay or burning of organic matter. Processes that remove CO2 : absorption by plant and animal tissue. When plants are turned into fossil fuels, the CO2 in their tissue is stored with them. So CO2 is removed from the atmosphere. What does this do to Earths average temperature? What happens to atmospheric CO2 when the fossil fuels are burned? What happens to global temperatures? CO2 levels during glacial (blue) and inter- glacial (yellow) periods. Are CO2 levels relatively high or relatively low during in- terglacial periods? Current carbon diox- ide levels are at around 400 ppm, the highest level for the last 650,000 years. BP means years before present.


instructional diagrams

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which of these are greenhouse gases?

a) carbon dioxide

b) methane

c) water vapor

-->  d) all of the above

carbon dioxide and methane levels in the atmosphere are correlated with temperature.

-->  a) true

b) false

which of these can cause climate to change?

a) the amount of energy the sun produces over the years

b) the tilt of the earths axis

c) asteroid impacts

-->  d) all of the above

the climate cycle correlates with the sunspot cycle.

a) true

-->  b) false

plate tectonics processes can alter climate such as

a) when there is a supercontinent, heat is distributed more evenly around the planet.

-->  b) when continents are near the poles, ice accumulates to maybe start an ice age.

c) when there is a supercontinent, there are more volcanic eruptions to block the sun.

d) all of these.

when earths axis has less different in its tilt, climate is more moderate throughout the year.

-->  a) true

b) false

atmospheric carbon dioxide levels

-->  a) are currently around 400 ppm.

b) have been higher than 400 ppm several times in the past 100,000 years.

c) are the highest they have ever been in earth history.

d) all of the above

ice ages happen predictably on a 100,000 year cycle that correlates with milankovitch cycles.

a) true

-->  b) false

what natural process removes carbon dioxide from the atmosphere?

a) volcanic eruptions

b) decay or burning organic matter

-->  c) absorption by plant and animal tissue

d) all of the above

diagram questions

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