5.5 GLOBAL CLIMATE

CHANGE

CHANGES IN CLIMATE You probably notice changes in weather very

frequently.

For example, it could be rainy one morning and sunny the same day in the afternoon.

Climate change isn’t as observable to you because climate changes very slowly.

Studies indicate human activity may be contributing to climate change.

However, natural factors also can influence changes in climate.

ICE AGES The geologic record of Earth indicates

Earth’s climate used to be much colder.

An ice age is a period of time during which ice collects in high latitudes and moves toward lower latitudes.

Scientists have found evidence of many major ice ages throughout the Earth’s geologic history.

The most recent began about 2 MYA.

GLACIAL AND INTERGLACIAL PERIODS During an ice age, there are cold and warm periods.

The periods of cold in an ice age are called glacial periods.

Enormous sheets of ice advance and get bigger, therefore covering a larger area.

Because a large amount of water is frozen during glacial periods, the sea level drops.

The periods of warmth in an ice age are called interglacial periods.

Ice begins to melt and sea level rises again.

The last interglacial period began 10,000 years ago and is still happening to this day.

Questions as to why these periods exist and if they will ever happen again have been debated for the past 200 years.

MOTIONS OF THE EARTH One theory explaining ice ages and why they alternate between

cold and warm periods is known as the Milankovitch Theory.

Milutin Milankovtich (Yugoslavia) Proposed the changes in the Earth’s orbit and in the tilt of Earth’s axis cause

ice ages.

The Milankovitch Theory looks at three things:

Eccentricity: how much a shape (like an ellipse) differs from a circle. In a 100,000 year period, the Earth’s orbit changes from elliptical to more circular. This changes Earth’s distance from the Sun and primarily results from gravitational attractions. e = 0 (circle), 0 < e < 1 (ellipse)

Tilt: the Earth’s axis is tilted approximately 23.5 degrees. However, over a period of 41,000 years, the tilt of Earth’s axis varies between 22.2 and 24.5 degrees. The poles receive more solar energy when the tilt angle is greater.

Precession: the Earth “wobbles” on its axis, and this affects the amount of solar radiation reaching different parts of Earth’s surface at different times of the year. Once cycle of precession takes about 26,000 years.

VOLCANIC ERUPTIONS

Natural events, such as volcanic eruptions can influence climate change.

Large amounts of gas, ash, and other debris.

Once in the atmosphere, these particles act as a shield, blocking some of the sun’s rays, causing Earth to cool.

ASTEROID IMPACT Scientists believe the impact of an enormous

asteroid could significantly change climate.

When a large piece of rock slams into the Earth, it causes debris to shoot into the atmosphere.

This debris can block sunlight, similar to the volcanic gases and dusts.

Scientists believe this has happened before approximately 65 MYA ago (Yucatan) led to dinosaur extinction.

THE SUN’S CYCLE Recall the Sun’s 11-year sunspot cycle, which

may also play a role in climate change.

During this time, the sun changes from a solar maximum to a solar minimum. Scientists observe this phenomenon by counting sunspots.

During the solar minimum sun produces a low percentage of high-energy radiation.

During the solar maximum sun produces a high percentage of high-energy radiation.

Although scientists believe this cycle is caused by a gravitational attraction between the sun and other bodies in space, the exact cause is unknown to this day.

GLOBAL WARMING A gradual increase in the average global

temperature due to a higher concentration of gases, such as carbon dioxide, in the atmosphere is called global warming.

To understand how this works, its important to understand something else:

Greenhouse Effect: The Earth’s natural heating process in which carbon dioxide, water vapor, and other gases in the atmosphere trap thermal energy.

Some scientists believe this current rise in global temperature is from an increase in CO2, mainly from burning fossil fuels.

GLOBAL WARMING Another factor possibly adding to global warming

is thought to be the clearing of forests, or deforestation.

Burning trees releases even more CO2.

In addition, plants use CO2 to make food, and destroying the trees decreases a natural way of removing carbon dioxide from the atmosphere.

CONSEQUENCES OF GLOBAL WARMING Many scientists think if global temperatures continue

to rise, the ice caps at the poles will melt and cause flooding.

Melted ice caps would raise the sea level and flood low-lying areas, such as the coasts.

Areas receiving little water, such as deserts, may receive even less because of increased evaporation.

Desert animals and plants would find surviving harder.

Warmer and drier climates could harm crops in the Midwest US, but farther north in Canada, weather conditions for farming could improve.