Section 7.1

Climate: Definition:

the characteristic pattern of weather conditions within a region, including temperature, wind velocity, precipitation, and other features, averaged over a long period of time. (ON Science 10)

Fact: The climate IS changing.

Evidence:

Ice sheet depths are decreasing

Ocean levels are rising

Oceans are Acidifying

Average global temperatures have increased by 0.74 degrees Celsius (1.4 degrees in Ontario)

Wind patterns have changed over the past 50 years

Precipitation patterns have changed over the past 50 years

However:

Earth has experienced periodic climate changes before humans even existed.

Historic Global Temperatures and Natural Climate Variability Earth's climate has always been affected by a range of

natural factors

Its climate is known to have changed significantly during recorded history, before gaseous emissions from human activity

The graph below shows average global temperature changes plotted against a scale for time increasing in powers of ten, from millions of years ago to the present. Look CAREFULLY at the scale.

What do you notice?

rapid change in

temperature over the

last 100 years

A schematic representation of recent climate trends and future projections in historical perspective. The 20th century is shown on a linear scale. Earlier periods are shown in terms of increasing powers of ten years ago but are linear within each period. Source: Bureau of Meteorology, The greenhouse effect and climate change, Bureau of Meteorology, 2003, p. 33.

Natural Causes of Climate Change (Global Warming or Cooling) 1. Changes in Solar Activity

The amount of solar radiation fluctuates over time

Sunspots:

More radiation is emitted by the Sun

when the number of sunspots is high

Sunspots follow an 11 year cycle of

activity showing variations in solar

output of approximately 0.1% (Figure 7.2)

Natural Causes of Climate Change (Global Warming or Cooling) 2. Movement of Earth in Space

Earth rotates and revolves constantly through space around the sun

Seasons caused by the Earth’s (23.5 degree) tilted axis of rotation

Natural Causes of Climate Change (Global Warming or Cooling) 3. Changes in the Earth’s Rotation, Orbit and Tilt

Changes in movement or position can affect the intensity of solar radiation on different parts of the planet

Eccentricity: (Figure 7.4)

Orbit in space changes from circular

to elliptical over a period of 100 000 yrs

When more elliptical, Earth receives

more radiation when closest to the Sun

Natural Causes of Climate Change (Global Warming or Cooling) Tilt:

Earth’s tilt varies between 22.1 and 24.5

degrees over a period of 41 000 years

Greater the tilt, greater the temperature

difference between summer and winter

Wobble:

The Earth “wobbles” slightly as it

rotates since it is not a perfect

sphere

Natural Causes of Climate Change (Global Warming or Cooling) 4. Latitude

Sun’s rays hit Earth’s surface at different angles due to curved shape of Earth

At latitudes north or south of the equator, Sun’s rays spread over larger areas compared to equator surface heats up less compared to equator

Source: http://essayweb.net/geology/weather.shtml