Chapter 14

Climate

Defining Climate

• Climate = long term weather patterns… – Averages and variations in temp., precip., wind,

etc.

• Normals: – 30+ year averages of daily high and low temp,

rainfall, wind speed and wind direction, measured at a specific location

– Normals are not necessarily usual weather conditions

Factors that Influence Climate

• Latitude (north or south of the equator)• Topography (rain shadow effect)• Air masses

Climate Classification

• Köppen’s classification system—based on temperature, precipitation, and vegetation– Tropical (high temp. year round)– Dry—largest area (low precipitation)– Mild (warm summers, cool winters)– Continental (warm summers, cold winters)– Polar—also highlands (low temp. year round)

Microclimates

• Microclimate—small localized climate• Heat Islands

Long-Term Climate Changes

• Ice ages—currently we are in an interglacial period.

Short-Term Climate Changes

• The reason for the seasons: axial tilt

Short-Term Climate Changes

• El-Niño—changes in southern Pacific Ocean with global effects

• Volcanoes tend to decrease global temperatures

Natural Causes of Climate Change

• Solar/sunspot activity—11 year cycle• Maunder minimum: low sunspot activity from

1645 to 1716 corresponds to “Little Ice Age.”• Long-term changes in Earth’s orbit, tilt, and

wobble cause cycles in temperature (ice ages)

Natural greenhouse effect

• NOT related to the hole in the ozone layer!

Impact of Human Activities

• Anthropogenic climate change (global warming)

• Increase in carbon dioxide (CO2) in the atmosphere due to:– Burning fossil fuels– Deforestation