Illustrations from Ruddiman, 2001, Earth's Climate, Past and Future

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What causes climate to be different from place to place?

Solar radiation – How much sunshine does a place get, based on sun angle and day length

Latitude: Where you are relative to the Equator and Poles
higher latitude = colder; lower latitude = tropical warm

Seasons: higher latitude, greater seasonality
Long days in summer (warmer); short days in winter (colder)

At Equator: 12 hours of day, 12 hours of night, all year round

At Poles: 6 months of day, sun above horizon; 6 months of night, sun below horizon

Atmospheric circulation: large scale winds such as the polar jet stream, westerly winds

Always blow from High Pressure to Low Pressure


Water distribution: oceans, lakes, ocean currents

Ocean Currents Driven by General Wind Circulation
Red = Warm; Blue = Cold


Ocean's Conveyor Belt -- Thermohaline Circulation


Water versus land: continentality, greater seasonal temperature range on land than near oceans or lakes

Elevation: higher = colder; lower = warmer

Ice Sheets, glaciers, at high latitudes, Arctic and Antarctic, and high elevations, mountains

More Ice = lower sea level (Ice Ages)

Less Ice = higher sea level (Global Warming)

Vegetation: influences temperature, humidity, precipitation



What Causes Climate to Change Naturally?

Causes Vary by Time Period --

Over tens to hundreds of millions of years, continental drift

Over thousands to a hundred thousand years, changes in earth's orbit around sun

Example: Earth is in the middle of a series of Ice Ages (Pleistocene), about 60 glaciations occurring in the past 2.5 million years.
The last Ice Age began about 120,000 years ago and ended about 10,000 - 12,000 years ago. The current warm period is called the Holocene and should be ending with another ice age beginning sometime in the next few thousand years.

Over decades to hundreds of years, changes in sun spots, changes in ocean circulation ( thermohaline circulation, pools of warmer and colder water) and winds -- not too well understood yet

E.G. El Nino - Southern Oscillation (ENSO)

Shorter term variations, volcanic eruptions, droughts, wet periods

E.G. Dust Bowl era, 1930s



Climate naturally varies somewhat over decades, generally fairly slowly.

However, times in the past, (end of the last ice age), climate has been extremely unstable, and has changed abruptly (in as little as a decade).

E.G. Younger Dryas: 12,900 years ago -- May have been caused by a comet exploding in the atmosphere over the Great Lakes Area -- possible cause of extinction of mammoth, megafauna, also Clovis culture -- new research.

Lasted for a thousand years -- return of the ice age. Also ended very rapidly, within a decade or two.