Regional climatic influences and climate variation

MAIN LEARNING GOALS:
* Understand how regional climates are influenced by land mass, mountains, and development of high/ low pressure systems
* Learn the factors that have influenced climatic changes at decadal to millenial time scales

Proximity to oceans, mountains, and vegetation can influence climate at a regional (e.g. sub-continental) scale

Maritime &  Continental Climates
Heat capacity (energy needed to raise the temperature) of Earth’s surface is higher for water than for land
Regions near large bodies of water (oceans) have cooler temperatures in the summer, and warmer temperatures in the winter (heat storage of water)
Oceans also source of moisture for humidity and clouds
Maritime climate characterized by relatively small seasonal temperature change & higher humidities
Continental climate associated with center of large continents (Asia & N. America) in the temperate zone; large seasonal changes in temperature

Influence of Mountains on Climate

Heat capacity of air at higher elevations is lower, due to fewer air molecules (lower density); radiational heating of the air by the surface is therefore less effective
High amount of exchange of air with surrounding (cooler) atmosphere
In Rockies above Boulder, air temperature drops around 5.7 ºC for every 1000 m (3.1 ºF/1000 feet) climb in elevation
Mountains intercept air masses, and force them to rise and cool, leading to higher precipitation on windward side, and a drier climate on the leeward side  = Rain shadow effect
Differential heating of slopes can enhance storm formation

Presence and type of vegetation influences energy balance
Amount of sunlight reflected by the Earth surface  (albedo) is determined by the color- snow, light colored soils, and grasslands are good reflectors, and have high albedo
Forests are relatively dark, and have low albedo (high absorption of solar radiation)
Vegetation also enhances water movement from soil to the air (transpiration- evaporation of water from inside leaf to air + evaporation= evapotranspiration), which is a cooling process
Vegetation influences how effectively heat is removed by wind (sensible heat loss) - surface roughness; smooth surface (e.g. grassland) loses heat more effectively than a rough surface (mixed-age forest)

Temporal Climatic Variation
Climate cycles occur at daily, seasonal, decadal, and even 100,000+ year scales

Climate variation is associated primarily with changes in the amount of solar radiation received at Earth’s surface

Seasonality of climate in the temperate and polar zones is associated primarily with changes in temperature
Seasonality in the tropics is associated primarily with changes in precipitation
The zone of maximum heating and therefore maximum uplift (Intertropical Convergence Zone, ITCZ) and storm formation changes seasonally

Seasonal changes in some temperate and polar lakes associated with layering (stratification) of waters
Water is most dense at 4 °C
* surface layer (epilimnion) in summer is uniformally warm
* deeper, most dense layers (hypolimnion) uniformally cold
* intermediate layer (thermocline) is zone of temperature change
Lack of mixing between top and bottom is important for nutrient cycling and oxygen supply

Decadal Changes in Climate
examples include El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and the North Atlantic Oscillation (NAO)
Associated with changes in atmospheric circulation and high/ low pressure cells
ENSO occurs when equatorial Pacific easterly trade winds, and associated ocean currents, weaken
El Niño conditions last for around 18 months, and cycle at 3-8 year intervals

Long-term (100,000+) year cycles in climate are associated with variations in Earth’s orbit
Glacial-interglacial periods have occurred repeatedly over the last 3 million years, with glacial periods lasting around 80,000 years, and interglacial (warmer) periods lasting 20,000 years
Shape of Earth’s orbit and tilt of its axis change with time
known as Milankovitch cycles
1) orbital shape changes from elliptical, to more circular on 100,000 year time scales- influences seasonal amount of solar radiation received
2) Tilt of Earth’s axis changes on 41,000 year time cycle- larger angle of tilt accentuates the seasonal change in temperature
3) orientiation of the axis relative to other celestrial bodies (wobble) changes at 22,000 year cycles- influences Earth-sun distance during the seasons

READ TEXT TO LEARN ABOUT SALINITY, ACIDITY, AND OXYGEN IN SOILS AND WATER
> learn (or review) what salinity, acidity, and hypoxia are
> understand the factors that determine natural and anthropogenic variation in salinity, acidity, and oxygen concentrations