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` Wh t k What key ffeatures t d determine t i th the earths th weather? th ? ` What key features determine the earths climate? ` How does climate affect the location of the major biomes? ` Desert Biomes ` Grassland Biomes ` Forest Biomes ` Mountain Biomes ` Weather is an areas short-term short term atmospheric conditions, typically describe in terms of ◦ ◦ ◦ ◦ ◦ ◦ ` Temperature Pressure Moisture Precipitation Sunshine Wind direction and speed Two key yp principles p affect the weather ◦ Air Masses ◦ Pressure Changes ` ` o o o o Most of the dramatic changes g in weather occur along g a front,, the boundary y between two air masses with different temperatures and densities. A warm front is the boundary between an advancing warm air mass, and the cool one it is replacing. Warm air is less dense than cool air, and rises. As warm front rises the moisture begins condensing into droplets Gradually y the clouds thicken , descend to a lower altitude, and release their moisture. A moist warm front brings days of cloudy skies and drizzle ` o o o o A cold front is the leading g edge g of an advancing g mass of cold air. The cool air is more dense than the warm air, so stays close to the ground, and wedges underneath the less dense warm air. The rapidly p y rising g warm air produces towering clouds called thunderheads. As the cold front passes p through we experience high surface winds and thunderstorms. After the cold front passes we usually have cooler temperatures and clear skies ` Weather is also affected by changes in atmospheric pressure. pressure ` Atmospheric pressure is greater near the earth’s surface because the molecules l l are squeezed d ttogether th under d th the weight i ht off the th air. i ` An air mass with high pressure, called a high, contains cool, dense air, i thi this descends d d ttowards d th the surface f and db becomes warmer. F Fair i weather follows. ` A low l air i pressure mass, called ll d a llow, contains i warm, llow d density i air. This warm air rises, cools and condenses into clouds. ` ` ` ` Tornadoes and cyclones are two examples of weather extremes. Tornadoes are swirling funnel shaped clouds that form over land. land The US and Australia or most prone to tornadoes. Tornadoes occur when a large, dry cold front runs into a large mass of humid air. As the large warm air mass moves rapidly over the more dense mass of cool air it rises rapidly and forms t ti t th k strong convection currents thatt suck air upwards. ` ` ` ` ` Tropical op ca cyclones cyc o es a are e large, a ge, da dangerous ge ous sto storms s tthat at form o o over e warm tropical seas. They form when a cold air mass is located above an organized cluster of tropical thunderstorms. Convection occurs which leads to strong updrafts that lift the air and moisture upwards. The air cools as it rises and condenses. d As the h air expands d it is forced to diverge. The removal of air at the upper levels reduces pressure at the surface, increasing convection. ` ` ` Tropical cyclones can kill and injure people, and damage property and agricultural production. However they sometimes have long-term ecological benefits. I 1990 H In Hurricane i B Brett tt struck t k th the G Gulf lf off M Mexico. i IIn T Texas, costal bays and marches had become closed off from freshwater inflows. The hurricane calved fresh channels allowing ll ffresh h water to flush fl h out dead d d vegetation and d excessive algae. This s lead ead to tthe eg growth o t o of sea g grasses asses p providing o d g a su suitable tab e habitat for shrimps, crabs, fish and ducks, providing and ecological and economic benefit to the city. ` ` Climate is a regions long long-term term atmospheric conditions. The e ttwo o main a factors acto s dete determining g a region’s eg o s climate are ◦ Average temperature ◦ Average precipitation ` The temperature and precipitation patterns that lead to different climates are caused primarily by ◦ The amount of incoming solar energy ◦ Air circulation patterns p ◦ Water circulation patterns ` Uneven heating of the earths surface ◦ Air is heated much more at the equator where the sun’s rays hit directly. ◦ At the poles, the rays must travel further, and heat a greater area. ` Seasonal Changes ◦ The earths axis is tilted at 23.5 degrees, as a result different regions are tipped towards, or away from the sun. ◦ This creates opposite seasons in northern and southern hemispheres ` Rotation of the earth on its axis ◦ As the earth rotates, the surface moves faster under the air masses at the equator and slower at the poles. ◦ This causes the major prevailing winds. ` Mountains affect local and regional climates climates. ◦ Prevailing winds pick up moisture from an ocean ◦ On the windward side of a mountain range, air rises, cools and releases moisture. ◦ On the leeward side of the mountain range, air descends warms and releases little water. ` ` ` ` ` ` Wind is a vital p part of our p planets climate. Wind also transports nutrients from one place to another. Dust rich in phosphates and iron blows across the Atlantic from the Sahara Desert. This helps p to build up p agricultural g soils in the Bahamas and supplies nutrients for plants in the canopy of rain forests in Brazil. Wind also transports harmful viruses, bacteria, fungi and particles i l off long-lived l li d pesticides. i id Particles of reddish-brown soil and pesticides banned in the US are blown from Africa’s desert into skies over Florida This makes it very difficult to meet air pollution Florida. standards during summer months. Some types of fungi in the dust are also playing a role in destroying corral reefs in Florida Florida. Pollution from rapidly industrialising China and central Asia blow across the Pacific Ocean and degrade air quality over the western US. US ` ` Different climates lead to different communities of organisms, especially vegetation. The world can be divided into different biomes ` ` ` ` ` Deserts have little precipitation and little vegetation. Deserts cover about 30% of the earths land surface. They are found inland away from moist coastal airs, or on the downside of mountains in rain shadows. Temperatures tend to vary greatly between day and night due to a lack of vegetation or moisture to hold the heat. They can be found in tropical, temperate and polar regions. ` Plants: ◦ ◦ ◦ ◦ ` No leaves to reduce water loss Open pores to take up CO2 only at night Either deep roots to find ground water Or network of shallow roots to absorb maximum surface water Animals ◦ Animal tend to be small ◦ Hide by day or become dormant during long periods of heat ` Natural Capital Degradation ◦ ◦ ◦ ◦ ` Large desert cities Soil destruction by off road vehicles Depletion of underground water supplies Land disturbance and pollution from mineral extraction Deserts take a long time to recover from disturbances due to slow plant growth and slow nutrient cycle, it can take decades to recover from human activities ` ` Grasslands have enough precipitation to support grasses, but insufficient to support large strands of trees. There are three main kinds of grassland ◦ Tropical ◦ Temperate ◦ Polar ` Al called Also ll d savannas, these th grasslands l d have h high hi h temperatures year round. ` They have two prolonged dry seasons and abundant precipitation in the remaining two. ` They contain a large amount grazing and browsing hoofed animals that feed on a variety y of savanna p plants. ` Humans have attempted to raise cattle on tropical grasslands, this often helps in the destruction of grasslands into desert through overgrazing, and increased reliance on water. ` Temperate Grasslands cover vast expanses of plains and rolling hills in North and South America, Europe and Asia. ` In these grasslands grasslands, winters are very cold cold, summers are hot and annual precipitation is fairly sparse and falls unevenly through the year. ` Over-ground plants die each year and decompose producing deep, fertile soil. This is held in place by the vast network of roots from draught-tolerant grasses. ` Many of the world temperate grassland have been destroyed through overgrazing, and ploughing of the land for crop growth. This breaks up the soil roots and leave it vulnerable to erosion. ` ` ` ` ` ` ` ` During g most of the year y polar p g grasslands are bitterly y cold,, swept p by frigid winds, and covered by ice and snow. Winters are long and dark, and the rare precipitation falls mostly as snow. Th biome The bi is i carpeted t d with ith a thi thick, k spongy matt off llow-growing i plants, primarily grasses and mosses. Trees or tall plants can not survive in the cold windy conditions. Most annual growth takes place during the 6-8 6 8 week summer summer. The constant frozen groundwater leads to bogs and ponds in summer, under which mosquitoes and flies thrive. These feed g colonies of migrating g g birds. large Animals consist of hares, voles and ground squirrels which burrow underground to escape the cold, and predators such as the lynx, snow owl and arctic fox. B th cold, ld d iti iis slow. l Th f h Because off the decomposition Therefore human activities such as oil drilling, mines and military bases leave scars that persist for centuries. ` Forests have enough precipitation to support stands of trees and are found in tropical, temperate and polar regions ` ` ` ` ` ` ` ` Tropical p rain forests are found near the equator q They have heavy rainfall for the majority of the year, meaning a high humidity. They have a warm average temperature which varies little by day or by b year. Tropical rainforests are dominated by broadleaf evergreen plants. Typically the tall trees have shallow roots roots, and wide bases. bases The top of the trees for a dense canopy blocking most light from reaching the ground. Tropical p rainforests are teeming g with life and have incredible biological diversity. Much of the animal life, particularly bats and birds live in the sunny canopy layer. Alth h these th f t cover just j t 2% off the th earth’s th’ land l d surface f Although forests they are habitats for half of the earth’s terrestrial species. ` ` ` ` ` Temperate forests grow in areas with moderate average temperatures that change significantly with the season. They have long warm winters winters, cold but not severe winters, and abundant precipitation spread evenly throughout the year. Trees typically include oak, oak hickory hickory, maple maple, poplar and beech. They survive cold winters by dropping their leaves. Penetration of more sunlight means a greater diversity of plant life at ground level. The most common animal species include deer, and small mammals such as squirrels squirrels, rabbits rabbits, raccoons and mice. ` Th These forests f t exist i t in i cold ld climates li t and d consist i t mostly tl off cone-bearing evergreen trees. ` They keep their narrow pointed leaves (needles) all year long. This adaptation allows them to take advantage of the brief summers without having to take time to grow new leaves. ` Beneath the trees p plant diversity y is low because few species p can survive the winters when soil moisture is frozen. ` wolves Boreal forests contain a variety of wildlife wildlife, such as wolves, moose, martens and hares. ` ` ` ` ` ` Mountains make up almost a quarter of the worlds land surface. Dramatic changes in altitude, climate and soil take place over a very short h t distance. di t Because of steep slopes mountains soils are particularly vulnerable to erosion, especially after the removal of trees or vegetation. They contain the majority of the worlds forests. They play an important role in the hydrological cycle by gradually releasing melting snow and ice. Mountains are particularly vulnerable to human activities such as timber extraction, mineral resources extraction, hydroelectric dams and reservoirs, tourism through hiking and skiing, g, and soil damage g from off road vehicles.