4 THE ATMOSPHERE AND CLIMATE Weather - A description of physical conditions of the atmosphere. Climate - A description of the long-term weather pattern in a particular area. Weather and climate are primary determinants of biomes and ecosystem distribution.
5 Energy and the Greenhouse Effect Of the solar energy that reaches the outer atmosphere: About one-quarter is reflected by clouds and the atmosphere. Another quarter is absorbed by carbon dioxide, water vapor, ozone and a few other gases. About half reaches the earth’s surface.
7 Energy and the Greenhouse Effect Surfaces that reflect energy have a high albedo (Reflectivity). Fresh clean snow 80-85% Dark soil 3% Net average of earth 30%
8 Energy and the Greenhouse Effect Most solar energy reaching the earth is visible light. Energy reemitted by the earth is mainly infrared radiation (heat energy). - Longer wavelengths are absorbed in the lower atmosphere, trapping heat close to the earth’s surface. Greenhouse Effect
9 Convection and Atmospheric Pressure Lighter air rises and is replaced by cooler, heavier air, resulting in vertical convection currents. Transport energy and redistribute heat. Much of solar energy absorbed by the earth is used to evaporate water. Energy stored in water vapor as latent heat. - If condensation nuclei are present, or if temperatures are low enough, condensation will lead to precipitation.
10 Convection Currents Releasing latent heat causes air to rise, cool, and lose more water vapor. Rising, expanding air creates an area of relatively high pressure at the top of the convection column. - Air flows out of high-pressure zone towards areas of low-pressure, where cool, dry air is subsiding.
11 Convection Currents Subsiding air is compressed as it approaches the earth’s surface where it piles up and creates an area of high pressure at the surface. Air flows out of this region back towards low pressure, closing the cycle.
13 Coriolis Effect As air warms at the equator, rises, and moves northward, it sinks and rises in several intermediate bands, forming circulation cells. Surface flows do not move straight North and South, but are deflected due to Coriolis Effect.
14 Coriolis Effect Major zones of subsidence occur at about 30 o north and south latitude. Where dry, subsiding air falls on continents, it creates broad, subtropical desert regions. - Winds directly under regions of subsiding air are often light and variable.
15 Ocean Currents Warm and cold ocean currents strongly influence climate conditions on land. As surface water moves, deep water wells up to replace it. - Ocean circulation also driven by differences in water density. Gyres
18 El Nino Southern Oscillation Large pool of warm surface water in Pacific Ocean moves back and forth between Indonesia and South America. Most years, the pool is held in western Pacific by steady equatorial trade winds. - Every three-five years the Indonesian low collapses and the mass of warm surface water surges back east.
19 El Nino Southern Oscillation During an El Nino year, the northern jet stream pulls moist air from the Pacific over the U.S.. - Intense storms and heavy rains. During intervening La Nina years, hot, dry weather is often present. Pacific Decadal Oscillation - Very large pool of warm water moving back and forth across the North Pacific every 30 years.
21 Human-Caused Global Climate Change In 1988, the Intergovernmental Panel on Climate Change (IPCC) was formed. Released third climate report in February 2001. - Recent changes in world’s climate have had discernable impacts on physical and biological systems. Human activities must be at least partially responsible.
23 Sources of Greenhouse Gases Carbon Dioxide - Fossil-fuel burning. - Atmospheric levels increasing steadily. Methane - Ruminants, Coal-mines. - Absorbs more infrared than CO 2. Chlorofluorocarbons (CFC’s) - Refrigerants - Declined in recent years. Nitrous Oxide - Burning organic material.
24 Aerosol Effects Aerosols have a tendency to reflect sunlight and cool surface air temperatures. Short-lived, thus effects are temporary. Mt. Pinatubo erupted in 1991 and ejected enough ash and sulfate particles to cool global climate about 1 o C for nearly a year.
25 Current Evidence of Climate Change Global average surface temperature rose 0.6 o C during 20 th century. Droughts are more frequent and widespread. Severe weather events have increased dramatically. Polar regions have warmed much faster than the rest of the world. Ice shelves on Arctic peninsula are disappearing. Many animals breeding earlier and extending their ranges. Amphibians disappearing.
26 Current Evidence of Climate Change Retreating alpine glaciers. Mt. Kilimanjaro Glacier National Park Coral reefs are “bleaching.” Northern growing seasons are longer. Sea level has risen. Arctic sea ice is 40% thinner.
27 Winners and Losers Residents of extreme northern areas would enjoy warmer temperatures and longer growing-seasons. Plant growth patterns may be altered. One-third of population living in areas likely flooded by rising seas. More evaporation may cause severe storms. Infectious disease likely to spread faster. Circulation patterns may cause more snowfall at poles - New ice age ?
28 International Climate Negotiations Kyoto Protocol (1997) 160 nations agreed to roll back carbon dioxide, methane, and nitrous oxide emissions about 5% below 1990 levels by 2012. - Sets different limits for different countries, depending on prior output. Developing countries exempted. 126 countries have ratified the Protocol. U.S. has not.
29 Controlling Greenhouse Emissions Reducing carbon dioxide levels. Renewable energy sources may offer a better solution to climate problems. Capturing and storing carbon dioxide. Carbon Management - Planting vegetation - Emissions trading system - Deep water injection