Ch. 15 - Air, Weather, and Climate 1 Outline The Atmosphere and Climate Convection Currents Greenhouse Effect Weather Winds Frontal Systems Cyclonic Storms Climate El Nino Climate Change Kyoto Protocol 2 Saturday, 18 June 2011 1
The Atmosphere and Climate Weather - daily temperature and moisture conditions in a place Climate - a description of the long-term weather pattern in a particular area 3 4 Saturday, 18 June 2011 2
Troposphere The Atmosphere and Climate Ranges in depth from 18 km over the equator to 8 km over the poles. - All weather occurs here. - Convection currents redistribute heat and moisture around the globe. - Air temperature drops rapidly with increasing altitude. Tropopause - transition boundary that limits mixing between the troposphere and upper zones 5 Stratosphere The Atmosphere and Climate From tropopause up to about 50 km - Has almost no water vapor, but 1000X more ozone than the troposphere - Ozone absorbs ultraviolet light, which warms upper part of stratosphere. - Ozone protects all life on Earth since UV radiation damages living tissues. - Ozone being depleted 6 Saturday, 18 June 2011 3
Mesosphere The Atmosphere and Climate Middle Layer Thermosphere Begins at 80 km - Ionized gases and high temperatures Lower thermosphere has ions which are struck by high energy radiation. Aurora borealis (northern lights) 7 8 Saturday, 18 June 2011 4
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. 9 Energy Balance 10 Saturday, 18 June 2011 5
Energy and the Greenhouse Effect Surfaces that reflect energy have a high albedo (reflectivity). Fresh clean snow 80-85% Surfaces that absorb energy have low albedo. Dark soil 3% Net average of earth 30% Absorbed energy evaporates water and runs photosynthesis. Absorbed energy released as heat. 11 Energy and the Greenhouse Effect Most solar energy reaching the Earth is near infrared (short wavelength). Energy reemitted by the earth is mainly far infrared radiation (long wavelength, heat) - Longer wavelengths are absorbed in the lower atmosphere, trapping heat close to the earth s surface. Greenhouse Effect Atmosphere transmits sunlight while trapping heat. 12 Saturday, 18 June 2011 6
Greenhouse Effect Gases in the atmosphere, especially carbon dioxide and water vapor, are the substances that retain heat. Burning fossil fuels releases extra carbon dioxide. Deforestation destroys carbon sinks. Positive feedback loop - poles covered with ice reflect solar radiation back into space. Now that ice is melting, open water is absorbing more heat, which in turn is melting more ice, leading to more warming. 13 Convection and Atmospheric Pressure Much of solar energy absorbed by the Earth is used to evaporate water. Energy stored in water vapor as latent heat. When water vapor condenses, heat energy is released. Heat and water move from warmer areas near the equator towards cooler areas at poles. Heat redistribution prevents extreme temperature fluctuation. 14 Saturday, 18 June 2011 7
Circulation Patterns 15 Convection Currents Releasing latent heat causes air to rise, cool, and lose more water vapor as precipitation. Warm air close to equator vs. cold air at poles also produces pressure differences that cause weather. Air near surface warms and becomes less dense than the air above it; rises above cool air creating vertical convection currents. - Low pressure - air is rising - High pressure - air is sinking Pressure differences cause winds. 16 Saturday, 18 June 2011 8
Convection Currents 17 Weather Happens Weather - physical conditions in the atmosphere (humidity, temperature, air pressure, wind and precipitation) over short time scales Rain - Air cools as it rises, and water condenses as air cools. - Cooling occurs because pressure decreases as air rises. - Condensation nuclei (tiny particles) must also be present to have precipitation. 18 Saturday, 18 June 2011 9
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. The curving pattern results from the fact that the earth rotates in an eastward direction as winds move above it. Winds and currents move clockwise in Northern Hemisphere and counterclockwise in the Southern Hemisphere. 19 Coriolis Effect Major zones of subsidence occur at about 30 o North and South latitude. Where dry, subsiding air falls on continents, it creates subtropical deserts. On a regional scale, the Coriolis effect produces cyclonic winds, which spiral clockwise out of an area of high pressure in the Northern Hemisphere and counterclockwise into an area of low pressure. You can see these on weather maps. 20 Saturday, 18 June 2011 10
Jet streams - hurricane force winds at the top of the trophosphere which follow an undulating path Jet Streams 21 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 due to temperature and saltiness of water Gyres - huge cycling currents carrying water north and south Currents can shift abruptly. 22 Saturday, 18 June 2011 11
Seasonal Winds and Monsoons Monsoon - seasonal reversal of wind patterns caused by differential heating and cooling rates of oceans and continents Most prevalent in subtropical and tropical areas. Tilt of Earth s axis changes location where the Sun is most intense over the course of the year. Places where the Sun shines most directly have evaporation and convection currents which bring thunderstorms. Seasonal rains support tropical forests and fill great rivers such as Ganges and Amazon. 23 Summer Monsoons in India 24 Saturday, 18 June 2011 12
Frontal Weather Cold Front - boundary formed when cooler air displaces warmer air Cold air is more dense, thus hugs ground and pushes warm air up. - Warm air cooled adiabatically (without loss or gain of energy), precipitation. Warm Front - boundary formed when warm air displaces cooler air Warm air is less dense and slides over cool air, creating a long wedge-shaped band of clouds and precipitation. 25 26 Saturday, 18 June 2011 13
Cyclonic Storms When rising air is laden with water vapor, latent energy released by condensation intensifies convection currents and draws up more warm air and water vapor. Storm cell will exist as long as temperature differential exists. - Hurricanes (Atlantic) Katrina in 2005 caused greatest natural disaster in North American history. - Typhoons (Western Pacific) - Cyclones (Indian Ocean) 27 Cyclonic Storms Tornadoes - swirling funnel clouds Rotation not generated by Coriolis forces Generated by supercell frontal systems where strong dry cold fronts collide with warm humid air - Greater air temperature differences in the spring, thus more tornadoes Downbursts - disorganized supercells that cause downdrafts and straight line winds 28 Saturday, 18 June 2011 14
Cyclonic Storms 29 Studying Climate Ice cores - collected from glaciers reveal light and dark bands caused by annual snow accumulation on glacier Gas bubbles can be analyzed for atmospheric composition. Ash and sulfur deposits correlate with volcanic eruptions. Vostok ice core gives us a record back 420,000 years. 30 Saturday, 18 June 2011 15
Data show that: Climate Abrupt climatic change has catastrophic effect on living things as organisms are unable to adjust before conditions exceed their tolerance limits. Species may become extinct. There is a close correlation between carbon dioxide concentration and temperature of the atmosphere. 31 Climate What causes climate change? Sunspot cycles Solar magnetic cycles Cycle of shift in angle of moon alters tides and currents. Milankovitch Cycles - periodic shifts in Earth s orbit and tilt which change distribution and intensity of sunlight - Ice cores show drastic changes may have occurred over short periods of time (years to decades). Volcanic eruptions can cool planet suddenly. 32 Saturday, 18 June 2011 16
Milankovitch Cycles 33 El Nino/Southern Oscillation 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. Surface waters driven westward by trade winds are replaced by upwelling of cold, nutrient rich waters off west coast of South America. Nutrients supply food for fisheries. Every three-five years the Indonesian low collapses and the mass of warm surface water surges back east and we call this an El Nino. 34 Saturday, 18 June 2011 17
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 from California to the Midwest - During intervening La Nina years, hot, dry weather is often present. - ENSO events are becoming stronger and more irregular due to global warming. 35 El Nino/Southern Oscillation High sea surface temperatures cause hurricanes to be more violent. Pacific Decadal Oscillation - very large pool of warm water moving back and forth across the North Pacific every 30 years. Affects fishing harvest. 36 Saturday, 18 June 2011 18
37 Global Warming is Happening Most important environmental issue of our time In 2007, the Intergovernmental Panel on Climate Change released its fourth report. Represents a consensus by more than 90% of all scientists working on climate Gives a probability value of 90% that the warming we are now seeing is caused by humans 38 Saturday, 18 June 2011 19
Global Warming Range of temperature increase predicted to be from 1.1 to 6.4 C (2 to 11.5 F) by 2100 depending on population growth, energy conservation, etc. Best estimate is 1.8 to 4 C (3.2 to 7.8 F) To put that in perspective, there has been a 5 degree C rise since the middle of the last ice age (about 20,000 years ago). 39 Global Warming Most people will experience more extreme weather including droughts, floods, heat waves and hurricanes. These extremes have increased significantly in the last decade. In the worst outcome, we could see millions of human deaths. Sea levels are projected to rise 17-57 cm (7 to 23 in). If we do nothing, Greenland s ice will melt and raise sea levels 20 ft. 40 Saturday, 18 June 2011 20
Global Warming If Greenland s ice melts, a great deal of land will be flooded including: Most of Florida Some of the Gulf Coast Most of Manhattan Shanghai Hong Kong Tokyo Bush administration praised the report but said it opposes mandatory cuts in greenhouse gas emissions as too costly. 41 Sources of Greenhouse Gases Carbon Dioxide - fossil-fuel burning - Atmospheric levels increasing steadily - Most important cause of warming Methane - ruminants, rice paddies - Absorbs more infrared than CO 2. Chlorofluorocarbons (CFC s) - refrigerants - Declined in developed countries, but now produced in developing nations. Nitrous Oxide - burning organic material 42 Saturday, 18 June 2011 21
Carbon Dioxide Concentrations on Mauna Loa 43 Sources of Greenhouse Gases U.S. has less than 5% of world s population but produces 28% of carbon dioxide. China, with 1.3 billion people, is second. Japan and Europe produce half as much carbon dioxide per person as the U.S. 44 Saturday, 18 June 2011 22
45 Evidence of Climate Change is Overwhelming As best as can be determined, the world is now warmer than it has been at any point in the last two millennia, and, if current trends continue, by the end of the century it will likely be hotter than at any point in the last two million years. American Geophysical Union 46 Saturday, 18 June 2011 23
Evidence of Climate Change is Overwhelming Ave. global temperature climbed 0.6 C (1 F) in last century. 19 of 20 warmest years in the past 150 yrs have occurred since 1980. Hottest year since temperature records were begun was 2005; 2007 is expected to surpass it. Poles are warming fastest (4 C, 7 F over past 50 years). Permafrost is melting in Alaska and Canada and houses, pipelines and trees are being toppled. 47 Evidence of Climate Change is Overwhelming Arctic Sea ice is half as thick as it was 30 years ago, and the ocean area covered by ice has decreased by 1 million sq. km. in 30 yr. Polar bears are dying. Antarctic ice shelves are disappearing. Penguins declined 50% in last 50 yrs. Glaciers are melting all over the world. Sea level has risen 6 to 8 inches in last century. 48 Saturday, 18 June 2011 24
Evidence of Climate Change is Overwhelming Oceans have been absorbing some of the extra CO 2 but that is acidifying the ocean and damaging coral. Growing seasons are lengthening in Northern hemisphere. Some animals are breeding earlier or extending their range. Others are disappearing. Droughts are more frequent and widespread and storms more severe. 49 Global Warming will be Expensive At present, reducing greenhouse gas emissions would cost 1% of world GDP according to Stern report. (IPCC report says less than that.) If we delay, it could cost as much as 20% of world GDP. Energy production will need to be 80% decarbonized by 2050 to stabilize climate. Ethical issue Poor will suffer the most; at least 200 million people will become refugees of flood and drought. 50 Saturday, 18 June 2011 25
Steps For Combating Climate Change Emissions trading markets already exist Technology sharing Reducing deforestation Helping poorer countries adapt to climate change Tropical areas will not change as much as middle and high latitudes. If both Greenland and Antarctica melt, 1/3 of Earth s population will be displaced. - South Pacific island nation of Tuvalu already abandoned due to climate change 51 Combating Climate Change Insurance companies have $2 trillion in insured properties along U.S. coastlines at risk from flooding or severe storms. Infectious diseases will increase as insects that spread them are able to move to places where they could not live before. West Nile, malaria, and dengue fever have appeared in North America. Melting of permafrost may release stores of methane hydrate. Uncertainty about whether that would increase warming or cooling. 52 Saturday, 18 June 2011 26
Predicted Warming for 2090-2099 53 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. took a leading role in the 1990s, but Bush declined to honor U.S. commitments. 54 Saturday, 18 June 2011 27
Kyoto Protocol Bush claimed reducing carbon emissions would be too costly for the U.S. But in 2007, the CEOs of the 10 largest business conglomerates in the U.S. called for legislation to reduce greenhouse gases. A single national standard would be better for business than a patchwork of state and local rules. Companies engaged in international business will have to modify their products anyway to compete abroad. 55 Controlling Greenhouse Emissions Reducing carbon dioxide levels Renewable energy sources - Double average fuel economy - Switch to efficient lighting and appliances - Wind turbines - Biofuels Capture and store carbon dioxide - Planting vegetation - Injection into wells 56 Saturday, 18 June 2011 28
Progress Made United Kingdom has rolled back its CO 2 emissions to 1990 levels and is aiming for a 60% reduction by 2050. Germany has reduced CO 2 by 10%. Denmark gets 20% of its electricity from windmills, and plans to increase that to 50%. China reduced its emissions 20% between 1997 and 2005. (At its present rate, U.S. will be 25% above 1990 emissions in 5 years. No progress.) 57 Carbon Management Capturing and storing carbon dioxide Build trees in which calcium hydroxide solution would absorb carbon dioxide Plant forests Fertilize the oceans with iron to permit phytoplankton growth, which would take up carbon dioxide Inject carbon dioxide underground or in ocean 58 Saturday, 18 June 2011 29
Synthetic Trees that Capture Carbon Dioxide 59 Saturday, 18 June 2011 30