Chapt15 lecture

William P. Cunningham University of Minnesota Mary Ann Cunningham Vassar College Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Chapter 15 Lecture Outline *

Outline The Atmosphere and Climate Zones of the Atmosphere Greenhouse Effect Convection Currents Weather Winds and Ocean Currents Frontal Systems and Cyclonic Storms Climate Variability El Nino Climate Change and its Effects Reducing Greenhouse Gases

The Atmosphere is a Complex System Weather – short-lived, local patterns temperature and precipitation. Climate – long term patterns of temperature and precipitation. The atmosphere is composed of: Nitrogen gas Oxygen gas Water vapor Aerosols-minute, suspended particles & droplets

The Zones of the Atmosphere Troposphere 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

The Zones of the Atmosphere Stratosphere 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 is being depleted by pollutants including Freon and bromine.

The Atmosphere and Climate Mesosphere 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 )

Absorbed Solar Energy 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. Some of this solar energy is reflected back by portions of earth’s surface covered with water, snow, ice and sand.

Absorbed vs. Reflected Solar Energy Surfaces that reflect energy have a high albedo (reflectivity). Fresh clean snow 80-85% Surfaces that absorb energy have low albedo . Dark soil 3% Overall net average albedo of earth = 30% Absorbed energy evaporates water and runs photosynthesis. Absorbed energy released as heat.

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 The atmosphere transmits sunlight while trapping heat.

Greenhouse Effect Greenhouse Gases -Gases in the atmosphere, especially carbon dioxide, water vapor, nitrous oxides, methane and other 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.

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.

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.

Weather Events Follow General Patterns Weather - physical conditions in the atmosphere (humidity, temperature, air pressure, wind and precipitation) over short time scales Why does it 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.

The Coriolis Effect Makes Winds Curve 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 . Winds and currents appear to move clockwise in Northern Hemisphere and counterclockwise in the Southern Hemisphere. These curving pattern results from the fact that the earth rotates in an eastward direction as winds move above it.

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, These winds spiral clockwise out of an area of high pressure in the Northern Hemisphere and spiral counterclockwise into an area of low pressure. You can see these on weather maps.

Jet Streams Jet streams - hurricane force winds at the top of the trophosphere which follow an undulating path

Ocean Currents Modify Weather 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.

Billions of People Rely on Seasonal Rains 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.

Frontal Systems Create Local 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.

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 differences exist. H u rricanes (Atlantic) Katrina in 2005 caused greatest natural disaster in North American history. Typhoons (Western Pacific) Cyclones (Indian Ocean)

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

Natural Climate Variability Climates shift on scales of decades, centuries or millenia. Ice cores - collected from glaciers, have revolutionized our understanding of climate history. Cores reveal patterns of dark and light bands caused by annual accumulations of snow. 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.

Major Climatic Changes The data show that: There is a close correlation between carbon dioxide concentration and temperature of the atmosphere Gradual climate changes give species time to adapt. Abrupt climatic changes have catastrophic effects on living things as organisms are unable to adjust before conditions exceed their tolerance limits. These changes can cause species extinctions.

Historical Climate Changes A historical climate change that had disastrous effects on human populations was the Little Ice Age that began in the 1400’s. Temperatures dropped, crops failed, fish migrations changed and shipping lanes were blocked with ice. Ice cores show drastic changes may have occurred over short periods of time (years or decades rather than centuries).

Earth’s Movements Explain Some Cycles Milankovitch Cycles - periodic shifts in Earth’s orbit and tilt which change distribution and intensity of sunlight.

ENSO is an Ocean/Atmosphere Cycle There are also decades long oscillations in the oceans and atmosphere. The ocean and the atmosphere have regular patterns of flow or currents, but these may shift from time to time. Winds and rains may change as a consequence of these shifts. El Niño or ENSO is an example of such a shift.

ENSO ENSO, The El Niño Southern Oscillation, occurs when warm surface waters in Pacific Ocean move 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 allow upwelling of cold, nutrient rich waters off west coast of South America benefiting fisheries. Every three-five years the Indonesian low collapses and the mass of warm surface water surges back east

ENSO Affects North America During an El Niño 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 Niña years, hot, dry weather is often present. Resulting high sea surface temperatures cause hurricanes to be more violent. Long term studies of coral reefs indicate that ENSO events are becoming stronger and more irregular due to global warming.

Multi-Decade Oscillations Pacific Decadal Oscillation - very large pool of warm water moving back and forth across the North Pacific every 30 years. This affects salmon harvests in Alaska and the Pacific Northwest. North Atlantic Oscillation, or NAO is another oscillation which occurs between Canada and Europe. Evidence for this phenomenon can be seen in tree-ring growth records.

Recent Changes are Unusually Rapid Many scientists believe that anthropogenic climate change is the most important environmental issue of our time. The earliest data on came from an observatory on Mauna Loa volcano in 1957. Initial measurements showed carbon dioxide levels increasing at 0.5% per year since data collection began. Levels have risen from 315 ppm in 1958 to 387 ppm in 2009. If this trend continues, we could double atmospheric CO 2 levels by 2109.

CO 2 Measurements from Mauna Loa

The IPCC Provides Data to Policy Makers Intergovernmental Panel on Climate Change or IPCC -an international group of scientists and governmental representatives formed to review the scientific evidence for climate change. The 2007 report stated that there is a 90% probability that the observed climate changes are the result of human activities. The report projects warming of 1-6 °C by 2100 with the best estimate being 2 to 4°C (3.2 to 7.8°F) For perspective, there has only been a 5°C rise since the last ice age 20,000 years ago.

Affects of Global Warming People will experience more extreme weather including droughts, floods, heat waves and hurricanes. These could have disastrous economic and human costs. Estimates published in 2009 project a sea level rise of 1 meter by 2100. This could flood low-lying coastal cities like New Orleans, Miami, Boston, New York and London and Mumbai.

Projected Sea Level Rises by 2100

How Do We Know it is Human Caused? Traditional controlled experiments on the climate are impossible, but complex computer models can be used to simulate climate based on known natural fluctuations and human inputs. If a computer model can accurately predict past climate, this is an indication of its effectiveness at predicting future climate. When the models are run without human inputs the predictions don’t match historical climate records. When they are run with the human inputs they do predict historical climate records.

Climate Models vs. Observed Climate Change

CO 2 is the Most Important Green House Gas Carbon Dioxide – emissions have increased 80% from 1970 to 2004 fossil-fuel burning is the major human caused source of carbon dioxide (constitutes 77%). Methane – ruminants and rice paddies are sources Absorbs more infrared than CO 2 . Nitrous Oxide – vehicle engines, agriculture processes are major sources. Highly effective at capturing heat energy. The relative effects of each green house gas can be seen by converting them to CO 2 Equivalents.

Warming Ability of Various Green House Gases

Contributors to Global Warming

Climate Change Effects: Why Should I Care? 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

Observations of Climate Change 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. 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.

Observations of Climate Change 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 as they hunt on pack ice, which is declining. Antarctic ice shelves are disappearing. Penguins declined 50% in last 50 yrs. Alpine glaciers are retreating all over the world. The oceans are absorbing and storing more heat. Sea level has risen 15 to 20 cm in last century.

Observations of Climate Change Oceans are absorbing some of the extra CO 2 but that is acidifying the ocean and damaging corals. 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. Animals breeding and migratory schedules are changing. Some species are declining or going extinct due to warming temperatures and loss of habitat.

Observations of Climate Change Corals are bleaching due to warming water temperatures in the oceans. Storms are becoming stronger and more damaging. ie. Increased number of category 5 hurricanes in recent years.

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. Those in richer countries will be able to blunt the effects of climate change. Those in poorer countries will suffer the most; at least 200 million people in will become refugees of floods or victims of drought.

4 Steps For Combating Climate Change Implement emissions trading Technology sharing with less developed countries Reducing deforestation Helping poorer countries adapt to climate change

Flooding, Storms and Disease Melting of the glacial ice caps in Greenland and Antarctica could raise global seal levels 100 meters flooding coastal areas where 1/3 of the world’s population live. 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.

Envisioning Solutions Kyoto Protocol (1997) Called on nations 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 China and India were both exempt from this agreement. 126 countries ratified the Protocol. The legislatures of both Australia and the U.S. declined to ratify the agreement.

2 Main Options for Controlling Emissions Cap and Trade Controls: legal limits on emissions are set and countries that want to emit more must purchase emissions credits from others. This approach is favored under Kyoto. Voluntary Limits: governments, communities and individuals voluntarily cut emissions for altruistic, economic or conservation reasons. New local initiatives suggest this approach may work.

Cap and Trade A global market for trading carbon emissions has already developed. In 2006 700 million tons of carbon credits were exchanged with a value of 3.5 billion dollars. This market may grow to 500 billion dollars a year by 2050. Some large businesses like BP America, Dupont and GE are for this approach if the rules are clear and fairly applied.

Stabilization Wedges Could Work Now By utilizing Wedge Analysis, the problem of climate stabilization can be broken down into smaller, bite-sized peices. To stabilize carbon emissions we would need to cut 7 GT (gigatons) over the next 50 years. Doubling vehicle efficiency, and halving the miles we drive would save up to 1.5 GT. Installing energy efficient appliances, lighting and insulating building could save another 2 GT. Capturing and storing carbon emissions from power plants and gas wells could save another GT.

Alternative Practices Can Be Important Carbon capture and storage is beginning to be practiced. Some companies, like Norway’s Statoil, are pumping carbon dioxide into an aquifer beneath the seafloor via a gas well. The carbon is sequestered, the company avoids carbon taxes on emissions and the increased pressure on oil reserves enhances oil recovery.

Should We Focus on Methane Instead? Methane is a more powerful absorber of heat energy than carbon dioxide. James Hansen of NASA believes that focusing on reducing methane emissions might be the best short-term strategy to slow global warming. Reducing methane emissions from landfills, rice paddies, oil wells and coal mines could reduce warming. Reducing the number of ruminants could help also.

Regional Initiatives Are Emerging The U.K., New Zealand, Germany and many other countries are working to reduce carbon emissions voluntarily. The United Kingdom has rolled back its CO 2 emissions to 1990 levels and is aiming for a 60% reduction by 2050. New Zealand has pledged to be the first Carbon Neutral country-reducing green house gas emissions to zero. Germany has reduced CO 2 by 10%.

Conservation and Renewable Energy Offer the Best Solutions Denmark gets 20% of its electricity from windmills, and plans to increase that to 50%. China reduced its emissions 20% between 1997 and 2005 by implementing more efficient burning of coal in power plants and industry. Individual cities like Copenhagen, Helsinki and Toronto have pledged to reduce carbon emissions by 20% by 2010. Benefits: Conservation efforts save energy costs and shifting to renewable energy frees us from dependence on foreign oil.

Chapt15 lecture

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Chapt15 lecture