Climate Change, Greenhouse Effect and Global Warming
Earth’s Climate: A Dynamic SystemThe Earth is a unique planet where our atmosphere, the oceans and soils combine to support a webof life of diversity and continual change. The daily needs of more than six billion people now stressthe limits of this naturally regulated system.
Is Our Climate Changing?
Weather changes both rapidly and slowly. The passage of a thunderstorm can change a bright sunnyday into a dark, windy, rainy one in less than an hour. Farmers know that in one year the amountand timing of rainfall can be nearly ideal for growing crops, while the next year might bring droughtor floods. In some years no hurricanes reach the Atlantic Coast, while in other years coastal statesare battered by one storm after another. All of these things are dictated by the Earth’s climate.
Is the Earth’s climate changing? One extreme summer in the United States can’t answer thatquestion. Our picture of the climate develops slowly as we watch many seasons pass. Only bycomparing measurements taken over many years and decades can we sense the shifting patterns ofclimate. The hottest ten years in recent history have taken place since 1987. Climate is a complexsystem that ties together the atmosphere, oceans, land surface and the living kingdoms of plants andanimals. Climate describes the weather over a long period of time. The Earth has experienced major climate changes long before humans inhabited the planet. Thedinosaurs roamed a world much warmer than today. The Earth has also gone through an ice age thatsent massive glaciers spreading over North America and Europe. Animals and plants have beenforced to either go extinct or to adapt to new conditions. Such natural shifts in climate havedistinguished the different eras in Earth’s history. Climate change is a natural phenomenon due tosolar variability, volcanic activity, biological evolution and El Nino. These changes can influenceglobal warming and global cooling.
We now face the prospect of a different kind of climate change. Many scientists believe this changeis being brought on primarily by human actions. Our industry, agriculture and daily living causeimportant gases such as carbon dioxide (CO2) and methane (CH4) to accumulate in the atmosphere.Scientists predict severe consequences may await us in the not too distant future if we do not changeour behaviors.
The Light from AboveIf we were to look at our Earth from space, we would see a multi-colored sphere. Clouds and snow-coated lands create patches of cottony white that interweave with the royal blue background of theoceans. Breaks in the cloud cover would reveal the continents as brown hues while lighter splotchesof color indicate desert regions. The white areas make Earth a bright planet. About 30% of the sun’s radiation gets reflectedimmediately back into space by the Earth’s atmosphere and snow. This is called the Albiedo Effect.Solar energy that doesn’t reflect off clouds and snow is absorbed by the atmosphere and surface of
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How do scientists study past climates?
If scientists had to rely on writtenweather records for historical climateinformation, they would be in trouble.Such records only exist for the last 150years or so. However, clues in theenvironment can provide informationfrom thousands of years ago.
Ice cores -- Ice in polar-regions containsair bubbles trapped thousands of years inthe past. Scientists can check the gases inthe bubbles and provide a good estimateof the temperature at that time. Also, thethickness of the ice layers givesinformation about past climates.
Tree rings -- Trees can live for centuries,and for each year of their lives they add aring of growth to their diameter. Thewidth of these rings can give scientistsinformation about climate during thatyear of growth.
Fossils -- The bones of long-deadanimals indicate which species lived incertain areas and when they were there.Since each species has a set of food andtemperature requirements, scientists candeduce the climate of their time and area.
Sediment cores -- Columns of sedimentfrom lake bottoms contain pollen grainsin each layer. The farther down the layer,the older the sediment. After determiningthe age of the layers, scientists can studywhat plants were growing when thesediment was deposited.Archaeological records -- Humans haveleft their traces throughout the world forages. How they lived and what theyneeded to survive provide importantclues about the climates theyexperienced.
the Earth. As the surface warms, it sends infrared radiation, or heat, back toward space. This type ofradiation resembles the warmth we feel when sitting at a distance from a hot stove or campfire.
Aside from gases in the atmosphere, clouds alsoplay a major climatic role. By reflecting solarradiation away from Earth, some clouds cool theplanet. Satellite measurements have recentlyproved that clouds exert a powerful cooling effecton the Earth. In some areas, such as the tropics,heavy clouds may markedly warm the regionalclimate by reflecting the infrared heat backtowards the Earth. This trapping of heat near thesurface contributes to the Earth’s naturalgreenhouse effect.
Clouds and greenhouse gases fit into somethingcalled the global radiation budget. Just like awell-constructed economic budget, the radiationbudget must balance itself. Solar energy reachingEarth must equal the energy leaving the planetotherwise the oceans would eventually boil awayor freeze solid. Scientists warn that we are currently upsetting theEarth’s radiation balance through activities such asburning fossil fuels and cutting forests. Theseactions cause carbon dioxide and other gases toaccumulate in the air and therefore strengthenEarth’s greenhouse effect. We expect the planet’ssurface will warm up until a new radiation balanceemerges.
The Greenhouse EffectLooking at other planets, we can see both strongerand weaker greenhouse effects than that of Earth.Our nearest neighbor, Venus, has a thick cloak ofcarbon dioxide that heats the planet’s surface to anaverage of 4200 C. Mars, with a mean surfacetemperature hovering around –500C, has a verythin atmosphere that provides little greenhousewarming.
Earth’s atmosphere lets in rays of sunshine andthey warm the surface. The planet keeps cool byemitting heat back into space in the form ofinfrared radiation. But while the atmosphere is
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fairly transparent to sunshine, it is almost opaque to infrared radiation. It traps the heat inside muchlike a garden greenhouse. About 70% of the solar energy that reaches Earth passes through theatmosphere and is absorbed at the surface. About 90% of the infrared radiation emitted by thesurface is re-absorbed by the atmosphere before it can slowly escape to space. The layer of airsurrounding the Earth contains important gases such as water vapor and carbon dioxide. Thesegases absorb the heat radiated by the Earth’s surface and reemit their own heat at much lowertemperatures. The atmosphere “traps” the Earth’s radiation. This planetary warming mechanism iscalled the “greenhouse effect.” The greenhouse effect is good, without it we would not be able tolive here. The atmosphere saves usfrom a frigid fate.
If all greenhouse gases wereremoved from the atmosphere, theaverage surface temperature ofEarth would drop from its currentvalue of 60°F (15°C) to about 0°F(-18°C). Earth would be a frozenand nearly lifeless planet withoutthe greenhouse effect. It is thedistinctive molecular structures ofthe greenhouse gases that makethem strong absorbers and emittersof infrared radiation. About 99% ofair molecules are nitrogen (N2) andoxygen (O2). They have simple structures consisting of two identical atoms. They have a relativelyminor effect on the transmission of solar and infrared radiation through the atmosphere because ofthis simple structure.
Molecules with three or more atoms like water vapor (H2O), carbon dioxide (CO2), ozone (O3) and ahost of other trace gases can efficiently absorb and emit (give off) infrared energy. Though some ofthese gases make-up only a tiny fraction of the atmosphere they can make significant contributionsto the greenhouse effect. The molecule that makes the largest contribution is water vapor. Watervapor is the most important greenhouse gas. Because we have no direct control over it we focus onthe other greenhouse gases that we have more control over. An average water molecule stays in theatmosphere only a few days from the time it evaporates from the surface to the time it falls out ofthe atmosphere as precipitation. Because of this the water vapor content of the atmosphere adjustsquickly to changes in surface temperature.
Why Are Greenhouse Gas Amounts Increasing?Carbon dioxide gas makes-up a tiny fraction of the atmosphere. Only about one air molecule inthree thousand is CO2. Yet, despite their small numbers, CO2 molecules can have a big affect on theclimate. Carbon dioxide (CO2) has a much longer lifetime in the atmosphere than water vapor. Itcan take 100 to 200 years to establish a new atmospheric balance if CO2 is suddenly added to theatmosphere. That’s because the carbon in CO2 is cycled between the atmosphere and the ocean orland surface by slow chemical and biological processes. Plants, for example, use CO2 to produceenergy in a process known as photosynthesis. Through millions of years of Earth’s history, trillions
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of tons of carbon were taken out of the atmosphere by plants and buried in sediments that eventuallybecame coal, oil or natural gas deposits. In the last two centuries humans have used these deposits atan increasing rate as an economical energy source. In a similar way, cement manufacture releasescarbon atoms buried in carbonate rocks. Today human activities release about 5.5 billion tons ofcarbon to the atmosphere every year through burning fossil fuels and cement manufacturing.Approximately another 1.5 billion tons per year are released through land use changes such asdeforestation. These releases result in an increase of atmospheric CO2 of about one-half percent peryear. The burning of coal, oil and natural gas and the destruction of forests has raised the totalamount of atmospheric carbon dioxide by nearly 30% since the beginning of the industrialrevolution in the early 1800’s.
Other naturally occurring greenhouse gasessuch as methane and nitrous oxide have beenincreasing. Entirely man-made greenhousegases such as CFC’s have also been introducedinto the atmosphere. Many of these gases areincreasing more rapidly than carbon dioxide.The amount of methane, or natural gas, in theatmosphere has doubled since the IndustrialRevolution.
Greenhouse Gases and Global WarmingSince the Industrial Revolution, however,atmospheric concentrations of the mostimportant human-influenced greenhouse gases– CO2, methane and nitrous oxide – haveincreased at an unnatural rate. In the last 200years, CO2 levels have risen almost 30%,methane levels have gone up 145%, and nitrous oxide levels have increased by 15%. Eachgreenhouse gas differs in its ability to absorb heat in the atmosphere. Where are all these "extra"greenhouse gases coming from? They are coming from our daily activities. Large-scale burning offossil fuels for industry and motor vehicles, intense agricultural activity, population growth, landpractices, mining and other human activities pump more and more greenhouse gases into theatmosphere, creating a heightened greenhouse effect that leads to a higher average globaltemperature. This is called global warming. While water vapor is the most important GreenhouseGas, humans have very little control over it. Carbon dioxide (CO2) is the greenhouse gas that humans are contributing to most directly. Carbondioxide is a colorless, odorless gas which was naturally in the air before humans were around. Nowwe continue to emit the gas into the air with our cars, our manufacturing, burning of rain forests andour cutting down of trees. The destruction of trees creates a shortage of plants to remove CO2 fromthe air. We also release CO2 into the atmosphere when we burn fossil fuels for the generation ofelectricity.
Methane (CH4), also called marsh gas, is another greenhouse gas that was in the air, naturally,before humans. It is used in industries as starting material for many other chemicals. This gas is
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lighter than air, colorless, odorless, nontoxic, and highly flammable. It is created naturally fromdecomposing matter in swamps. Methane comes from cow burps, coal mining, natural gas fumes,landfills and wood burning. Methane is also the gas your stomach may release after a hearty meal.In other words, when animals burp, they release methane and add to global warming. Methane trapsover 21 times more heat per molecule than carbon dioxide. CFCs or chlorofluorocarbons (also called Halocarbons) were never naturally in the air. They werefirst manufactured in the 1940s. Because they do not readily react with other chemicals they canhave a lifetime in the atmosphere of more than 100 years. This gas was used mostly in aerosolsprays cans such as spray paint and hair spray, refrigeration units, air conditioning, cleaningsolvents and packing materials. Using CFCs in aerosol sprays has now been banned in the United
States and most other parts of the world. Not only is it a greenhouse gas and keeps infrared lightfrom leaving, but it also damages the ozone layer. The ozone layer is a layer in the upperatmosphere that keeps the sun's harmful ultraviolet rays from reaching us. Global warming andozone destruction have little to do with each other. CFCs trap more heat than any of the othergreenhouse gases. Nitrous oxide (N2O) is given-off during agricultural and industrial activities and during combustionof solid waste and fossil fuels. Nitrous oxide (N20) is more known under the nickname laughing gas.Nitrous oxide, also called nitrogen monoxide, is a colorless, odorless, nonflammable gas which mayalso attack the ozone layer. It is used in industry as an aerosol propellant. Nitrous oxide absorbs 310times more heat per molecule than carbon dioxide.
Sources and Sinks
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The elements that compose greenhouse gases, (carbon, oxygen, nitrogen, etc.), normally cyclethrough the environment between sources and sinks freely. Sources release elements to theatmosphere. Sinks store the elements. Soil, oceans and trees tend to act as natural sinks for carbon.Each year hundreds of billions of tons of carbon, in the form of CO2, are absorbed by soils, oceansand trees. When trees are cut down and burned, the stored carbon is released into the atmosphere ascarbon dioxide. The burning of trees is a carbon source.
For two centuries, we've been releasing greenhouse gases into the atmosphere at unprecedentedrates while destroying forests and other natural sinks that could absorb those gases. We've created agreenhouse that’s a little too effective while trying to improve the quality of life.
The Consequences of Too Many Greenhouse GasesIf the climate cycle were to follow its natural course, in a few thousand years the Earth would startsliding into another ice age. But our activities threaten to send the climate speeding in anotherdirection toward globalwarming. The build-up ofgreenhouse gases and othergases have alreadyenhanced the Earth’sgreenhouse effect. It maytake several decades to feelthe warming becauseatmospheric temperatureswill rise significantly onlyafter the oceans of the worldhave slowly warmed. The increase in temperaturepostponement may seemlike an advantage. It givesus more time to prepare.However, the time lag couldlead us to underemphasizethe importance of theproblem while we still have a chance to prevent drastic climate change. We have already committedourselves to some degree of warming even if we could instantly halt the buildup of greenhousegases in the atmosphere. As human population and economic activities continue to grow, carbon dioxide emissions coulddouble again in the next three decades unless the nations of the world limit their consumption offossil fuels. Such action would benefit society in many ways. Through energy conservation we cansave substantial amounts of money and help reduce our nation’s dependence on foreign fuels.Despite our uncertainty about future climate change we are already beginning to take certain stepsthat will slow the buildup of greenhouse gases.
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Global Warming and WisconsinGlobal warming: It’s a phrase that has been heard on weather broadcasts and news reports, inscience classrooms and around supper tables since the early 1990s. It is a concept that seems farremoved from our everyday lives, something that concerns scientists digging into polar ice capsthousands of miles away – not us in Wisconsin. But global warming and the changes it could causein world climate should concern us.
Historical records indicate the average global temperature increased in Wisconsin by 0.50 to 10 Fbetween 1890 and 1990. Thus, the Earth has warmed. This is where the term global warmingcomes from. In the next 100 years, scientists predict the temperature may rise another 20 to 60 F.Such increases have occurred previously in Earth’s history, but never over such a short time span. Infact, the average global temperature has risen more in the last century than at any time in the past10,000 years.
The great majority of scientific research agrees that between now and the end of this century theglobe will continue to warm up. It is difficult to predict what an increase in global temperature willbring because of the various climatic factors. However, the results could significantly alter life inWisconsin. All of the items listed below are potential changes Wisconsin could face:
wetter winters and drier summers with longer, hotter and more frequent heat waves
weather and climate changes that could require farmers to raise different crops
dairy cattle and other livestock stressed by heat exhaustion and growing pest populations
poor air quality and higher concentrations of ground-level ozone could causes health problems
warmer and more shallow river waters could hurt populations of cold-water fish like trout
denser algae blooms and lower oxygen levels in ponds and lakes
more frequent floods, droughts, forest fires and damaging storms
changes in tree species that could affect the forestry industry and wildlife populations
increases in disease-carrying insect populations
The Effects of Global Warming on WisconsinBecause the models scientists use to study climate change are not precise enough to offer specificpredictions for an area as small as the state of Wisconsin, the following discussion is taken frompredictions for the upper Midwest region. While it’s fairly safe to say that global climate changewon’t turn our state into a tropicalparadise, scientists agree that itcould significantly alter the way welive.
Weather and ClimateThe upper Midwest may becomewarmer and wetter, with the
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average temperature increasing by about 40 F. The increase doesn’t mean we’d simply up the dailytemperature by 4 degrees. A more likely scenario is that summer heat waves would be longer andhotter and nighttime winter temperatures would not sink so low. Precipitation could increase by asmuch as 10% on average, but much of the increased precipitation would come in the form of intensestorms, leading to flooding and more runoff. Precipitation patterns could also change, with morerain coming in the winter and less in the summer. Less rain in the summer, paired with increasedevaporation caused by warmer temperatures, could trigger severe summer droughts.
Water ResourcesLake Superior water levels could drop over time by 1 to 1.5 feet, while Lake Michigan levels couldfall 3 to 8 feet. Such drops could result from longer and drier summers during which more of thelakes’ waters would be claimed by evaporation.
Winters might have less snow and shorter periods of snow cover. Lowered Great Lakes levels couldstrike a heavy blow to industries like shipping and hydropower generation. Smaller inland lakescould also get shallower. Some ponds and wetlands might disappear, jeopardizing wildlife habitat,tourism and recreation industries. Groundwater levels could drop significantly threatening drinkingwater quality and quantity due to increased concentrations of pollutants.
Warmer water would encourage algae blooms and other aquatic plant overgrowth in the summer.This would transform clear blue waters into a thick, smelly pea soup that turns off boaters, anglersand swimmers. Algae blooms also make survival difficult for fish and other aquatic species. Cold-water species like trout could decline in number or disappear from their traditional areas altogether.Decreased winter ice cover could disturb both lake ecology and the ice fishing season.
AgricultureAnything that affects farming affects the state’s economy. Southern Wisconsin farms may begin toresemble those in present-day Kansas. Wheat would do well, but the ideal range for corn andsoybeans would shift northward, and these crops might not grow as well in the soils of northernWisconsin. High levels of carbon dioxide in the atmosphere may actually increase crop production,because certain plants can become larger and more productive in a CO2–rich environment.However, gains in crop productivity might be counter-balanced by more frequent and severedroughts, and by more weed, pest and disease problems.
Dairy and other livestock farmers might see productivity decline as their herds suffer from heatstress, the feed supply is disrupted (from changing crop yields), and the water supply reduced.Warmer, longer summers might encourage the growth of pest populations that could further stresslivestock and spread disease. Forests and WildlifeAs temperature and precipitation patterns change, habitat ranges for plants and animals are expectedto shift northward. Some species might be able to migrate with their ideal habitat, but others,especially those already endangered, could face extinction. Researchers predict that mixed northernhardwood and oak forests would be transformed to oak savannas and grasslands within 30 to 60years. Typical northern forests could completely disappear from Wisconsin along with the easternhemlock and the sugar maple.
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Human HealthMore frequent and severe heat waves would threaten the elderly, especially those living alone, andpeople suffering from cardiovascular and respiratory diseases. The U.S. Environmental ProtectionAgency (EPA) projects that a 30 F warming could almost double heat-related deaths in Milwaukeeduring a typical summer, from 30 to about 55.
A longer, hotter summer, along with increased emissions from power plants trying to keep up withgreater air conditioning demands, would likely intensify air pollution problems. This could result inmore and more serious cases of asthma, emphysema and lung disease for Wisconsin residents.Wisconsin’s allergy season could lengthen because some plants would flourish in the extendedsummer. Warmer weather might also be beneficial to disease-carrying insects like mosquitoes andticks, leading to more cases of Lyme disease, tick-borne encephalitis and possibly even malaria.Finally, more frequent severe weather events like forest fires, floods and dangerous storms couldcause injuries and take lives and damage properties. All of these would increase insurance rates.
Responding to a Global ThreatThe Wisconsin Department of Natural Resources (DNR) has completed several studies showing thatthe use of energy-efficient technologies could reduce the state’s emissions of greenhouse gases withlittle or no net cost. One study showed that if Wisconsin adopted improved energy efficiencymeasures, we could realize a 12.5 million ton decrease in the growth of greenhouse gas emissionsby 2010 (compared to projected levels) and save $490 million in energy expenditures at the sametime. Another study predicted that investing in energy efficiency measures could create a $490million increase in disposable income, a $41 million increase in gross state product and 8,500 newjobs in 2010.
In 1992, 154 nations and the European Union adopted the United Nations Framework Conventionon Climate Change. It was a voluntary agreement to stabilize greenhouse gas emissions at 1990levels. In December 1997 at a United Nations meeting in Kyoto, Japan, some industrializedcountries went a step further and agreed to the Kyoto Protocol, which required developed nations toreduce their greenhouse gas emissions to an average of 5% below 1990 levels by 2008-2012.Specific reduction commitments varied among nations. If the protocol had gone into effect for theU.S., it would have required the U.S. to reduce greenhouse gas emissions to 7 percent below 1990levels. The U.S. refused to sign the Kyoto Protocol. At current rates of activity, our nation stands toincrease its emissions to 30% above 1990 levels by 2010. Our country is already the world’s largestemitter of greenhouse gases, contributing approximately 23% of global emissions despite havingonly 5% of the world’s population.
How Can We Help?Many of the things we can do to reduce greenhouse gas emissions offer personal benefits as well.The biggest contribution individuals can make is to use less energy. By tuning cars, insulatinghomes and using energy-efficient appliances, we can decrease our use of fossil fuels and savemoney. We can car pool, use public transportation, walk or bike to our destinations. These activitiescut fuel consumption, decrease traffic congestion, decrease emissions of other air pollutants andmay even help us become healthier. Finally, we can purchase items with reusable, recyclable, or
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reduced packaging. All of these options help decrease the amount of energy and resources beingused to make new packaging.
Those willing to invest even more in guarding against climate change have further options.Alternative energy sources like solar power, wind power and geothermal heat pumps can supplyhome energy needs. Vehicles using propane, natural gas or ethanol, fuels that burn cleaner thangasoline, are already on the roads. Hybrid cars, which use electricity from batteries along withgasoline for power, are another viable alternative for transportation. Solar-powered cars and fuel-cell cars, powered by hydrogen, may be available within the next 10 years.
Global Warming and Sea Level RiseOne of the most significant potential impacts of climate change is sea level rise that may causeflooding of coastal areas and islands, shoreline erosion, and destruction of important ecosystemssuch as wetlands. River water salinity may also be an issue. As global temperatures increase, sealevel rise already underway is expected to accelerate due to a thermal expansion of upper layers ofthe ocean and melting of glaciers. Over the last 100 years, the global sea level has risen by about 10 to 25 cm. On this time scale, thewarming and the consequent thermal expansion of the oceans may account for about 2-7 cm of theobserved sea level rise, while the observed retreat of glaciers and ice caps may account for another2-5 cm. Other factors are more difficult to measure. The rate of observed sea level rise suggests thatthere has been a net positive contribution from the huge ice sheets of Greenland and Antarctica, butobservations of the ice sheets do not yet allow meaningful measurement estimates of theircontributions. The ice sheets remain a major source of uncertainty in accounting for past changes insea level because of insufficient data about these ice sheets over the last 100 years.
Warmer temperatures also increase precipitation. Snowfall over Greenland and Antarctica isexpected to increase by about 5 percent for every 1°F warming in temperatures. Increased snowfalltends to cause sea level to drop if the snow does not melt during the following summer, because theonly other place for the water to be is the ocean. (The amount of water in the atmosphere is less than
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Dairy and other livestock farmers may see productivity decline as a result of __43__ in theiranimals.
If the U.S. had adopted the Kyoto Protocol, we would have been required to reduce greenhouse gasemissions to __44__% below 1990 levels by 2008-2012. However, at the current rates our nationstands to increase its emissions to 30 percent above 1990 levels by 2010.
The U.S. is the world’s largest emitter of greenhouse gases, contributing approximately __45__% ofglobal emissions despite having only __46__% of the world’s population.
The biggest contribution individuals can make is to __47__.
Considering all of these factors, the Intergovernmental Panel on Climate Change (IPCC) estimatesthat sea level will rise __48__ cm by the year 2100.
List the nine potential changes Wisconsin could face if global warming continues: (write out)
49. 50. 51. 52. 53. 54. 55. 56. 57.
List five of the clues scientists use to study past climates: 58. 59. 60. 61. 62.
Short Answer Questions: Write the answers to these questions in your notebook.
63. What is the difference between climate and weather?64. What is the greenhouse effect and why is it important to life on Earth?65. What is the difference between global warming and climate change? 66. How does nature contribute to climate changes?67. How have humans contributed to the global warming?
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