Seperate Subjects, 1 page each Essay Example | Topics and Well Written Essays - 1750 words

Seperate Subjects, 1 page each - Essay Example Through exploration of these ratios using statistics, can help in limiting the inter-industry effect of inflation. Statistics also help in giving data in a summary form the prices of foreign currencies. This information is useful in controlling inflation rate from outside the country, and thus leads to the success of domestic industries. Statistics are helpful when doing comparison of different economy sectors or organizations Sai Ram Centre for Financial Management Research, 2006). Multinational Companies carry out Research and Development (R&D) to determine their share of R&D in foreign countries. By comparing the ratios, the MNCs are able understand which sector or organization to give more effort in terms of resources, or which country to increase their share of R&D. This has boosted many business organizations as R&D has helped to come up with innovative means of doing business Sai Ram Centre for Financial Management Research, 2006). To increase shareholder value in an organization, correlation is used to quantify association of the shareholder value and the earnings per share or net income. Statistics are important in valuation and monitoring of business operational alternatives (Narayanan, 2004). From previously recorded statistics a manger can alter or adjust a business strategy. However, in making decision regarding the shareholder value, the share price should not be used to make decision as this has no causation relationship with the shareholder value (Glene, 2003). Scenario forecasting is important in any organization that wishes to have a successful planning in future. Scenario forecast prompts team members in an organization to think outside the box by trying to anticipate dynamics that may affect business activities or the team. Scenario forecast goes past simple, straight-line extrapolation of the project performance of a company to portray how different factors interact to

Assessment of National Express Group Operations, Macroeconomic Essay

Assessment of National Express Group Operations, Macroeconomic Environment and Challenges - Essay Example This essay presents an informative analysis of the National Express Group company economic position. The company was founded in 1972 by the state owned National Bus Company. The company has grown tremendously since its privatization in 1988 from a small transport service provider to a multinational firm. It currently has its operations in UK, Canada, Morocco, Spain, US and Portugal. The company has recently expanded its business in other parts of Europe also. The company currently runs more than 1600 busses across UK and is a leader in urban bus service provider. It also provides bus service in North America in which daily 1 million students go to school. National Express Group is focused in achieving excellence in their existing markets and to explore new market opportunities to drive their company to the utmost peak. Its main objective is the growth of its business through customer satisfaction Macroeconomic environment consists of those variables upon which the company has no control. Companies cannot control the macroeconomic factors but can minimize its impact by taking strategic decisions accordingly. These factors exist outside a company and usually have a great affect on the functioning of the company. In UK, the market conditions were challenging but still due to strong market hold and flexible coach supply model, the company delivered high profit for the business. As of National Express bus service in UK, there was a rise in cost for the company during the year 2009 due to the increase in the cost of fuel.

Bad School System Essay Example for Free

Bad School System Essay What are schools doing for us? If nothing then what can we do to improve them? I think they aren’t doing anything. I have never really thought about this idea until I started research. I think that I am fairly smart, but it is more of after school rather than school itself. I was watching a TED TALK from Ken Robinson and he was talking about how schools kill creativity. He talks about how schools are good at making people who do their jobs successfully. He also says that those same people are doing that job because they don’t have any other choice. By showing this he is trying to show that school kills creativity. Salman Khan the founder of Khan Academy talks about how students don’t get to work on their own pace. Dave Eggers the founder of 826 Valencia talks about how students need 1-1 attention to learn their talents. Ken Robinson has many different videos on school all talking about how school has problems that need to be solved. The one that I watched was â€Å"Ken Robinson says schools kill creativity†. He talks about how school trains you in a way that creates a fear of making mistakes. He says, â€Å"If you’re not prepared to be wrong, then you will never be original†. We are being educated out of creativity. Teachers are not ready to have things be wrong. When grading test or any kind of work there is no such thing as maybe, it is just right or wrong. There are always those kids who are over the top smart and there are those kids that are very creative but not as smart. In this scenario you know that the kid who has the brains is going to get the popularity. Nobody is going to go to the creative kid for help even though he/she might have something worth saying. Then those creative kids will also have to adapt to the school system and eventually lose their creativity. Salman Khan has one very important video on TED and it talks about how students do really get to learn on their own pace in school. The TED TALK is called â€Å"Let’s use video to reinvent education†. In this video he talks about his website www.Khanacademy.com. In this website he has different topics for which he has videos for. He also has sort of an online learning system on the same website. In that learning system they want you to master different concepts that you are having trouble with. So they show you videos on how to do the problem then set you on your own. If you still don’t have perfection then they allow you to repeat. They want you to master the concept by letting you do the whole process as many times as you like. By this you are allowed to learn at your own pace. In school you learn a chapter take a test then move on. Even if you didn’t understand you move on, also the students who get like 90 to 99.9% they still might have some problems that they didn’t understand. I also experienced Khan Academy, I have an account and I am always using it when I need help on something. Dave Eggers has one video on TED and it talks about why students are happier to go to tutoring rather than school itself. In his TED TALK â€Å"Once Upon a School† he shows the audience of a place that he created called 826 Valencia. This is a shop that he founded in which he connected a newspaper editor center, a pirate shop, and a after school tutoring center. He says that students come there running after school to do homework. That’s not really something that you think of. The students get help on any HW especially their English homework. He has his Newspaper crew and volunteers help students 1-1 on HW. He has students write books and then publishes the books. He says that students need 1-1 time with whomever they are working with. In school students don’t really get 1-1 time during school to talk about things that they are having trouble with and stuff like that. In a year he has over 1,400 volunteers helping run 826 Valencia. He thinks that if students are able to have 1-1 time with teachers on their work then they would be more creative. They students would never know if they were doing well or if they needed to improve in certain areas. If you haven’t watched this TED TALK them I recommend every one the watch it. All three of these guys show great ways to improve the School system. These guys are already doing it outside of school, which shows that our School System isn’t really great. There are many problems with our School System we just never think about them as students. You would never think that School would kill your creativity, but when you think about it†¦

Assignment On Aircraft Power Systems

Assignment On Aircraft Power Systems In this assignment, I intend to provide a brief presentation about the principle of operation of the aircraft electrical power systems, specifically, Integrated Drive Generators (IDG) in a modern aircraft. I will compare and contrast the fluid and electrical methods of power generation and give a brief on the safety precautions to be followed when handling aircraft electrical power supplies and during a functional test. There are various kinds of power generation on an aircraft, namely electrical (generators batteries), fluid (hydraulics pneumatics). Depending upon the application, the power sources may vary. AIRCRAFT ELECTRICAL SYSTEM The main function of any aircraft electrical system is to generate, regulate and distribute the electrical power in the aircraft. Modern aircrafts use more electrical power as they are equipped with more Electronic Flight Instrument System (EFIS). This is done so as to reduce pollution in the environment, for a clean and safe flight. Electrical power is used to operate: Aircraft Flight Instrument- Electronic Centralized Aircraft Monitoring (ECAM) Essential Systems- Primary Flight Display (PFD), Navigation Display (ND) Passenger Services- In-Flight Entertainment (IFE) Most of the aircraft systems use a power standard of 115 [emailprotected] 400Hz; 28VDC. There are various electrical power sources on the aircraft: Engine Driven AC Generators (EDG) Auxiliary Power Units (APU) Ram Air Turbine (RAT) Battery Supply External/Ground Supply (Spoor, 2012) Components in an electrical system include: AC Generator/Alternator produces AC power. Constant Speed Drive Unit (CSDU) regulates the rotating speed (input) to deliver a constant output from the engine to the generator. Integrated Drive Generator (IDG), Generator and CSDU connected either coaxially or side-by-side. Mostly coaxial connection. Transformer Rectifier Unit (TRU) converts the AC power to DC power Generator Control Unit (GCU) monitors and controls the generator output. Each engine powers up one or more generators. Airbus A380 has four engines and four generators. Whereas, Boeing 777 has two engines and two generators. The power produced by these generators is used to power up the entire aircraft. (Boeing, 2012) All the other power sources, except external supply, are used in case of emergencies only. External power supply is used on ground when the engines and the APU are not running. It is supplied via Ground Power Unit (GPU). GPU can be portable or stationary and they provide AC power through the external plug on the nose of the aircraft. They can be used to power up an entire aircraft or a specific area in the aircraft. (Spoor, 2012) Figure : Aircraft Electrical System (Classic Jet Sims, 2012) AIRCRAFT HYDRAULIC SYSTEM The principle of a hydraulic system is to convert fluid power into mechanical power and then use it for various applications on the aircraft, such as extension/retraction of landing gears, flaps, and speed and wheel brakes. The power source here is the hydraulic fluid. The pressure for generating the hydraulic power is supplied by the Engine Driven Pump (EDP) and the Electric Motor Driven Pump (EMDP). They are both mounted on the engines. Commonly used hydraulic fluids on the aircraft are: MIL-H-5606 (Mineral Based Fluid) MIL-H-83282 (Synthetic Hydrocarbon Based Fluid) MIL-H-87257 (Same as MIL-H-83282, but it has been improved in its low temperature viscosity) MIL-H-8446 (Phosphate-Ester Based Fluid) (Wikipedia, 2012) Special care must be taken when handling the hydraulic fluid. Some of the hydraulic fluids are skin/eye irritant. Also it is extremely important for the fluid to be free from any contamination for flight safety. Advantages of the hydraulic system as a power source includes: Lightweight Easy installation Simplified Inspection Minimum Maintenance Approximately 100% system efficiency, with only negligible loss due to friction. (EAC, 2012) Figure : Basic Hydraulic System (Free Online Private Pilot Ground School, 2006) COMPARISON OF AIRCRAFT ELECTRICAL AND HYDRAULIC SYSTEM FEATURE ELECTRONIC HYDRAULIC Construction Power is generated by the engine, by rotation of turbine shaft. Power is generated by incompressible hydraulic fluid. Pressure for hydraulic actuation is supplied by EMDP and EDP. Similar to that of an electric circuit. Components include: Generators/Alternators, Batteries, Switches, Bus bars, Fuses, Circuit Breakers, Voltage Regulators, Ammeters, and Wires. (Free Online Private Pilot Ground School, 2006) Components include: Reservoir, Pump, Hydraulic Fluid, Accumulators, Actuators, Filters, Hydraulic Fuses, Tubing, Pipes, Valves, and Seals. Uses Lights, Radio Equipment, Indicators, Warning Systems, Heaters, Starting motor. (FlightLearnings, 2012) Extension/retraction of landing gears, flaps, and speed and wheel brakes. Principle of Operation Generate, Regulate and Distribute electrical power generated. Work is done by moving an incompressible fluid, Pascals Law. (EAC, 2012) EMERGENCY DEPLOYMENTS IN EVENT OF GENERATOR(S) FAILURE In case of main engine driven generator (EDP) failure, there are various methods to ensure continued power supply for safe landing: Auxiliary Power Unit (APU) Ram Air Turbine (RAT) Battery When the main engine generators fail, APU or RAT is deployed. When the secondary methods fail, batteries are used as the last resort for a safe landing and evacuation. AUXILIARY POWER UNIT (APU) Auxiliary Power Units (APUs) is a small gas turbine engine which provides electrical, hydraulic and pneumatic power (depending on the design) for ground or in-flight operations. It is also used as a backup source in emergency situations. It is commonly found on large aircrafts. It is usually located in the tail end of the aircraft. When started, it normally runs on 100% speed. It produces 115VAC @ 400Hz. Some can also generate 28VDC. The main purpose of the APU is to start the engines in the aircraft. This is because the engine requires high rotational speed for its self-sustaining operation. In this case, APU is started by battery or hydraulic accumulator and then used to generate the necessary rotational speed. It is also used to run the equipment when the engines are shutdown. This is used for air conditioning for the passengers prior to engine start. However, it can also be connected to a hydraulic pump to power up hydraulic equipment (flaps and flight controls). (Wikipedia 2012) RAM AIR TURBINE (RAT) Ram Air Turbine is a small airflow driven turbine that is connected to either a hydraulic pump or an emergency alternator or a main generator. In normal flight, it is stowed away in closed compartment in wing or fuselage. It is deployed only when there is total power loss due to engine failures. It provides enough power to run the critical systems, such as, flight controls. The power generated by the RAT depends on the airspeed. More the speed, more the power generated will be. Some aircrafts use RAT in normal operation. For example, in crop dusting RAT is used to power up the chemical sprayer. (Wikipedia, 2012) BATTERY Aircraft batteries are used to start the engines or the APU. But they are also used in emergency situations as a last resort for safe landing. There have been cases where it has been used to restart the engines even after engine flame-out. They also act as a buffer for the DC connections. It regulates the voltage to ensure the power quality for the equipment connected to it. Two types of batteries are used in aircrafts today, Lead-acid and Nickel Cadmium (Ni-Cd). Lead-acid batteries are either valve regulated or vented. They are used in light and general aircrafts. Ni-Cd batteries are used in larger aircrafts. Lead-acid batteries are generally heavier and have less capacity than the Ni-Cd ones. (Dr. Thomas, 2010) Figure : Lead-Acid Battery (Chief Aircraft, 2012) Figure 4: Nickel-Cadmium Battery (Surplustraders.net, 2012) AIRCRAFT ELECTRICAL SYSTEM USING FREQUENCY WILD AC GENERATOR From 1950s to early 1960s some turboprop aircrafts used frequency wild, now Variable Frequency (VF) system. Airbus A380 and Boeing 787 Dreamliner are some of the modern civil aviation aircrafts that have adopted the VF system again. Figure : Simplified Frequency Wild System (Scribd, 2012) CONSTRUCTION As shown in Fig.4, the Variable Frequency Generator (VFG) is directly connected to the engine gear box. (Langlois, 2004) states: VFG is a conventional wound rotor synchronous alternator. There is no CSD or IDG in this system. This is done so as to improve the reliability of the system and also to reduce the weight of the aircraft. Airbus A380 uses aluminium cables instead of copper for weight reduction. The system is also fully computerized. Contactors and Breakers have been replaced by solid-state devices for increased reliability and performance (Global Aircraft, 2012). OPERATION Frequency Wild AC power can only be supplied to the resistive circuits such as the electrical heater, engine de-icing heaters, windshield heating, etc. as shown in Fig. 4. The AC power generated is sent to the TRU where the voltage is stepped down from 360Hz-760Hz (Langlois, 2004) to 28V and then rectified to DC voltage. Then it is used by the DC components. CONTROL PROTECTION A traditional Constant Frequency unit has only a constant frequency of 400Hz voltage supply. A constant speed drive unit drives the generator. It is also expensive and not easy to maintain. A VFG is flexible as it can handle a range of frequencies rather than a constant one. In this unit, there is no CSD or IDG. It is more advantageous over Constant Frequency Unit because: It has low maintenance Long lifespan Cheaper Process temperature is controlled within VFG itself. Equipment protection from excess torque damage The variable frequency generator (VFG) is used on applications with a high percentage of resistive AC or DC loads and provides power to many of the next generation aircraft. Hamilton Sundstrands variable frequency starter generator (VFSG) and motor controller system provides main engine start and control. The voltage is controlled around the generator. This is done by controlling field strength of the AC generator by feedback signal from the voltage regulator, which keeps the voltage constant irrespective of the speed and load variations. VFGs are preferred over DC systems because they were much less affected by poor brush performance at higher altitudes and they had better power to weight ratio. AC/DC ELECTRIC MOTORS AND ACTUATORS PERFORMANCE DC actuators are typically high-speed reversible series-wound motors. Their output is converted to driving torque using step-down gearbox. These motor actuators are self-contained units, as they combine both electrical and mechanical devices. They can exert linear thrust over a short distance. AC MOTOR DC MOTOR

American Public Education Essay examples -- School Education

The American public educational system is filled with an assortment of problems. Most students are graduating with less knowledge and capability than similar students in other industrialized countries. Classroom disruptions are surprisingly common, and in some classrooms, nearly continuous. The public education system is having difficulty adjusting to the no child left behind act. The No Child Left Behind(NCLB) is a landmark in education reform designed to improve student achievement and change the culture of American’s schools. The primary sponsors of NCLB were President George W. Bush and Sen. Ted Kennedy of Massachusetts, a decades-long advocate for raising the quality of public education. This law was signed in 2001. Unfortunately not everything was taken into consideration for the long term affect. There needs to be a middle ground for individualized learning because each child learns at a different pace. According to LdPride.com there are roughly three different ty pes of learning styles ranging from visual, auditory, and kinesthetic. Visual learners learn through pictures and visually stimulation. Auditory learners learn though sound and music. While kinesthetic learn through hands on material. So while you may have a teacher standing up giving history lessons though a lecture, only the auditory learns are really picking up what the lesson is.The education system should be one that meets the needs of the parents, the teachers, and the students. The view point of all involved should be taken into consideration through the entire process. During the last 10 years, there has been an explosion in our knowledge of ways in which humans develop and learn. The No Child Left Behind Act of 2002(NCLB) was initi... ...LB) was passed with strong bipartisan backing by the House of Representatives on December 13, 2001 by a vote of 381-41, and by the Senate on December 18, 2001 by a vote of 87-10. President George W. Bush signed it into law on January 8, 2002. America's Promise Alliance | 1110 Vermont Avenue, N.W., Suite 900 | Washington, DC 20005 The New York Times Dropout Rates for Minority Students Keep Rising in Cities Published: September 28, 1994 SOURCE: U.S. Department of Education, National Center for Education Statistics. (2010). The Condition of Education 2010 (NCES 2010-028) 1990 K Street, NW Washington, DC 20006, USA Phone: (202) 502-7300 U.S. Secretary of Education Margaret Spellings www2.ed.gov/news/pressreleases/2007/03/03122007.html http://www.ldpride.net/learningstyles.MI.htm http://www.ndt-ed.org/TeachingResources/ClassroomTips/Learning_Styles.htm

romeo and juliet vs. west side story :: essays research papers

Romeo and Juliet’s balcony scene vs. Westside Story’s rooftop scene   Ã‚  Ã‚  Ã‚  Ã‚   The romantic tension between Romeo and Juliet and Tony and Maria in Shakespears original play and its modern day remake, Westside Story, is what makes them have such passionate and entrancing scenes. The main reason for romantic tension in these two plays is because the two couples can’t be together like they want to be. There are many different aspects that create different quality of romantic tension in these two scenes. Although the two plays have similar plots, the romantic tension between the two lovers is very different because of the setting, the language and the circumstances in which the lovers face.   Ã‚  Ã‚  Ã‚  Ã‚  In Romeo and Juliet the setting takes place on Juliet’s balcony after she has just come home from the Capulet ball and has met fair Romeo. She is speaking aloud to herself when Romeo hears her and interrupts. This scene contains so much tension because Romeo has snuck into her garden and if he were to be caught, he would be killed. In Westside Story, however, the fear is of Bernardo coming home and seeing them together creates a different kind of tension.   Ã‚  Ã‚  Ã‚  Ã‚  The language used in these two scenes is quite different. In Romeo and Juliet the majority of the scene is of the two lovers confessing their undying love for each other using beautiful language and many metaphors. They also discuss marriage and serious commitments to each other. In Westside Story, this scene is spent singing to each other, which I find, makes it more romantic but has less tension. They also don’t seem as serious about commitment towards each other.   Ã‚  Ã‚  Ã‚  Ã‚  The circumstances that Romeo and Juliet and Tony and Maria are in differ in many ways. For example, Romeo and Juliet come from rival families that would not allow them to be together. Tony and Maria, on the other hand, come from families of different backgrounds, which isn’t nearly as bad. Tony and Maria’s parents have no say in whether or not they are together, it is just their friends and gangs that are against it.

Are Humans Responsible for Global Warming?

Are Humans Responsible for Global Warming? A REVIEW OF THE FACTS APRIL 2007 AUTHORS James Wang, Ph. D. Bill Chameides, Ph. D. Are Humans Responsible for Global Warming? The case for attributing the recent global warming to human activities rests on the following undisputed scientific facts: †¢ Carbon dioxide (CO2) is a greenhouse gas that warms the atmosphere. †¢ Since pre-industrial times, atmospheric CO2 concentrations have increased from about 280 parts per million (ppm) to over 380 ppm.Current concentrations of CO2 and other greenhouse gases are unprecedented in at least the last 650,000 years, based on records from gas bubbles trapped in polar ice. †¢ Independent measurements demonstrate that the increased CO2 in the atmosphere comes from burning fossil fuels and forests. The isotopic composition of carbon from these sources contains a unique â€Å"fingerprint. † †¢ Since pre-industrial times, global average temperatures have increased by about 0. 7? C , with about half of the warming occurring over the past few decades. The only quantitative and internally consistent explanation for the recent global warming includes the intensified greenhouse effect caused by the increase in CO2 and other greenhouse gases. The U. S. National Academy of Sciences—the independent organization of the country’s most renowned scientists established by Congress to advise the nation on scientific and technical issues—has concluded: â€Å"The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action. Some argue that the recent global warming is due to natural fluctuations and not to human activities. This argument and its fallacies are discussed below. Argument 1: CO2 is not coming from human activities CO2 has natural sources: volcanoes for example. All animals exhale it. How can human activities be affecting the concentration of CO2 on a global scale? The Facts Natural processes e mit large quantities of CO2 into the atmosphere, but they also remove it—at nearly identical rates.This balance maintained the concentration of CO2 at a stable level for thousands of years prior to the Industrial Revolution. In the case of global warming, the question is: What is causing the increase in CO2 concentrations? The answer turns out to be incontrovertible. The isotopic composition of carbon in atmospheric CO2 provides a unique â€Å"fingerprint† that tells scientists that the lion’s share of the additional CO2 accumulating in the atmosphere is from the burning of fossil fuels. Argument 2: No one really knows why the climate variesThe global climate has fluctuated considerably over the Earth’s history, either for unknown reasons or because of â€Å"internal variability† in the climate system. We do not know enough about the climate system to attribute the present global warming to any specific cause. The Facts It is true that the Earthâ⠂¬â„¢s climate has exhibited wide swings over geologic time due to natural processes. However, scientists have reasonable qualitative explanations for most of the significant variations in 2 limate over geologic time;1 they can be largely attributed to specific processes, not to unknown internal oscillations. Many of the major climatic changes can be traced to changes in the Earth’s orbit around the sun (Hays et al. Science, 194, 1976, pg. 1121). Others can be linked to specific events (such as the impact of a comet or meteorite or the assembly or breakup of supercontinents) that led to large changes in the concentration of atmospheric greenhouse gases.For more recent times (the past millennium), scientists have been able to quantitatively attribute the major temperature fluctuations to changes in solar activity, volcanic eruptions, and human-produced greenhouse gases and particulate pollution. These natural processes can not explain the current warming. Argument 3: The Medie val Warm Period disproves global warming The current warming trend is analogous to the Medieval Warming Period (MWP). Since the MWP was obviously a natural event, the current warming is also likely caused by natural processes. The FactsThe Medieval Warm Period (MWP) refers to a relatively warm period lasting from about the 10th to the 14th century. 2 However, the initial evidence for the MWP was largely based on data3 gathered from Europe, and more recent analyses indicate that the MWP was not a global phenomenon. A number of reconstructions of millennium-scale global temperatures have indicated that the maximum globally averaged temperature during the MWP was not as extreme as present-day temperatures and that the warming was regional rather than global. Perhaps the most well-known of these is that of Michael Mann and colleagues (Nature, 392, 1998, pg. 779).Their reconstruction produced the so-called â€Å"hockey stick† graphic that contributed to this conclusion in the 2001 assessment of the Intergovernmental Panel on Climate Change: â€Å"The†¦'Medieval Warm Period' appear(s) to have limited utility in describing trends in hemispheric or global mean temperature changes in past centuries. † The accuracy of the â€Å"hockey stick† graphic was widely discussed in the press when the Mann et al. methodology was criticized by McIntyre and McKitrick (Geophys. Res. Lettr, 32, 2005, pg. L03710). Less attention was given to subsequent studies, such as that of Moberg and colleagues (Nature, 433, 2005, pg. 13) and Osborn and Briffa (Science, 311, 2006, pg. 841) that were based on different, independent methodologies but reached conclusions similar to Mann. Observations of melting high altitude glaciers are perhaps even more telling. Andean glaciers that have been intact for more than 5,000 years are now rapidly melting (Thompson et al. Proc. Nat. Acad. Sci. , 103, 2006, pg. 10536). If the MWP was truly global, these glaciers would not have sur vived. More generally, it is a logical fallacy to argue that because the climate has changed in the past due to natural causes, the current warming trend must also be due to natural causes.The debate over the magnitude and causes of earlier climate change such as the MWP is of scientific interest, but it does not invalidate the considerable direct scientific evidence that human-produced greenhouse gases have been causing the Earth to warm recently. Argument 4: Recent predictions of a new ice age disprove global warming In the 1970s climate scientists were saying an ice age was imminent. Now they say the Earth is warming. They don’t know what they are talking about. The FactsThe Earth’s climate for the past 2 million years has been characterized by ice ages lasting close to 100,000 years, punctuated by relatively short (10,000- to 30,000-year) warm periods or â€Å"interglacials. † The swing from glacial to interglacial is caused by changes in the Earth’s orbit around the sun amplified by natural feedbacks involving greenhouse gases (Hays et al. Science, 194, 1976, pg. 1121). The Earth entered the present interglacial about 10,000 years ago. All things being equal (i. e. , in the absence of a large human-produced source of CO2) it is highly likely that the Earth will swing back into a glacial period or ice age.But this will not occur for thousands of years. 3 As early as the 19th century, scientists recognized that greenhouse gases warm the planet, and that increases in atmospheric carbon dioxide could lead to global warming on time scales of decades to centuries—much shorter than the fluctuations related to ice ages and interglacials. Around the same time, global temperatures began to increase and scientists became increasingly concerned that humans were interfering with the climate. In the 1950s the upward trend in global temperatures unexpectedly halted and temperatures declined somewhat.This led some scientists to become c oncerned about global cooling and, in turn, to headlines in the popular press about an imminent ice age. What the skeptics fail to admit is that within the scientific literature—as opposed to the popular press—global warming remained a serious concern. Many scientists of the time argued that whatever the cause of the cooling, natural or otherwise, it would be eventually overshadowed by the warming effect of carbon dioxide. In 1979, the National Academy of Sciences warned that a doubling of carbon dioxide would increase global temperatures by 1. 5 to 4. oC (Carbon Dioxide and Climate: A Scientific Assessment, NAS Press, 1979) and shortly thereafter a resumption of the upward trend in temperatures was detected. Over the past quarter century, scientific research on global climate change has intensified, and programs on an international scale have been organized. More and more data are included in computer models that are capable of recreating past trends and more precisel y predicting future scenarios. We now know that the mid-20th century pause in global warming was caused by pollution from burning coal, which produced tiny particles or aerosols that blocked the energy from the sun.As aerosol emissions were controlled but greenhouse gas pollution continued to increase, the cooling effect of the aerosols was overwhelmed by the greenhouse gases, and global warming resumed. Argument 5: Scientists cannot â€Å"prove† current warming is not natural Climate scientists can not prove that the current warming is not due to natural processes and therefore can not claim with certainty that the warming is due to human interference. The Facts It is of course true that, in a complex system like climate, it is virtually impossible to prove a negative; i. e. that natural processes are not causing the current warming. What we can do is eliminate every possible natural explanation that can be posited. Thermodynamics tells us that the warming of the Earthâ€⠄¢s lower atmosphere must arise from one or more processes that supply excess heat to the lower atmosphere. Besides the greenhouse effect, the viable processes are (1) increased output from the sun; (2) increased absorption of heat from the sun due to a change in the Earth’s planetary reflectivity or â€Å"albedo†; and (3) an internal variation in the climate system that transfers heat from one part of the Earth to the atmosphere.Direct observations confirm that none of these explains the observed warming over the latter half of the 20th century. For example there has been no appreciable change in solar output over the past two decades (see Figure 1). Figure 1. Change in solar output from 1980 to 2005. Figure 1 shows the relative change in solar output determined from two of satellite measurements over a two-decade period. The data show variability in solar output corresponding to the 11-year sunspot cycle, but no secular trend. Source: After Lean and Froelich, 2006. 4 Satellite data reveal that the Earth’s reflectivity increased (causing cooling instead of warming) in the ’60’s, ‘70s, and early ‘80s and has decreased modestly since. 4 The overall warming from the recent decrease in reflectivity is also small compared to the greenhouse warming. In the case of internal variations, the ocean is the only viable reservoir of internal heat that could have caused the atmosphere to warm on decadal time-scales. However, observations show that the heat content of the ocean has increased instead of decreased over the past few decades (See Figure 2).This indicates that the atmosphere has been a source of heat to the ocean rather than vice versa. Moreover, the amount of heat increase in the ocean is consistent with what is needed to balance the Earth’s energy budget given the excess heating from the enhanced greenhouse effect and the amount of excess heat observed to be stored in the atmosphere (Hansen et al. Science, 3 08, 2005, pg. 1431). In other words, the amount of heat stored in the ocean over recent years matches the amount of heat that models predict should be trapped on Earth due to the increase in greenhouse gases. Figure 2.Change in heat content of ocean 1955 to 2005 Source: After Levitus et al. 2005. FIGURE 2 SHOWS THE RELATIVE CHANGE IN THE HEAT COTENT OF THE OCEAN FROM 1955 TO 2005 BASED ON A COMPREHENSIVE ANALYSIS OF OCEAN TEMPERATURE MEASUREMENTS. THE DATA SHOW SHORT TERM VARIABILITY BUT A CLEAR UPWARD TREND ON DECADAL TIME-SCALES. Conclusion †¢ The Medieval Warm Period does not represent an analogy to the warming of the late 20th century, for which scientists have independent evidence of human causation, and the evidence strongly suggests that the MWP was a regional, rather than a global phenomenon. Our understanding of the climate system is sufficient to provide qualitative models for most global or hemispheric climatic variations over geologic history and quantitative models for variations over the past millennium. †¢ The Earth’s climate may return to ice age conditions in thousands of years, but this does not preclude devastating effects from global warming over the next few centuries. 5 †¢ All known natural explanations for the current global warming trend have been eliminated by direct observations.The human-intensified greenhouse effect provides the only quantitative explanation for the current warming trend. About the authors Dr. Wang received his doctorate from Harvard University and works as a climate scientist at Environmental Defense. He has published several peer-reviewed papers on the global methane budget and was the author of â€Å"The Latest Myths and Facts on Global Warming,† which was read into the congressional record by Senator John McCain in 2005. The report is available at http://www. undoit. org/pdfs/mythsvfacts. pdf. Dr. Chameides, chief scientist at Environmental Defense, is a member of the U.S. National A cademy of Sciences and has been named a National Associate of the National Academies. He is also an American Geophysical Union Fellow, and has received the American Geophysical Union's Macelwane Award. Dr. Chameides has served as editor of the Journal of Geophysical Research and is the author or coauthor of more than 120 scientific publications and five books. He received his doctorate from Yale University. The explanations are qualitative instead of quantitative because we do not have quantitative data from these events in the distant past to construct their exact histories. It has been suggested based on temperature reconstructions and model simulations that the MWP may have been caused by increased solar activity or a dearth of volcanic activity. 3 th Because worldwide temperature measurements do not exist before the 19 century, temperature records before th the 19 century are based on reconstructions of the temperature from the variations in temperature-sensitive proxies (e. g. , tree rings, isotopes in ice cores). 4 These variations are possibly due to changes in the concentrations of atmospheric aerosols produced from the burning of fossil fuels and biomass. 1 6 Are Humans Responsible for Global Warming? Are Humans Responsible for Global Warming? A REVIEW OF THE FACTS APRIL 2007 AUTHORS James Wang, Ph. D. Bill Chameides, Ph. D. Are Humans Responsible for Global Warming? The case for attributing the recent global warming to human activities rests on the following undisputed scientific facts: †¢ Carbon dioxide (CO2) is a greenhouse gas that warms the atmosphere. †¢ Since pre-industrial times, atmospheric CO2 concentrations have increased from about 280 parts per million (ppm) to over 380 ppm.Current concentrations of CO2 and other greenhouse gases are unprecedented in at least the last 650,000 years, based on records from gas bubbles trapped in polar ice. †¢ Independent measurements demonstrate that the increased CO2 in the atmosphere comes from burning fossil fuels and forests. The isotopic composition of carbon from these sources contains a unique â€Å"fingerprint. † †¢ Since pre-industrial times, global average temperatures have increased by about 0. 7? C , with about half of the warming occurring over the past few decades. The only quantitative and internally consistent explanation for the recent global warming includes the intensified greenhouse effect caused by the increase in CO2 and other greenhouse gases. The U. S. National Academy of Sciences—the independent organization of the country’s most renowned scientists established by Congress to advise the nation on scientific and technical issues—has concluded: â€Å"The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action. Some argue that the recent global warming is due to natural fluctuations and not to human activities. This argument and its fallacies are discussed below. Argument 1: CO2 is not coming from human activities CO2 has natural sources: volcanoes for example. All animals exhale it. How can human activities be affecting the concentration of CO2 on a global scale? The Facts Natural processes e mit large quantities of CO2 into the atmosphere, but they also remove it—at nearly identical rates.This balance maintained the concentration of CO2 at a stable level for thousands of years prior to the Industrial Revolution. In the case of global warming, the question is: What is causing the increase in CO2 concentrations? The answer turns out to be incontrovertible. The isotopic composition of carbon in atmospheric CO2 provides a unique â€Å"fingerprint† that tells scientists that the lion’s share of the additional CO2 accumulating in the atmosphere is from the burning of fossil fuels. Argument 2: No one really knows why the climate variesThe global climate has fluctuated considerably over the Earth’s history, either for unknown reasons or because of â€Å"internal variability† in the climate system. We do not know enough about the climate system to attribute the present global warming to any specific cause. The Facts It is true that the Earthâ⠂¬â„¢s climate has exhibited wide swings over geologic time due to natural processes. However, scientists have reasonable qualitative explanations for most of the significant variations in 2 limate over geologic time;1 they can be largely attributed to specific processes, not to unknown internal oscillations. Many of the major climatic changes can be traced to changes in the Earth’s orbit around the sun (Hays et al. Science, 194, 1976, pg. 1121). Others can be linked to specific events (such as the impact of a comet or meteorite or the assembly or breakup of supercontinents) that led to large changes in the concentration of atmospheric greenhouse gases.For more recent times (the past millennium), scientists have been able to quantitatively attribute the major temperature fluctuations to changes in solar activity, volcanic eruptions, and human-produced greenhouse gases and particulate pollution. These natural processes can not explain the current warming. Argument 3: The Medie val Warm Period disproves global warming The current warming trend is analogous to the Medieval Warming Period (MWP). Since the MWP was obviously a natural event, the current warming is also likely caused by natural processes. The FactsThe Medieval Warm Period (MWP) refers to a relatively warm period lasting from about the 10th to the 14th century. 2 However, the initial evidence for the MWP was largely based on data3 gathered from Europe, and more recent analyses indicate that the MWP was not a global phenomenon. A number of reconstructions of millennium-scale global temperatures have indicated that the maximum globally averaged temperature during the MWP was not as extreme as present-day temperatures and that the warming was regional rather than global. Perhaps the most well-known of these is that of Michael Mann and colleagues (Nature, 392, 1998, pg. 779).Their reconstruction produced the so-called â€Å"hockey stick† graphic that contributed to this conclusion in the 2001 assessment of the Intergovernmental Panel on Climate Change: â€Å"The†¦'Medieval Warm Period' appear(s) to have limited utility in describing trends in hemispheric or global mean temperature changes in past centuries. † The accuracy of the â€Å"hockey stick† graphic was widely discussed in the press when the Mann et al. methodology was criticized by McIntyre and McKitrick (Geophys. Res. Lettr, 32, 2005, pg. L03710). Less attention was given to subsequent studies, such as that of Moberg and colleagues (Nature, 433, 2005, pg. 13) and Osborn and Briffa (Science, 311, 2006, pg. 841) that were based on different, independent methodologies but reached conclusions similar to Mann. Observations of melting high altitude glaciers are perhaps even more telling. Andean glaciers that have been intact for more than 5,000 years are now rapidly melting (Thompson et al. Proc. Nat. Acad. Sci. , 103, 2006, pg. 10536). If the MWP was truly global, these glaciers would not have sur vived. More generally, it is a logical fallacy to argue that because the climate has changed in the past due to natural causes, the current warming trend must also be due to natural causes.The debate over the magnitude and causes of earlier climate change such as the MWP is of scientific interest, but it does not invalidate the considerable direct scientific evidence that human-produced greenhouse gases have been causing the Earth to warm recently. Argument 4: Recent predictions of a new ice age disprove global warming In the 1970s climate scientists were saying an ice age was imminent. Now they say the Earth is warming. They don’t know what they are talking about. The FactsThe Earth’s climate for the past 2 million years has been characterized by ice ages lasting close to 100,000 years, punctuated by relatively short (10,000- to 30,000-year) warm periods or â€Å"interglacials. † The swing from glacial to interglacial is caused by changes in the Earth’s orbit around the sun amplified by natural feedbacks involving greenhouse gases (Hays et al. Science, 194, 1976, pg. 1121). The Earth entered the present interglacial about 10,000 years ago. All things being equal (i. e. , in the absence of a large human-produced source of CO2) it is highly likely that the Earth will swing back into a glacial period or ice age.But this will not occur for thousands of years. 3 As early as the 19th century, scientists recognized that greenhouse gases warm the planet, and that increases in atmospheric carbon dioxide could lead to global warming on time scales of decades to centuries—much shorter than the fluctuations related to ice ages and interglacials. Around the same time, global temperatures began to increase and scientists became increasingly concerned that humans were interfering with the climate. In the 1950s the upward trend in global temperatures unexpectedly halted and temperatures declined somewhat.This led some scientists to become c oncerned about global cooling and, in turn, to headlines in the popular press about an imminent ice age. What the skeptics fail to admit is that within the scientific literature—as opposed to the popular press—global warming remained a serious concern. Many scientists of the time argued that whatever the cause of the cooling, natural or otherwise, it would be eventually overshadowed by the warming effect of carbon dioxide. In 1979, the National Academy of Sciences warned that a doubling of carbon dioxide would increase global temperatures by 1. 5 to 4. oC (Carbon Dioxide and Climate: A Scientific Assessment, NAS Press, 1979) and shortly thereafter a resumption of the upward trend in temperatures was detected. Over the past quarter century, scientific research on global climate change has intensified, and programs on an international scale have been organized. More and more data are included in computer models that are capable of recreating past trends and more precisel y predicting future scenarios. We now know that the mid-20th century pause in global warming was caused by pollution from burning coal, which produced tiny particles or aerosols that blocked the energy from the sun.As aerosol emissions were controlled but greenhouse gas pollution continued to increase, the cooling effect of the aerosols was overwhelmed by the greenhouse gases, and global warming resumed. Argument 5: Scientists cannot â€Å"prove† current warming is not natural Climate scientists can not prove that the current warming is not due to natural processes and therefore can not claim with certainty that the warming is due to human interference. The Facts It is of course true that, in a complex system like climate, it is virtually impossible to prove a negative; i. e. that natural processes are not causing the current warming. What we can do is eliminate every possible natural explanation that can be posited. Thermodynamics tells us that the warming of the Earthâ€⠄¢s lower atmosphere must arise from one or more processes that supply excess heat to the lower atmosphere. Besides the greenhouse effect, the viable processes are (1) increased output from the sun; (2) increased absorption of heat from the sun due to a change in the Earth’s planetary reflectivity or â€Å"albedo†; and (3) an internal variation in the climate system that transfers heat from one part of the Earth to the atmosphere.Direct observations confirm that none of these explains the observed warming over the latter half of the 20th century. For example there has been no appreciable change in solar output over the past two decades (see Figure 1). Figure 1. Change in solar output from 1980 to 2005. Figure 1 shows the relative change in solar output determined from two of satellite measurements over a two-decade period. The data show variability in solar output corresponding to the 11-year sunspot cycle, but no secular trend. Source: After Lean and Froelich, 2006. 4 Satellite data reveal that the Earth’s reflectivity increased (causing cooling instead of warming) in the ’60’s, ‘70s, and early ‘80s and has decreased modestly since. 4 The overall warming from the recent decrease in reflectivity is also small compared to the greenhouse warming. In the case of internal variations, the ocean is the only viable reservoir of internal heat that could have caused the atmosphere to warm on decadal time-scales. However, observations show that the heat content of the ocean has increased instead of decreased over the past few decades (See Figure 2).This indicates that the atmosphere has been a source of heat to the ocean rather than vice versa. Moreover, the amount of heat increase in the ocean is consistent with what is needed to balance the Earth’s energy budget given the excess heating from the enhanced greenhouse effect and the amount of excess heat observed to be stored in the atmosphere (Hansen et al. Science, 3 08, 2005, pg. 1431). In other words, the amount of heat stored in the ocean over recent years matches the amount of heat that models predict should be trapped on Earth due to the increase in greenhouse gases. Figure 2.Change in heat content of ocean 1955 to 2005 Source: After Levitus et al. 2005. FIGURE 2 SHOWS THE RELATIVE CHANGE IN THE HEAT COTENT OF THE OCEAN FROM 1955 TO 2005 BASED ON A COMPREHENSIVE ANALYSIS OF OCEAN TEMPERATURE MEASUREMENTS. THE DATA SHOW SHORT TERM VARIABILITY BUT A CLEAR UPWARD TREND ON DECADAL TIME-SCALES. Conclusion †¢ The Medieval Warm Period does not represent an analogy to the warming of the late 20th century, for which scientists have independent evidence of human causation, and the evidence strongly suggests that the MWP was a regional, rather than a global phenomenon. Our understanding of the climate system is sufficient to provide qualitative models for most global or hemispheric climatic variations over geologic history and quantitative models for variations over the past millennium. †¢ The Earth’s climate may return to ice age conditions in thousands of years, but this does not preclude devastating effects from global warming over the next few centuries. 5 †¢ All known natural explanations for the current global warming trend have been eliminated by direct observations.The human-intensified greenhouse effect provides the only quantitative explanation for the current warming trend. About the authors Dr. Wang received his doctorate from Harvard University and works as a climate scientist at Environmental Defense. He has published several peer-reviewed papers on the global methane budget and was the author of â€Å"The Latest Myths and Facts on Global Warming,† which was read into the congressional record by Senator John McCain in 2005. The report is available at http://www. undoit. org/pdfs/mythsvfacts. pdf. Dr. Chameides, chief scientist at Environmental Defense, is a member of the U.S. National A cademy of Sciences and has been named a National Associate of the National Academies. He is also an American Geophysical Union Fellow, and has received the American Geophysical Union's Macelwane Award. Dr. Chameides has served as editor of the Journal of Geophysical Research and is the author or coauthor of more than 120 scientific publications and five books. He received his doctorate from Yale University. The explanations are qualitative instead of quantitative because we do not have quantitative data from these events in the distant past to construct their exact histories. It has been suggested based on temperature reconstructions and model simulations that the MWP may have been caused by increased solar activity or a dearth of volcanic activity. 3 th Because worldwide temperature measurements do not exist before the 19 century, temperature records before th the 19 century are based on reconstructions of the temperature from the variations in temperature-sensitive proxies (e. g. , tree rings, isotopes in ice cores). 4 These variations are possibly due to changes in the concentrations of atmospheric aerosols produced from the burning of fossil fuels and biomass. 1 6