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The Earth has been warming over the past years. The warmest global mean temperature occurred in 1998. For the past 30 years, there has been a strong warming trend. Last year alone was the fourth warmest year. This could be because of the increase of greenhouse gasses in the atmosphere. The year to year variability could be due to shortterm climate affects such as volcanic eruptions and whether or not the year is a strong El Nino year.Picture: from “Earth gets a Warm Feeling all over” showing the increase of global annual mean temperatureBecause the Earth receives more solar shortwave energy than the terrestrial longwave radiation that goes out to space, the Earth is out of energy balance. A result of this is the probability that the year 2005 will be even warmer than 2003 or 2004 and that it may even surpass 1998.Every year the U.S. emits 6.6 tons of greenhouse gasses per person per year. This has increased 3.4 percent since 1990. Most of these greenhouse gasses (82%) are from burning fossil fuels.Shows that the US leads the world greenhouse gas emission per personGreenhouse gasses increase the temperature of the Earth by absorbing longwave and a few of the also absorb shortwave radiation and emitting it back to Earth, which increases the energy received at the surface. These gasses include water vapor, carbon dioxide, methane and ozone.Carbon dioxide is at its highest levels in over 400,000 years, and it has increased 31% in the past 250 years. Methane is also at its highest levels in over 400,000 years, andit has increased 150% in the past 250 years. Nitrous oxide is at its highest levels in 1,000 years.Picture: from http://www.ncdc.noaa.gov/oa/climate/globalwarming.html#Q9We can already see some effects of global warming such as the melting of ice sheets and also the increase in sea level. Sea level today is rising at a rate of two millimeters per year. However, 150 years ago the rate of sea level rise was only one millimeter per year, half of what it is today. The changes in ice volume are the cause for this rise is sea level. The snow cover in the northern hemisphere has been below average for nearly 20 years and has decreased 10% since 1966. This is due to the decreased snowfall in spring and summer. The glaciers have decreased in length. The following figure shows the current length of the glaciers. In the Arctic the ice cap has decreased by about 20% in the past three decades.From http://www.ncdc.noaa.gov/oa/climate/globalwarming.html#Q9 showing the current lengths of glaciersThe Arctic is warming twice as fast as the rest of the world, and it has gotten 40 percent thinner in the past thirty years. By 2070, the ice in the Arctic is expected to disappear completely. Some of the ice shelves in the north part of Antarctica have collapsed recently, such as the Larson A ice shelf in January 1995 and the Larson B in 1998. The waters around Antarctica have warmed by 0.17 degrees Celsius, and in the Antarctic Peninsula the melt season has increased by two to three weeks in just the past twenty years. Also the penguin population has declined by about 33% in the past twenty five years. In the Canadian Rockies, the Athabasca Glacier has retreated one third of a mile in the past sixty years.Picture: from “Extended scenarios for glacier melt due toanthropogenic forcing”Picture: from “How Much More Global Warming and Sea level rise” showing sea level riseHurricanes form in warm tropical waters. The water must be warm (at least 27 degrees Celsius. A thunderstorm changes into a hurricane through three stages: a tropical depression, a tropical storm, and then a hurricane. A tropical depression contains swirling clouds and not very fast winds. A tropical storm contains winds of 39 to 73 miles per hour. A hurricane has winds greater than 74 miles per hour. The winds converge at the surface and push warm, moist air up. There is a pressure gradient between the surface andat high altitudes, and there also is a continuing evaporation-condensation cycle. The high altitude winds must be blowing at a uniform speed. The hurricane season lasts from June 1 to November 3. The amount of damage of hurricanes has increased, while the total fatalities have decreased because we have better at forecasting them.Picture: From http://science.howstuffworks.com/hurricane8.htm showing the increase in property loss and the decrease in deaths since 1900 In the northern hemisphere these storms rotate counter clockwise.Picture: from http://science.howstuffworks.com/hurricane8.htm shows a hurricane rotating counter clockwiseHurricanes can produce strong winds, storm surges, flooding tornadoes and rip tides. According to the Saffir/Simpson scale, hurricanes are categorized according to theirwing speed. A category 1 hurricane has winds 74-95 mph, and it causes damage to unanchored mobile homes and trees. A category 2 hurricane has winds 90-110 mph, and it causes damage to vegetation and some roofing material. A category 3 hurricane has winds 111-130 mph, and it can destroy mobile homes and causes some structural damage to small residences. A category 4 hurricane has winds 131-155 mph, and it causes major erosion of beach areas. A category 5 hurricane has winds greater than 155 mph, and it causes complete roof failure and also the evacuation of cities.There is a relationship between hurricane intensity and frequency and increasing sea surface temperatures. Many people suggest that global warming is the reason for theincrease in sea surface temperatures. In the tropical ocean sea surface temperature has increased by about 0.5 degrees Celsius between 1970 and 2004.Picture: from “changes in tropical cyclone number, duration, and intensity in a warming environment” shows that the sea surface temperature has beenincreasing since 1970There is no increasing or decreasing trend in the frequency of hurricanes except inthe North Atlantic Ocean. In the North Atlantic Ocean there is an increasing trend in the frequency of hurricanes and also in the duration of hurricanes.” The observation that increases in North Atlantic characteristics have occurred simultaneously with a statistically significant positive trend in sea surface temperature has led to the speculationthat the changes in both fields are the result of global warming.”(P.J. Webster) In the Eastern Pacific, the number of storm days reached a maximum in the mid 1980s, and it has been generally decreasing ever since. However, in the west North Pacific,


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UT GEO 387H - Lecture Notes

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