Global warming is the rise of average temperature in the earth’s atmosphere since the late 19th century. Since the beginning of the early 20th century, the earths mean surface temperature had increased by around 0.8 degrees. Warming of the climate system had become more obvious and scientists are 90% sure that the main cause of the increase in temperature in due to the increasing concentrations of greenhouse gases due to human activities such as deforestation and burning of fossil fuels. Glaciers are melting, sea levels are rising, forests are drying and wildlife is suffering, these are all results of the apparent rise in global temperatures and it has become more obvious that humans over centuries are releasing harmful heat-trapping gases into the atmosphere known as greenhouse gases.
The greenhouse effect causes the increase in global temperature as the gases which are released into the atmosphere allow light to be entered, but prevents heat from escaping. The sun firstly releases short-wave radiation which skinks into the earth’s surface, causing it to warm the atmosphere. A long wave infrared radiation which is emitted by the earth’s surface is absorbed, and then re-emitted back into space. The climate changes occur due to the increase of greenhouse gases. The greenhouse gases then trap some of the heat and the rest escapes back into space. Essentially, the more greenhouse gases released into the atmosphere, the more heat is trapped, resulting in an increase of global climate.
The above graph shows the rise in global temperatures since 1860 to 2000. The increase in global temperature can be recording using methods such as: Ice core samples; temperature recordings; dendrochronology and peat bogs.
Ice core samples
Within Ice sheets, holds records of hundreds of thousands of past climates trapped in ancient snow. Scientists can obtain the climate history by drilling cores in ice up to 3, 500 metres deep. Throughout every year, layer of snow cover the ice sheets in Antarctica and Greenland. Within these layers of snow, contains a different chemistry and texture as the summer snow is different from the winter snow. Each of these layers provides scientists with information about the climate each year. An ice core provides a vertical timeline of previous climates which are stored in ice sheets and mountain glaciers. In able to see the layers, scientist dig into two pits which are separated by a wall of thin snow. One of the pits is covered and the other exposed to sunlight. By standing in the covered pit, scientists are able to study the yearly layers of snow wall as the sunlight filters through the other side.
The ice cores can provide a yearly record of temperature, atmospheric composition, precipitation, wind patterns and volcanic activity. Using marine fossils and the ratio of oxygen isotopes in the snow can reveal the temperature. When snow is formed, it becomes crystallized around the tiny particles in the atmosphere, the amount of trapped particles, such as dust, volcanic ash, smoke or pollen can reveal to scientists the climate and environmental conditions of when the snow formed. As the snow is being settled on the ice, air fills into space between ice crystals and a tiny sample of atmosphere is trapped. These small bubbles can tell scientists what gases were in the atmosphere and the climate at that time. Ice cores can also be used to correlate the concentration of CO2 in the atmosphere with the change in climate, as shown in the graph. Advantages of Ice core dating is that the process can be completed quickly and results are easily obtained. Disadvantages would be that is the predetermined age markers are incorrect, then the age that is assigned to the ice core would also be incorrect.
Through use of satellites, temperature of the troposphere can be measured. This method has been effective since December 1978.
The Graph shows how the satellites can be used to measure the temperature anomaly. There is a positive correlation as the year increases so does the temperature anomaly. Satellites are useful as they measure the radiances in wavelength bands, which are then mathematically inverted to form indirect readings of temperature.
Dendrochronology is a method using the annual nature of tree growth to determine changes in climate settings. Each year trees develops a new layer of wood under its bark. The thickness of each layer is dependent on various factors, especially climate. The conditions encouraging growth will result in a wider tree ring, whereas the unfavourable conditions would result in narrow rings. By measuring the width of each tree ring and plotting them as graphs, scientists are able to determine the climate changes throughout the years. They do this by comparing the tree rings and dating them to the calendar year in which they were formed. By matching the patterns (crossdating) the ring growth of different trees, scientists are able to assign the rings to specific dates.
Crossdating can even be achieved in spite of the human interference to the tree ring growths and other factors such as extreme weather conditions. Overall dendrochronology is a very accurate technique where determination of absolute dates to year is either theoretically or practically possible. Limitations of dendrochronology may lead to invalid results. In parts of the world, specifically the tropics, species of trees will not have a distinct seasonal pattern; therefore it would be difficult to determine the climate change over the years. Also if the correct species are obtainable, the layers of wood must be preserved well enough so that the rings can be read, essentially there should be a minimum of 30 rings in one sample.
To eliminate individual variations in tree ring growth, dendrochronologists take the average of the tree ring widths of various tree samples to build up a ring history. This process is known as replication. If a tree rings history is not known it is called a floating chronology. This is where cross dating is used. Peat Bogs
Peat bogs are formed from flooded hallows and basins that provide ideal conditions for growth of reeds and sedges. When vegetation dies, it does not rot away completely due to water remains in the hallows that prevent oxygen. Partly rotted plants then gradually build up to form peat. Most of the nutrients are tied up within the peats, meaning that the only minerals available for plant growth are the ones dissolved in rainfall. A report by Natural England found that farming practices such as ploughing the earth, results in three quarters of peat bogs to become damaged. This results in three million tonnes of carbon dioxide which is stored in the soil to be released every year. It is estimated that globally, peat bogs stores twice as much carton as forest, and the UK contains about 15 per cent of the world’s peatlands.
A review by Peter Stott of the Met Office Hadley in Exeter, found that ‘fingerprints of human activity on many different aspects of climate change. “The fingerprint of human influence has been detected in many different aspects of observed climate change. We’ve seen it in temperature, and increases in atmospheric humidity, we’ve seen it in salinity changes. We’ve seen it in reductions in Arctic sea ice and changing rainfall patterns,” Dr Stott said. “What we see here are observations consistent with a warming world. This wealth of evidence we have now shows there is an increasingly remote possibility of climate change being dominated by natural factors rather than human factors.” Overall, through the information obtained through ice core samples, Tree rings, temperature settings and damage to peat bogs proves that humans are to blame for global warming. Scientists have proven that the warming effect on the earth is mainly due to the millions of carbon dioxide emitted into the atmosphere due to human activity over the years.
2.http://environment.nationalgeographic.com/environment/global-warming/gw-overview/ 3.http://earthobservatory.nasa.gov/Features/Paleoclimatology_IceCores/ 4.http://en.wikipedia.org/wiki/Temperature_record