The term ‘global warming’ refers to an overall increase in the Earth’s temperature which may be caused by a number of factors, including the greenhouse effect. The atmosphere has a ‘natural supply’ of greenhouse gases which keep the Earth at a suitable temperature (above freezing). Scientists have said, however, that there being too many of these gases in the atmosphere is causing the temperatures rise too much and too quickly, causing many problems for the environment.Although it has become a worldwide phenomenon over the last few years, there are many people with the attitude that global warming doesn’t really exist. There has been debate all over the world and there are a number of different popular theories. Whilst some people believe the world is getting warming and it is being made worse by humans, others have the opinion that it is a natural process that is nothing to do with us.There have been numerous investigations done by scientists and records gathered from over a long period of time that may indicate different patterns in temperatures in relation to human activity on Earth, but these are almost always scrutinised by critics. Not all the signs of global warming come from scientific research though, some of the effects we can notice in our everyday lives, such as the reduction of ice cover, the rise in sea levels, animals moving north, and increasing severe storms.One argument against humans being to blame for global warming is that water vapour is the most important greenhouse gas, as appose to carbon dioxide or methane as it accounts for around 98% of all warming. This would suggest that the carbon emissions that come from our cars and factories don’t play as big a part in climate change as people are lead to believe. On the other hand, changes in its concentration are considered to be a result of climate feedbacks related to the warming of the atmosphere rather than a direct result of industrialization. The air is able to hold more water when it is warmer, so increasing temperatures do lead to more vapor in the atmosphere. Then in theory, with more water vapor more heat is stored and this cycle continues.A common argument is that although there maybe records showing the earth warming now, it has been warmer in the past and we are merely in the middle of one of many temperature cycles. Records show a medieval warm period when temperatures in Europe especially were higher than they are now. It has been recorded that at this time grapes were grown in Northern England and the arctic was warmer in the 1930’s than it is today.When interpreting this information though, it must be remembered that any data on global temperatures so long ago must be estimations. Although thermometer readings are said to date back as far as 1659, accurate readings only date back around 140 years. Technology is much more accurate now and it can be monitored and studied on a larger scale unlike the data from years ago. Thus comparing the results from now and then is not totally fair. To find data about temperatures for before records begin, scientists have to use natural indicators such as tree rings. Information about past temperatures can be shown in the distance between each ring.It has been discovered that a tree said to be over 9,500 years old has revealed that summers that long ago are likely to have been warmer than summers currently, however, with the current increase in temperatures the modern climate is quickly catching up. It is difficult to know how reliable this is a source as there can be no exact figures taken from it and many experts arguing for man-made climate change would use this fact as an argument against the Earth being warmer in the past. There are fluctuations in almost all of the temperature records which can be due to natural events such as the eruption of volcanoes or changing weather patterns. This is evident in 1998 when temperatures rose following the El Nino event.It is disputed that the change in temperature over time could also be down to a number of things. The position of thermometers around the globe could be hugely affecting their temperature readings. Urbanisation over time for example would have a big impact. Cities are generally much warmer than rural areas, as the heat from the sun is stored for longer in concrete floors and buildings. In rural areas it is very much the opposite, with little concrete and a lot of vegetation, which use heat in transpiration and evaporation.The positioning of thermometers recording temperatures also causes debate as they have been placed close to air conditioning ducts and even next to burn barrels. On the other hand, analysis by Nasa for example only use rural stations to calculate trends. It has also been discovered that if you analyse data in both windy and calm conditions and compare them there is very little or no difference in the results. This suggests that the urban heat island effect was a big problem, it would be more evident on calm days where less heat leaves the cities.One of the most controversial views on humans being to blame for global warming comes in the form of the graph known as the ‘hockey stick’. The hockey stick graph shows the temperatures from over the past 1000 years starting. The graph shows a steady, fairly flat trend from 1000 years to 1900, before increasing dramatically between 1900 and 2000, giving the distinct shape of a hockey stick. Although the hockey stick graph is now used to urge people to cut down on carbon emissions, it has also been condemned on a large scale for many reasons.The creators of this graph gathered their information on temperature from a variety of different sources including ice cores, tree rings, coral, and historical data. This data has been challenged by specialists who believe it is flawed and can no longer be viewed as valid. It has been described as ‘an exaggeration of recent trends’. The debate as to whether this is a sound piece of evidence is still pondered.Ice cores from over a million years ago show evidence that co2 and temperature rise at around 100,000 year intervals. But the co2 rise always comes a few hundred years after the rise of temperature. Most probably because the warmer temperatures release gas from the oceans. This would back the argument that humans emitting carbon dioxide into the atmosphere is not what causes global warming. The counter argument would be that although true, these facts are irrelevant because the ocean takes this long to respond to atmosphere changes driven by shakes in the Earth’s orbit. The extra emissions today are also at a 35% increase above pre-industrial levels caused by humans. This is higher than ever found in ice records.To conclude, it would seem that there are hundreds of theories voiced about what is happening to the temperature of the world currently, however, some are very contrasting and all are debated. It remains unclear as to which side of this argument is correct as there are so many possibilities in between. However, what seems to be clear is that the Earth is warming, whether caused by humans, naturally, or just as part of the Earths cycle.With every argument put forward by specialists, there is a counter argument put forward too.This uncertainty could make it difficult in finding ways to stop it, and some would argue that we just shouldn’t bother instead letting nature take its cause. With sea-levels undoubtedly rising and problems being caused for wildlife, even if some are convinced that humans are not responsible for global warming no one can deny that these events are occurring and people should work to change.