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Global climate change main concepts
Dig deeper into the history of climate change to discover the causes and effects of global warming.
Evidence over the last 20,000 years
Climate change is a long term issue. The causes of global warming, whilst almost certainly having an impact here and now, are yet to be fully assessed in terms of their long-term impact. Opinion is divided in the scientific community and there is no way of saying for certain what will happen in the future.
Indisputable evidence shows that the temperatures are increasing globally. The average global temperature has been 14°C for the last 10,000 years but in the last 100 years it has increase relatively rapidly, by over 1°C. The increases in temperature have been recorded on land and in the world’s oceans. The sea is a very good indicator of long-term change in temperature.
Patterns of precipitation have changed too, with increased frequency and intensity, manifested by more frequent flooding events which seem to be a regularly reported in the media. In contrast, marginalised areas in semi-arid areas are experiencing increased desertification. Changes in water availability meaning that land is no longer productive.
Sea Level change is considered to be a major threat to coastal and low-lying inland areas. Even the smallest changes in sea level can cause flooding, increased erosion of land and in some cases, whole islands may be at risk from submergence.
These are long cylinders of ice that are drilled from ice caps and glaciers. They are treasure troves on information as they give scientists an insight into climatic history, long term and at an annual frequency. Information can be gleaned from the cores such as; the air temperature, the amount of snow fall, the length of the seasons and the degree of contrasting weather patterns. One of the longest cores was over 3 km, drilled from the Greenland ice sheet. A core of this length gives scientist a record of the past 110,000 years. Some ice cores from Antarctica have gone back much further than this, up to 750,000 years of information.
Rocks and Fossils
Paleontological research gives us an insight into the animal and plant life from millions of years ago. Fossils can be found on excavations on land or under the sea bed. The types of flora and fauna indicate the climate at the time. In addition to this, the study of geology can also give clues about the climate from the types of material in samples. When glacial deposits are analysed they can give important information about what ice movement was at the time. For example, much of the North Norfolk coast is covered in glacial material from Norway. Some of the samples show that over a period of 10,000 years the ice advanced and retreated several times over the area. Scientists can use this data in conjunction with other sources and build up a picture of past climatic patterns.
Dendrochronology is the study of internal tree rings. By examining the thickness of tree rings, data can be collected about the length of seasons and the severity of fluctuations in temperature. The amount of growth is shown in the rings of a tree stump. By looking at tree rings in different locations it is possible to map a longer term pattern of temperatures and other data.
There are other methods of tracking climate change which scientists can use but the main purpose of them all is to build up a complete picture of the past variation in climate, especially changes in global temperature, to enable scientists to try and predict what the future will bring whilst they assess the impact of humans. There are increasing responses by humans on a local to international scale, but the level of commitment to them varies. Whilst generally those that are more under threat from rising sea levels are more concerned than those who are safer, the problem is global and sea level change is not the only issue. Global food production faces an uncertain future with increased marginalisation of land, a growing world population and greater competition for water agricultural purposes.
Historical evidence essays
'Earth's climate has always been changing; it is the rate of change that is of current concern to scientists.' With reference to Figure 1, and other evidence which you have come across, discuss the validity of this statement.
Causes of climate change
The biggest contributor to global climate change, caused by humans, is the amount of CO2 in the atmosphere. As with many aspects of climate change, opinion is divided, but evidence supports the theory that since the 1800s and the start of industrialisation, there has been an overall trend of warming and increases in levels of CO2. Burning of fossil fuels has been, and continues to be the biggest contributor to rising levels of greenhouse gasses. Methane production is also a problem and with 28% of this coming from livestock farming (34% of methane comes from fossil fuels). Methane levels have doubled in the last 150 years. The burning of fossil fuels and livestock farming are the two biggest contributors to methane in the atmosphere, however when you look at other sources; such as rice production (10%) and methane from landfill sites (16%) you can see that these are only going to increase.
The increase in greenhouse gasses cause the “Greenhouse effect”. Increased accumulation of these gasses help to trap solar radiation that would disperse more easily without them. The effect, increased global temperatures.
Effects of climate change
Whilst climate change, and global warming in particular, is everyone’s problem; its effects are felt at varying scales and severity. The physical effects are associated with sea-level change and the increase in extreme weather events due to warmer temperatures. Extreme weather events include flooding and droughts which are increasing in frequency.
Biodiversity is under threat because an increase in temperature could cause loss of habitat or simply too much heat for some species to survive for example because of food chain disruption. It is estimated that an increase of 3°C or 4°C could lead to extinction of up to 30% of species.
Social impacts can be both positive and negative. Many people in the UK claim that they would be happy with longer, warmer summers, farmers would certainly welcome the increased growing season. Unfortunately LEDCs (Less Economically Developed Countries) tend to be in the areas that are most affected and many of them already have high temperatures, even greater increase makes life very hard to adapt to. People are likely to have to migrate to cooler areas.
Large scale ice-melt is one of the best indicators of global temperature and the media portrays the impact of global warming by showing calving of glaciers and ice-sheets into the sea. Scientists estimate that an increase of between 1.5°C and 7°C could lead to deglaciation of Greenland and the West Antarctic ice sheets to such an extent that sea levels could rise by 4 – 6 metres.