In 2001, the earth warmed between 1900 and 1940, then subsequently cooled between 1941 and 1965, but surface temperatures have been warming ever Data from millions of thermometer measurements taken from all over the world from as far back as 1860, allow calculation of average surface air temperatures. This data is believed to be the most useful when describing the state of the global climate. It can be seen that 1998 is the warmest year on record, with the ten warmest all occurring since 1990. Records show that global temperature has risen by approximately 0.6°C since the beginning of the 20th century, and 0.4°C of this warming has occurred since the 1970s. This indicates that global warming is occurring. However, many scientists are sceptical, and the issue is subject to debate on whether surface temperatures are rising or not.
The current climate change is not just part of a natural cycle. Earth's climate is complex and influenced by many things, particularly changes in its orbit and variations between the sun and earth- milankovitch’s cycle volcanic eruptions, and changes in the energy emitted from the Sun. other factors are such as variation in solar energy, astronomical, changes in oceanic circulation, meteorites, plate tectonics and the composition of the earths atmosphere It is well known that the world has experienced warm or cold periods in the past without any interference from humans. The ice ages are good examples of global changes to the climate, and warm periods have seen grapes grown across much of Britain.
Over the several hundred thousand years covered by the ice core record, the temperature changes were primarily driven by changes in the Earth's orbit around the Sun. Over this period, changes in temperature did drive changes in carbon dioxide (CO2). Since the Industrial Revolution (over the last 100 years), CO2 concentrations have increased by 30% due because to human-induced emissions from fossil fuels.
The bottom line is that temperature and CO2 concentrations are linked. In recent ice ages, natural changes in the climate, such as those due to orbit changes, led to cooling of the climate system. This caused a fall in CO2 concentrations which weakened the greenhouse effect and amplified the cooling. Now the link between temperature and CO2 is working in the opposite direction. Human-induced increases in CO2 are driving the greenhouse effect and amplifying the recent warming.
One of the arguments from scientists who do not accept global warming is happening, say that while surface records may show that temperatures on the earth’s surface are rising, satellite temperature records are unable to detect any warming occurring higher up in the troposphere. Climate change models have predicted that this level of the atmosphere should be experiencing warming, at a level similar to that occurring at the earth’s surface.
However, recent warming cannot be explained by the Sun or natural factors alone. There are many factors which may contribute to climate change. Only when all of these factors are included do we get a satisfactory explanation of the magnitude and patterns of climate change over the last century.
Over the last 1,000 years most of the variability can probably be explained by cooling due to major volcanic eruptions and changes in solar heating.
In the 20th century the situation becomes more complicated. There is some evidence that increases in solar heating may have led to some warming early in the 20th century, but direct satellite measurements show no appreciable change in solar heating over the last three decades. Three major volcanic eruptions in 1963, 1982 and 1991 led to short periods of cooling. Throughout the century, CO2 increased steadily and has been shown to be responsible for most of the warming in the second half of the century.
As well as producing CO2, burning fossil fuels also produces small particles called aerosols which cool the climate by reflecting sunlight back into space. These have increased steadily in concentration over the 20th century, which has probably offset some of the warming we have seen.
Changes in solar activity do affect global temperatures, but research shows that, over the last 50 years, increased greenhouse gas concentrations have a much greater effect than changes in the Sun's energy.
Climate models predict the main features of future climate. There have been major advances in the development and use of models over the last 20 years and the current models give us a reliable guide to the direction of future climate change.
Computer models cannot predict the future exactly, due to the large number of uncertainties involved. The models are based mainly on the laws of physics, but also empirical techniques which use, for example, studies of detailed processes involved in cloud formation. The most sophisticated computer models simulate the entire climate system. As well as linking the atmosphere and ocean, they also capture the interactions between the various elements, such as cryosphere (ice) and geosphere (land).
Climate models successfully reproduce the main features of the current climate (e.g. rainfall in the map below), the temperature changes over the last 100 years, the Holocene (6,000 years ago) and Last Glacial Maximum (21,000 years ago).
Current models enable us to attribute the causes of past climate change, and predict the main features of the future climate, with a high degree of confidence. We now need to develop the models to provide more regional detail of the impacts of climate change, and a more complete analysis of extreme events.
Some scientific studies suggest that global warming is happening whilst others say it is not, with all the evidence I have come to the conclusion that climate change is happening but do to natural causes, humans however, are speeding this process up.
