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The data period have been extended to 1880 – 2008 from which an excel trend chart of CO2 against temperature anomaly is drawn. This reduces error that can occur when conclusion is drawn from one small piece of the puzzle or sample without viewing overall broader picture (Flannery, 2006). However, it is apparent that there is a distinct upward tendency in the general rate. The carbon dioxide trend is also rising. From the graph, the temperature and CO2 records over the past decades show that there are short-term periods of cooling even in a long term global warming trend (Flannery, 2006).
By extrapolating the graph using a straight line, we get a linear relationship with an equation y = 88.471x + 351.75, which means that an increase in temperature anomaly of 0.0092 C for each 1 ppmv (parts per million volumes) increase in carbon dioxide.
At a glance, it may seem that the global warming experienced for the last 100 years or so occurred owing to an increase CO2 concentration in the atmosphere and is therefore a good indication for global warming due human activities. But preparation of climate related visualizations warrants careful scrutiny in order to obtain a sensible result.
The straight-line correlation between temperature and carbon dioxide level does not adequately explain the going on between these two variables. There are three difficulties concluding using this method. First, it ignores the fact that the 20th-century global warming was not steady and a significant rise in temperature happened before 1940s, before the greenhouse gases effect from human activities existed. Therefore, the early 20th-century global warming must be most natural (Gerald, 1980). At most only a few tenths of a degree of the 0.5 C rise experienced during this period can be attributed to the rise in greenhouse gases.
Global temperature may increase due to other factors such as urban-heat-island effect in growing modern cities owing to the machinery and pavement of Cities which record extra warmth (Mac Donald, 1982). In addition, greenhouse gases effect is also caused by other such as water vapor in form of water droplets in the air, methane (CH4) and other minor greenhouse gases such as chlorofluorocarbons (CFCs) in the air (Mac Donald, 1982). A third problem is that 100 years is not sufficiently enough to gauge the size of natural climatic fluctuations (Mac Donald, 1982).