Who is to blame climate change? Scientists have measured global temperatures for over a hundred years and see that the Earth is getting hotter. Ice core data suggests the Earth should actually be cooling if it were following its natural cycles. The trend can be best visualized by comparing each year’s average temperature with the long- term average. Figure 1 shows observations of the world’s annual average temperature made by the National Oceanic and Atmospheric Administration (NOAA). In recent decades, the years have always been hotter.
Over geologic time, the Earth’s average temperature has changed as a result of the sun’s output, the tilt and position of the Earth in its orbit, and the concentration of greenhouse gases. Scientists have developed a good understanding of the natural variations in these factors by examining different data sources in order to estimate ancient temperatures. Observations tell us that these natural factors have not been changing over the last hundred years or so in a way that would explain the observed temperature increases.
In contrast, greenhouse gases have been changing in a way that can explain the observed temperature increases. Figure 2 shows the change in atmospheric CO2 concentration over the last thousand years. At the Scripps Institute of Oceanography in Hawaii researchers have been sampling pristine mountaintop air every month since 1958. Their observations show that both the concentration and isotopic composition of CO2 is changing, and is consistent with manmade sources, including the carbon emissions from burning fossil fuels. The industrial revolution marked a drastic increase in CO2 concentrations in the atmosphere when humans began using fossil fuels on a large scale.
Scientists attribute the global warming trend observed since the mid-20th century to the human expansion of the "greenhouse effect"1 — warming that results when the atmosphere traps heat radiating from Earth toward space. Certain gases in the atmosphere block heat from escaping. CO2 along with other gases are known as greenhouse gases. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric CO2. In its Fifth Assessment Report, the Intergovernmental Panel on Climate Change, a group of 1,300 independent scientific experts from countries all over the world under the auspices of the United Nations, concluded there's a more than 95 percent probability that human activities over the past 50 years have warmed our planet.
Give evidence and reasoning!!