In Graph 3, the independent and dependent variables are the years
(independent) and the carbon dioxide levels in ppm (dependent). This data clearly shows a direct relationship; when the years increase, the amount of carbon dioxide levels increase as well. Unlike the previous two graphs, there is a clear direct relationship between the years and the carbon dioxide levels in ppm. A reasonable explanation for this direct relationship is that in 1959 (where the graph started), greenhouse gas emissions really started to spiral, and this caused the increase in CO2 amounts in ppm. Because more greenhouse gases were emitted, the steady greenhouse effect was disturbed and this resulted in more sunlight being trapped and made into heat instead of getting
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From 1900 to 2010, there is a 5 km² difference (11 km² to 6 km²; the smaller volume means more has ice has melted). In this graph, the independent and dependent variable are the years (independent) and the ice cap volume during summer melts (dependent). From the years 1900 to 1960, numbers were relatively around the same range, sometimes decreasing by one but then eventually reverting back, but from the years 1970 to 2010, the ice cap volume went directly down, coinciding with the year increase. A reasonable explanation for this (mostly) direct relationship is the recent emissions of greenhouse gases starting from 1970. Since the ice cap volume steadily decreased from that point on, it is fair to say that it is due to the increase of carbon dioxide and greenhouse gas emissions. As more greenhouse gases are emitted into the atmosphere, more of the sunlight directed at Earth is trapped as heat, as opposed to shining back at the sun. Since this heat is trapped in the atmosphere, it warms the Earth more and increases the global average temperatures. When there is an increase in global average temperatures, the seasons are notably warmer (summer is hotter and winter is warmer than it should be). Since the ice caps are meant to melt somewhat in the summer but then freeze back in the winter, the increase in temperatures actually melts them faster than normal during the summer and does not allow them to freeze back enough during the winter. Slowly but steadily, the ice cap volume decreases and more and more melts in the summer as the temperatures