Posted: November 9th, 2015
Scientific Thinking
The mean surface temperature of the earth is positively correlated with the density of greenhouse gases in
the atmosphere. Carbon dioxide is a greenhouse gas.
Over the past 70 years, the level of solar activity as measured by the frequency of sunspots has been
exceptionally high.[1] The mean surface temperature of the earth has also increased markedly since 1950.
GHG Hypothesis: The increased mean surface temperature of the earth over the past half century has been
caused by the increase of greenhouse gases in the atmosphere.
Sunspot Hypothesis: The increased mean surface temperature of the earth over the past half century has been
caused by the increase in solar activity.
Based only on the information provided in the above paragraphs, please state whether the statement is true or
false (or that this cannot be determined from the information in the article), and explain your answer in a
sentence or two.
a) (2 pts) Increases in CO2 cause the mean surface temperature of the earth to increase.
b) (2 pts) If the sunspots returned for a long period of time to their original lower rate, and the
temperature of the earth continued to increase, this would provide evidence against the Sunspot Hypothesis.
2 pts) If the sunspots returned to their original lower rate and the temperature of the earth continued to
increase, this would prove the GHG Hypothesis.
[1] Unusual activity of the Sun during recent decades compared to the previous 11,000 years.
S.K. Solanki1, I. G. Usoskin2, B. Kromer3, M. Schüssler1, and J. Beer4. Nature, Vol. 431, No. 7012, pp. 1084
– 1087, 28 October 2004.
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