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While there have been countless attempts at correlating sunspot cycles with such diverse phenomena as the economy, crop yields, and the weather, there has been little evidence to support these correlations. The past few decades have seen a renewed interest in the sun-climate relationship with a comprehensive analysis of many different historical records of solar observation. Late in the seventeenth century, a period known as the Maunder Minimum, there were virtually no sunspots observed, indicating a “ quiet” period in the sun’s activity coinciding with the height of a time known as the Little Ice Age, a period of lower temperatures in Europe. Once this evidence had been synthesized, it has become much clearer that there are indeed robust correlations between the Earth’s temperature and sunspots. Perhaps the most important development in the solar-climate link came when satellites were developed to measure, in rough terms, the Total Solar Irradiance ( TSI ), a factor shown to be directly related to these “activity” cycles. At the maxima of these cycles, there are more sunspots (magnetic phenomena that attenuate local irradiance), but new instruments show that these dark sunspots are more than compensated for by bright areas on the sun called faculae; therefore, the overall irradiance increases in correspondence with higher numbers of sunspots.
Unfortunatedly, identifying this evident increase in minimum values as a trend provokes concern, as there have been only two minima ever measured in this way. We must be aware that the warming trend in the surface temperature goes far beyond the last two decades, and that an extension of the solar record is necessary to assess whether solar activity and irradiance is indeed increasing at the minima of the cycles and what the potential effect on the climate may be. The solar record has been extended by the use of the historical sunspot records already mentioned and correlations have been drawn between solar irradiance and the temperature curve since 1610, suggesting a predominant solar influence in the pre-industrial period. But since 1860 only half the observed warming could be attributable to the irradiance increase, indicating that some other influence is becoming more influential in controlling the temperature change: most likely industrial carbon-dioxide.
Recent studies of global warming have necessitated a more comprehensive effort to quantify the natural climate variability so that the residual change may be attributed to the anthropogenic emissions of greenhouse gases. This attempt at quantification of the many different forces effect on the climate has re-emphasized the complexity of the climate system and the simultaneous interaction of many influences. Solar irradiance may indeed account for some of the temperature increases recorded over the last several decades, but as the atmospheric CO2 rises, due to the exponential increase in emissions from industrial sources, the influence of solar variability on the Earth’s climate will most likely decrease, and its relative contribution will be far surpassed by “greenhouse” gases.
31. The author focuses primarily on ____.
A. pointing out the success of a certain line of scientific inquiry into the terrestrial effects of solar activity while qualifying its successes with regard to climate change
B. giving a brief overview of some recent scientific developments in solar physics and explaining their possible implications for future research
C. discussing the successes in linking terrestrial phenomena with solar activity and indicating how they may have an impact on preventing further climate change
D. presenting two competing scientific theories for the cause of post-industrial climate change and evaluating the body of evidence behind each one
32. Which of the following statements concerning the comparison between preindustrial and post-industrial climate change, as described in the passage, is accurate?
A. The pre-industrial period experienced a much greater degree of climate change, owing to solar activity
B.The post-industrial period experienced a much greater degree of climate change, owing to greenhouse gases.
C. Both periods have experienced a degree of change, but their primary causes are different.
D. Both periods have experienced a degree of change, and their primary causes are identical.
33. According to the passage, extending solar record is important for which of the following reasons?
A. It would allow scientists to establish whether the warming trends owe to industrialization or to natural factors existing prior to industrialization.
B. It would help establish whether the data supporting the existence of the Maunder Minimum is reliable.
C. It would determine the extent to which sunspots plays a role in increasing the sun’s irradiance.
D. It could possible corroborate the information on sunspots provided by satellites.
34. According to the passage, sunspot cycles have which of the following characteristics?
A. During the minima phase of the cycle, there is lower overall irradiance but greater local irradiance, and fewer sunspots.
B. During the minima phase of the cycle, there is greater overall irradiance but lower local irradiance, and fewer sunspots.
C. During the maxima phase of the cycle, there is lower local irradiance but greater overall irradiance, and more sunspots.
D. During the maxima phase of the cycle, there is lower overall irradiance but greater local irradiance, and more sunspots.
35. It can be inferred from the passage that the author regards the correlations drawn in recent decades between sunspots and terrestrial phenomena as
A. more reliable than similar correlations drawn in the past, but still inconclusive
B. solid evidence of the complexity of the climate system and the simultaneous interaction of its many influences
C. poorly supported by the statistics mentioned at the beginning of the passage
D. unlikely given the predominant role played by greenhouse gases