Q4.14. which factor or factors are responsible for the timing and severity of the numerous ice ages that occurred over the past 800,000 years? a) changes in solar forcing only b) changes in co2 levels only c) changes in solar forcing amplified by changes in co2 levels d) very large volcanic eruptions q4.15. the following statements describe four distinct types of evidence that climate scientists have collected. which of these actually enables scientists to attribute recent changes in earth's climate to human activity? a) observations from multiple sources show that mean global surface temperature has increased since the industrial revolution. b) various observations suggest that small changes in earth's orbit are the primary driver of historical ice ages. c) global climate models (gcms) can only reproduce recent temperature increases when anthropogenic greenhouse gas emissions are included as a forcing. d) gcms describe the climate system so well that weather phenomena such as hurricanes arise even though they are not specifically coded into the models.