GLOBAL WARMING 

PART 1:  The Evidence for Global Warming

Air temperatures measured at the land surface in various locations have been used to create a plot of "average annual global temperatures" since 1880 (orange line on linked figure).  Although this graph suggests that "average global temperatures" are increasing through time, not all stations show this trend.  In addition, air temperatures measured in the atmosphere above the earth with satellites (available since 1979) do not show an upward trend  (see blue line on linked figure). 

1. Because of the uncertainties associated with temperature data, some scientists have
    questioned the significance of an upward trend to "average global temperatures", and
    others have looked at different evidence to support the hypothesis of global warming.
    As described on pages 309-311 in your textbook, the geologic evidence for warming
    includes:   
                            Changes in mountain glaciers (see Figure 11.4)
                            Thawing permafrost in boreal and subarctic regions
                            Rising sea levels
                            The thinning polar ice cap

    Why might the evidence cited above be a more reliable indicator of the temperature
    trends than actual air temperature measurements?

2. Figure 11.13 from your text shows that the evidence for global warming from modern
    glaciers is not entirely consistent.  If average temperatures are rising worldwide, how
    can some glaciers be advancing while others are receding?

3. Evidence for global warming from sea level trends is also not consistent.  If global air
    temperatures are rising, why aren't sea levels rising uniformly along all shorelines?
    To answer this question, see the EPA sea level site and the last paragraph before
    Local Erosion on page 272 in your text.
 

PART 2:  Carbon Dioxide and Air Temperatures

1. Figure 11.24 in your text shows temporal variations in land-surface air temperatures
    and atmospheric carbon dioxide concentrations at Mauna Loa, Hawaii, 1880-2000.
    Does there appear to be a correlation between these two variables?

2. Figure 11.27 in your text shows temporal variations in atmospheric temperatures and
    carbon dioxide concentrations inferred from air bubbles trapped in an ice core taken
    from the Antarctic ice sheet (details about how the data were collected are described
    on pages 308-309).  What auxiliary assumption is made when using the analysis of
    air bubbles to infer past climatic information?
 

3. Do the data in Figures 11.24 and 11.27  prove  that carbon dioxide concentrations in
    the atmosphere affect air temperatures?  Why or why not?
 

4. Is there a plausible causal mechanism to explain why carbon dioxide might affects air
    temperature?  Has this hypothesis been adequately tested to demonstrate that there 
    is a cause and effect relationship?
 

5. Given the temporal variations in temperature shown in Figure 11.27, is it possible that
    the climatic changes we are observing today have entirely natural causes?