Science Practice Challenge Questions

35.5 Climate and the Effects of Global Climate Change


Twenty targets for the protection of biodiversity by 2020 were established by the 2010 Convention on Biological Diversity. Midway to the target date it is widely agreed that the goals will not be met. The 2016 Living Planet Report from the World Wildlife Federation claims global populations of animals fell by 58 percent between 1970 and 2012 and extrapolates the loss by 2020 to 67%. E.O. Wilson's estimate of the current extinction rate is three species per hour. Geologic periods are defined by mass extinctions. The proposed name for the current geological period is the Anthropocene (Waters et al, Science, 2016).

During the current period of mass extinction, human activities are driving loss of habitat and climate change. Climate change during the last 500,000 years is a direct consequence of rising atmospheric CO2 levels, as the graph shows. The relative abundance of O16 and O18 isotopes can be used to infer temperature because as temperature increases the lower mass isotope is enriched in the atmosphere (objects with a smaller mass have a higher velocity at equal molecular kinetic energy that is proportional to temperature).

This graph shows that the concentration of atmospheric carbon dioxide and temperature have fluctuated up and down in a cyclical pattern four times over the past 450 million years. Today, the concentration of carbon dioxide is higher than at any time other time shown in the graph, and the temperature is rising as well.
Figure 35.31

The role of humans in the last great extinction, the Holocene Extinction, during which the megafauna such as the wooly mammoth, the wooly rhinoceros and the giant deer disappeared, has long been debated. Did we hunt these creatures to extinction? By examining all available DNA evidence, Cooper et al.(Science, 349, 2015) have compared time extinction intervals with these oscillations of climate as shown in the table.

Animal Label Location Beginning extinction date (thousand years ago) Ending extinction event (thousand years ago)
Bear a Beringia 24 21
Bison b Europe 35 32
Rhinoceros c Britain 36 32
Rhinoceros d Russia 14 13
Horse e North America 15 13
Horse f Beringia 43 38
Mastodon g North America 12 11
Mammoth h Europe 13 12
Mammoth i Eurasia 11 10
Musk Ox j Eurasia 48 44
Deer k Europe 13 12
Cave Lion l Beringia 14 12
Cave Bear m Europe 29 27

Additionally, the data shown in the graph below are obtained from ice cores. The deeper the sample, the older the sample. The percent departure from the current O18 percentage that is graphed above is a measure of temperature relative to the present temperature. The higher the isotope concentration, the higher the average temperature of the ocean.

The graph shows that the percentage of the oxygen-eighteen isotope fluctuated up and down between 10 and 50 thousand years ago, indicating that the temperature fluctuated as well. Spikes occurring at 12, 13, 14, 24, 26, 28, 32, 33, 34, 37, 41, 42, 44, 47, and 49 thousand years ago indicate that the temperature was highest in these years. The extinction of the bear occurred between 21 and 24 thousand years ago, corresponding approximately with the spike at 24 thousand years.
Figure 35.32
  1. Refine the graph by adding the interval of time of extinction with a label drawn from the table as shown by “a”.
  2. Analyze these data in terms of the clustering of extinction events.
  3. Based on your analysis, explain how ecosystems have changed during the last 40,000 years, and identify the factor that caused these changes.
  4. Based on the correlation between Earth’s temperature and the concentration of CO2 in the atmosphere, predict what will happen to animal populations in the future.