Evidence of Anthropogenic Warming

Referring to figure 3 on page 182 in Weart, how would you argue that we have entered a time of anthropogenic warming?  If you had been living in the 16th to 19th centuries and had the data of figure 3 to that point in time how would you argue the possibility of climate change?

 Extrapolating a story from climate change data is difficult because there is a great deal of variability involved.  Weather and temperature change constantly so exact numbers often fade to averages and estimates.  The further back in history one explores, the more uncertainty there will be simply because of less technology and attention paid to the subject.  However, through ice, pollen, soil, and fossil samples, scientists have pieced together the story of earth’s climate.  The graph on page 182 of Weart’s The Discovery of Global Warming, shows temperature changes from the year 1000 AD to 2000.  From 1000 to the mid-1800s, there is a huge range of data, but the numbers each year average to about 0.5 degrees of change or less.  Although there is natural change, it fluctuates up and down and only slightly.  During this time period, humans had far less technology and burned less fossil fuel.  Humans still impacted the earth but not on the scale of today. 

In the 1850s, the industrial revolution began in Europe and society changed.  As it became easier to create, people became more accustom to consuming.  The amount of fossil fuels humans burned increased immensely.  On the graph, it is clear when this change occurred because the temperature appears to increase without as much up and down fluctuation.  From the early 1900s to 1998, the average temperature increased by over one degree Celsius.  This seems insignificant, but because of the amount of carbon dioxide humans continue to emit into the environment today, nothing is going to stop this trend from continuing.  A few degrees change in temperature is enough to alter the global environment which would have vast negative ramifications for humans.  In comparing the graph to the evolution of human society, it is safe to say that people, primarily through the burning of fossil fuels, are causing the climate to warm.

It would be difficult to argue that climate change was occurring prior to the mid-1800s using this graph.  There are trends which look like large fluctuations, but the temperature bounces back up or down rather quickly.  There are no time periods which parallel the 1900s in consistent temperature change.  To some extent, this makes sense because humans were producing minute amounts of greenhouse gases compared to the post-industrial revolution time period.  The fact that climate change is only clear in the last century further supports the theory that we have entered a time of anthropogenic warming.