The Question

In 1966, the World Meteorological Organization (WMO) put forth the term “climatic change” to refer to climatic variability on time-scales longer than ten years, regardless of the cause for such change. During the next decade, scientists began to suspect that human activities had the potential to drastically alter the global climate in ways that would have negative impacts on our environment. The term evolved into “climate change” and is now used to describe both the process of change and the perceived problem. Sometimes the term “global warming” is used, though in many ways this fails to adequately describe the variability in impact, since climate change can cause both hot and cold extremes in weather. Anthropogenic climate change is change that is caused by human activity, as opposed to the Earth’s natural processes. However, in the context of environmental policy, the term “climate change” is often used to mean anthropogenic climate change.

Mauna Loa Observatory is a world-renowned atmospheric research facility. It has been continuously monitoring and collecting data since the 1950’s and its remote location makes it very well-suited for monitoring atmospheric components that can contribute to climate change, including the heat-trapping greenhouse gas carbon dioxide (CO2). Carbon overload from burning fossil fuels and deforestation is cited as the primary cause of anthropogenic climate change by proponents of such theories, while opponents assert that natural process (such as photosynthesis) contribute more to atmospheric CO2 than humans and observed changes are simply Earth’s cycle.

Monthly Mean CO2: The Last Five Years

Create your own version of the plot found here. Do not replicate it, but rather design your own. Use one of the themes found in the ggplot2 or ggthemes packages. You are encouraged to make style adjustments to help you informatively display the data.

'data.frame':   731 obs. of  8 variables:
 $ year          : int  1958 1958 1958 1958 1958 1958 1958 1958 1958 1958 ...
 $ month         : int  3 4 5 6 7 8 9 10 11 12 ...
 $ date          : num  1958 1958 1958 1958 1959 ...
 $ mean_co2      : num  316 317 318 -100 316 ...
 $ int_mean_co2  : num  316 317 318 317 316 ...
 $ trend_mean_co2: num  315 315 315 315 315 ...
 $ numdays       : int  -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 ...
 $ decade        : chr  "1950s" "1950s" "1950s" "1950s" ...
      year          month             date         mean_co2     
 Min.   :1958   Min.   : 1.000   Min.   :1958   Min.   :-99.99  
 1st Qu.:1973   1st Qu.: 4.000   1st Qu.:1973   1st Qu.:328.52  
 Median :1988   Median : 7.000   Median :1989   Median :351.49  
 Mean   :1988   Mean   : 6.506   Mean   :1989   Mean   :349.88  
 3rd Qu.:2003   3rd Qu.: 9.500   3rd Qu.:2004   3rd Qu.:376.08  
 Max.   :2019   Max.   :12.000   Max.   :2019   Max.   :411.24  
  int_mean_co2   trend_mean_co2     numdays         decade         
 Min.   :312.7   Min.   :314.6   Min.   :-1.00   Length:731        
 1st Qu.:328.6   1st Qu.:329.5   1st Qu.:-1.00   Class :character  
 Median :351.5   Median :352.0   Median :24.00   Mode  :character  
 Mean   :353.9   Mean   :353.9   Mean   :18.39                     
 3rd Qu.:376.1   3rd Qu.:376.6   3rd Qu.:28.00                     
 Max.   :411.2   Max.   :410.5   Max.   :31.00                     
[1] "year"           "month"          "date"           "mean_co2"      
[5] "int_mean_co2"   "trend_mean_co2" "numdays"        "decade"        

Monthly Mean CO2: A Major Milestone

An atmospheric CO2 level of 400 ppm is considered by many to be a symbolic threshold with regard to climate change. “In the centuries to come, history books will likely look back on September 2016 as a major milestone for the world’s climate. At a time when atmospheric carbon dioxide is usually at its minimum, the monthly value failed to drop below 400 parts per million.” (source)

Adapt your plot above to include a red dashed line at 400 ppm and a large red dot on September 2016, with appropriate annotations to indicate what these additions represent.