Temperatures over the last 100+ Years
This visualization explores how temperatures have varied in the United States over the last 100+ years. Though the United States is undoubtedly getting warmer, there remains significant variation state-by-state and year-by-year. In the map visualization above each datum is show as the difference between the mean temperature in a state on a given year and that state’s mean temperature over the last 118 years. A dark blue state indicates a year that is much cooler than average, while a dark red state indicates a year that is much warmer than average. The video below shows these deviations from the temperature mean for the continental US from 1900 to 2017.
Perhaps the most easily dicernable takeaway from this visualization is the lack of a clear trend. Yes in the 1990s there began to be increasingly more states colored dark red, but cool years did not go away. 1998 set a record for the hottest year ever recorded in the United States, then this record was exceeded in 2006, 2012, 2015, 2016, and 2017. Other years in this span however, such as 2008, 2009, 2013, and 2014, had mean temperatures only slightly above the long-term average. A clear trend is similarly difficult to identify on the state level from year to year. There is no apparent correlation to suggest that an abnormally warm year in a state predicts that same state will be warm the next year as well. The only clear trend in this vein is that warm or cool years tend to affect regions, not independent states. For example say Alabama had a mean annual temperature well below its average, it is likely that Missouri and Georgia also recorded lower than average temperatures that year.
Some trends that are exposed by this visualization are nonetheless unsettling. Each of the last 20 years in the United States has had an above average temperature. Since 1900 there have been 20 years where over 90% of states have had higher than average temperatures—16 of those 20 have been since 1990. There have been 10 years where every state in the continental US recorded a higher than average temperature—9 of them have happened in the last two decades. If those 10 abnormal years were to be distributed randomly over the period of 1900–2017, the probability is around 1 in 60 million that nine of the ten would land in the last 20 years.
On years that the average national temperature is abnormally high, it tends to be true that the temperature in most states is also above average. This means that a high mean national temperature, as seen in many recent years, is generally the outcome of collective high temperatures, not a few outlier states that bring up the average.
Of course, there are significant trends that this visualization misses. One significant example are temperature spikes within a year. A noticeable affect of climate change has been the increase of extreme and erratic weather patterns. Say Oregon in a given year recorded extremely high temperatures during the summer, and then extremely cold temperatures in the winter. The summer heat could cause devastating wildfires across the state, and the winter freezes could greatly increase energy usage and impact travel. In this visualization those extremes would cancel, and that year would register as unremarkable.
Click here to see the full interactive data visualization
This data is collected from the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information.
