The world is getting hotter! The year 2017 has been confirmed as the second (NASA1 and Berkeley Earth2) or third (NOAA3 and University of Alabama in Huntsville (UAH)4) warmest year on records. Further, 2017 has been ranked the warmest non-El Niño year on record. Records for land-based observations typically begin between 1850 and 1880 while the satellite data interpreted by the UAH team dates back to 1979. But what does the year-to-year and monthly variation and temperature increase look like?

Today’s chart illustrates monthly global temperatures for every year from 1880 to 2017 using NOAA data5. Each line is a separate year and the lines are colored on a graduating scale from early years in the record (blue) to recent years (red). Key years are colored and labeled separately. The four most recent years—2014 to 2017—are the four hottest years on record and are colored red (2015), green (2014), blue (2016), and orange (2017). Four representative years are colored in bold grey including 1998 (eighth hottest year), 1989 (32nd hottest), 1951 (63rd hottest) and 1908 (138th hottest… the coldest year on the 138-year record). The 19th (20 years), 20th (100 years), and 21st (18 years) century averages are shown as straight dashed lines. Temperature anomalies for this NOAA dataset are temperature offsets from the 20th century average, hence the 20th century dashed line is at 0 °C.

Several observations are clear from the chart:

  • The world is getting hotter! Annual temperatures show a clear progression from lower-temperature early years (blue lines) at the bottom of the chart to higher-temperature later years (red lines) towards the top of the chart.
  • There is significant variation between years, but also across the 12 months in a single year. For example, in 1951 (thick grey line on the chart), February was the 129th warmest (10th coldest) on record while December was the 44th warmest (95th coldest) December.
  • The most four recent years are significantly warmer than previous years. For instance, the years 2015 (three months) and 2016 (nine months) hold all the individual monthly temperature records for the 138-year record.
  • On average, the coldest month on record occurred in 1906 and coldest month record has not been broken since 1911.
  • March, on average, is the hottest month globally, followed by December and then September. Since 1950, that order is March, April, then December.

Data and software: Monthly global temperatures data were sourced from NOAA5. The data were compiled and visualized using Microsoft Excel6.