Washington recently experienced its highest January temperature on record, reaching a high of 80 degrees. This is the first monthly record since 2019 when October saw a record-breaking temperature of 98 degrees. However, while warm-weather records have been more frequent, the number of cold-weather records has been significantly lower.
The increase in record warmth can be attributed to human-caused climate change, resulting from rising greenhouse gas concentrations in the atmosphere and urbanization. In recent decades, there has been a noticeable disparity between the number of record highs and record lows, with record highs surpassing record lows by a factor of 20.
In terms of historical data, February was the only other winter month to reach such a high temperature as 80 degrees before this recent record. This temperature is also the earliest in the calendar year on record, with the previous earliest occurrence being on February 21, 2018, when Washington reached 82 degrees.
Interestingly, many of the maximum temperature records, especially for each month, are quite old. Out of the monthly records, only June 2012, October 2019, and January 2024 have occurred in the 21st century, while the observations date back to the 1870s.
While monthly warm-weather records have been relatively few, calendar day records have been more frequent. Due to rising temperatures, it is likely that more monthly records will be broken in the future.
Comparing recent trends with the past, the last decade, the 2010s, saw a significant disparity between the number of calendar day record highs and lows. There were 46 record highs and 107 record-warm lows, compared to only three record lows and six record-cold highs. In contrast, the 1880s exhibited the opposite pattern, with eight record highs and 11 record-warm lows, compared to 37 record lows and 50 record-cold highs.
Furthermore, record-warm lows, which indicate abnormally warm nights, have become more common in the past decade or two. The 2020s have already seen 20 such records, in addition to the 107 set in the 2010s. In contrast, the first five decades of the record, from the 1870s to the 1910s, only saw 38 record-warm lows.
Although warm overnight temperatures may not receive as much attention as record-high afternoon temperatures, they have been increasing rapidly.
Examining the distribution of records seasonally, the majority of cold-weather records during the winter occurred between 1880 and 1909, with very few occurring in recent decades. December has not seen any record lows since 1989, and February has only had one record low (in 2015) since the 1970s.
In the summer months, July has seen a dramatic increase in record-warm lows, with 19 of these records occurring since 2010. The 2010s also had the highest number of record highs in July compared to any other decade.
Considering the influence of the climate pattern El Niño, it is expected that the year following its onset will have more heat records. With the additional impact of human-caused climate change, it is likely that more heat records will be broken in the coming months.
