“The forecast for today is sunny and clear with a high of 85 degrees, which is above average for this time of year.” This is information that people generally like to hear each day-the weather. But when forecasters say “above average” or” below average” what do they really mean? The National Oceanic and Atmospheric Administration (NOAA) began tracking climate data in 1901 and both every 30 years and every 10 years they release new climate “normals,” or temperature and precipitation averages based on this data. This can serve as an indicator for the future. The most recent of of these time blocks ended last year. Why 30 years? There is a general rule is statistics that 30 numbers are needed for a reliable estimate, which is why this time frame was chosen to define what is “normal” in climate, which includes annual, seasonal, monthly, and hourly averages of temperature, precipitation, and other variables. Michael Palecki, the Normals Project Manager for the NOAA, stated that the World Meteorological Organization, which is part of the UN and helps its members adapt to a changing climate, requires member nations to release normals every 30 years. However, in 2015 they also began requiring normals every 10 years ending in 0, though Palecki stated that the US started updating normals every 10 years in the the 1950’s. 2020 was both the end of the 30 year and 10 year period which made it particularly significant.
The general trends the NOAA released for each quarter of the year are as follows:
January: Temperatures rose 0.5-1.5 degrees Fahrenheit over most of the country. The north-central region cooled by more than 1.0 degrees F and precipitation increased by 10-25%. Texas and Florida were also much wetter from 1991-2020.
April: Temperatures were lower in the north-central U. S. West and East of the Mississippi River were considerably warmer and the Southeaster quarter of the country was wetter. The Southwest was drier, though there was higher precipitation in the northern Rockies and the Great Lakes.
July: The Northwest was drier, though most of the West was near the same temperatures. There was a cooling trend in the north-central U. S. and a warming trend in the Northeast, entire West and Rocky Mountains. Texas was up to 2 degrees F. warmer.
October: The western 2/3 of the northern U.S. was wetter and cooler. The rest of the country was consistently warmer and the Southwest and South-Central was also drier. The East was warmer with alternating zones of wetter and drier.
The above information are the general trends the NOAA released in their report, but of course there are variations from season to season and in different parts of the country, which is largely due to differences in air currents, snow pack, and surface temperatures. Palecki explained that changes in the U.S. vary with season and location due to “differences in how atmospheric circulation responds to green house gas induced climate change. In recent decades, reduction between polar and equatorial regions causing the jet stream circulations above the mid latitudes to move further north and south as it becomes more sluggish. More northerly movements over the western U.S. and more southward plunges in the eastern U.S. have occurred especially in the winter and spring. This impacts temperatures and precipitation patterns. It is further complicated by changing patterns of soil moisture, snow cover, and other atmospheric feedbacks.”
Palecki also stated that climate change has “accelerated” in recent decades beyond the rate of change in earlier decades. Globally 2013-2020 was in the top ten all time for temperatures. The World Meteorological Organization stated in their “State of the Global Climate” that 2020 was one of the 3 warmest years on record and the 6 warmest years have all been since 2015. The WMO was contacted for an interview, but did not respond.
The climate is a complicated aspect of our planet and it is affected by many different factors. When certain parts of the country are negative 20 degrees the phrase “global warming” may not seem to be all that accurate. But climate is not based on relatively short time frames, but overall trends. An understanding of what these trends are and how climate is affected is crucial to our understanding of how we impact the planet as well as how we plan for the future.