Weather vs. Climate: How Do They Differ?

Article by Commodities Management Group

People often try to dispute or confirm climate change due to a single weather event. There are big differences between what we call “weather” and “climate”. Weather refers to short-term changes in the atmosphere, and climate refers to the weather over a very long period.¹

The normal temperatures that the market weather vendors use are averages of temperatures over a 10- or a 30-year period. The 30-year normal is updated by the National Atmospheric and Oceanic Administration (NOAA) every 10 years, while the 10-year normal is the running average.

Climate data can tell someone what they can expect during a given time of year. Usually there is cold and snowy weather across the Midwest from December through February, while the Southeast tends to be hot and humid during the summer months. While descriptions of a location’s climate can tell someone what to expect, it does not provide any specific details about what the weather will be on a given day.¹ There could be a very warm day across the Midwest during the winter months and a cool/dry day across the Southeast during the summer months.

While descriptions of a location’s climate can tell someone what to expect, it does not provide any specific details about what the weather will be on a given day.

The 2021 snowstorm in Texas known as Winter Storm Uri may be used as a point to either prove or disprove climate change. While global climate change has been linked to increased temperature volatility, this one volatile cannot prove or disprove climate change. This event was purely a weather event; however, the frequency of such volatile events has been increasing over the past several decades. This long-term uptick in volatility can be linked to climate change since the period is quite long.

Climate change does not mean that it will never be cold again.² There will still be wintry weather conditions despite a warming planet. Climate change tells us that warm days may be a little warmer and cold days may be a little less cold. Days of record cold temperatures are still expected, however a lot of small warmer changes over a long timescale (decades) can ultimately add up to something more substantial. For example, the current 10-year normal is quite a bit warmer than the current 30-year normal.

In fact,  experts at the World Meteorological Organization (WMO) concur that 2011-2020 was the warmest decade on record.³ Additionally, a 2021 report by the United Nations Intergovernmental Panel on Climate Change stated the global average temperature has risen by about 1.1° Celsius above the late 19th century average.⁴

The WMO concurs that 2011-2020 was the warmest decade on record.

The starkest difference is seen during the summer months. For example, for 2021, the current 30-year normal (1991-2020) for population-weighted cooling degree-days (PWCDDs) is 917, while the 10-year normal (2011-2020) is 978. To put this into context, if this summer had come in right at the 10-year normal of 978 PWCDDs, it would be the 7th hottest summer since 1950. If this summer came in right at the 30-year normal of 917, it would be the 21st hottest summer since 1950.

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References

1. https://www.noaa.gov/
2. http://climate.org/
3. https://public.wmo.int/en/media/press-release/2020-was-one-of-three-warmest-years-record#:~:text=All%20five%20datasets%20surveyed%20by,2020%20being%20the%20top%20three
4. https://www.bloomberg.com/news/articles/2021-08-09/ipcc-report-on-climate-science-5-key-takeaways