Weather vs. Climate

by Sebastian Hettrich

“It is snowing here, where is the global warming?” – this and similar statements are sometimes heard when current weather conditions do not seem to fit “global warming”. There is however a widespread misconception about what weather and climate actually are and, despite not being the same thing, these two terms are often used synonymously, yet.

The term “weather” refers to current – and often very local – atmospheric conditions. Whether it is right now sunny or cloudy, whether it rains, snows or storms, and whether it is cold or warm outside, falls under the definition of weather. Weather is a local phenomenon, and may be different only a few kilometres away. Weather conditions can be fast-changing, or long-lasting, depending on many factors such as the season, geography, or the current atmospheric conditions in other regions, as these are very often interconnected. Weather is therefore highly variable. Knowledge of current weather conditions is important for many economic sectors, for example agriculture or transport, and of course since everyone needs to know what to wear before going out.

In contrast, “climate” is the long-term average of all weather events at a given location over a certain period of time. It is therefore based on the weather statistics, for example, the calculation of a daily average temperature based on all temperatures recorded during the day. The average of all these daily averages over one month results in the monthly average temperature, and the average of all monthly averages over one year  results in the annual average temperature. 

Let’s take for example data from Berlin in 2019 [1]:  The average temperature for January was 1.6°C; however this does not mean that every day in January was 1.6°C. In fact the lowest temperature measured was -7.0°C and the highest was 8.3°C, so there were colder and warmer days. The same goes for annual average temperatures – while you experience cold winter months like January and warm summer months like August with 21.2°C , the annual average temperature could be just 9.3°C. 

Due to statistics, a single extreme value, for example from one very cold or very hot day, will not really affect the annual average temperature. However, if there are many days in a year, which are either colder or hotter than normal, these will add up and vary the annual average temperature. In fact, scientists refer to the “natural variability of the climate system” to describe the fact that temperature fluctuations between warmer or colder years can deviate from the multi-annual average by a range of +/- 0.3°C  [2]. The longer the time-period considered for averaging, the smaller this variability becomes, and in an ideal world, the resulting average would remain nearly the same for each period of time.

This would be true in an ideal world, i.e. one that is not subject to “climate change”. Climate change, as can be observed in the real world, refers to changes in the average climate that show a certain continuous trend and are driven by external factors like changes in the chemical composition of the atmosphere.

So, is the term “global warming” now any different to climate change? – Not necessarily – “global warming” just states that one aspect of climate, namely the global average temperature, is increasing. If you are interested in why or how that is happening, then stay tuned for our next articles.

References:

[1] German meteorological service, climate data worldwide, https://www.dwd.de/DE/leistungen/klimadatenweltweit/klimadatenweltweit.html, retrieved on 2^nd Nov. 2020[2] Wigley, T.M.L., Raper, S.C.B., Natural variability of the climate system and detection of the greenhouse effect, 1990, Nature, Vol. 344, pp 324-327, doi:10.1038/344324a0.