Weather versus Climate

What's the difference?

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Weather in Montana varies tremendously, with 50-degree temperature swings occurring on a single day at times, and thunderstorms, rain, heavy snowfall, and extremely hot sunny days scattered throughout the year.

So with all of the talk about climate change, what exactly is the difference between weather and climate?

And how can we tell if our climate really is changing with so much natural variability in our weather from year to year?

Photo: iStock.

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Weather occurs on a short-term basis - from day-to-day or week-to-week - and is a mixture of events that include temperature, humidity, precipitation, wind, and cloudiness.  When we say things like,"What time is it supposed to start raining today?", we are talking about weather.

Climate, on the other hand, is the average weather pattern in a geographical location over a much longer period of time, typically 30 years or longer.  When residents of Montana talk about how much colder winters used to be in the 1970's than they are now, they are talking about climate.

An easy way to remember the difference is that climate is what you expect (a cold, snowy day in winter), while weather is what you get (an early spring thaw).

Figure: iStock.

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Climate is a very complex phenomenon, and varies over extremely long periods of time, as well as shorter periods of time.

In Montana, short-term changes in climate happen every 3-7 years during El Niño events, when normal patterns of wind, temperatures in the ocean and the atmosphere, and ocean currents change dramatically in the Pacific Ocean. These changes cause a lot of severe weather around the globe.

These El Niño events are associated with decreases in winter snowfall and increases in forest fires, while La Niña (the climate event that follows El Niño) brings cold air and heavy snowfall to our state - as happened in the winter of 2010-2011.

Figure: National Oceanic and Atmospheric Association.

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The complexities of climate mean that it is impossible to point to one weather event and say that it was caused by climate change.

It is possible, however, to determine that sharp increases in severe weather events in a geographical area may be associated with changing climate conditions.

By comparing average temperatures (or average levels of rainfall or snow) in the past several decades to average temperatures (and rain or snowfall) a century ago, scientists can see that Montana's climate is different now than it used to be 100 years ago.

Photo: iStock.

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Montana is warmer and drier than it used to be in the early 1900's, for example.

The above map shows changes in precipitation across the United States between 1958 and 2008, with areas in brown becoming drier over time, while areas in blue have become wetter during the same period (report by the U.S. Global Change Research Program).

Figure: Intergovernmental Panel on Climate Change.

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In the end, understanding changes in our climate over the past century will help us to plan more effectively for the future, and to take care of our families, businesses, land, and wildlife species here in Montana.

Much of our planning for the future is likely to center around our precious water resources, because we depend on water for everything here in Montana:  to drink, to water our crops and cattle, to keep our forests healthy, and as a home for our native trout fisheries.

To learn what members of your communities are doing to address climate change, click here.

Photo: iStock.