Weather vs. Climate
“Climate is what you expect; weather is what you get,” (Robert Heinlein).
“Climate lasts all the time, weather lasts only a few days,” (Mark Twain).
Weather tells you what to wear on any given day; climate tells you what wardrobe to have.
Other examples include:
While we can’t predict the exact temperature on January 1 in Fairbanks, Alaska (weather), we can say with a large degree of certainty that January in Fairbanks will be colder than July (climate).
Left: A diagram of the physics behind the seasonal cycle. Evaluation of the basic physical principles that drive Earth’s weather, like the Earth’s tilt, are what climate scientists do. This is a different exercise than actually trying to predict what the weather will be like in a few days at a particular location, which is what meteorologists do.
Climate determines the possible range of weather events. It can get hot during the summer, but the thermometer will not reach 200 degrees. It can get windy, but the winds won’t reach 400 miles per hour. Similarly, how high the waves can get when you make a splash in a swimming pool is determined by the pool depth; the deeper the pool, the higher the possible waves. It’s hard to make much of a splash when the pool is only two feet deep! The waves generated when someone jumps in are like day-to-day weather events, which fall within certain parameters that are set by the depth of the pool. Likewise, the parameters of the weather are determined by the state of Earth’s climate system, which changes as it collects or loses more energy.1
Image left: The more water there is in a swimming pool, the bigger the waves you can make. The more energy there is in the climate system, the more extreme the weather events can be. Image Earth Gauge.
As anyone who watches their weight knows, weight fluctuates from day to day. Charting your weight over the course of a few months, however, can be used to establish a general trend of gaining or losing weight. Determining if and how climate is changing requires more than just one day, week, month, year or even decade of measurements and recordings of weather events. Similarly, determining whether you are gaining or losing weight requires more than one day or week of weighing yourself.2
Remember old-fashioned pinball mazes? Let’s say that each ball is the weather. Forecasting the weather is like forecasting the path of one ball dropping down an old-fashioned pinball maze. After a few pegs, you cannot predict where the ball will go next. After watching many balls, you can see where most of them land, but any particular one might go anywhere. Disturb the system and many, but not all balls, shift. Climate is like the average distribution of balls at the bottom of the maze. Climate is not one ball. It is the average of thousands of balls. So, climate is the average weather over 10, 20, 30 years.
In Brief: The stock market, like the weather, fluctuates from day to day. Finding a trend in either weather or the stock market requires looking longer-term.
Weather forecasting is similar to buying a stock on Monday and expecting to sell it on Friday at a profit. You can track every uptick or downtick in the stock market, but still not guess which stock will go up or down in just one week. That’s like weather: day-to-day changes. Climate is the weather conditions averaged over 10, 20, 30 years. A stock market analogy for climate is an indexed mutual fund. You buy a mutual fund for a long-term investment over years, not days. Here, you follow the major market moves, not the daily wiggles.
- Sub-analogy: Taking a five minute snapshot of the Dow on any given day and using that trend to predict the closing value is foolish.3
- Sub-analogy: Despite 2008 being a terrible year for the market, in October 2008 the DOW set an all-time record for a one day gain of almost 900 points. The one day gain is like weather; the trend over the entire year is like climate. If you picked that one day, you would think it was a great year for the stock market, when we know it was the opposite.4
1. Concept from Dan Satterfield, WHNT, Huntsville, Alabama
2. Concept from Brady Phillips, NOAA
3. Concept from Michael Mogil, weatherworks.com
4. Concept from Paul Gross, WDIV, Detroit, Michigan