The Difference Between Weather & Climate
While both weather and climate are similar concepts in that they both refer to temperature, precipitation, wind and other related factors, they are actually very different phenomena. The primary differences between the two concern: 1. the time frame they refer to and, 2. their geographic extensiveness.
At its simplest, weather is what you see outside everyday. It may change from day to day, month to month, or year to year, but it is essentially both a /short-term/ and /localized/ phenomena.
Climate is much different. Climate is what we speak of when we discuss global warming, for instance. Climate is what we speak of when talk about ice ages versus warmer periods throughout geological history. The “little ice age” which gripped Europe between roughly 1500 to 1850 A. D. could also be referred to as a climate change, because it is sufficiently long-term and extensive.
Thus the difference between climate and weather is not the difference between one day and the next, one month and the next, or even one year and the next. Climate changes over a much longer period. Changes in climate are also not localized, they are global changes affecting entire regions and the planet itself.
Thus where weather refers to a /local/ and /short-term/ phenomena, climate refers to a /global/ and /long-term/ change in weather patterns. “Long-term” meaning on the order of centuries, not months or years.
Much confusion has been added to the entire debate concerning global warming, in fact, by people who use weather statistics to argue for changes in climate. It is not uncommon to hear people say that the 1990s were the warmest decade on record, and also contained three of the warmest years on record. They then go on to claim that this indicates a change in climate.
But it doesn’t, a year, or a few years, or even a decade of warmer weather is not enough to establish a long-term, global change in climate.
A better indicator, according to Gregg Easterbrook, is that the number of frost free days has been increasing consistently for over 50 years. In that time the “frost free season” in the continental United States, for example, has increased by about 11 days.
The effect is even more pronounced at higher latitudes. The Inuit who inhabit the high arctic report a clear trend over the past century towards longer summers and shorter winters. This change has become so pronounced in recent years that it has begun to affect the health of polar bears, who are beginning to starve due to changing ice conditions and temperatures.
When an animal species which evolved in order to adapt to the climatic conditions in a particular region over thousands of years begins to suffer from changes in the weather, then we can certainly speak of a long-term change in climate with some degree of certainty.
Coral reefs are an even better example. Coral are tropical species which live where there is little fluctuation in temperature. Consequently, they are adapted to only a narrow window of temperature. If the water becomes too warm the colonies of coral can die off, leaving a forest of skeletal reefs devoid of life (or bleached coral). Such bleaching events also leave a material trace in the coral itself (like a tree ring). Scientists can measure how long a span there is between such events as a consequence.
The last El Nino event (a periodic warming of the Pacific Ocean) lead to corral bleaching in areas throughout the Pacific. From the severity and extensiveness of the bleaching, we can conclude that this was the warmest El Nino event the Pacific has experience in several centuries.
So changes in the health or successfulness of species adapted to a particular area’s climate over the long-term are really the best indicator of long-term changes in climate. Changes in the weather, being short-term and local, do not have the same effect.
References, addition reading:
Gregg Easterbrook (1999) Warming Up: The Real Evidence for the Greenhouse Effect,” The New Republic, November 8.
Thomas R. Karl & Kevin E. Trenberth (1999) The Human Impact On Climate, Scientific American, December.