Comprehension of a complex process is often aided by a clear, common understanding of the vocabulary. This is especially true in the study of climatology.
"Global Warming" and "Climate Change" are two terms that are often, and erroneously, used interchangeably. While it is important to know the difference between these two terms, we must also know how they interact.
Global warming is exactly what the term implies, a warming of Earth. It is the warming of Earths' land, water and atmosphere, and is measured by network of temperature observations at scattered around the globe. Global warming is real, and is readily observed from the temperature measurements which show that the surface of the Earth increased steadily through the last century, with a total increase of approximately 0.75oC, or 1.33oF during the past 100 years. This data is so overwhelming that it has been endorsed by virtually all scientific societies and national Academies of Science throughout the world.
This definition immediately raises two questions:
- “Can’t the observed warming be natural variability?” Certainly natural variability has always been present, but in the past changes of this magnitude have occurred over thousands, or millions, of years. There is no known natural explanation for such a rapid temperature increase. Secondly, the Earth should actually be in a cooling phase as the Earth is in that part of its elliptical orbit around the sun where it is moving away from the sun, not closer.
- “How can such a small change make any difference?” The answer to this question is found in high school physics. Heat is energy and is measured by temperature, therefore if the temperature of the planet increases, the planet contains more energy. And in accord with the First Law of Thermodynamics energy and matter cannot be created or destroyed, but merely transformed in nature.
Thus the simplest description of “global warming” is the addition of energy to the planet.
Having defined global warming as the addition of energy to the planet, we can now view Climate Change as a consequence of that added energy. The addition of energy to the system has a number of effects upon the Earths’ systems, including the alteration of thermal gradients between the polar and equatorial regions on the planet. These thermal gradients are a primary driver of the air currents, such as the jet streams, and the ocean currents; which in turn are determinants of the Earths’ climatic patterns. A planet with increased energy also exhibits greater volatility, or variability, in its weather.
But, what is “weather” and how does it differ from “climate”? The answer is both duration and scale. Weather is what we experience today, this year, this decade. Weather is short-term. Only when we average weather conditions over a long-term is it climate. There is no universally accepted agreement on how long “long-term” should be before weather becomes climate, but the generally accepted minimum is 30 years. Weather is also a local feature, and at times may be quite different just a short distance away, while climate is a regional feature, shared by many localities.
It should also be noted that since the climate of a region is largely determined by large-scale air and ocean currents, climate change may result in the climate of a region becoming either warmer or cooler, wetter or drier, due to shifts in the air and ocean currents. For example, if melting of arctic ice causes a shift of the gulf stream, the eastern U.S. and western Europe may experience a much cooler climate, as has happened in the past.
“Global warming”, “climate change”, “weather”, and “climate” – four terms describing four distinctly different, but related, parameters. Proper usage of these four terms is essential for meaningful communication and for the formulation of effective public policy necessary to address climate change.
