Here’s a phrase heard often in the winter, when temperatures are, naturally, colder than at any other time of year: “Global warming? Yeah right, more like global cooling.” But that reveals a basic misunderstanding of what “weather” and “climate” are.
The difference between weather and climate comes down to time. Weather refers to the state of the atmosphere at a particular time or over a few weeks and months. Temperature, humidity, precipitation, cloud cover, windiness and other factors make up a particular time period’s weather.
Climate refers to the average weather for a place over a period of many years. Climate scientists often use 30-year intervals to define a region’s climate, according to the National Snow and Ice Data Center.
For example, sunny, cloudless and 62 degrees Fahrenheit describes the weather this morning here in central Missouri, in other words, a perfect spring day. However, yesterday’s weather was cloudy with scattered showers, while a few days before it was 90 degrees F. These were changes in the weather, not the climate.
The weather in Missouri varies greatly from day to day and even hour to hour. However, on average, the surface temperatures here have been increasing during the past several decades. Other places, especially the polar regions, experienced more dramatic average temperature increases during the same time period.
The gradual alteration of average weather patterns defines climate change. Earth’s climate changes naturally, which is why we no longer sit under a mile of ice in Missouri, nor do we have lush jungles anymore.
However, certain human activities can influence the climate. Burning fossil fuels releases carbon dioxide. Domesticated cattle release methane when they pass gas, as do the termites that devour wood scraps left by loggers. Methane and carbon dioxide can change the climate. Those gases allow the sun’s light to pass through the atmosphere. Yet after that light strikes Earth’s surface and transforms into heat, the gases trap that warmth, just like the glass or plastic panes of a greenhouse. Chemists define that process as the greenhouse effect.
The term “anthropogenic” describes human-caused climate change. Athrōpos means human in ancient Greek. The suffix -genic means produced or generated by something. Since no natural explanation exists for the current rapid increases in average temperature, geophysicists and climate scientists consider the past several decades of climate change to be anthropogenic.
Image: The map depicts land surface temperatures of March 8-15, 2012 compared to the average of the same eight day period from 2000-2011. Areas with warmer-than-average temperatures are shown in red; near-normal temperatures are white; and areas that were cooler than the 2000-2011 base period are blue. Credit: NASA Earth Observatory image by Jesse Allen, Wikimedia Commons