Consider the tomato. I say tow-may-tow and you say tow-mah-tow. I talk about weather and you talk about climate. Same things, right?
Not so much.
While it really doesn’t matter how one pronounces “tomato,” it makes a difference when we use the terms “weather” and “climate” interchangeably.
In short, the difference between the two is all about time. Weather describes atmospheric conditions over a short period of time, often no more than a week to 10 days. Climate, however, talks about overall atmospheric conditions over long periods of time, generally around 30 years.
Here’s a handy way to keep them straight: “Climate is what we expect. Weather is what we get.”
First, the Weather
Meteorologists, or weather forecasters, seek to answer short-term questions. What will the high and low temperatures be tomorrow? What about next week? Will it snow? Will there be too much wind tomorrow for small boats to leave harbor?
Temperature, humidity, air pressure, wind and other measurements from the recent past let forecasters build models to simulate what conditions the near-future may bring. There are many ways to interpret such data, which explains why forecasts issued simultaneously can vary, as well as why forecasts on Monday about Thursday’s weather can be drastically different from forecasts on Wednesday about Thursday’s weather.
It’s that same variability and uncertainty that contributes to skepticism about climate projections over the next 20 to 30 years. How can scientists have any better handle on the distant future’s climate than they do on whether we need to carry umbrellas next week?
To understand that, it helps to see where meteorologists and climatologists diverge.
While a meteorologist may be trying to determine whether a 40-square-mile area will get wet two days from now, a climatologist seeks to understand whether huge swaths of the Earth will be drier or wetter decades from now. How much might sea levels rise or fall? Will chemical components in the atmosphere trap more of the sun’s heat? What happens if there are more or fewer trees covering the Earth’s surface?
Such answers require global climate models built on a scale far beyond anything used by a local meteorologist. At the same time, the meteorologist must provide far more fine-grained, localized forecasts than are required of any climatologist.
So where a weather forecaster might be grappling with the influence of mountains and shorelines on the speed and direction of winds and waves, a climate scientist must figure out whether ice sheets melting from Greenland’s land mass affect the Atlantic Ocean differently than does floating sea ice (short answer: yes).
Climate scientists have been making projections about the planet’s changing climate for a few decades now. By and large, their projections of overall global warming have been accurate, if underestimated.
Just as forecasting next week’s weather requires careful analysis of last week’s patterns, climate scientists base their future projections on history’s patterns. Glaciers – essentially massive mountains of snow packed down over millennia – have been the keepers of that history. By drilling deep into glacial ice, and then studying the ancient layers of snow like tree rings, scientists measure previous climate fluctuations.
But because the atmosphere contained different chemicals thousands of years ago than it does today, it turns out that climate changes occurred much more slowly back then than they do currently.
Why? It began at the dawning of the Industrial Age in the late 18th century. Before then, the atmosphere contained just enough of so-called “greenhouse gases,” such as carbon dioxide and methane, to keep only a small portion of the sun’s daytime warmth from radiating back out into space at night.
Plants maintain the delicate balance between carbon dioxide and oxygen in the atmosphere. Through photosynthesis, plants (as well as some algae and bacteria) can combine water and carbon dioxide to make carbohydrates, releasing oxygen as a by-product. In return, we breathe in that released oxygen and we release carbon dioxide that plants can take up to repeat the cycle over and over again.
But when humans began burning oil, natural gas and coal to power our machines and make our electricity, we began to release more carbon dioxide into the atmosphere than plants could handle. We also started cutting down large swaths of the forests that helped convert that carbon dioxide back into oxygen. That extra carbon dioxide becomes trapped in thin layers within Earth’s atmosphere, stopping more and more of the sun’s heat from leaving.
Think of it like tossing an extra blanket on your bed to ward off a cold winter’s night. If that blanket is never removed, and you keep tossing on more blankets all winter, by the time spring comes your bed will feel too warm.
So the next time someone says that weather and climate are the same thing, remind them that time makes all the difference. It’s a matter of what we expect versus what we get.
- 1981 Climate Change Predictions Were Eerily Accurate, Universe Today, April 6, 2012.
- How the IPCC Underestimated Climate Change, Scientific American, December 6, 2012.
- Loss of Land Ice (Not Sea Ice) = More Sea Level Rise, Yale Climate Connections, November 14, 2014.
- Maximum Rates of Climate Change Are Systematically Underestimated in the Geological Record, Nature Communications, November 10, 2015.
- The Carbon Cycle and Earth’s Climate, Dr. Vic DiVenere, Columbia University, 2013.
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