No pun intended, but there’s no question that climate is a hot topic these days. Every week, you likely come across articles describing new research into the earth’s warming, or how certain cyclical effects are having an impact on the weather. In this article, we’re going to break down what is meant by “climate change” and by “climate variability.”
What's the difference?
First, however, let’s discuss the differences between “weather” and “climate.” "Weather” refers to the atmospheric conditions experienced or expected in a particular location during periods of hours or days, whereas “climate” typically refers to an average of how such atmospheric conditions behave over years or decades.
While the climate tends to change quite slowly, that doesn’t mean we don’t experience shorter-term fluctuations on seasonal or multi-seasonal time scales. There are many things that can cause temperature, for example, to fluctuate around the average without causing the long-term average itself to change. This phenomenon is climate variability, and when scientists talk about it they are usually referring to time periods ranging from months to as many as 30 years.
For the most part, when discussing climate variability, we’re describing natural (that is, non-man-made) processes that affect the atmosphere. For example, the North Atlantic Oscillation (NAO) refers to anomalous changes in atmospheric pressure at sea level that occur near Iceland and the Azores High. NAO-positive phases are often associated with above-average storm counts over parts of Europe and the U.S.
You're also likely familiar with the El Niño Southern Oscillation (ENSO) phenomenon near the equatorial Pacific Ocean, where fluctuations of sea surface temperatures typically alternate every few years between a warming phase (El Niño) and cooling periods (La Niña), with a neutral phase in between. Many researchers have found that negative ENSO years are correlated with a higher probability of Atlantic hurricane formation, as well as warmer, dryer weather in northern states.
Alterations to the earth’s atmosphere that occur over much longer periods—decades to millennia—are characterized as “climate change.” While climate change can be caused by natural processes—such as volcanic activity, solar variability, plate tectonics, or shifts in the Earth’s orbit—we are usually referring to changes attributable to human activity when talking about climate change, such as increased greenhouse gas emissions. The latest (Fifth) Assessment Report from the Intergovernmental Panel on Climate Change (IPCC 2013), for example, found that on average global temperatures increased about 0.85°C from 1880 to 2012 (33.53°F), and concluded that more than half of the observed increase in global average temperatures was caused by elevated emissions of carbon dioxide and other greenhouse gases.
At AIR, we’ve done considerable research into how climate change impacts extreme weather, and in our new white paper, we examined how the frequency and intensity of both “weak to moderate” and “strong to extreme” events will change over time. For example, we found that while the overall number of tropical cyclones is likely to decrease, the most intense storms (Saffir Simpson Scale Categories 4 and 5) are likely to increase in frequency and become even more intense.
1. Length of bar indicates degree of uncertainty. Note that the relative positions of the bars represent globally-averaged estimates; significant regional differences may exist and would need to be considered separately. Note, too, that the direction of the bars is consistent with moderate-to-high emissions trajectories (RCP 4.5 – 8.5), but the degree of uncertainty may vary as a function of a given emissions scenario.
Rob Savitsky is a product marketing manager for AIR Worldwide. This article first appeared in AIR's In Focus blog and is reprinted with permission.