Let's talk about Climate Variability.

The climate where you live is called regional climate. It is the average weather in a place over more than thirty years. To describe the regional climate of a place, people often tell what the temperatures are like over the seasons, how windy it is, and how much rain or snow falls. The climate of a region depends on many factors including the amount of sunlight it receives, its height above sea level, the shape of the land, and how close it is to oceans. Since the equator receives more sunlight than the poles, climate varies depending on its distance from the equator.

However, we can also think about the climate of an entire planet. Global climate is a description of the climate of a planet as a whole, with all the regional differences averaged. The climate where you live is called regional climate. Overall, global climate depends on the amount of energy received by the Sun and the amount of energy that is trapped in the system. These amounts are different for different planets. Scientists who study Earth's climate and climate change study the factors that affect the climate of our whole planet.

While the weather can change in just a few hours, climate changes over longer timeframes. Climate events, like El Ni?o, happen over several years, small-scale fluctuations happen over decades, and larger climate changes happen over hundreds and thousands of years. Today, climates are changing. Our Earth is warming more quickly than it has in the past according to the research of scientists. Hot summer days may be quite typical of climates in many regions of the world, but global warming is causing Earth's average global temperature to increase. The amount of solar radiation, the chemistry of the atmosphere, clouds, and the biosphere all affect Earth's climate.

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 Ni?o 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 Ni?o) and cooling periods (La Ni?a), 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.