Climate Change Vocabulary: Natural Variability

This is part of an ongoing series on the language of climate change.

Skeptics and believers both use individual weather events as proof that climate change is fake or real. This is patently wrong. No single event is caused by any single factor in the climate system. There are a number of factors that affect individual single weather events, seasons, and even longer time spans. While climate change is a factor in the longer run, natural variability is also extremely important both in the present and the future.

Natural variability has been around as long as the Earth has had an atmosphere. There are a number of factors that won't matter in our lifetime because they take place over millennia. These include the tilt of the Earth, it's wobble, and the slight eccentricity of its orbit around the sun. What matters more in both our lifetimes and their interactions with climate change are decadal and seasonal variability.

Along those lines, one that has come up regularly in the climate change section is El Nino-Southern Oscillation (ENSO). Changing on what's known in climate science as an interannual scale of 3-7 years, ENSO affects precipitation and temperature in a number of regions. It happens on shorter-term timescales, which makes it perhaps the best-known piece of natural variability.

There are also oscillations the act on timescales a little longer than ENSO. These include the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO)which further affect climate in certain regions. Changes in these oscillations take place over decades. In contrast, the Madden Julian Oscillation (MJO) changes over a period of 30-70 days.

Much of climate is driven by changes in the ocean. While climate change will alter the ocean, there's plenty of natural variability within ocean temperatures, commonly referred to as sea surface temperatures (SST). These oscillations are all tied to SSTs in certain parts of the ocean, which in turn drives temperature, cloud cover, and precipitation over land.

Climate change is a piece of the puzzle, but it's not the only answer. For some perspective, here's a look at annual temperature and precipitation anomalies (deviation from the average) in Colorado since 1900. Each of these is then broken up into three categories: "climate change" signal, decadal variability, and interannual variability.

In the case of temperature, 25% of the annual anomalies can be attributed to climate change. However, interannual variability accounts for 63% of the annual anomalies.

In the case of precipitation, the split is even more dramatic. Climate change plays a very minor role, accounting for only 1% of the variability. In contrast, interannual variability accounts for 74% of the anomalies.

Colorado is only one example. In other areas such as the Arctic, climate change has a much stronger signal and accounts for a higher percentage of observed anomalies. This points to the fact that climate change will not affect all areas equally, and in some cases, have varied effects on different climate phenomena.

It's important to acknowledge natural variability in the debate about what to do about climate change. In many ways, adapting to natural variability will insulate communities against the added effects of climate change.

Photo Credit: Flickr