ENSO Blog

When the climate doesn’t behave like we expect, whether it’s for an individual season or for several decades, we often hear scientists blaming internal variability. Scientists use this term a lot (even on Twitter) and I’ve noticed that I usually obtain a few blank faces depending on the audience. I also remember being a junior scientist in this field and wondering why everyone was going on about internal, or its counterpart, external variability. Internal/External what? And who cares? Me! And you should, too!  In our climate and weather there are: (1) The things that are pushed around by other (external) things (2) The things that would change or move (internally) without any pus…   Read article

Our second-year La Niña has materialized, as indicated by the ocean and atmosphere in the tropical Pacific. There’s an 87% chance of La Niña this winter, the season when North American weather and climate are most affected by ENSO (El Niño/Southern Oscillation, the entire El Niño/La Niña system). The winning numbers The first step on our “Is it La Niña?” decision tree asks “is the monthly Niño-3.4 Index equal to or less than -0.5°C?” The Niño-3.4 Index, our primary metric for ENSO, is the anomaly in sea surface temperature in the central equatorial Pacific (anomaly = the difference from the long-term average; “average” is 1991–2020 nowadays). The September Niño-3.4 Index was -…   Read article

Last month, the Intergovernmental Panel on Climate Change released their Working Group 1 report on the Physical Science Basis of Climate Change (1). This huge report, both in terms of importance and length (the thing is nearly 4000 pages!), covers literally everything you can possibly imagine about Earth’s climate. Past changes, current observations, future projections of warming are all in there. So what does this exhaustive summary of climate research have to say about the El Niño-Southern Oscillation (ENSO) and climate change? Let’s dig in! How has ENSO changed in the past? Often when discussing climate change, the conversation stays firmly placed in discussing future changes. But i…   Read article

It’s likely that the tropical Pacific is on the verge of getting into the La Niña groove, and forecasters estimate a 70-80% chance of La Niña this winter. NOAA’s forecast discussion says “the ocean-atmosphere system reflected ENSO-neutral [in August], but is edging toward La Niña.” Let’s dig into that! The age of Aquarius First things first: a reminder of why we’re here every month, rain or shine, talking about ENSO (El Niño-Southern Oscillation, the entire El Niño/La Niña system of the tropical Pacific). We do it because when it comes to the global climate, the tropical Pacific has all the influence of Jimi Hendrix playing guitar in the middle of a concert crowd. Sure, those closest b…   Read article

If you live in the U.S. Southwest or northwestern Mexico, you may already be familiar with the annual climate phenomenon called the North American Monsoon, especially since rainfall in some spots has been way above average this summer. In fact, this monsoon may turn out to be the wettest on record for some places! More on that later… Now, let’s take a sojourn through some North American Monsoon basics (1). What is the North American Monsoon? The North American Monsoon is a seasonal change in the atmospheric circulation that occurs as the summer sun heats the continental land mass. During much of the year, the prevailing wind over northwestern Mexico, Arizona, and New Mexico is westerly…   Read article