El Niño is back.
What does that actually mean for Australia?

Climate models expect the Pacific to continue warming through spring, likely peaking in late spring or summer. Most models currently forecast a peak above +3.0°C, potentially pushing the relative Niño3.4 index beyond anything observed since reliable records began in 1950.^[1]

That’s significant. A strong El Niño is one of the biggest climate influences operating on Australian weather, and this one is shaping up as a serious event. But there’s an important distinction to make before anyone writes off the summer.

First: what actually is El Niño?

El Niño is one phase of a natural climate cycle called the El Niño–Southern Oscillation, or ENSO.

Normally, trade winds blow across the tropical Pacific from east to west, helping push warm surface water towards Australia and Indonesia. During an El Niño, those trade winds weaken and unusually warm water spreads further east across the Pacific.

That shift changes where clouds and tropical rainfall tend to form, which can then alter atmospheric circulation and weather patterns around the world. Australia happens to sit in a part of the world where those changes can matter quite a lot.

Historically, El Niño is associated with lower winter and spring rainfall across parts of eastern Australia and warmer conditions across much of the south. But Australia’s weather is also influenced by things like the Indian Ocean Dipole, the Southern Annular Mode, sea-surface temperatures around Australia and individual weather systems.^[2]

There is no single switch labelled El Niño.

More recently, the 2023–24 El Niño was moderate to strong. August to October 2023 became Australia’s driest three-month period on record, but a strong positive Indian Ocean Dipole was developing at the same time. By late 2023, El Niño’s influence had weakened and summer rainfall returned across widespread areas.^[4]

El Niño matters. It just never acts alone.

And what’s the deal with 1877–78?

The 1877–78 El Niño has been getting some attention because it was a big one. It also coincided with catastrophic droughts and famines in several parts of the world.

There is one fairly major problem with comparing it neatly with today:

1877 didn’t exactly have a Pacific full of satellites and monitoring buoys.

Scientists have to reconstruct what happened using the much smaller number of historical observations that survive. A 2020 study led by NOAA researchers concluded that 1877–78 was a strong and statistically significant El Niño, but the uncertainty around its exact strength is much larger than it is for modern events.

Once those uncertainties were taken into account, the researchers couldn’t confidently say the 1877–78 event was stronger than the huge El Niños of 1982–83, 1997–98 or 2015–16.^[5]

So when you see claims that we haven’t experienced anything like the current event since the 1800s, they need some context.

We just have much better measurements now.

Okay, what does any of this have to do with sun protection?

Heat and UV radiation aren’t the same thing. You feel infrared radiation as heat; you can’t feel UV. That’s why a relatively cool day can still have very high UV, and why deciding whether you need sun protection based on temperature is a pretty unreliable system.^[7]

UV levels are influenced by things including the height of the sun in the sky, latitude, season, cloud cover, ozone, altitude and reflection from the surrounding environment.^[7]

Good weather isn’t the same thing as safe UV

None of this is an argument for hiding inside all summer. More good days outside is one of the better parts of living here.

A nice day is not automatically a safe UV day.

By January, average clear-sky UV Index values are forecast to reach 11 or higher across most of Australia. That’s the Extreme range. On a fine Australian summer day, ARPANSA says someone with fair, unprotected skin can receive enough UV to cause sunburn in around 15 minutes.^[8]

Cancer Council recommends using sun protection whenever the UV Index reaches 3 or above. That means protective clothing, SPF50 or SPF50+ broad-spectrum water-resistant sunscreen, a broad-brimmed hat, shade and sunglasses.^[9]

There’s useful nuance here too. When UV is below 3, Cancer Council generally doesn’t recommend sun protection unless you’re outdoors for an extended period or around reflective surfaces such as snow.^[9]

If El Niño gives your part of Australia more warm, dry days, chances are you will use them. Beach, sport, golf, gardening, working outdoors or just spending more of the weekend outside. That is exactly why checking the thing that actually matters becomes more important.

More time outside is a good thing. It also adds up, often on days that don’t feel dangerous at all. That’s the easiest way to get cooked without noticing.