La Niña could re-appear in 2024

ABC NEWS (Australia)

Australia's most dominant climate driver, La Niña, has a strong chance of re-appearing in 2024, according to global weather models.

Transcript

00:00 The El Nino has now passed its peak and it's starting to weaken and most of the global

00:06 models predict we'll quickly see a return of La Nina, so the fourth La Nina in five

00:11 years developing this year.

00:12 This is the current state of the sea surface temperatures across the Pacific compared to

00:16 average.

00:17 We've still got this warm tongue along the equator, so that's El Nino.

00:21 But the models are predicting the sea surface temperatures will rapidly cool along the equator

00:25 over the next six months or so.

00:27 So let's take a look at that model data then.

00:29 You can see at the moment we are in El Nino, that's the red line, with a rapid drop in

00:33 the percentage of models that predict El Nino will continue as we move through the autumn

00:37 period.

00:38 Look what happens by winter, the blue line, La Nina, more than 50 percent, and by spring

00:42 more than 60 percent of the models predict will transition into a La Nina, which is the

00:47 wet phase for Australia.

00:48 Now the question is, in January, do you trust the models?

00:52 Well typically there's something called an autumn predictability barrier, meaning any

00:56 forecast made for the Pacific before autumn is fairly unreliable.

01:01 But I'm paying more attention to these models than I normally would.

01:04 There's a reason why.

01:06 Governing all of this is something called the inter-dictator Pacific oscillation, and

01:10 it's currently in a negative phase.

01:12 Now here's a map of the sea surface temperatures from back in November 2022.

01:16 It's cooler than normal in box two, and it's warmer than normal in box one and box three.

01:21 That's called a negative IPO.

01:24 Now when you have a negative IPO state, which we have seen for nearly 20 years now, it is

01:28 far more likely you will have La Ninas.

01:31 So here's the stat then.

01:32 Over the past 17 years, eight have been La Nina, and Ros, that is well above the climatological

01:39 average of 25 percent.

01:40 Okay, so if La Nina were to redevelop then, Tom, what would be the likely impact on Australia's

01:45 weather, more rain?

01:47 Well that's a really good question, and here's the key message I want to get across.

01:52 La Nina impacts our weather at a much greater scale than El Nino, and here's a stat that

01:57 sums it up.

01:58 If you look at all La Nina years, averaging the rain across the whole of Australia, we

02:02 see a 23 percent increase in rainfall.

02:05 El Nino years we only see a 7 percent decrease in rainfall.

02:09 Now the main reason for that is El Nino only drops Australia's rainfall in the winter and

02:14 spring.

02:15 La Nina increases rainfall through winter, spring, summer, and occasionally even into

02:19 early autumn.

02:21 Now it's far too early to make a direct forecast for this, but certainly the chance of La Nina

02:26 developing this year is well above the climatological average, which is about one in every four

02:32 years.

02:32 [BLANK_AUDIO]

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