Chances are bleak for the La Nina weather to emerge at least until February, the Australian Bureau of Meteorology (BoM) said today.

“The chance of a La Niña event developing in the coming months has decreased compared to recent outlooks. If a La Niña were to develop, it is forecast to be relatively weak (in terms of the strength of the sea surface temperature (SST) anomaly) and short-lived, with all models forecasting neutral values in February,” BoM said in its latest Climate Driver Update.

The weather agency’s model suggests that SSTs are likely to remain within the ENSO-neutral thresholds (−0.8 °C to +0.8 °C) throughout its forecast period to February 2025.

Of the six other climate models surveyed, four also suggest SSTs will remain within the El Nino-Southern Oscillation (ENSO) neutral thresholds.

Weak, inconsistent signals

Only one model suggests SSTs in the tropical Pacific are likely to exceed the La Niña threshold (below −0.8 °C) during November-January. Another model forecasts SSTs to briefly exceed the threshold, but only during December and January. 

ENSO is neutral with both SSTs in the central equatorial Pacific Ocean and atmospheric patterns at ENSO-neutral levels. Atmospheric indices, such as those related to patterns of surface pressure, cloud and trade winds, are broadly consistent with an ENSO-neutral state. Although some have displayed La Niña-like signals over the past several weeks, these signals have not been consistent, said BoM.

The Australian weather agency said the Indian Ocean Dipole (IOD) is currently neutral, despite the weekly IOD index value (−0.58 °C) dropping below the negative IOD threshold (−0.40 °C) in the week ending October 13. 

IOD to be neutral

All models indicate that the IOD is likely to remain neutral, but weakly negative, for the rest of the year. Forecasts indicate a sustained period of negative values is unlikely, but due to fluctuations in the tropical Indian Ocean SST patterns, the IOD index may drop, briefly, below the negative IOD threshold, it said.

Global SSTs remain at near-record levels, with temperatures since July being just short of the record temperatures observed during 2023. Yet, they are well above all other years since observations began in 1854. 

The sustained nature of this significant global ocean heat suggests that climate indicators such as ENSO and IOD may not necessarily behave or evolve as they have in the past, it cautioned.

For India, prospects look good from the outlook as the country will unlikely go through any unseasonal weather pattern. 

Climate change is raising winter temperatures faster than those of summer, especially in high-altitude areas. This “asymmetric” warming could spell trouble for the vast amount of carbon stored in soils there by altering microbial activity more than expected.

The planet’s soils store more carbon than any ecosystem other than the oceans, and could store much more if better managed. But soil carbon is threatened by climate change. Researchers expect warmer temperatures will boost the amount of soil carbon lost to the atmosphere as greenhouse gases, largely due to changes in the behaviour of soil microbes. However, the scale of this warming feedback remains uncertain.

Ning Ling at Lanzhou University in China and his colleagues heated soils in an experimental grassland on the Tibetan plateau to test how different patterns of warming might change microbial activity. Some of the soils were kept at ambient temperatures, while others were exposed to a “symmetric” warming of 2°C throughout the year. A third group was exposed to warming of 2.5 to 2.8°C during winter and 0.5 to 0.8°C during the rest of the year, a more realistic simulation of actual warming patterns.

After a decade of this treatment between 2011 and 2020, the researchers tested microbial activity of samples from the different soils. They focused on two measures in particular: growth rate and an indicator of how the organisms are using carbon, known as carbon use efficiency. This has been shown to be a major determinant of the amount of organic carbon stored in soils.

“When a microbe eats carbon, it can do one of two things with it: it can break it down for energy and breathe that carbon as CO2, or it can use it to make new body structures,” says Daniel Rath at the Natural Resources Defense Council, an environmental non-profit organisation based in New York. A higher growth rate means microbes are using more carbon, and higher carbon use efficiency means more of that carbon is being made into body structures, rather than respired as CO2, he says.

Ling and his colleagues found both warming patterns substantially reduced microbial activity. Soils under symmetric warming saw growth rate decline 31 per cent and carbon use efficiency decline 22 per cent relative to soil exposed to ambient temperatures. Under asymmetric warming, this effect was even stronger, with growth rate lowered by 58 per cent and carbon use efficiency lowered by 81 per cent relative to soils exposed to ambient temperatures. They ascribed the differences to factors including a change in the nutrients available to the microbes.

“Their findings suggest that soil carbon storage likely will decrease, reducing the capacity of terrestrial ecosystems to sequester carbon and degrading the soil’s efficacy for nature-based solutions to climate change,” says Yiqi Luo at Cornell University in New York.

Rath says the fact that current models don’t take asymmetric warming into account means we are probably underestimating soil carbon losses due to climate change. However, he says the findings may only apply to soils from frigid ecosystems, and more research is needed to understand exactly what these changes in microbial activity mean for carbon. For instance, despite the significant change in microbial activity, the total amount of carbon stored in the soil didn’t change over the course of the experiment.

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