Home » Science: Climate Change and Other Topics » Wullie Davidson Climate Change Blog: Global Ocean Temperature Reaches Record High – El Nino Brewing Up

Wullie Davidson Climate Change Blog: Global Ocean Temperature Reaches Record High – El Nino Brewing Up

Second warmest March despite no El Nino

Globally, March, 2023 was the second warmest March, since record keeping began in 1850.The warmest March was in 2016 and that temperature was boosted by a very strong El Nino. Currently, the tropical Pacific is ENSO neutral, but the average global sea surface temperature (SST) reached a record high in late March and that will have boosted the temperature.

Most of the world’s ocean is in the southern hemisphere, and March is when SSTs peak there. Since modern SST recording began, the global average SST has oscillated betwen a record low of 19.7 C and a record high of 21.0 C. The new record remained above 21.0 C until late April, when SSTs should have been falling. By this time it was just under 0.2 C warmer than the previous record for the date. This may not sound much, but it takes a lot more energy to warm water by 0.2 C than it does for the same degree of warming over land, so it represents a considerable and unexpected step change in temperature, which has taken scientists by surprise. They have no explanation for it and are waiting to see if it is a short term anomaly, or the beginning of a long term trend. If it proves to be the latter, that would be very bad news, as it might signal the onset of a potentially large positive feedback effect caused by ocean surface stratification. This means that warming surface water becomes more resistant to mixing with deeper water, with more of its energy being released to the atmosphere.

What goes on in the ocean . . .

(Chart with data from NASA^[9] showing how land and sea surface air temperatures have changed vs a pre-industrial –  baseline) https://en.wikipedia.org/wiki/Ocean_temperature#/media/File:Land_vs_Ocean_Temperature.svg)

What goes on in the ocean doesn’t stay in the ocean. The global ocean is like a giant storage heater, and current record high SSTs will have been responsible for much of the great number of national April temperature records that have been set throughout the world. As has so often been the case in recent years, southeast Asia has been the most extensive region affected by record heat, and new national temperature records for April have been set in China, Japan, Vietnam, Myanmar, Cambodia and Laos. The most extreme temperatures above normal have been in Morocco, Algeria and Tunisia where national records for April were exceeded by a scarcely believable 5 C, even beating the records for May. This heat spread into southern Europe and a new national April record of 38.8 C (102 F) was set in Cordoba, Spain. This was also a new European record for April.

El Nino is on the way

Image title: El nino waves piers ocean seagulls cafes Image from Public domain images website, http://www.public-domain-image.com/full-image/nature-landscapes-public-domain-images-pictures/waves-public-domain-images-pictures/el-nino-waves-piers-ocean-seagulls-cafes.jpg.html

The US National Oceanic and Atmospheric Administration (NOAA) is predicting a 62% chance of an El Nino in the May to July period, and an 82% chance of it for August to October. Currently, SSTs in the tropical Pacific are around 0.4 C above normal. The threshold for a weak El Nino is +0.5 C, sustained for five months. However, in the coastal waters off Peru and Ecuador, the sea is anomalously warm by 2.4 C, which is by far the greatest temperature anomaly anywhere in the world.

Since 1900, there have been at least 30 El Nino events, with 1982-83, 1997-98 and 2014-16 among the strongest on record. El Nino suppresses the upwelling of cold, nutrient rich water that sustains large numbers of fish off the Peruvian coast. During the 1972 El Nino, the world’s largest fishery there collapsed due to a dramatic reduction in the number of anchovies. The populations of many species of sea birds dependent on the fish also collapsed, some by 98%. If prolonged, the current ‘coastal El Nino’, off Peru, seems likely to have a similar effect.

El Nino causes seasonal droughts and flooding in many regions of the world, but this can be inconsistent. The most consistent effects are flooding in Peru and Ecuador, and very dry conditions in Indonesia and northern and eastern Australia, resulting in an increase in wildfires. Dry conditions in the Indonesian rainforests encourage ‘slash and burn’ clearance of the forest for palm oil plantations. The fires rage out of control in the very dry conditions, with devastating effects on wildlife and smoke pollution as far away as Singapore.

coastal area Peru devoid of vegetation (Photo by www.world-wide-gifts.com/)

The effect of El Nino on global temperature is most pronounced in the year after onset and even a weak to moderate event will probably result in a significant global temperature record in 2024. Scientists estimate that a strong El Nino could result in the record being broken by as much as 0.3 C, which would take us well into uncharted territory.

1 in 1,000 year rain event

As the world warms, more water vapour will evaporate from the sea surface and the warmer atmosphere will be able to hold more moisture. This will result in more rainfall and much more intense rain events and flooding. Changes to the jet stream, which were not anticipated by climate scientists appear to be exacerbating these effects. But, the frequency and intensity of extreme rain events throughout the world in recent years has taken scientists by surprise.

On April 12, multiple slow moving supercell thunderstorms developed across Florida, each following similar tracks. Fort Lauderdale bore the brunt of the flooding, recording 25.9 inches of rain in 24 hours. The previous daily record was 14.6 inches in 1979. Even hurricanes rarely drop so much rain. Fort Lauderdale’s average rainfall for the month of April is just 3 inches. It was described by meteorologists as a ‘1 in 1,000 year event’.

Wullie Davidson, May 2023

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