Reuters: Hottest oceans in 400 years endanger Great Barrier Reef, scientists say

[OKIsItJustMe]

https://www.reuters.com/business/environment/hottest-oceans-400-years-endanger-great-barrier-reef-scientists-say-2024-08-07/

Hottest oceans in 400 years endanger Great Barrier Reef, scientists say
By Alasdair Pal
August 7, 2024 11:38 AM EDT

SYDNEY, Aug 8 (Reuters) - Water temperatures in and around Australia's Great Barrier Reef have risen to their warmest in 400 years over the past decade, placing the world's largest reef under threat, according to research published on Thursday.

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A group of scientists at universities across Australia drilled cores into the coral and, much like counting the rings on a tree, analysed the samples to measure summer ocean temperatures going back to 1618.

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From 1960 to 2024, the study's authors observed an average annual warming for January to March of 0.12°C (0.22°F) per decade.

Since 2016, the reef has experienced five summers of mass coral bleaching, when large sections of the reef turn white due to heat stress, putting them at greater risk of death.

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[OnlinePoker]

1. GBR is doing fine

Northern and Central GBR are at the highest recorded hard coral levels since monitoring began 38 years ago. The Southern GBR is the 4th highest recorded coral. Impact of bleaching still has to be determined, but the worst reductions in coral in the past have mostly come from cyclones and Crown of Thorns starfish. Bleaching has had little long term effect on the coral cover unless there's actual mortality.

https://www.aims.gov.au/monitoring-great-barrier-reef/gbr-condition-summary-2023-24

[OKIsItJustMe]

2. Call me naive, I trust university scientists more than government agencies

https://www.nature.com/articles/s41586-024-07672-x

Article Open access
Published: 07 August 2024
Highest ocean heat in four centuries places Great Barrier Reef in danger

Benjamin J. Henley, Helen V. McGregor, Andrew D. King, Ove Hoegh-Guldberg, Ariella K. Arzey, David J. Karoly, Janice M. Lough, Thomas M. DeCarlo & Braddock K. Linsley

Abstract
Mass coral bleaching on the Great Barrier Reef (GBR) in Australia between 2016 and 2024 was driven by high sea surface temperatures (SST)¹. The likelihood of temperature-induced bleaching is a key determinant for the future threat status of the GBR², but the long-term context of recent temperatures in the region is unclear. Here we show that the January–March Coral Sea heat extremes in 2024, 2017 and 2020 (in order of descending mean SST anomalies) were the warmest in 400 years, exceeding the 95th-percentile uncertainty limit of our reconstructed pre-1900 maximum. The 2016, 2004 and 2022 events were the next warmest, exceeding the 90th-percentile limit. Climate model analysis confirms that human influence on the climate system is responsible for the rapid warming in recent decades. This attribution, together with the recent ocean temperature extremes, post-1900 warming trend and observed mass coral bleaching, shows that the existential threat to the GBR ecosystem from anthropogenic climate change is now realized. Without urgent intervention, the iconic GBR is at risk of experiencing temperatures conducive to near-annual coral bleaching³, with negative consequences for biodiversity and ecosystems services. A continuation on the current trajectory would further threaten the ecological function⁴ and outstanding universal value5 of one of Earth’s greatest natural wonders.

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[hatrack]

3. And here's part 1 of the rest of the report summary (emphases added).

This report summarises the condition of coral reefs in the Northern, Central and Southern Great Barrier Reef (GBR) from the Long-Term Monitoring Program (LTMP) surveys of 94 reefs conducted between August 2023 and June 2024 (reported as ‘2024’).

Over the past 38 years of monitoring by the Australian Institute of Marine Science (AIMS), hard coral cover on reefs of the GBR has decreased and increased in response to cycles of disturbance and recovery.

Percent hard coral cover is one standard measure of reef condition recorded by scientists worldwide, it provides a simple and robust measure of reef health and is used in this report. Other important data, such as diversity or composition of coral assemblages, are collected and reported by LTMP in other ways.

Changes in coral cover are qualified with respect to the margin of error, defined by 95% credible intervals (CIs). Credible intervals describe the level of uncertainty in the estimates of hard coral cover.

Above-average water temperatures (i.e. sea-surface temperature anomalies of 1–2.5°C) occurred on the GBR over the austral summer, peaking in March 2024 and resulting in the fifth mass coral bleaching event since 2016.

The mass coral bleaching on the GBR was part of a global event declared by NOAA and ICRI in April 2024.

The Central GBR was impacted by two tropical cyclones: Cyclone Jasper (Category 5 – December 2023) and Cyclone Kirrily (Category 3 – January 2024). Although Cyclone Jasper was a Category 5 in the Coral Sea, it was only Category 2 when traversing the GBR.

Crown-of-thorns starfish (COTS) outbreaks have persisted on four Southern GBR reefs, while four reefs of the Northern GBR have low numbers of starfish.

In 2024, hard coral cover has increased across the GBR, but regional hard coral cover remains similar to that reported in 2022 and 2023. Importantly, most surveys were conducted prior to the mass coral bleaching event and passage of two cyclones, and the full impact of these events is yet to be determined. It's also important to note that bleached coral is still recorded as live coral during surveys, and the fate of these corals is not yet known.