Longest Global Coral Bleaching Event Officially at an End; But Severe Worldwide Risk to Corals Remains

In the Equatorial Pacific, the chances for an ocean-surface-cooling La Nina are on the rise (more on this later). But even with a cool pool of water upwelling in this key climate region, the risk to corals in a record-warm world remains high.

This risk comes despite the fact that by June of 2017, NOAA had officially declared an end to the longest global coral bleaching event on record. The event lasted from 2014 to 2017 and impacted multiple major coral reefs for 2-3 years in a row. According to NOAA, the event affected more reefs than any other previous global coral bleaching event. Meanwhile, some reefs that had never before seen significant bleaching — like northern sections of the Great Barrier Reef — saw severe damage.

(A portrait of the world’s worst global coral bleaching event shows that 70 percent of the world’s corals took a major hit. Image source: NOAA.)

In total, more than 70 percent of the worlds reefs experienced heat stress capable of producing bleaching. An extent never before attained. One that is difficult to imagine. The NOAA graphic above provides some context of the terrible expansiveness — with dark red areas representing widespread bleaching and significant coral mortality and light red regions representing significant coral bleaching over the totality of the 2014 to 2017 event.

To be very clear, the primary driver of this very widespread event was a human-forced warming of the world through fossil fuel burning. This driver has resulted in sea surfaces that are, in many regions, more than 1 degree Celsius above 19th Century temperature averages. Temperatures that are now enabled to spike to 3, 4, or even 5 C above average during variable warming events like the recent strong 2015-2016 El Nino. Temperatures that now never really back off to previous lows. A regime that provides little respite for corals.

For these heat-sensitive creatures, such systemically warming ocean temperatures represent a rising risk of mass mortality in the coming years. And over the next decade alone, global temperatures are expected to continue to increase by between 0.15 and 0.3 C above already harmful ranges.

(4-Month NOAA forecast shows that widespread risk for major coral mortality remains despite an end to El Nino conditions, increasingly likely La Nina conditions, and an official end to the 2014-2017 global coral bleaching event. Image source: NOAA.)

Even with the longest global coral bleaching event officially over and with a potential La Nina on the way, risk of widespread heat stress to corals remains. NOAA’s 4-month heat stress forecast shows a 60 percent that large areas of the Pacific, the Caribbean, and the tropical Atlantic will experience significant bleaching, widespread bleaching, and mass coral mortality (light and dark red areas).

These are severe impacts. Ones that should not be occurring as the Equatorial Pacific is going through a variable cool phase. Ones that have been set off by continued fossil fuel burning and the mass dumping of carbon into the atmosphere at the rate of around 11 billion tons per year annually which has pushed the world into an entirely new and already harmful temperature range.


NOAA Coral Reef Watch


Major Greenhouse Gas Reductions Needed

Leave a comment


  1. eleggua

     /  September 18, 2017

    Welcome home, Robert. Glad to read an excellent new article, especially one that includes some good news.


    • Thanks. Very much appreciated. I guess it’s now on to Maria.

      There’s a lot of news, both good and bad. But I am somewhat heartened to see that the UAE is promoting electrical vehicles and that China is looking to cut coal imports pretty considerably. More on that later 😉


      • eleggua

         /  September 18, 2017

        You’re welcome. After Maria, another 8 weeks-or-so’s worth of hurricanes to follow.
        It could be a grim couple of months. Thanks so much for (always) keeping focus on the positives, too.

        China will be standing tall when the other (two) goliaths fall. Sort of fun observing them tiptoeing around the geopolitical Russia/US nonsense and even taking economic advantage of it, without becoming embroiled in any of it.

        Eventually there’ll be a true people’s revolution in China, probably before anywhere else.
        I’d move there now if not commited to being a part of imminent positive changes here in the US.


  2. Ronald

     /  September 19, 2017

    Meanwhile, in the Amazon…
    After another exceptionally dry period (i.e. 2015/2016) in large parts of the Amazon, the situation should now be more normal and recovering (the great rainy season in much of the Amazon region is Jan through May).
    However, my impression is that parts of the region, in particular eastern/southern and into central (around Manaus) mat still be too dry.
    See for instance:

    (I did not manage to get the earlier map, Jan-March, or Dec-Feb, can you?).
    Or Brazilian INMET:

    Could you get recent reliable information on the situation in the Amazon?


  3. John Smith

     /  September 19, 2017

    Bit off topic, but below links show not all going that well down under, yet our stupid government still supports the Adani mega coal mine in the Galilee Basin of central Queensland, where today a number of brave souls were arrested for blockading the access road to the Abbott Point Coal Terminal.

    Queensland in for heatwave

    Warmest winter on record



Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: