The seasonal forecasting system recently developed by NOAA Coral Reef Watch suggests that coral reefs in the Caribbean and in part of the central equatorial Pacific (the Line Islands, including Kiritimati or "Christmas Island") are at risk of coral bleaching in the coming months due to warm ocean temperatures. The forecast is due to the seeming return of El Nino in the Pacific.
The word from the NOAA Climate Prediction Center is that El Nino conditions are expected to prevail though the winter. Climate buffs can "see" the El Nino development in maps of sea surface temperature anomalies (warm water in the central and eastern Pacific) the thermocline (deepening in the eastern Pacific, meaning less upwelling off of South America) and sea surface height (the wind reversal on the equator means higher water in the central and eastern Pacific).
Not all El Nino events are created equal, and the models currently disagree on the current trajectory. This is especially important to remember when predicting the effect that El Nino conditions may have on other parts of the planet, what we luddites call "teleconnections". For example, a terrific paper by Kim et al. in Science demonstrated clear differences between the effect of "central pacific warming" and "eastern pacific warming" - which can both be classified as an El Nino event, depending what metric is applied - on ocean temperatures and hurricane tracks in the Caribbean.
One silver lining: For people living in the central Pacific, especially the parched islands of the southern Gilberts (Kiribati) Islands like Arorae, the development of El Nino conditions hopefully also means an end to the two-year drought that has claimed many of the coconut trees.
UPDATE: More on the Caribbean bleaching threat here
Thursday, July 23, 2009
El Nino and the likelihood of mass coral bleaching
Friday, February 29, 2008
Lessons from the coral reefs of the Line Islands
The results from a comprehensive survey of the coral reefs of the Northern Line Islands - a chain of atolls south of Hawaii including several Kiribati islands - were published this week in PLOS-One. A companion essay by Jeremy Jackson and Nancy Knowlton appears in PLOS-Biology.
The surveys revealed startling differences in macro- (Sandin et al) and micro-biology (Dinsdale et al.) of the Line Islands coral reefs along a gradient of human disturbance, from the more polluted and fished reefs of equatorial Kiritimati, pronounced "Christmas" (the 'ti' sounds like an 's' in i-Kiribati), and more or less pristine Kingman Reef several hundred kilometres to the north. Taken together, the results also seem to suggest that more pristine reefs are more resilient to coral bleaching events.
Monday, February 25, 2008
The Phoenix Islands Protected Area in Kiribati
As was reported last week, Kiribati is working with international conservation groups to create the Phoenix Islands Protected Area, the largest marine protected area in the world. The project has been in the works for a couple years.
It's worth looking at a map of Kiribati to make sense of the announcement. The NY Times called Kiribati a 'tiny island nation'. Yes, the islands themselves are tiny; the 32 atolls plus Banaba Island have a total area of ~729 sq. km (depending on the tide). The nation is not. It covers 3.5 million sq. km, which is about the area of India, and includes three distinct island chains.
The 410 000 sq km Phoenix Islands Protected Area will encompass the central island chain in Kiribati, to the east of the International Date Line. Around 30-40 people live on Kanton Atoll and serve as informal caretakers for the island chain. Otherwise, the Phoenix Islands are uninhabited. In fact, you could argue they are uninhabitable.
The majority of the 100,000 i-Kiribati live in western "Gilbert" Islands chain, particularly the capital of Tarawa Atoll (*). Previous attempts by the British to (forcefully) resettle i-Kiribati from the more crowded Gilbert island chain to the Phoenix Islands failed because of prolonged droughts and the lack of groundwater resources.
Most of the Kiribati government revenue comes from foreign fishing licenses. The protected area status will limit large-scale commercial fishing around the Phoenix Islands and any marine resource development efforts. So the real key to this plan is the creation of an international endowment raise funds to offset the lost revenues for the Kiribati government. If successful, PIPA may serve as a model for the creation of marine protected areas in the developed world.
Some of the news reports have suggested that tourism will also help offset lost fishing revenue. While that's not impossible, don't get the idea you'll be able to book a seat on the 747 direct from LAX to Kanton and spend a week at a posh eco-resort. The Phoenix Islands are very remote, very inaccessible and have limited local resources. The only likely tourists are scientists on research expeditions and maybe people with the resources to spearhead a multi-week boat trip from Fiji. This announcement is very much about conservation, not tourism.
* I use quotations because the word Kiribati (Keer-ee-bas) is a local transliteration of Gilberts. The country was not really renamed upon independence from the UK in the 1970s. It simply adopted the spelling and pronunciation of Gilberts in the local language.
Monday, February 18, 2008
Coral bleaching and limits to ocean warming
A new paper by Kleypas et al in Geophysical Research Letters suggests that a possible upper limit to ocean temperatures – proposed by the “ocean thermostat” hypothesis – may spare some coral reefs from future coral bleaching events. The science has been more or less massacred by some of the press, so it’s worth explaining what is actually going on.
The “ocean thermostat” theory predicts that there is an upper limit to sea surface temperatures – somewhere around 30-34 C depending on the region. First things first: that does not mean if you put some ocean water on the stove, it is impossible to get the temperature over 34 C. The theory is based on a number of negative feedback mechanisms which only operate at relatively large scales, larger, say than the pot sitting on your stove. So the limit is expected to be 30-31 C in the open ocean, like the Pacific, and a bit higher, 33-34 C in enclosed seas like the Red Sea.
We’re used to hearing about positive feedbacks – temperature rises, sea ice melts, a darker surface (water) that reflects less radiation is exposed, causing temperatures to rise even more. In this case, rising water temperature would drive processes that would slow or stop the temperature rise. There are several candidate mechanisms. If the ocean thermostat really exists, it is likely caused by a combination of the mechanisms. One example is that as the ocean warms, more water evaporates, creating more clouds and reducing incoming solar radiation. Another is that warming of one area of ocean will create pressure gradients (with other cooler areas) creating currents that redistribute the water.
The sea surface temperatures across most of the tropics are well below the theoretical temperature limit suggested by the ocean thermostat theory. The maximum annual temperature could rise 3-4 C in most coral reef regions, well beyond the threshold for the corals, without hitting the thermostat limit. That's the case in the Caribbean, the eastern Pacific, much of the Indian Ocean, much of the Great Barrier Reef, etc.
The exception is in the Western Pacific. The warmest open ocean waters is the world are found in a zone that can stretch from the Indian Ocean well into the Central Pacific. It is affectionately known as the West or Western Pacific Warm Pool or WPWP. In a pathetic attempt to give you the illusion scientists are hip and clever, I will use the short form WP2.
You probably know of WP2, if not by name. For one, the Pacific section can be (loosely) thought of as the body of warm water in the equatorial Pacific that migrates eastward during El Nino events. Also, the Pacific section is home to the majority or at least a sizeable fraction, of what’s left of the world’s un-canned tuna and, in turn, to the majority of the world’s illegal fishing boats.
Many years, the WP2 is usually centered in SE Asian archipelago or the expansive territorial waters of the Pacific Island nation of the Federated States of Micronesia. Of course, the exact location changes each year, bringing the core of warm open ocean waters maybe closer to the Solomon Islands, or Palau, or Kiribati, or Tuvalu, or other neighbouring countries. The fishing vessels flying flags of convenience from Mongolia or Western Sahara or Suriname are usually close behind.
When the edge of the warm pool moves, say, western Kiribati, the rise in water temperatures (1-2 C) is quite likely to cause a coral bleaching event. If you take a look at the January degree heating week maps – that’s the accumulated heat stress metric we use to predict bleaching events – for the past several years, you’ll see that almost every year, there’s a hot spot somewhere outside of WP2’s home base. This has been the proximate cause of bleaching events in the Kiribati (Gilbert) Islands, the Phoenix Islands, Tuvalu and the Solomons in recent years - this may be, in part, a manifestation of long-term temperature trends.
That’s where Kleypas et al. comes in. The paper finds that open ocean waters with maximum annual SSTs above 29 C – in other words, our friend WP2 – have warmed less than any other parts of the ocean since 1950. The closer the SSTs are to 30-31 C, the lower the rate of warming. The data appears to support, at least, circumstantially the existence of the ocean thermostat. If correct, this would imply corals in the warm region could be spared from a dangerous temperature rise.
That’s what spawned the “corals saved from ocean thermostat” headlines. Here’s the catch – ok, three catches. These are not criticisms of the paper rather crucial issues touched on in the paper which were not addressed in the news pieces (and may lead to abuse of the results):
First, the notion of a temperature ceiling sparing coral reefs is limited to this very warm open ocean region. In fact, one of the most interesting results of the paper is that while WP2 has not warmed as rapidly as other parts of the tropical ocean, it has expanded. In other words, the edges have warmed. That, as we’ve seen, has caused bleaching events in a number of countries like Kiribati
Second, the extent and severity of coral bleaching is related to experience. Kleypas et al. compiled bleaching reports from islands within WP2. In these locations, coral bleaching tended to occur with temperatures only 0.2-0.3 C greater than the usual maximum experience by the corals. The threshold is generally thought to be 1-2 C. Corals, like any organisms, adapt or acclimate over time to their environment. Since temperatures historically have shown less variation in the WP2 than other parts of the tropics, the corals living there may be naturally more sensitive to temperature stress. If so, the ocean thermostat might not provide the protection that was suggested in the media reports.
Third, the ocean thermostat theory is predicated in part on warming being limited to the surface ocean. Historical temperature profile data suggest ocean warming is also occurring at greater depths. The implications of the warming at depth needs to be fully investigated before we propose an upper limit to surface ocean temperatures in the future.
In other words, there's much more to come on this story.
Monday, December 03, 2007
Re-opening: Climate change and Kiribati
The name of this blog is a local word that was once used to describes the waves on the outer reed in Tarawa, the capital of the equatorial island nation of Kiribati. Tarawa and the other 32 islands of Kiribati are coral atolls, low-lying circular chains of islands created entirely by corals.
An atoll is created by corals growing along the slopes of a sinking old oceanic volcano, a fascinating idea proposed by Charles Darwin during his famous voyages across the Pacific that was not actually confirmed until US scientists started drilling (and testing bombs) in the Marshall Islands in the 1950s. In short, the reef maintains itself near sea level, sand starts to collect, some seeds blow in, and you end up with a malleable ring of flat, narrow islands of sand, coral rock and a few trees all surrounding a shallow lagoon.
The islands in a developed atoll like Tarawa or others in Kiribati is protected - partly - from the erosive action of open ocean waves by a fringing or "outer" reef. When you visit a populated, claustorphobic atoll like Tarawa, you spend a lot of time looking at those waves and wondering about the future. That's why I called the blog Maribo.
Maribo's been on hiatus for six weeks while I was conducting field work in the namesake nation of Kiribati. Over the next few weeks, in addition to some of the usual news items, Maribo will feature stories about the reality - and the unreality - about climate change in what people assume is one of the most vulnerable places on the planet.
What's really happening in Kiribati? Is there evidence for sea level rise? Are other threats more prominent than climate change? What do the local people think? What can be done to help a low-lying nation cope with climate change? Stay tuned.
