As Seas Rise, Tropical Pacific Islands Face a Perfect Storm

Although they have done little to contribute to global warming, Pacific islanders may face some of the most dire consequences of rising seas. In a Yale e360 interview, geologist Chip Fletcher describes the threats confronting Hawaii and other islands and discusses potential adaptation strategies.

Among the places expected to be most hard-hit by sea level rise in the coming century or two are the islands of the tropical Pacific Ocean, ranging from sparsely developed archipelagos in Micronesia to heavily populated coastal areas on the Hawaiian Islands, such as Honolulu. 

Tracking the past, present, and future impacts of sea level rise on the Pacific region is University of Hawaii geologist Chip Fletcher. In an interview with Yale Environment 360, Fletcher discusses how rising seas are already causing flooding and other disruptions on various Pacific islands, how saltwater intrusion will pose a major threat to freshwater supplies, and how countless coastal residents may inevitably have to be relocated from disappearing shorelines.

Geologist Chip Fletcher.

Geologist Chip Fletcher.

Fletcher notes that while the tropical Pacific is on the front line of climate change’s destruction, it has done little to cause it. “The major industrial nations responsible for global warming have a debt to the Pacific islands to assist with the adaptation that is necessary to survive this challenge,” says Fletcher.

Yale Environment 360: Given current and projected rates of sea level rise, what can we anticipate in the coming decades?

Chip Fletcher: What used to be considered an absolute worst-case scenario of probably about one meter of global sea level rise by the end of the century has now been characterized in a recent report by the National Oceanic and Atmospheric Administration as an intermediate scenario. For the first time, the possibility of a two-meter rise in sea level by the end of the century is being taken seriously. There is even one model result published recently showing that we may see a near-three-meter rise by the end of the century. 

e360: Which Pacific islands will be most severely impacted by sea level rise?

Fletcher: Well every island, actually, because in the Pacific, island populations tend to cluster around the coastal zone and around ports. Most populations are highly dependent on shipping and goods made in faraway places. As sea level continues to rise, we are going to see coastal erosion. Port facilities will experience new currents and extreme water levels, making navigation challenging. Extreme high tides, which are already occurring, will lead to flooding in unexpected ways, such as water coming up through storm drains onto streets and waves flowing across beaches into buildings and roads.  Coastal wetlands, where important staples such as taro are grown, are experiencing saltwater intrusion. Saltwater is contaminating shallow aquifers and threatening freshwater availability.

e360: As a geologist, you have studied the history of the Pacific during recent millennia. How long has sea level been rising?

Fletcher: We cored the coastal plain in Western Samoa on the island of Upolu and found that at the same time that Polynesians were undergoing their journeys of exploration and discovery, 1,000 to 3,000 years ago, sea level was falling and exposing coastal plains that then became habitable, where previously the sea was up against clay banks or cliffs. 

After the last ice age about 20,000 years ago, sea level initially rose due to the melting of the glaciers. That peaked around 4,000 to 5,000 years ago. In the Pacific region, sea level started to fall until a few centuries ago. And now global warming is causing sea levels to rise again.

“People worry that these islands will drown with sea level rise, but their freshwater capacity will be challenged much sooner.”

e360: The impact of sea level rise on islands and coastal areas in the Pacific has been exacerbated by changes in the climate. Could you talk about one critical factor — the periodic El Niño phenomenon?

Fletcher: El Niño occurs when the trade winds are substituted by winds that blow from the west to the east. As we move into a warmer future, climate models are projecting that the Pacific will experience more frequent strong El Niño events. El Niño years bring with them enormous changes for all Pacific islands — changes in rainfall, in winds, in drought, in waves and erosion processes, in water temperature.

Globally, data show a shift to increased rain intensity. With more extreme precipitation, there is the possibility that less water will soak into the ground to recharge aquifers and more of it will remain on the surface as runoff. This can deplete freshwater reserves and increase flooding.  In some areas this trend is compounded by extended periods of drought. And El Niño puts an exclamation point on all of this. The typical variability of storminess and drought rises in magnitude when you superimpose an El Niño on top of it. 

e360: There have indeed been some punishing droughts recently in the Pacific.

Fletcher: Yes, for instance in Yap and Palau, during the 2015-16 El Niño, the drought was so severe that they were down to two-hour water days — one hour in the morning and one hour in the evening when people could take water. All the reservoirs were nearly at zero, the rivers were drying up, they were in desperate shape for freshwater. 

e360: Another threat to critical island fresh water supplies comes directly from sea level rise itself, isn’t that right?

Fletcher: In the atoll communities, which rely on a thin aquifer of fresh water, you get saltwater intrusion into that aquifer both by wave overwash and saltwater bubbling up from below. In fact, in 2007 and 2008 there was a state of emergency in the Federated States of Micronesia where a king tide [an unusually high tide] and a high wave event superimposed on it caused something like 80 communities to lose their food and freshwater because of saltwater intrusions. 

“Before the middle of the century, we’ll see thousands of homes in Hawaii threatened with erosion.”

e360: Saltwater intrusion can be a threat in some cases before actual flooding of the islands?

Fletcher: That’s correct. People worry that these islands will drown with sea level rise, but their freshwater capacity will be challenged — and is already being challenged — much sooner than the islands would be drowned. Freshwater is the fundamental element that allows life on an island. It is already being affected in many places. It is possible in atoll communities that rely on thin freshwater aquifers — if it breaks out onto the land surface, that water flows out into the ocean and you lose it. The freshwater lens becomes thinner and thinner. 

The water table in all our coastal locations goes up and down with the tides. That means the water table is connected to the ocean. So as the ocean rises, the water table rises. This has a couple of effects. If you have a thin freshwater aquifer, it will break out through the land surface and create a new wetland. At first it will only occur at the highest tides of the year, then monthly, and eventually during every high tide. This trend of flooding will be worsened when it rains.

Imagine the consequences when this occurs in downtown Honolulu and in Waikiki [as sea levels continue to rise]. 

We have one location [on Oahu] in particular that is over a mile from the coastline, an industrial area called Mapunapuna. And sea water flows up through the storm drain system, as well as comes under a small bridge out of a stream, and we’ve seen high tides over the past couple of months where there’s a foot or two of standing water in the streets. This nuisance flooding is an example of what we’re going to be experiencing more and more as sea level continues to rise.

e360: When you look to the future in Honolulu, what are the big concerns?

Fletcher: Erosion of the beaches — the tourists come here to go to the beaches. Storm drains flooding with saltwater up onto roads. Ground becoming saturated with groundwater and turning into wetlands. And then greatly increased vulnerability to tsunamis and hurricanes, because there is a non-linear aspect to storm surges and tsunami flooding. That is, if you raise sea level one foot, it’s more than just the equivalent of a one-foot-higher tsunami. If you raise sea level on the very flat topography of the coastal plain that stretches back landward of you, what a small tsunami might have caused with one foot of sea level rise could be ten times greater in terms of damage — not just doubling. 

e360: Are there any mitigation strategies being considered now in Hawaii to minimize the impact on Honolulu?

Fletcher: Yes, there is a committee that was formed by legislative mandate three years ago to study how we are going to adapt to climate change. And the first topic they took up was sea level rise, and there’s a report that’ll be coming out at the end of this year that discusses options. They will also report on the billions of dollars [in projected damages] and the numbers of people and the miles of roadway that are vulnerable to various aspects of sea level rise. 

“For Micronesians and Polynesians, moving would mean leaving behind one’s culture and the very basis of one’s identity.”

e360: What are some of those adaptation strategies?

Fletcher: So sea level rise is going to cause, and is already causing, accelerated beach erosion. How are we going to respond to that? Maybe in a few locations where the cost-benefit analysis permits it, we will spend millions of dollars on finding sand and putting it on the beach — doing beach nourishment. And that’s been done already and will continue to be done on Waikiki. That’s being contemplated and will occur in the next year or two for a tourism place on Maui called Kaanapali. It’s lined with hotels, and looks a lot like Waikiki. The cost-benefit ratio suggests that spending millions of dollars putting new sand on the beach is certainly worth it. 

But many beaches are not lined with hotels, and it’s problematic as to whether placing sand on those beaches will be a good long-term solution or if that sand will immediately erode away. Also where is the money supposed to come from? And so [we need] to simultaneously develop an exit strategy for coastal homes — if erosion starts to threaten those homes and they put sea walls up in front of them the beaches can just disappear. That will no doubt happen on many beaches, but what about beaches that we don’t want to disappear? Like Sunset Beach on the north shore of Oahu — a famous beach. We’re not just going to sea-wall that thing to death — we need to figure out an exit strategy for the homes, for the homeowners. So do we buy them out, or do we trade state-owned land with them away from the shoreline. All sorts of economic tools might be considered. 

e360: Could you briefly give an idea of how many homes in the Hawaiian islands will be threatened in the future by sea level rise. How many homes are that close to the ocean?

Fletcher: Thousands, thousands. Our modeling has looked at just a certain stretch of Sunset Beach and we see that at under one foot of sea level rise, over a hundred homes are threatened. Today there are 18 homes threatened, and with one foot of sea level rise it jumps up to over 100 homes. And one foot of sea level rise could happen within a few decades. And so if even half of those homes are allowed to put up sea walls, we’re going to see the end of Sunset beach.

e360: So thousands of homes on the Hawaiian islands are threatened in the next few decades?

Fletcher: I would say before the middle part of the century we’ll see thousands of homes threatened with erosion and we’re going to be faced with a choice: Do we build sea walls, which will end up killing the beaches and hurt the monk seals and the turtles and all the stuff that goes along with beaches, or do we develop an exit strategy for these homeowners somehow?

e360: Coral reefs are another key factor in the geology of many Pacific islands.

Fletcher: This is point number one related to the Pacific Ocean and climate change —  that our reefs are taking a hammering much faster than we thought would occur. An important paper came out a year or two ago that said that by 2050, 98 percent of the reefs in the world will be sustaining annual bleaching. That’s extinction, basically. The only reefs that won’t go extinct are reefs that can migrate to cooler waters, toward the poles. 

The Great Barrier Reef appears to be on its last legs. It got hammered in 1998 and again in 2010, 2014, 2015, and 2016. Reefs cannot sustain year after year bleaching. The Great Barrier Reef has moved beyond our ability to help. It is collapsing before our very eyes. The reefs throughout Micronesia, in the coral triangle, in Indonesia, even in Hawaii — which sits in slightly cooler water — these reefs have sustained, year after year, serious coral bleaching and they are highly endangered. 

e360: Reading about these threats, one might be under the impression that the smaller islands in the Pacific are doomed.

Fletcher: The Micronesians and Polynesians are place-based cultures. The bones of their ancestors are buried in these places. The land is considered a family member. This means moving is not a realistic option for many. Moving would mean leaving behind one’s culture, one’s family, and the very basis of one’s identity. However, rising sea levels, and changes in freshwater resources pose existential threats. 

Pacific island communities did not bring this upon ourselves. Our contributions to greenhouse gas emissions are negligible, yet we are among the earliest communities to experience the worst consequences. The major industrial nations responsible for global warming have a debt to the Pacific islands to assist with the adaptation that is necessary to survive this challenge. There is no time to spare. There are many steps that can be taken to bolster food resources, improve rainwater catchment, increase the elevation of the land, and envision new community designs that are resilient to storms, drought, and flooding.