Climate change-induced migration is a scary topic. What will happen when entire cities, nations discover they’re rooted on an unlivable landscape? How will cultural identities be preserved in the face of such catastrophic change? More practically, where will the displaced go? These will be tough questions for us in the next 100 years. But these are tough questions right now for the people of the tropical Pacific.
One Pacific nation asking these questions is Kiribati, a low-lying nation composed of many small islands in the central tropical Pacific.
I was down in Kiritimati, one of the Kiribati islands and the world’s largest coral atoll, earlier this summer. And boy was it raining. This was a good thing for me, since part of my research involves collecting rainwater and analyzing its chemistry. But the locals were puzzled. “This much rain right now is not normal,” they said. “It’s wetter than it used to be.”
Despite its tropical location, Kiritimati is normally pretty dry. This is due to the fairly cool ocean temperatures around the island—a result of wind patterns that push warm surface waters away from the equator, allowing cooler subsurface waters to rise to the surface. But is the mean climate of Kiritimati becoming wetter? Were the locals right? Are there signs of human-induced climate change here?
It’s hard to say what’s been happening here over the last century, because there are not many long climate records from this vast, relatively uninhabited oceanscape. Luckily, though, archives of climate information can be found in the natural world. Scientists can use these archives—things like coral skeletons, and marine and lake sediments—to figure out how climate varied in the 20th century, and how recent climate change compares to climate in the deeper past.
Evidence from these natural archives, corals in particular, shows that the ocean waters around Kiritimati have indeed warmed over the 20th century. Real temperature observations, pieced together from ship observations, also suggest warming across much of the tropical Pacific. And, a recent analysis shows a trend toward more rain, more clouds, and lower sea-level pressure over Kiritimati.
Sophisticated climate models also produce a warming tropical Pacific when their simulated atmospheres are packed with greenhouse gases like CO2. The pattern of warming simulated in these models is such that the most warming occurs along the equator, with reduced warming to the north and south. In the atmosphere the average pattern of circulation across the Pacific weakens, and there is far more moisture in the atmosphere, poised to become extreme rain events. This is the fingerprint of climate change in the central tropical Pacific.
There is another very important factor to consider when thinking about climate change in Kiritimati: El Niño. El Niño, the mischief weather maker for the world (think mudslides in California, forest fires swathing Indonesia in smoke, and missing monsoon rains in India), makes its home in the tropical Pacific. Model simulations, climate observations, and paleoclimate data are still unable to provide certainty about what, if anything, will happen to El Niño (and his sister, La Niña) in coming decades with climate change. There doesn’t seem to be unequivocal evidence that there will be more or fewer of these events.
But, there is some evidence that the ‘flavor’ of El Niño may be changing. During the typical El Niño that scientists are used to thinking about, ocean temperatures warm most off the coast of South America, way to the east of Kiritimati. But recent El Niño events look different. The maximum warming is centered right over Kiritimati, in the central tropical Pacific.
The island nation of Kiribati will be especially vulnerable to the gradual background warming and different flavor of El Niño events that define tropical Pacific climate change. These changes will pose a severe challenge to the i-Kiribati (as the citizens of Kiribati call themselves) in coming decades.
On Kiritimati, El Niños are devastating. The added warmth and rain alters the island’s ecosystem, killing off many seabirds. Bigger storms lead to storm surges that can cause coastal erosion. Those surges can also force salty seawater into the critical freshwater reserves of the island that are essential for households and agriculture.
The ultimate threat to Kiribati is this invasion of seawater, in the form of sea level rise. It will eventually wipe Kiribati off the map.
Earlier this year, the Kiribati government was in negotiations to buy land in Fiji for some of their soon-to-be displaced citizens, for agriculture, and to provide earth to build defenses against the onslaught of the ocean. During my stay in Kiritimati, the ocean already practically lapped walls of the kitchen hut I ate my meals in everyday. I could sense the coming emergency.
(Jessica Conroy is a National Science Foundation Postdoctoral Fellow in the School of Earth and Atmospheric Sciences at Georgia Tech. She is a paleoclimatologist by trade. Her research areas include the tropical Pacific, the Tibetan Plateau, and western North America.)