How is climate change going to affect Hawai`i?
Little by little, scientists here and abroad are tackling that question. A lot has already been done, from Chip Fletcher’s work on coastal erosion and flooding in Honolulu to Dennis LaPointe’s, Carter Atkinson’s and Tracy Benning’s work on the forest’s shrinking malaria-free zone to Jason Baker’s, Charles Littnan’s and David Johnston’s predictions on how rising seas will shrink monk seal and green sea turtle habitat in the Northwestern Hawaiian Islands.
Last March, the Hawai`i Conservation Alliance sponsored a forum on some of the latest research as part of the alliance’s effort to educate scientists and land managers about climate change so they can incorporate predicted effects into natural resource management here.
Held at the University of Hawai`i’s East-West Center, the forum was a chance to hear from both local and mainland scientists on the various ways climate change may affect the world’s natural resources in general, and Hawai`i’s in particular. Later that week, HCA members met at the U.S. Fish and Wildlife Service office in Honolulu to develop a climate change response strategy, which will be presented at this summer’s annual conservation conference this July 29-31.
Precipitation
As National Oceanic and Atmospheric Administration climatologist Henry Diaz put it, the models used by the Intergovernmental Panel on Climate Change show that Hawai`i is in an “increase-decrease dichotomy” when it comes to rainfall predictions under the most idealistic global warming scenarios. In other words, the models show a decrease in precipitation north of the island chain, an increase to the south, but directly over the islands, the models don’t agree on what will happen.
Diaz and other climate modelers who spoke at last March’s forum suggested that, even if the 20-plus models used by the IPCC did agree, they aren’t refined enough to predict small-scale, regional changes. Typically, global climate models have a resolution of 150-300 kilometers.
“Hawai`i almost fits inside one box,” Diaz said, referring to the global grid used by the IPCC models, where one box equals one data point.
So, Diaz, in cooperation with Thomas Giambelluca and Oliver Timm of the University of Hawai`i, is working on ways to better predict climate change impacts on weather in Hawai`i.
At the time the forum was held, there was little to report in the way of results. As Timm said, the group is still working on selecting the right model to use for Hawai`i, running different ones dozens of times to see how well they match up with observed weather data.
Using one promising model, Timm said, it appears that for one region in Hilo, there may be one more inch of rain a month as a result of climate change impacts on trade winds.
But even with the right model, predicting what rainfall will be throughout different climatic regions across the island chain will be difficult. How will dry Wai`anae or Pu`u Wa`awa`a be affected differently from Mt. Wai`aleale, the wettest place on earth?
Diaz said the tremendous local variation in annual rainfall – which can vary from 10 inches to more than 200 inches – will complicate things, as will the fact that the islands get most of their rainfall from just a handful of rainstorms a year. Between 1961 and 2003, he said, ten percent of the annual rainfall events accounted for 50 percent of total annual rainfall.
“The background noise in the system will make it difficult to predict change,” Diaz said. Even so, he did say that high and mid-level elevation changes in precipitation are possible with a two to three degree Centigrade change in temperature.
Giambelluca added that temperatures are not only increasing, they’re doing so rather quickly in some instances, noting that high-elevation nighttime temperatures have gone up 0.79 degrees Fahrenheit per decade over the past 30 years.
Also, he said that Hawai`i’s temperature normally tracks the Pacific Decadal Oscillation (an El Niño-like pattern that affects temperatures over long periods of time), but over the last 25 years, the temperature here has been departing from the PDO index, which may be another sign of global warming.
He added that the weather phenomenon known as the trade-wind inversion, which is associated with less precipitation, has also in the last 25 years become more frequent and may become more so with global warming.
The Ocean
While climate modelers have their hands full with Hawai`is unique weather system, Fletcher, a University of Hawai`i coastal geologist, has already made some highly publicized predictions about potential sea level rise effects on O`ahu. Earlier this year, when the East-West Center hosted President Bush’s international climate talks, environmentalists and students took to the streets, marking them with blue chalk to indicate which parts of Honolulu Fletcher predicts will be below sea level if global warming causes ocean levels to rise another meter, which it is predicted to do later this century.
At the March forum, Fletcher showed pictures of areas that are already threatened by saltwater inundation – cars driving through ocean-flooded streets in Mapunapuna, and an open manhole along the Ala Wai canal just inches from overflowing.
In addition to calling for a statewide retreat from Hawai`i’s disappearing shorelines, Fletcher said that government agencies with jurisdiction over coastal areas that will be affected by sea level rise need to start working better together.
On a broader scale, Stanford University chemical oceanographer Ken Caldeira offered some predictions about what high levels of carbon dioxide might do to the world’s coral reefs and other calcium carbonate-reliant organisms. Right now, our carbon dioxide output is on track to reach an atmospheric concentration level of about 550 parts per million in the next few decades, a level not seen on this planet since the dinosaurs went extinct, he said.
Based on computer simulations of ocean chemistry under various levels of atmospheric CO2, Caldeira and other scientists with the Carnegie Institution’s Department of Global Ecology have calculated that if current emission trends continue, by 2050, 98 percent of reef habitats will have become too acidic for reef growth.
Caldeira presented a map of what the ocean chemistry will be with an atmospheric CO2 concentration of 550 ppm that shows how areas where corals can survive will not only shrink dramatically, but they will move to places where they’ve never been before.
Local coral reef consultant Rick Grigg asked how such levels could be bad for reefs when 550 ppm is about the level that existed when corals first formed. Caldeira responded that the emission rate, not the atmospheric level, is what will kill corals, as well as other species that need calcium carbonate to survive. It takes a long time for the ocean to interact with sediments and to neutralize gases that it absorbs, he said.
“If humans had released [carbon dioxide] 100 times slower, it wouldn’t be a problem,” Caldeira said.
Species
In 2004, the journal Nature published an article that claimed the world could lose about 25 percent, or roughly 1 million, terrestrial species as a result of climate changes between now and 2050. Conservation International researcher Lee Hannah, one of the article’s co-authors, discussed how climate changes might affect Hawai`i, which has been described as the endangered species capital of the world.
While he pointed to the work by Denis LaPointe of the U.S. Geological Survey’s Volcano field office and others on the startling shrinkage predicted for the malaria-free zone of the Big Island and Kaua`i’s Alakai swamp, Hannah also highlighted the positive: The Big Island has a large elevational gradient that allows for upward movement of species displaced by warmer temperatures. Also, Hawai`i has steep drop-offs to deep water, which may alleviate coral bleaching caused by rises in sea temperatures, he said.
Whatever happens to the climate and waters around Hawai`i, Hannah concluded, there won’t be a sea change in the way managers try to protect species.
“Conservation tools will be pretty much the same, but managers will need to be able to deploy them in a dynamic environment,” he said.
— Teresa Dawson
Volume 18, Number 11 May 2008
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