“I don’t think we’re licked yet,” said one of the more optimistic presenters at this year’s Hawai`i Conservation Conference. But while he and several other speakers insisted that it’s not too late to try to protect Hawai`i’s natural resources from the predicted effects of climate change, it was difficult for many of those at the conference not to succumb to the “gloom and doom” that resource managers and scientists laid out in one sobering talk after another.
In March 2008, the Hawai`i Conservation Alliance held a two-day forum on some of the latest research in Hawai`i regarding climate change. The information presented at the forum was limited and in some cases very preliminary, but at this year’s annual conference, sponsored by the HCA, presenters brought into sharper focus the effects climate change is having on Hawai`i, the environmental changes the islands can expect over the next several decades, and what managers are planning to do to cope with them.
Held at the Hawai`i Convention Center July 28 to 30, most of the talks centered around the conference theme, “Hawai`i in a Changing Climate: Ecological, Cultural, Economic, and Policy Challenges and Solutions.” Several sessions also addressed more traditional research and management issues, as well as indigenous management approaches.
To judge from many of the talks, the outlook for Hawai`i is bleak, especially for
the northwestern islands. Regarding the state’s terrestrial environment, predicted changes in precipitation and temperature are likely to leave little or no suitable habitat for many native plants and forest birds.
Drying Up
Without water, there is no life. And according to long-term rainfall and stream flow data, Hawai`i’s water supply already appears to be dwindling.
Tom Giambelluca, a climatologist at the University of Hawai`i, has studied how climate change may be affecting the tradewind inversion (TWI) and temperature in Hawai`i. He’s found that in recent decades, the air temperature at night and at higher elevations has been increasing rapidly and significantly, up 0.79 degrees Fahrenheit per decade over the past 30 years. The temperature increase at the high elevations has been three times as great as at the lower elevations, he found. And because the state’s most intact native ecosystems are located at higher elevations, Giambelluca said, he’s fairly certain that climate change, which predicts greater warming across elevations, is “going to have an impact on our native biota.”
According to Giambelluca, the inversion, which traps moist air below the cloud line, has become more frequent in the last 15 or so years and has also gotten lower. A lower TWI means shallower clouds, which produce less rain and leave a larger area above the clouds with no moisture. While Giambelluca said he’s not sure whether the TWI trend is a result of global warming, he did say it has resulted in a 10-15 percent loss in precipitation.
In addition to the TWI trend, over the last 30 years, there has also been a weakening of the tradewind field surrounding the islands and to the southeast of the chain. This, according to Henry Diaz of the University of Colorado at Boulder, can have an effect on cloud cover and also on air temperatures.
Data from 1961 to 2003 show a 17 percent decline in annual rainfall, and a 27 percent decline in the average winter rainfall, he said, adding, “That’s a lot.”
He said that global temperature data from the National Oceanic and Atmospheric Administration does not show what the increases in air surface temperatures have been over Hawai`i, only that there has been a less-than-average increase in sea surface temperature. However, Diaz said, his work with Giambelluca shows that the air temperature over Hawai`i between 1950 and 2006 has increased by 1 degree Celsius, three times as much as the sea surface temperature. He added that changes in near-shore sea surface temperatures have mirrored that trend.
Under “middle of the road” emission scenarios of global climate models used by the Intergovernmental Panel on Climate Change, the temperature around Hawai`i is expected to increase by 2 degrees Celsius (about 3.5 degreed Fahrenheit) by 2100. This increase would result in more frequent and intense extreme temperatures as well as more frequent heavy rains.
Diaz added that models he and Oliver Timm of the University of Hawai`i have developed reveal that Hawai`i’s summers will become wetter and winters will be drier.
Complementing Diaz’s and Giambelluca’s findings about decreasing rainfall, Gordon Tribble, the Hawai`i and Pacific director of water progams for the U.S. Geological Survey, presented data, published in a 2004 USGS publication by Delwyn Oki, showing that base stream flows in Hawai`i have also decreased over the past 100 or so years.
In his study, Oki looked at the base flow at seven stream stations across the state – on Kaua`i’s Wailua River, on Kaukonahua and Kalihi streams on O`ahu, on Moloka`i’s Halawa Stream, and on Honokohau, Hanawi, and Honopou streams on Maui. The stations had been operating since at least 1913 and the streams at the station point had not been affected by pumping or diversions.
Oki found that stream flow decreased significantly at four of the seven stations (Kalihi, Halawa, Hanawi, and Honopou). For example, Tribble said that from 1910 to 2000, Halawa Stream’s average annual base flow declined from ten cubic feet per second (cfs) to between five and seven cfs.
With regard to Hawai`i’s drying trend, Tribble said that the tradewind inversion “has no doubt played a part.”
Poor Plants
To estimate how the predicted precipitation and temperature changes will affect Hawai`i’s ecosystems, Jonathan Price of the University of Hawai`i at Hilo, Loyal Merhoff and James Jacobi of the USGS Biological Resources Discipline, Giambelluca, Timm, and Diaz developed models to produce potential range maps for 1,167 native Hawaiian vascular plants. Using the climate models Diaz, Giambelluca and Timm have downscaled to predict temperature and moisture changes in different climatic regions in Hawai`i, as well as existing information on current environmental conditions (elevation, moisture, and substrate age), the researchers predicted the plants’ habitat ranges in the last three decades of this century.
Their preliminary results suggest that both wet- and dry-forest communities will be acutely affected by the disruption of the “moisture-temperature combination.” During his conference presentation, Price showed maps of how various climatic zones on each island will be affected. The coolest habitats, “the tops of any mountain, effectively,” will be lost by 2100, he said. “That’s simply a function of warming…. The amount of alpine climate would certainly diminish,” he said.
Hawai`i also stands to lose much of its cool, high-elevation wet forests, the researchers found. While the elevation of the tradewind inversion layer appears to be something that would stay in place, Price said, temperatures are predicted to rise. So what is now relatively cool, wet habitat just under the inversion layer would become warm and wet, he said. Drier montane forest habitat may expand, he added.
The habitats of certain plants will shrink severely, he continued. For example, the Ko`olau akoko (Chamaesyce celastroides var. amplectens), which lives along the wet summits of O`ahu’s entire Ko`olau mountain range, will be able to survive only on two of the range’s highest points. The same goes for certain Cyanea species that live in cool, wet habitats on the islands of Hawai`i and Kaua`i, which will be restricted to only one small point on each island. The habitats suitable for the invasive strawberry guava, on the other hand, will expand greatly, Price said, adding that many of the traits (high reproductive and dispersal rates) that make non-natives problematic also make them potentially more adaptable to climate change.
Despite the dire results, Price is optimistic about managing the effects of climate change. Although he did not include any suggestions during his presentation, he did so last year when he spoke at the conference.
“I would have liked to have reiterated them since the rest of the talk was a downer,” he told Environment Hawai`i. He pointed out that both native and non-native species are going to adjust to climate change and are already undergoing constant change with new invasive species arriving and previous invasions expanding and filling in.
“We’re on a treadmill of management actions and climate change speeds up that treadmill,” he says. But pollen and fossil records revealing how species responded to the last ice age suggest that some native species respond more quickly than others to climate changes.
“So in terms of management, we can make some assessment about how native species are going to respond, facilitate native species responses and preclude the invasive plant responses to changes. In a lot of ways, the management actions we would take are similar to what we’re doing…. The future will be like the present, only more so,” he says.
David Burney, director of conservation for the National Tropical Botanical Garden on Kaua`i, said that if plants are going to be stranded by habitats that shift too quickly for the plants to keep up with, they will have to be moved by managers, and “not like in the old Disney ‘Fantasia’ movie where the trees get up and walk.” The problem, however, will be finding suitable habitats for relocation, he said.
Coastal strand vegetation may have to be moved inland to protect it from sea level rise, while changes in the TWI may force managers to create relocation opportunities for populations at higher elevations, maybe even on other islands, he said.
Burney added that biological invasions may increase with climate change: “We are going to have to be willing to kill for conservation,” he said. And to create new habitats, he said, drastic action may be required.
“We have to literally do earth moving. We have to be able to take places nobody wants…scrape out seed banks and absolutely start over,” he said.
Bye-bye, Birdie?
With regard to Hawai`i’s native forest birds, Dennis LaPointe, an expert in mosquito-borne diseases with the USGS, reported that a 2 degree Centigrade increase in temperature – which is what several industrialized countries have agreed to try to limit global warming to – will likely result in a population decline for the `apapane (Himatione sanguinea) and almost certainly will drive the `i`iwi (Vestiaria coccinea) to extinction. Sara Hotchkiss of the University of Wisconsin cited the work of LaPointe and his USGS colleagues, which shows that that under the same global warming scenario, the Hanawi Natural Area Reserve on Maui would lose more than half of its bird-worthy habitat. According to the study, published earlier this year, the Hakalau Forest National Wildlife Refuge on Hawai`i island would likely lose as much as 96 percent of its best bird habitat.
Jeff Burgett, a recovery biologist with the U.S. Fish and Wildlife Service, also sounded the alarm about the perils native forest birds are facing.
In doing calculations on their “own dime,” Burgett and David Leonard of the state Department of Land and Natural Resources’ Division of Forestry and Wildlife found that, based on the models prepared by Price and his colleagues on the expected changes in plant species ranges, for some islands, the “disease-free line,” considered to be the upper limit of mosquito habitat (currently about 4,000 feet elevation), will be above the treeline by the end of the century. For the island of Kaua`i, which already lacks mosquito-free areas, there will be no safe forest bird habitat, Burgett said.
LaPointe himself, whose work on mosquitoes and avian malaria has led some to postulate the existence of the “mosquito-line,” does not support the idea that mosquitoes will be strictly limited by elevation. During his presentation, LaPointe said, “I know mosquitoes… I know they’re not that organized.” He added that mosquito distribution is patchy and hard to predict.
In any case, Hawai`i’s “thermal refuges” will eventually disappear and will have a useful life of no more than about 100 years, Burgett said.
In addition to the need for action on a global scale to limit warming to less than 2 degrees Centigrade, Burgett said the state also needs a long-term strategy to allow birds to live with disease.
But what can be done? Captive propagation may not be the best long-term strategy, since it’s so expensive, Burgett said. A contour pig fence would help keep upper elevation forests mosquito-free, but it’s not a century-long solution, he said. Selection for disease resistance may or may not be an option. “There may be none… Evolution may be too slow,” he said.
Translocating birds to higher ground may also not a permanent solution, Burgett said, since disease will eventually invade the area and translocation will also impact the source population, as well as their new ecosystem. He added that there are also regulatory hurdles to establishing endangered species outside their home ranges.
Regarding the regulatory hurdles, Burgett asked, “Is it better to have existing species on the wrong island or extinct species on the right island?”
Despite all of shortcomings of the various tools managers have to save Hawai`i’s forest birds, Burgett recommended using them anyway. From captive propagation to range expansion and restoration, he said, utilizing these tools to save birds was most definitely not pointless. But, he warned, “the clock is ticking.”
A Desert in the Ocean
According to Jeff Polovina of the National Oceanic and Atmospheric Administration’s Pacific Islands Fisheries Science Center, as global temperatures warm, the ocean will become more stratified. The surface will warm faster than the deep, which may make it more difficult for currents to mix the ocean’s deep nutrients into shallower waters. The result, Polovina said, will be a drop in nitrogen levels at the same time that more carbon dioxide is being absorbed by the ocean, he said.
The resulting change in the ocean’s carbon-to-nitrogen ratio may have an impact on food web structures, Polovina said. For example, phytoplankton that have a high carbon-to-nitrogen ratio have low nutritional value. Species of phytoplankton that thrive in a high carbon-to-nitrogen ratio may edge out those that don’t do as well, “and we’ll see a change in species going from the base of the food chain all the way up,” he said.
A global ocean satellite chlorophyll sensor (chlorophyll being used as a proxy for surface plankton) shows that Hawai`i lies within in an area of low productivity, a subtropical gyre that is basically a biological desert. These areas have a chlorophyll level ranging from about 0.2 mg of carbon per cubic meter down to about zero, he said.
Within these “deserts,” Polovina said, are virtual dead zones – regions with less than .07 mg carbon per cubic meter. And over the past decade, these dead zones have expanded globally by about 15 percent. The North Pacific “desert” spans 15 to 20 million square kilometers. The rate of expansion, depending on the area, has been about 1 to 4 percent a year.
“They’re such big areas that they’re adding 800,000 square kilometers of low productivity habitat every year,” he said. He added that the minimum size of the Pacific zones, which grow in the summer and shrink in the winter, has increased 40 percent, from 11 million square km to 14 million square km.
Climate models predicted that these low-productivity zones would increase, but they underestimated the rate and the extent of it, Polovina said. For example, a 2004 publication predicted that by 2050 the area of subtropical gyres (STG) in the southern hemisphere would increase 9.4 percent over their area in the pre-industrial period, and the northern hemisphere STGs would increase 4 percent in the same time frame. Instead, ocean sensors have determined that gyres in the Pacific and Atlantic have increased between 6.32 and 35.2 percent between 1998 and 2006 alone.
“We’re seeing a much more rapid increase than the models predicted,” he said, admitting that the increases reflect just 10 years of data. “The reason for caution in interpreting only a decade of data is that we’ve had a decade where we’ve had more La Niña than El Niño events so we haven’t really had a balanced decade in terms of the inter-annual variability.” With more El Niño events, the severity of the trend may decrease, but even so, he said, the results so far are an indication of a global warming signature, with impacts for the carrying capacities of both pelagic and nearshore ecosystems.
“The lower the level of plankton, the lower all food webs will be,” he said, adding that the ocean stratification will also result in less deep-water nutrients feeding reef ecosystems.
Lost Larvae
According to Rob Toonen of the Hawai`i Institute of Marine Biology, fish larvae listen for waves and smell far-away leaves to guide them to their ideal habitats. They can even smell the difference between rocks of their home reefs and those of another reef. But climate change-induced ocean acidification and temperature changes may make it harder for larvae to find their way.
In his presentation, Toonen said some evidence suggests that for larvae, changes in the ocean pH “screws up their sense of smell.” He noted also that sound travels better through warmer water, which would mean that a warmer ocean would also affect their hearing.
“So if you change the pH, suddenly they’re responding to things they didn’t use to respond to, and not responding to things they [did respond to],” he said. “We’re changing their cues and what they’re looking for…and which direction they’re going.”
He showed slides made by one of his students working on the effects of temperature, acidity and food changes in sea urchin larvae. The research suggests that if temperature and food is kept constant, larvae in water with lower pH (such as is predicted in most climate change scenarios for 100 years from now) develop more slowly, can’t swim as well, and don’t develop the same feeding capability. Toonen added that pH changes will also likely reduce fertilization and survival.
However, he added, “[T]his is something that other studies have predicted the exact opposite of.” Some models show that global warming increases the growth rate of larvae. An increased growth rate would, theoretically, also mean greater survival, since the larvae would not spend as much time in the top of the water column, where they can more easily be snatched up by predators. On the other hand, it could inhibit their ability to disperse, since the larvae would not be traveling as far in the ocean.
What will really happen to larvae and their distribution is still unknown, since, Toonen said, “We don’t understand how these synergies start to impact each other. The predictions for temperature get overwritten by pH or food and we don’t have a predictable pattern anymore.”
Given that uncertainty, as well as the unpredictability of climate predictions, Toonen said, “We have to build in resiliency…otherwise we will make mistakes and we will fail.”
‘A Patchwork Quilt’
“We’re seeing our study material disappearing,” local coral reef expert and plenary speaker Paul Jokiel said at the conference. Jokiel, who has led some of the best work in the islands on the effects of increasing ocean acidity on Hawai`i’s corals, said that if the atmospheric concentration of carbon dioxide reaches 450 parts per million, it will lead to severe changes in coral cover. By 2096, he said, there will be zero percent of what there is today. He displayed a chart showing the slope of the decline, which he described as “the trajectory of the hand-basket as it goes to hell.”
Kim Selkoe of the HIMB reported that her modeling of ecosystem responses in the Papahanaumokuakea Marine National Monument in the Northwestern Hawaiian Islands found that acidification will affect Laysan, Maro, and Nihoa atolls the most. Maro Reef and French Frigate Shoals will be most impacted by ultra-violet radiation, and Pearl and Hermes Reef will be most affected by disease and bleaching. Necker Island, on the other hand, may be buffered from the worst of the impacts of climate change.
Ronald Hoeke, of the University of Hawai`i’s Joint Institute of Marine and Atmospheric Research, also used modeling to predict coral cover changes in the Pacific. He used Midway Atoll, French Frigate Shoals, O`ahu, and Johnston Atoll as reference sites. In his presentation, he noted that his results were not predictions for those locations, but just provide a general pointer of what will probably happen to coral growth and calcification rates under the temperature changes and carbon dioxide inputs predicted in the “middle of the road” Intergovernmental Panel on Climate Change scenario of 720 ppm of carbon dioxide.
Hoeke found that some regions have higher probabilities of frequent bleaching events, while others may have faster recovery rates. As temperatures increase, the potential for bleaching is the greatest at Midway, he said, where bleaching events have already occurred in 2002 and 2004.
The area with the least potential for coral bleaching is Johnston Atoll. Based on Jokiel’s ocean acidification studies, Hoeke established a coral growth curve relative to temperature. Based on his models, temperature changes alone would cause coral growth rates to increase at Midway. Further south, at French Frigate Shoals and O`ahu, growth rates would appear to stay the same, while at Johnston, the most southerly of all sites, they would decline.
But when Hoeke incorporated the effects of bleaching into his models, coral growth rates decline sharply as a result of even just one bleaching event. In nearly every case where bleaching is incorporated into the models, “we’re left with no viable coral cover by the year 2100,” Hoeke said. The one exception is French Frigate Shoals, where, according to some scenarios, a little coral will survive.
Even so, he said, corals will cease to be significant components of the shallow benthic ecosystem by 2050. If we assume corals have some ability to adapt to thermal tolerances, the picture is somewhat better, he added.
“We’ve got a lot of gloom and doom here,” Hoeke concluded, but he added that the results he presented were based on his models using only general sea surface temperature data and not site-specific data, which may skew his results. At Pearl and Hermes Reef, for example, the temperature at 20 meters doesn’t get as high as the peak surface temperatures he used in his models.
Hoeke said he ran the models with some site-specific data that were not statistically significant. They showed that Hawai`i might not lose its coral cover by the end of the century, but will lose it at the shallower depths more quickly. Because long-term in-situ data is scarce, he said, he cannot make predictions based on it. Still, he said, “Looking at the in situ data, I think we’ll have much more of a patchwork quilt” than a wasteland.
Waterworld
Elizabeth Flint, a wildlife biologist with the U.S. Fish and Wildlife Service, was one of a few conference speakers to address the effects sea level rise will have on species that live in low-lying areas. Some focused on the devastation to human habitats, but Flint offered a qualitative risk assessment of how the 33 species of seabirds in Hawai`i and the central Pacific might be affected by a 25-meter rise in sea level, which is what is predicted if global warming leads to substantial melting of land ice.
And what she found spells disaster for the seabirds: 90 percent of their terrestrial habitat in the Northwestern Hawaiian Islands will disappear.
A rise of one to two meters, which is what is predicted by 2100 due to thermal expansion alone, will be devastating, she said. But the more extreme scenario of a 25-meter rise would wipe out critical habitat in the NWHI for 5,795,000 breeding seabirds. The islets in the Rose Atoll Marine National Monument, located in American Samoa, may be the first to go, she said, adding that their loss would result in the displacement of an additional four million breeding seabirds.
“If you consider the entire population that is dependent on those [low-lying] islands….the number is closer to 14 million in Northwestern Hawaiian Islands and almost that much in the central Pacific,” she told Environment Hawai`i.
In addition to those islands that would be submerged by such a rise, other islands will become more vulnerable to “wash-overs” and will be “reduced in value because of the higher stand of the ocean,” she said.
The Phoenix petrel (Pterodroma alba), the Polynesian storm petrel (Nesofregetta fuliginosa), the Laysan albatross (Phoebastria immutabilis), and the black-footed albatross (Phoebastria nigripes) are the most vulnerable to sea level rise because their populations are concentrated on low-lying islands and/or their numbers are so few that they would be unable to establish a new colony.
Given the previous talks about climate change effects to corals and other marine life, Flint said that numbers could be worse. “We don’t know how the marine environment will be affected. What we can do on land is only part of the story,” she said.
Note: The print version of this article erroneously identifies the chlorophyll concentrations in dead zones found in the Pacific Ocean. The correct figure should be less than 0.07 mg of carbon per cubic meter, not .7 as stated in the print version of the article.
— Teresa Dawson
Volume 20, Number 3 September 2009
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