The scientific projections are ominous.

If substantial steps aren't taken globally to counter the effects of climate change, reefs in Hawai'i and around the world eventually could become coral wastelands, decimated by increasingly acidic and warming ocean waters.

Some scientists say such a scenario, which would wreak havoc with Hawai'i's fisheries and the state economy, could come by the end of the century, perhaps even a few decades sooner.

But the projections are just those — projections.

Although they are based on computer models and reams of scientific data, much uncertainty remains.

No one knows, for instance, how a complex marine ecosystem, such as a reef in the middle of the Pacific, will be precisely affected by the increasing temperatures and higher levels of acidity brought on by the burning of fossil fuels.

One wild card is whether corals, resilient organisms that can rebound from some major stresses, will be able to adapt to climate change-related chemical alterations in the environment that are occurring at rates not seen for millions of years.

Scientists also are uncertain whether the predicted effects will happen as quickly or as severely as the models indicate.

"The thing to worry about is not that it will be as bad as we think," said Paul Jokiel, researcher at the Hawai'i Institute of Marine Biology. "It's that it will be much worse than we think."

Developments in Hawai'i waters already are raising alarms.

In recent years, several major bleaching events, linked to increasing ocean temperatures, have killed corals in the Northwestern Hawaiian Islands, an indication that climate change is affecting even Hawai'i's most remote, pristine reefs.

Over the past decade, rising temperatures also have led to an expansion of an area considered the Pacific's biological desert, or its least productive waters, according to ocean biologist Jeff Polovina, who has studied the trend using satellite data. The expansion has encroached into part of the Hawaiian archipelago, and if the trend continues, the pristine conditions of the northern-most atolls could start to become more like the conditions off O'ahu, he said.

Researchers also recorded an expansion of the least productive waters in the Atlantic.

What is worrisome, Polovina said, is that the expansions occurred at a pace much quicker than what the models predicted.

"It's something we've started to focus on now," he said of the accelerating impacts of climate change on marine ecosystems. "It's sort of taken us by surprise."

FOSSIL FUELS

In the complicated link between climate change and reefs, the burning of fossil fuels is the main culprit.

Burning fossil fuels produces carbon dioxide that remains in the environment for years. The carbon dioxide tends to trap heat in the atmosphere, warming the planet. Some of that gas — as much as half by some estimates — eventually is absorbed into surface waters.

Increased levels of carbon dioxide in the oceans lead to greater acidification, which slows coral growth and affects the ability of other calcifying organisms to form their shells. If the acidity gets too high, corals actually start to dissolve, a tipping point that some scientists say could be reached in roughly 65 years.

Adding to the seriousness of the climate change or global warming phenomenon is time. Even if no more fossil fuels were burned, a completely unrealistic scenario, so much human-generated carbon dioxide already is in the environment that normal conditions wouldn't return for thousands of years, scientists say.

"The scary part is the effects are compounding," said oceanographer Rusty Brainard, chief of the National Oceanic and Atmospheric Administration's coral reef ecosystem division in Hawai'i.

Part of the uncertainty surrounding the impact on reefs is due to the relative infancy of the efforts to study those effects.

Ocean acidification, for example, was barely considered a serious threat as recently as several years ago.

At an international conference of coral reef experts in 2004, they ranked ocean acidification as one of the least significant threats — 37th out of 38. When the group gathered again four years later, acidification was ranked No. 1.

Yet the scientists acknowledged much more research was needed to understand the threat.

"What we know (about acidification) is dismally low," said NOAA's Brainard. "It's a science that is just exploding."

RISING SEAS

Hawai'i actually plays a key role in increasing the understanding of climate change.

Two of the longest-running efforts to monitor the level of carbon dioxide in the atmosphere and ocean are in the state, and the numbers from those studies are cited frequently by researchers around the world.

Atop the Big Island's Mauna Loa summit, carbon dioxide levels in the atmosphere have increased more than 20 percent since 1959, according to a landmark monitoring effort that was started by the late Charles David Keeling, considered the first scientist to confirm the rise of atmospheric carbon dioxide.

And at an ocean monitoring site about 60 miles north of O'ahu, Hawai'i scientists since the late 1980s have recorded substantial increases in carbon dioxide in the water. The data from Station Aloha also show a corresponding spike in acidification levels. The Hawai'i initiative and a similar one in Bermuda are considered the best data sets for showing the steady rise of acidity in the ocean.

Though skeptics question whether humans are contributing to global warming or whether the problem is as serious as the models suggest, scientists, environmentalists and others continue to sound the alarm as more becomes known.

The White House recently released a report that said global warming was unequivocal, primarily human induced and the cause of changes throughout the United States. The report said Pacific and Caribbean islands face unique challenges.

Due to climate change, the islands will continue to experience rises in ocean surface and air temperatures, and in the Pacific, the number of heavy rain events and the intensity of hurricanes likely will increase, according to the report. In addition, flooding will become more frequent due to higher storm surges, and coastal land will be lost to a rising sea level.

The authors said the low-lying Northwestern Hawaiian Islands will be particularly vulnerable to the rising sea.

Also, they noted that Honolulu's harbor experienced the highest daily average sea level ever recorded in September 2003 and that the intervals between such extreme events has declined to about five years, compared with more than 20 previously.

What's the outlook for coral reefs?

Not good, according to the authors.

Reefs are especially vulnerable to climate change because even small increases in water temperature can cause bleaching, the report said. Higher acidity adds to the carnage.

"These impacts, combined with changes in the occurrence and intensity of El Ni—o events, rising sea level and increasing storm damage will have major negative effects on coral reef ecosystems," the report said.

NOT TOO LATE

While some fallout from climate change is irreversible, many scientists say the damage can be reduced if substantial steps are taken soon to curb the burning of fossil fuels by switching to renewable energy.

Hawai'i this year enacted a law requiring electric utility companies to produce at least 25 percent of their power from renewable sources by 2020 and at least 40 percent by 2030.

Scientists also say that effectively addressing sediment runoff, overfishing, invasive species and other more short-term threats to reefs will better position the marine ecosystems to weather the longer-term impacts of climate change.

"There is a lot of reason for being optimistic," Jokiel said. "We can turn this thing around."

Yet mustering the political will and financial resources to turn things around will be difficult, in part because the creeping effects of climate change can be tough to detect. Many people see the problem in abstract terms, not connected to their daily lives or too big for any one person or community to address.

But that kind of thinking is dangerous, experts say, given the stakes involved. Because Hawai'i relies so heavily on its environment, they add, the state cannot afford to take a lax approach to the issue and should be a model for other islands and coastal areas to emulate.

"Even if (climate change) seems far away, it's not. We're talking about irreversible losses," said Maxine Burkett, director of the Center for Island Climate Adaptation and Policy at the University of Hawai'i.

"We have to be the best stewards we can be from here on out."

"The thing to worry about is not that it will be as bad as we think. It's that it will be much worse than we think."

Paul Jokiel | researcher at the Hawai'i Institute of Marine Biology

"What we know (about acidification) is dismally low. It's a science that is just exploding."

Rusty Brainard | chief of the NOAA's coral reef ecosystem division in Hawai'i