Hawaii’s climate, renowned for its trade winds and distinct microclimates, is facing significant changes driven by global climate change and shifts. The forces that have shaped the islands’ weather for millennia – their unique geography and position in the tropical Pacific – are interacting with a warming planet in ways that alter established patterns and present new challenges across multiple environmental fronts, including air quality.
The foundation of Hawaii’s weather is deeply intertwined with its volcanic terrain and the persistent trade winds. As John Bravender, Warning Coordination Meteorologist for the NOAA National Weather Service, explained, “The island terrain is the biggest driver for where and how much rain we receive.” This is largely due to a phenomenon called orographic lift, where wind encounters mountains and is forced upward. As this air rises, it cools, and moisture condenses, leading to the formation of clouds and precipitation on the windward slopes. Bravender elaborated, “Wind blowing across the mountains is forced upward. As it is lifted upward, it cools and moisture condenses, forming the clouds and rain we see along the mountains.” Dr. Pao-Chin Chu, Hawaii’s State Climatologist, also highlighted how “Topography and terrain influence precipitation,” underscoring the critical role of the landscape.
Trade winds are the most common weather pattern, prevailing about 90% of the time in summer and 50% in winter, driven by a semi-permanent high-pressure area to the northeast. These winds are crucial because, as Bravender noted, they “drive most of our weather and rainfall patterns based on the way they interact with the island terrain.” The intensity and stability of trade winds also matter. Stronger trade winds can push showers farther downwind, while weaker winds allow for localized sea breezes in sheltered leeward areas.
The altitude of the trade wind inversion, a stable layer in the atmosphere typically around 6,000-7,000 feet, also limits cloud height. A lower inversion can mean less rain despite clouds, while a higher or absent inversion can lead to heavy rain or even thunderstorms, as Bravender described.
Seasonal shifts are also a natural part of Hawaii’s climate, influenced by larger-scale patterns like the El Niño-Southern Oscillation (ENSO). ENSO is a recurring climate pattern involving fluctuations in sea surface temperatures in the central and eastern tropical Pacific, coupled with changes in the overlying atmosphere. Its two main phases, El Niño and La Niña, have different impacts. During El Niño years, when equatorial Pacific waters are warmer than normal, Hawaii tends to see weaker trade winds and less rainfall, according to Bravender.
La Niña years, with cooler waters, don’t show as strong a consistent rainfall signal, though weak La Niñas can mean more rain. Dr. John Marra, Regional Climate Services Director for NOAA, linked El Niño years to a breakdown of the normal east-to-west warm water push across the Pacific, releasing warm water eastward towards California. Beyond ENSO, Dr. Chu pointed to the Pacific Meridional Mode (PMM) as important, particularly for spring rainfall. In its positive state, the PMM is associated with weaker trade winds in the northeast Pacific, leading to warmer sea surface temperatures.
However, layered upon these natural variations are the discernible impacts of climate change. Both temperature and rainfall patterns are showing long-term trends. Dr. Marra stated unequivocally, “Definitely warmer, rising sea levels, warmer oceans, more moisture, more intense rains like cyclones, not necessarily more rainfall or cyclones, just the intensity.” Dr. Chu has observed that Hawaii is “Getting warmer and warmer,” with temperature increases being “more pronounced than at lower elevations.”
The state climatologist also noted a significant shift in rainfall patterns over the past 20-30 years, with a “decrease more drought” being a continuous pattern. Looking back further, Dr. Chu sees a “decline in rainfall in the past 50 years.” This drying trend may be linked to observed changes in the trade winds, which Dr. Chu says have “changed, decreased, become more intermittent, brings moisture, and the east trade mountains are affected, less and less stable, very muggy lately because it was weak.” While the east sides of the islands remain wetter, the general trend over the last 50-60 years has been drier, a pattern Dr. Marra suggested “may be due to climate change or something else, not sure,” highlighting the complexity.
Even as overall rainfall may decrease in some areas, the intensity of rain events is increasing. Bravender noted that Hawaii’s tropical location makes it easier for systems to tap into very humid air, leading to “very intense rainfall rates and flash flooding.” He cited the U.S. record for most rain in a 24-hour period, 49.69 inches on Kauai in April 2018, as an example. An anonymous interviewee from the National Weather Service (NWS) also highlighted this event as a demonstration of how Hawaii’s geography can “help anchor certain weather features, impressive scenarios of higher outcome.” Warmer ocean temperatures play a significant role here, providing the energy for stronger storms.
Bravender explained that ocean temperature “has a big influence on tropical cyclones… Tropical cyclones need warm water to develop and to maintain their strength.” He added, “When waters near Hawaii are warmer than normal, we can see more tropical activity near us during the summer hurricane season.” There is also an observed “poleward shift in TC (Tropical Cyclone) tracks across the world… that could be related to warmer ocean temperatures,” according to Bravender. While there is significant year-to-year variability in tropical cyclone activity, influenced by cycles like ENSO and the Pacific Decadal Oscillation (PDO), a pattern of climate variability spanning decades, the potential link between warmer oceans and changing storm tracks is a concern.
The increasing complexity and observed atypical behavior of climate patterns are making forecasting more challenging. The anonymous NWS interviewee remarked that a strong El Niño last year “behaves differently from what we traditionally expected, than what should happen, things have become a little less predictable.”This “mashup of ingredients” is becoming “more perplexing,” with “different flavors of El Niño and La Niña that don’t traditionally happen.”
This raises questions about how to “rectify this and or improve forecasts, taking into account the general warming trend of the globe.” Forecasting is already difficult in Hawaii due to the rapid changes over short distances and time, a problem Bravender described as the “biggest problem we have is that the weather changes so much from mile to mile and from minute to minute. It’s really hard to capture nuance across the state when things vary so much.” While the NWS uses a high-resolution database, it’s still often too coarse to capture the true microclimates. Climate modeling for isolated island regions also presents challenges, as Dr. Chu noted, with current models having resolutions of 100-200 kilometers, making downscaling techniques necessary and leading to “very contradictory studies” and “no definitive answer to predict.”
These changing weather patterns have profound implications for Hawaii’s ecosystems, natural resources, and communities, and they directly tie into the state of air quality. Marianna Rosio and her team, including Lisa and Mike, describe the overall state of air quality in Hawaii as “Very good,” largely thanks to the trade winds having “a good impact and dispersing pollutants.” However, this varies by location, with the Big Island often experiencing lower air quality due to volcanic eruptions.
The main factors influencing air quality come from both natural and human-caused sources. Human sources include “electric plants, anything man-made, boilers, mobile sources.” But, as the team pointed out, “when a volcano erupts, it’s the biggest emitter for SO2 100s of thousands.” Comparing the two, they stated, “Volcano causes more impact on SO2,” which is sulfur dioxide, a gas that reacts in the atmosphere. The most significant natural contributor is volcanic smog, or vog, a mix of sulfur dioxide (SO₂) and fine particulate matter (PM₂.₅) from volcanic activity, particularly Kīlauea and Mauna Loa.
Climate change is expected to exacerbate Hawaii’s air quality challenges. Dryer conditions linked to changing rainfall patterns “will lead to a likelihood of wildfires releasing pollutants and affecting respiratory issues.” Crucially, the anticipated decrease in trade winds could severely impact pollutant dispersion. Marianna Rosio’s team explained that if “trade winds decrease in frequency, it would stagnate and not have it disperse.” This not only affects local pollution but can also “bring volcanic emissions to other islands” and means “kona winds bring the vog as well.” These climate shifts make air pollution “linger longer or become harder to disperse in the future.”
Monitoring air quality is a key task for the team, who use both “regulatory monitors, and monitoring stations” that compare measurements nationally and “non-regulatory to give info to the public” which answers general questions like “can I exercise today?” via several websites. In response to Vog events, their preparation involves ensuring ” working websites are up to date” and issuing “press releases, work with hazard evaluation to figure out the health effects and precautions, and issue press releases.” They work closely with the National Weather Service for information.
Poor air quality has significant public health impacts in Hawaii, particularly for vulnerable communities. According to John Jacob, State Toxicologist in the Hazard Evaluation and Emergency Response Office, Hawaiʻi faces unique air quality challenges due to both natural and human-made sources of pollution. Depending on the type of pollutant and its concentration, it can lead to potential negative effects on human health, especially in a vulnerable community.
Jacob detailed the specific health effects of key pollutants. Sulfur Dioxide (SO₂), described as “A sharp-smelling gas that forms sulfurous acid upon contact with moisture in the respiratory tract,” can cause from short-term exposure “the irritation of the eyes, nose, and throat, bronchoconstriction (especially in individuals with asthma), and increased respiratory symptoms such as coughing and chest tightness.” Long-term exposure “can cause chronic airway inflammation, worsening of asthma and bronchitis, and increased risk of respiratory infections.” Fine Particulate Matter (PM), which “includes dust, dirt, and smoke” and is “Composed of tiny airborne particles that can penetrate deep into the lungs and enter the bloodstream,” causes “Acute effects include coughing, wheezing, shortness of breath, and respiratory infections.” Furthermore, John Jacob stated that “Chronic exposure is associated with cardiovascular disease, decreased lung function, cognitive decline, and adverse pregnancy outcomes.” Carbon monoxide (CO), a “colorless, odorless gas mainly produced by the incomplete combustion of fuels, “can reduce the oxygen-carrying capacity of the blood, which would lead to various health effects such as hypoxia and suffocation.”
According to Jacob, certain populations are particularly sensitive to air quality changes. Children and infants are highly vulnerable due to higher breathing rates and developing systems. Their health impacts include “Increased incidence and severity of asthma,” “Higher rates of bronchitis and respiratory infections,” and “Reduced lung function and potential long-term pulmonary damage.” Older adults (65+) face elevated risks due to declining resilience and existing conditions, experiencing “Exacerbation of heart disease and respiratory illnesses,” “Increased risk of hospitalizations and mortality rates,” and “Greater reliance on medical interventions like oxygen therapy.” Individuals with chronic respiratory diseases (Asthma, COPD) have hyperreactive airways that respond severely, leading to “Triggering of acute asthma attacks,” “Worsening of COPD symptoms and increased emergency care needs,” and “Accelerated decline in lung function.”
Those with cardiovascular disease are vulnerable because airborne particulates can enter the bloodstream, causing “Elevated risk of heart attacks, strokes, and arrhythmias,” “Worsening of congestive heart failure,” and “Increased likelihood of cardiac-related hospital admissions during vog episodes.” Pregnant women and unborn children are sensitive due to physiological changes, facing “Higher rates of preterm births and low birth weights,” “Potential developmental effects on fetal lungs and nervous system,” and “Increased maternal risk for complications such as gestational hypertension.” People with diabetes are also vulnerable due to already compromised systems, with “Increased cardiovascular risk and hospitalizations” and “Worsening of diabetes complications, particularly during prolonged exposure events.” Environmental and social factors like limited access to healthcare in rural communities, poor housing ventilation allowing indoor exposure, and economic constraints limiting protective measures further amplify the health impacts associated with air pollution, as highlighted by Jacob.
To protect health and improve air quality, Marianna Rosio’s team of Lisa and Mike advises public action: “Overall, everyone is responsible, use public transportation, carpool, ride bikes, conserve energy, less gas, reduce waste, plant more trees, more green places, more awareness, and education.” They also highlighted the importance of policy and community involvement, such as public hearings and investing in clean energy.
Beyond air quality, these changing weather patterns due to climate change have profound implications for Hawaii’s ecosystems, natural resources, and communities. Warmer temperatures threaten native species adapted to specific elevations, potentially causing biomes to disappear. Dr. Marra warned that “As Hawaii gets warmer, biomes disappear, birds live in different sweet spots, no more snow for the Big Island, ecosystems move up and can wipe out other ecosystems.” Warmer conditions also “enhance growth of invasive species,” alter nutrient and oxygen levels in ecosystems, and make high mountains and Hawaiian birds particularly vulnerable.
Freshwater resources are also impacted by changes in rainfall and increased drought, as highlighted by Dr. Chu’s discussion of the PMM’s influence. Rising sea levels, while perhaps not the most immediate concern compared to temperature increases over the next few decades, will become a “big deal by the end of the century, by 3 feet,” according to Dr. Marra, threatening low-lying coastal areas and infrastructure. Climate risks extend to human health, transportation, agriculture (especially from saltwater intrusion), and fisheries, which could collapse due to ocean changes like acidification and warming (Dr. Marra).
Understanding Hawaii’s climate future requires acknowledging its deep connection to the broader Pacific and global climate systems. As the anonymous NWS interviewee pointed out, there is an extensive network of international collaboration in weather services, and the general public may not realize “how connected our climate is to the rest of the world.” The Earth system is complex, with interactions between the ocean and atmosphere creating a system that is “trying to reach some sort of equilibrium,” but occasionally produces “high impact big events” that can even surprise scientists, such as the unique Tonga volcanic event in 2023 that injected an unusual amount of water vapor into the atmosphere.
Given the inevitability of some level of change, building resilience is crucial. Strategies include reducing carbon emissions globally (“bend the curve,” “co2 reduce emissions,” as Dr. Marra put it), but also adapting locally through measures like rerouting water, elevating roads, designing infrastructure to withstand flooding (e.g., ground-floor garages), and creating shade to combat heat. Climate data collected by entities like NOAA and the NWS is vital for providing situational awareness and informing policy and planning. Dr. Marra noted that data, such as that from tide gauges dating back to 1898, helps “verify what’s happening.” This data is used in key decisions, from building setbacks to water management policies and flood mapping, as described by the anonymous NWS interviewee and Dr. Marra, who cited the University of Hawaii’s use of data for policy recommendations.
For young people in Hawaii who are concerned about climate change, the message from these experts is one of engaged action and hope. Dr. Marra urged them to “don’t give up hope, take action, try to make change,” emphasizing both daily actions and advocating for policy change. The NWS interviewee also highlighted avenues for engagement, including the formal cooperative observer program, though acknowledging challenges in recruiting younger participants compared to past generations. Dr. Chu sees climate science as a “very promising future, a growing field,” with opportunities at institutions like the University of Hawaii across various disciplines, from STEM to social sciences, encouraging students to understand how their coursework can be applied. Involvement can start with learning the basics of communication and research and connecting with organizations like the Surfrider Foundation, as suggested by Dr. Marra. While the challenges are significant, the increasing public awareness of climate change’s importance, noted by Dr. Chu, suggests a growing foundation for addressing these complex issues in Hawaii.
