In 2022, the State Legislature passed Act 238 which tasks the Hawai‘i State Energy Office to “analyze pathways and develop recommendations for achieving the State’s economy-wide decarbonization goals.” Additionally, the study will evaluate emission reduction pathways from all emitting sectors economy-wide.

Pursuant to Hawai’i Revised Statutes §225P-5, Hawai’i has a target “to sequester more atmospheric carbon and greenhouse gases than emitted within the State as quickly as practicable, but no later than 2045”, effectively establishing a net-negative emissions target.

Hawaiʻi seeks to lead by example in adapting to the impacts and mitigating the extent of climate change. Hawai’i was the first state in the nation to declare a climate emergency. Through Senate Concurrent Resolution 44 SD1 HD1, Hawai’i recognized the global climate crisis endangers the health, safety, and welfare of the people, warranting preemptive and protective action. The resolution further requested statewide entities to pursue climate mitigation and adaption efforts and established “a statewide commitment to a just transition toward a decarbonized economy…”


The concept of intergenerational equity specifies that each generation has the right to inherit the same diversity and cultural resources enjoyed by previous generations and to have equitable access to the use and benefits of these resources.

The Hawai’i Constitution states:

For the benefit of present and future generations, the State and its political subdivisions shall conserve and protect Hawaii’s natural beauty and all natural resources, including land, water, air, minerals and energy sources, and shall promote the development and utilization of these resources in a manner consistent with their conservation and in furtherance of the self-sufficiency of the State. All public natural resources are held in trust by the State for the benefit of the people.”

Article XI, Hawai’i Constitution

The data presented above are rounded to the nearest tenth and are for demonstration purposes. Data were obtained from the United States Environmental Protection Agency (EPA) Greenhouse Gas Inventory to show annual measurements since 1990. The State of Hawai'i Greenhouse Gas Inventory, published annually, will ultimately determine state emissions. Data published by the EPA closely coincide with the data in the state inventory published by the Department of Health. EPA data is used above to show emissions through time. State data should be used for sector-specific data.

The Decarbonization Strategy

  1. Recommend regulatory or other state action; that will ensure the attainment of the State's decarbonization goals;
  2. Include measures to reduce emissions from electricity, including accelerating the adoption of clean energy and improving energy efficiency for residential, commercial, and government users;
  3. Include land use and transportation planning measures aimed at reducing emissions from the transportation sector;
  4. Recommend state actions to address emissions associated with air travel and shipping, including how to encourage electrification and adoption of alternative fuels;
  5. Recommend best management practices in the agricultural sector;
  6. Include long—term carbon sequestration and carbon capture and utilization opportunities;
  7. Make recommendations to aid in the transition of the state workforce to meet the needs of a decarbonized economy;
  8. Consider impacts to environmental justice, frontline, and low-income communities and make recommendations for how to mitigate any impacts to these communities and to facilitate a just transition to a decarbonized economy;
  9. Determine the most cost-effective pathway to decarbonization;
  10. Rank recommendations based on level of impact, cost, and ease of implementation;
  11. Make recommendations on whether the goals established pursuant to section 225P—5, Hawaii Revised Statutes, should be adjusted, or if additional interim goals between the completion of the analysis and 2045 should be adopted
  12. Examine contributions of different carbon sources, how each source can be reduced, what entities are responsible for the reduction of each source, and how each source factors into the determination of statewide greenhouse gas reduction goals; and
  13. Include other relevant considerations as deemed appropriate and necessary.

Act 238 Session Laws of Hawai'i 2022



*Sinks, or carbon reservoirs, are places where more carbon is stored than released into the atmosphere. Sinks include natural sinks such as soil, rocks, forests, and the ocean, as well as technological sinks. Technological sinks are a newer concept and include engineered materials that store carbon captured from the air, or geological reservoirs where captured carbon dioxide is mineralized into a stored form.

2019 Hawai'i Statewide Estimated GHG Emissions by Gas

Why focus on Carbon?

“Carbon” is often used interchangeably with greenhouse gas emissions, and "Decarbonization" is used to denote actions that reduce greenhouse gas emissions.

Carbon dioxide is Hawai'i's dominant source of greenhouse gas emissions, comprising ~ 91% of estimated in-state emissions.

Other carbon-based greenhouse gases include methane (CH4), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs).

Non-carbon-based GHGs include nitrous oxide (N2O) and sulfur hexafluoride (SF6).

To standardize emission measurements, carbon dioxide equivalent (CO2e) is used.

All greenhouse gas contributions must be addressed to achieve net-negative emissions or decarbonization.

The Carbon Cycle

Understanding the carbon cycle is fundamental to understanding the impacts of continued fossil fuel usage.

Arrows show the movement of carbon between the land, atmosphere, and oceans. Yellow text indicates natural fluxes or active carbon, white text indicates stored carbon, and red text indicates human emissions.

Adapted from NASA Earth Observatory

Coal is compressed dead plant matter that has not decayed, but instead accumulated over millions of years.

Petroleum (crude oil) and natural gas are made of plankton that has not decayed and has accumulated on ancient sea floors eventually getting buried deeper by sediment and mud. The increased pressure as well as heat gradually turned the sediment into a rock and the dead plankton into oil and gas.

When fossil fuels such as coal and oil are burned all the carbon these organisms have captured and accumulated over millions of years is released. Thus millions of years’ worth of sequestered/stored carbon have been released over a period of several decades (since the industrial revolution).

The Keeling Curve shows measurements of atmospheric CO2 through time. Measurements at Mauna Loa began in 1958. Pre-dating regular in-situ measurements, data from polar ice core air bubbles provide information on past atmospheric CO2 concentrations. In 2013, CO2 levels surpassed 400 ppm for the first time in over 400,000 years.

Source: Scripps Institution of Oceanography at UC San Diego

Since the industrial revolution, temperature changes track closely with atmospheric carbon dioxide concentrations. The graph shows yearly temperature compared to the twentieth-century average (red bars show mean temperature warmer than average, blue bars show mean temperature colder than average) from 1850–2022 and atmospheric carbon dioxide amounts (gray line): 1850-1958 from IAC, 1959-2019 from NOAA ESRL—original graph by Dr. Howard Diamond (NOAA ARL), and adapted by NOAA


  • The State Department of Health (DOH) is responsible for publishing an annual emissions inventory.
  • Pursuant to Hawai‘i Revised Statutes 342B-71, DOH shall complete a greenhouse gas emissions inventory report each year beginning after 2017 to track emissions and determine the State’s progress in GHG emission reduction.

To analyze emission sources, the UN Intergovernmental Panel on Climate Change (IPCC) provides estimation methods for different economic “Sectors”. Sectors are further divided into individual categories and subcategories.

Estimates are as good as the granularity of input data available. Some data categories are more challenging to estimate than others. For example, emissions from point sources such as stationary combustion power plants are regulated under the Clean Air Act, thus emissions from these sources are monitored and publicly available. Whereas, emissions from the Transportation Sector are made up of many non-point sources, therefore, estimation methods must be applied using accessible data. Emissions from the Agriculture, Forestry, and Land-Use Sectors can be even more challenging to quantify due to climatic variations, entropic (changing) system states, and non-point source emissions.

IPCC provides standardized guidance to minimize omission or double counting for categories with potential overlap.

(Hawai'i examples)
(Hawai'i examples)
Energy1. Electricity Production / Stationary Combustion
2. Transportation 3. Waste Incineration
4. International Bunker Fuels
2a.  Ground
2b. Domestic Marine Transportation
2c. Domestic Aviation Transportation
Industrial Processes and Product Use (IPPU)
Hawai‘i categories are few due to the lack of large industry.
Categories not applicable to Hawai'i include – electronics, metal, chemical, and mineral industries.
1. Substitution of Ozone Depleting Substances (ODS) (Fluorinated gases)
2. Mineral Industries
3. Electrical Transmission and Distribution (different from combustion)
1a. Refrigeration
1b. Air Conditioning
1c. Aerosols
2a. Cement Production (mineral industries) (HI production ended 2001)
Agriculture, Forestry, and Other Land Uses (AFOLU)1. Land-based Agriculture (Soil Carbon)
2. Livestock
3. Forestry
4. Other Land Uses / Land Use Change
1a. Cropland – plant/nutrient management
1b. Grazing Lands
1c. Synthetic Fertilizer Application
2a. Enteric Fermentation
2b. Manure Management
3a. Deforestation
3b. Forest Management
4a. Fires
Waste1. Landfills
2. Wastewater treatment
3. Composting
1a. Food Waste
1b. Garden Waste
1c. Paper Waste
1d. Textiles
1e. Plastics
IPCC Sectors or Categories are further defined in the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Volume 1 General Guidelines and Reporting, Chapter 4 Methodological Choice and Identification of Key Categories. Applicable Hawai'i sectors are defined in the Statewide Inventory.

GHG Emissions are aggregated, summarized, or presented in terms of Carbon Dioxide Equivalents, or CO2e. The CO2e metric standardizes emissions – makes the comparison “apples to apples”.

Global Warming Potentials (GWP) are used to standardize non-CO2 emissions of other GHGs.

GWPs are determined using two metrics:

1) Radiative efficiency – the ability of the GHG molecule to absorb heat energy in the atmosphere

2) Lifetime – an estimate of how long the molecule resides in the atmosphere

CO2 has a GWP of 1 because it is the reference gas.

Some climate warming pollutants are more dangerous to the climate than carbon dioxide. For example, methane is said to be more “potent”; the estimated GWP of methane used by EPA/IPCC is 25 for over 100 years. If evaluated on a shorter time frame methane is more potent.  When considering the impact over 20 years GWP increases to 84-87. Underscoring the importance of reducing potent GHGs.

100-year GWPs are used for inventories. This is standard practice, however, the downside, of using this accounting should be acknowledged. This includes the impact of GHGs on shorter timeframes.

In Hawai'i, the Energy Sector, inclusive of electricity production, transportation (ground, domestic marine, and domestic aviation), waste incineration, oil and natural gas systems, and refining account for ~88% of emissions.

Stationary combustion, or electricity production is currently the largest single emitter of climate-warming GHGs in Hawaii.
However, when combined, emissions from the transportation sector, collectively make up the most considerable portion of emissions in the state, with domestic aviation and ground transportation having the largest share.

Domestic aviation includes only domestic flights originating in Hawai‘i. In other words, one-way flights to the continental U.S. and interisland travel. The aviation category is not inclusive of international travel or round-trip travel outside of the islands.

International Bunker Fuels - marine and aviation travel originating in Hawaiʻi and ending in a foreign country. International bunker fuels are not included in totals but instead reported separately.

Other sectors including Industrial Products and Product Use (IPPU), Agriculture Forestry and Land Use (AFOLU), and Waste while small contributors to overall GHG emissions are also critical due to the high global warming potential of the gases emitted in these sectors (See Global Warming Potentials above).

For more information on current statewide emissions, please see the State of Hawaii Department of Health, GHG Inventory.



HSEO is developing the Decarbonization Strategy and welcomes community and stakeholder input and inquiries. If you would like to provide feedback on the economy-wide strategy, please complete the survey below. Responses will be recorded and published as a part of the report.