The City of Honolulu’s Climate Change Commission presented the “Sea Level Rise Guidance and Climate Change Brief” to Mayor Kirk Caldwell on July 16, prompting him to sign a directive requiring all departments and agencies under his jurisdiction, to take action to prevent sea level rise.

The Commission says the city should plan for 3-feet of sea level rise by the mid-century and if action isn’t taken now, nearly 4,000 structures on Oahu would be flooded, and nearly 18 miles of coastal roads would become impassable.

“The sea is rising, we see it all around our island, everyday everyone in this room, when you go to the beach everyone sees the erosion,” Mayor Caldwell said. 

“If you take no action and we live with the consequences, then what happens to Waikiki?” he added. “Our largest industry $15 billion in revenue—what happens? If we don’t take action now we’ll have worse consequences later.”

The Mayor’s directive requires all city departments and agencies under the mayor’s jurisdiction to take several actions, including:

  • View climate change and the need for both climate change mitigation and adaptation as an urgent matter, and take a proactive approach in both reducing greenhouse gas emissions and protect and prepare the city for the physical and economic impacts of climate change;
  • Use the Sea Level Rise Guidance and Hawaii Sea Level Rise Vulnerability and Adaptation Report in their planning, programing, and capital improvement decisions to mitigate impacts to infrastructure and critical facilities subject to sea level rise, which may include elevation or relocation of infrastructure and critical facilities, the elevating of surfaces, structures, and utilities, and/or other adaptation measures;
  • Propose revisions to shoreline rules and regulations to incorporate sea level rise and conserve a natural, unarmored shoreline wherever possible; and
  • Work cooperatively to develop and implement land use policies, hazard mitigation actions, and design and construction standards that mitigate and adapt to the impacts of climate change and sea level rise.

Specific to the City and County of Honolulu, the commission included in its detailed Sea Level Rise Guidance that rising seas will threaten Oʻahu communities and natural ecosystems in multiple ways, including: increased vulnerability to flooding; land loss and coastal erosion; saltwater intrusion into streams and coastal wetlands; and increased damage when hurricanes, tsunamis, and seasonal high waves strike. The commission further concluded that rising seas will negatively impact local communities, habitats, property, infrastructure, economies, and industry.

The commission, which carefully tracks a combination of international research and local modeling to underpin its decisions, also stressed that impacts from high tide flooding will arrive decades ahead of permanent inundation. Tidal flooding is projected to become more frequent and erode beaches, flood roads, and in times of rainfall bring local transportation to a standstill. According to modeling by NOAA, under their “Intermediate scenario,” flooding exceeding last year’s “king tide” level could be present an average of twice per month in Honolulu before mid-century.

In terms of costs?

“At the end of the day it’s going to be hundreds of millions of dollars,” Mayor Caldwell said. “We’re talking about real estate around here, the most valuable real estate in state of Hawaii is impacted.”

“There’s $12.9 billion of property at risk from the 3.2 foot of sea level rise,” said Josh Stanbro, Honolulu’s Chief Resilience Officer. “So $12.9 billion is on the line—so spending a little bit now will save a whole lot later.”