Editorial: Policies needed on sea level rise

Here’s what climate-change researchers proffer as a certainty: sea level is rising and the rate of change is accelerating. What’s uncertain is the final rate. That depends on the handling of emission scenarios and other environmental matters here and around the planet.

If emerging projections hold, for starters, Hawaii can expect to see a lot more high-tide nuisance flooding — the sort that already sometimes soaks Mapunapuna streets — within the next two or three decades.

That alone should prod county and state leaders to quickly push forward efforts to fend off climate change woes while also contemplating response to potential hard hits — such as how to pay for infrastructure that could be rendered insufficient or, at worst, dangerous, such as sewers and coastal roads.

In a big-picture study published last month in the Nature journal, Scientific Reports, a team of researchers from the University of Hawaii at Manoa and the state Department of Land and Natural Resources found that in addition to land edging Oahu’s shoreline, some low-elevation areas — up to a few miles inland — are also vulnerable to rising ocean waters.

This latest study is held out as the most realistic yet as it more thoroughly folds in factors of chronic erosion and wave run-up, which can yield more flooding. It was conducted to support the Hawai‘i Sea Level Rise Vulnerability and Adaptation Report, which was completed in December to help with government planning.

The jarring takeaway from the new report: The sum of at-risk land is twice as large as mapped out in previous projections. Oahu’s south shore — Waikiki to the Daniel K. Inouye International Airport, and Ewa Beach — fall into the vulnerable bracket.

In recent years, Hawaii has rightly assembled panels to size up the future. There’s the state’s Climate Commission, which includes nearly 20 officials representing various levels of local government. There’s also the Honolulu Climate Change Commission, a five-member panel of academics and sustainability experts tasked with poring over the latest scientific data tied to current and future impacts.

The Honolulu commission works in tandem with the city’s Office of Climate Change, Sustainability and Resiliency, which was created in 2016 when voters approved a City Charter amendment. Among its marching orders: pinpoint ways to design infrastructure that will endure in the face of impacts, thereby avoiding spending many more millions in taxpayer dollars to rebuild.

Altogether, there’s a lot of valuable think-tank work underway. However, based on the emerging picture, we do not have the luxury of time.

County councils and state lawmakers should now be drafting legislation — straightforward rules and regulations — that can help the islands effectively brace for a future that’s more than likely to include climbing rates of coastal erosion and flooding.

Hawaii should be proud of green pledges, such as the one taken by Gov. David Ige and all four mayors to abide by the Paris climate change accord despite President Donald Trump’s decision to step away from it. The long-term goals of the accord require the state to expand already ambitious strategies to reduce greenhouse gas emissions.

In the short-term, state and county leaders should incorporate fresh data into shoreline setback rules. Maui County is now weighing a proposal to push inland its erosion hazard line. Kauai responded to erosion projections a decade ago when, in a move to retain coastal integrity, it created one of the most aggressive setbacks in the country.

Also, public-private partnerships that share planning and price tags should also be in the mix as sea-level rise will not discriminate between the two types of property. According to the just-published report, potential impacts of 3.2 feet of sea-level rise on Oahu (by the century’s end) include the loss of $12.9 billion in structures and land, and the loss of nearly 18 miles of major roads.