As hot as August and September 2015 were in Honolulu, they were barely a foretaste of what lies ahead.

By the year 2038, just 22 years from now, assuming we do not achieve greenhouse gas stabilization, the coolest day in the tropics is very likely to be hotter than anything we have seen in the past 150 years, according to research conducted by Dr. Camilo Mora and his colleagues at the University of Hawaii and published in Nature, a leading science journal.

So what do we do?

Obviously we need to reduce carbon emissions worldwide, and especially in the United States and China, as quickly as possible. Even if all the climate change deniers become believers, this will still be a tall order.

What do we do in Hawaii?

We reduce our own carbon emissions, but also begin to plant and nurture trees at an astoundingly rapid rate and for three very good reasons:

>> Trees reduce carbon dioxide emissions into the atmosphere.

>> Living in an urban area with relatively high levels of greenery contributes to an attractive and inviting environment and our own well-being.

>> Walking or sitting or playing is much cooler in shady areas than where there is no shade.

The 2015 action plan, “Making Honolulu an Age-Friendly City,” recommends increasing trees and other greenery as part of achieving clean and attractive outdoor spaces.

The plan notes that the city is responsible for about 235,800 trees on Oahu; about 60 percent, or 141,500, are along streets and 40 percent are in parks.

It also notes that Honolulu has 0.16 street trees per capita, or about one tree for every six people — significantly below the mean ratio of 0.37 reported for 22 U.S. cities — and that the “street tree canopy” in Honolulu shades approximately 2.74 percent of paved surfaces.

We have to do a lot better than this if Honolulu is to be a walkable city 10 years from now.

And we had better begin now because it takes a while for saplings to grow into mature trees.

Just walk along key streets in Honolulu to experience the difference between treeless streets and those lined with trees.

As part of a tree-planting initiative, Hawaiian Electric Co. might take lessons from East Coast cities, subject to freezing ice storms in wintertime, and simply place their wires in sheaths to protect them and thus not have to make those dreadfully ugly Y cuts that reduce shading.

What else is to be done?

We need a major initiative in Honolulu, as is occurring in New York and other cities, to plant trees along our streets.

We need a greatly expanded and well-funded Urban Forestry Division in our city government.

We probably need at least a million more shade trees than we have today.

A million trees calls for a major city initiative supported by the city administration and City Council, The Outdoor Circle, Sierra Club, Blue Planet, the Urban Land Institute, the American Planning Association, the American Institute of Architects, AARP, the Chamber of Commerce of Hawaii and every retail business and every green organization in town, the media, key university faculty members, and Hawaiian Electric/Next Era and the telephone and cable companies.

The mayor, working with the City Council, needs to appoint a “Trees for the Future” task force immediately to formulate a massive tree-planting plan.

The alternative is that Honolulu sidewalks will be bare of people between 10 a.m. and 5 p.m. every day. We will all be in our air-conditioned cars or homes or offices seeking to stay cool and using more electricity every day than ever before.