The thick haze that's blanketed much of Southeast Asia for the last month carries the ashy remains of Indonesian forests and peatlands — burned in many cases to clear land for producing palm oil, the world's most popular edible oil. It's an annual occurrence dating back decades, and this year it's particularly bad: According to one report, the 2015 fires have emitted enough greenhouse gases to rival Germany's annual output of carbon dioxide. And they're growing worse.

Many proposals to fix the problem target the palm oil supply chain — from farmers and refiners, to the bankers and politicians who fund and license companies. That's crucial. But to be successful, such efforts have to address demand as well. Unless consumers insist on buying palm oil that's been sourced sustainably — and are willing to pay for it — companies and middlemen will continue to look for the cheapest possible way to clear land, which means burning.

For several years now, campaigns promoting sustainable palm oil — oil produced with as little impact as possible on the surrounding environment — have been gaining momentum in Europe. The Netherlands has committed to using only sustainable palm oil by the end of this year. Indeed, the Roundtable on Sustainable Palm Oil (RSPO) — an industry group founded in 2004 — says that all of the palm oil used in the EU will be certified sustainable by 2020. Public education, advocacy and consumer pressure have all had an impact.