Increasingly, I find myself embracing the idea that we need to leave this world a little better than we found it. I'm also fairly tolerant of people who don't feel the same way, the so-called climate-change deniers.

However, I could not help but feel sick to my stomach when I read that a cub of Cecil the lion was recently shot dead by a game hunter in Zimbabwe. Cecil, you may recall, was Africa's most famous lion. It has its own entry in Wikipedia. Two years ago, the lion was killed by another trophy hunter, American dentist Walter Palmer.

The worldwide condemnation and outrage that ensued forced Mr Palmer to abandon his practice for months. Given the public vitriol against Mr Palmer, it is not surprising that the identity of the hunter who killed Xanda the cub has been kept under wraps.

But so what even if his identity is revealed? Media reports suggest that Mr Palmer has resumed his normal life as the anger towards him has dissipated.

People forget. The human tendency to move on once a crisis is past or averted means that those who indulge in anti-environmental acts can get away with no more than a slap on the wrist. They won't change unless you hit them where it hurts most - in the pocket.

For years, Singapore and other parts of South-east Asia were shrouded in haze around this time of the year due to indiscriminate use of the slash-and-burn method to clear forest and farmland to plant or replant crops. Appeals to the big palm oil and paper pulp businesses to do so in a more environmentally friendly manner had fallen mostly on deaf ears.

In September 2015, armed with regulatory teeth under the Transboundary Haze Pollution Act, the National Environment Agency (NEA) named a list of firms, including Singapore- headquartered Asia Pulp and Paper (APP), that it was investigating for their links to forest fires that caused severe haze in Singapore that year.

The Singapore Environment Council (SEC) and the Consumers Association of Singapore also followed up with retailers that carry the products of the businesses named. As a result, the major supermarket chains here withdrew all APP products, including its popular Paseo brand of toilet rolls.

The boycott had the desired effect as soon after, APP hired former SEC chief executive Jose Raymond as vice-president of corporate affairs. Mr Raymond left after eight months on the job.

Last month, APP parent company Sinar Mas Group announced it had appointed retired Singapore army general Bernard Tan as managing director for corporate affairs and sustainability in APP, and country president for Sinar Mas in Singapore.

Mr Tan, who officially assumed his roles on June 1, will have his work cut out. In a media update in March, the NEA said information provided by APP to help with its investigation had been limited.

Perhaps that explains why the supermarket shelves continue to be devoid of Paseo toilet rolls.

The pressure the authorities have brought to bear on errant businesses in this instance is gratifying. But their power is limited to investigating firms that cause haze. There are countless unethical transboundary businesses that are polluting or causing harm to the earth in other ways. We cannot just rely on the authorities.

As consumers, we can choose not to buy products that are not sustainably produced even if they are cheaper.

There are many reasons why a product can be cheaper than its substitutes. But one of the most egregious is the cutting of corners by the manufacturer.

Here is a simple example. Factory A makes widgets by discharging a toxic by-product into a nearby river. Factory B, which makes similar widgets, treats and neutralises its effluents. Naturally, it will cost you less to buy from Factory A. But the community as a whole will pay a higher price because the pollution caused by Factory A will result in a costly clean-up of the river in the future.

Beyond consumer boycotts, we can also do our part by starving unethical businesses of financing.

In this respect, Norway's US$960 billion (S$1.3 trillion) sovereign wealth fund - the world's biggest - is leading the way. A total of 66 companies are excluded from its investment universe on ethical grounds, based on the recommendation of the fund's ethical watchdog, the Council on Ethics. Another 69 firms are excluded directly by the fund based on their dependence on thermal coal.

The ban is not without cost. The fund returned 1.11 percentage points less between 2006 and last year as a result of exclusions of companies on ethical grounds such as tobacco manufacturers and certain weapon makers, including those that deal in nuclear, cluster munitions and anti-personnel mines, according to its own estimates.

This works out to about 12 billion krone (S$20.9 billion), according to the fund's chief executive, Mr Yngve Slyngstad. But he was unapologetic. "There is a broad consensus among Norwegians that the fund should not earn money from companies that take people's lives," he told reporters.

Some familiar names are on the fund's exclusion list, including Malaysia-listed Tenaga Nasional, British-American Tobacco (BAT), Lingui Developments, IJM Corp, Malakoff Corp and Genting.

Ethical investing practised by the Norwegian sovereign fund is a relatively new phenomenon.

I believe it is on the right side of history and more investors will come on board. Even our very own Temasek Holdings is investing in environmentally sustainable businesses such as its Impossible Foods, which makes plant-based burger patties that are almost indistinguishable from meat, and Modern Meadow, a developer of lab-grown biofabricated leather.

When I was younger, I kept my moral compass at arm's length from my investment decisions.

I bought shares of number forecast operator Magnum even though I knew, or ought to have known, that running a gaming business is a zero-sum game: It can thrive only on someone else's misery.

I didn't smoke, and understood the health hazard of smoking but that hadn't stopped me from investing in Rothmans International shares. Although I didn't like the smell of second-hand smoke, I had occasionally bought duty-free cigarettes at the behest of friends in Malaysia.

I'm not sure why I did it. Maybe it was my live-and-let-live approach to life. But no more. Cigarettes are not only harmful to smokers but also to those around who breathe in the smoke. In fact, some studies have shown that breathing in second-hand smoke is even more hazardous than puffing directly from a filtered cigarette.

Profiting from someone else's misery is also unconscionable.

As such, stocks that I used to track like BAT, Tenaga and Genting Singapore are no longer on my investment radar. The same goes for any company I know of that is helmed by a game hunter.

I'm realistic enough to know that my decision matters not a jolt to these corporate behemoths.

But the personal satisfaction from taking an ethical stance is pretty colossal for my soul.