There is a concept in sociology called Dunbar’s number. It refers to the size of a social group that a single person can comfortably maintain. The number usually given is 150. That means that at around 150 social relationships, we hit a psychological ceiling and have trouble keeping up with more. Robin Dunbar, the British anthropologist who researched the idea, suggests it reflects a natural limit in our primitive brain, after which we don’t have much more mental energy to expend on others.

To me, Dunbar’s number is an expression of a greater human limitation. We tend to have a natural upper limit on what we can care about both in proximity and time: a care horizon. Most will prioritize their immediate family over their neighbours and their neighbours over people in the next town. The exception being if you have terrible neighbours.

Similarly, most people concern themselves events happening in the near future. The latest event someone might plan for is their retirement, or even funeral. But something 100 years from now? That’s rare.

Here and now

This makes sense. We only have so much mental bandwidth, so we typically concern ourselves with the here and now.

For thousands of years, this built-in local limit did not impact our planet as a whole. That’s because two thousand years ago – even two hundred years ago – what a single person did in the Americas, for example, had virtually zero impact on someone who lived in Asia.

Today, though, it is causing major issues. As everyone knows, our planet is now incredibly interconnected and inter-reliant. Not only virtually. Clothes worn by Americans, Chinese, Brazilians, and many others will come from Bangladesh or Lesotho. Plastic waste disposed improperly in El Salvador makes its way to giant gyres of plastic in the Pacific Ocean, where it enters the food chain, and ends up consumed by humans in high-end sushi restaurants all along the Pacific Rim.

Yet our care horizon remains firmly in place. It is difficult enough to conceive of how connected everything is, before we even get around to conceiving solutions.

How to expand the care horizon?

The question I’m often asked is: What has to be done in the coming decades to handle environmental issues like climate and resource use, and the need for economic development?

My answer to this question is contained in the answer to another question: How do we extend our care horizon? When people care about getting something done, we are virtually unfettered in what we can achieve. And the problems of environment and development are relatively easy challenges.

There is no shortage of money on the planet to fund the solutions. We do not lack the technology to address these problems. No, the fundamental problem is lack of political will to address these issues with the speed and effort needed.

Political will is the single most important currency we lack today.

And political will flows from the will of the people. When people care, politicians act.

So what do we have to do to make people care about a gaseous chemical that is invisibly accumulating in our atmosphere and insidiously changing the planet? How do we stop people damaging ecosystems for short-term profit? How do we encourage the bankers and the businesses with the money and technology to go green? How do we extend the care horizon?

Unfortunately, the fact is that we may not be able to. It’s been burned into us since the dawn of human evolution. But if we are clever we can work around this ingrained limit.

Millions are dying

We do this by making an appeal within the horizon. So instead of talking about carbon dioxide emissions, for example, which very few people can relate to directly, we talk about air pollution. Billions live in cities where smog and bad air are a constant irritant. Some 7 million die from air pollution every year. Air pollution is something we can directly see, smell, taste, and die from. People don’t like air pollution. They let their politicians know. And governments hustle to fix it. In China, there has been enormous economic success, but it has come at the expense of the environment. The Chinese people endure a frightful amount of air pollution as a result. But the population made it clear they have had enough, and the government is now working hard to fix the problem.

Of course, the trick is that by ridding ourselves of air pollution, we are ridding ourselves of countless greenhouse gases that are contributing to climate change.

Making broad-based appeals to protect nature, especially in countries where it is the easiest source of income for impoverished people, is often ineffective. People struggling to get by or feed their family don’t think twice about cutting down protected forests or hunting endangered species. We need to show exactly how protecting the environment is profitable by holding up successful examples. In Kenya, fishermen have traditionally cut down mangrove forests to make boats. But through carbon markets, some are now being paid tens of thousands of dollars a year simply to protect mangrove ecosystems along the shore. They have found another, abundant and fast-growing wood from which to make their boats. And as the mangroves come back, so do long-depleted fish stocks, helping their core business, and restoring the marine ecosystem as well. By appealing to the immediacy of the fishermen’s financial needs, multiple ecosystems are being saved and rejuvenated.

Sustainability as the norm

In other countries with higher incomes, we can instill a desire to protect nature by improving accessibility to parks. Canada will make all of its national parks free next year in celebration of its 150th birthday. But countries need not find such an anniversary to do so. They can bring the beauty of our planet into people’s care horizon at any time, giving people a personal reason to recycle, or use clean energy, or bike to work.

The business and finance worlds have care horizons like people. Theirs relate more to profit than proximity and time. As a result, they need the least encouragement. Many recognize the potential damage to their long-term interests from climate change and environmental degradation. But they also must compete in the short-term with those who don’t see into the future. To counteract this short-termism, business and finance leaders can push politicians to institute rules and laws that encourage and incentivize environmentally friendly businesses.

With climate change and the scale of environmental damage we are seeing across the planet, we are in unchartered territory. And it is well beyond our care horizon. By bringing the environmental issues close to people, inside this boundary, we give them a reason to care. This drives the political will. And this political will in turn makes sustainability the norm.

We may have limits on the number of problems we can care about, but there are no limits on what we can do to solve them.