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In total, 536 humans have been in space. Ever. They’re the only ones who have seen our spheroid planet from above. And yet most of the seven billion of us alive today would agree that the earth is round. Ask yourself why you believe that. How do you know?

Consider a few more. How do you know that…

… everything around you is made up of things called “atoms”?

… there are black holes?

… smoking causes cancer?

… Plato existed?

If you’re not a physicist, oncologist, or historian, how do you know these things?

We take these truths to be self-evident because we trust experts. We trust history, written and spoken record, common understanding, and the assembled evidence of science. We listen to our teachers, our doctors, our parents, our journalists (most of us, until recently), and others. And yet, with climate change, it seems everyone is an expert.

I’ve received many emails lately from colleagues who have a [friend/uncle/in-law] who doesn’t believe in the phenomenon known as climate change. Someone asked me to send over my “quick paragraph” on why we should consider climate change a real and dangerous problem.

My attempt to explain will certainly fail to an extent. Those who don’t buy climate change yet may not come around for any reason. I’ve heard the full panoply of climate denier arguments. (I apologize to those who bristle at the word “denier,” but finding a better word is for another time.) I wrote a couple of articles on climate denial recently that got heavy traffic. Check out the comment section on “Denying Climate Denial,” which was the #1 article on Medium for a day, to see most of the major arguments. I can’t cover all possible objections here. (More on that in a moment.)

All I can do is say what I know to be true.

Why do I believe in climate change? The short answer is because of science. Overwhelming, abundant, multi-generational science.

Why Do I Believe in Climate Change?

The short answer is because of science. Overwhelming, abundant, multi-generational science. And to clarify, that means evidence, assembled over 150 years, that:

a) The Earth is warming at a radically abnormal rate.
b) It’s almost entirely because of human-related carbon (and other gas) emissions.

I trust scientists and science itself. I trust them every day when I eat, get in my car, take medicine, fly in a plane, and do thousands of other things.

On climate change, the effort of the scientific community to figure out what’s going on has been historic. The Intergovernmental Panel on Climate Change has led what is likely the largest coordinated scientific effort in history. Read the basic IPCC story.

One of the best summaries I’ve seen on climate science came from the American Association for the Advancement of Science, the “world’s largest general scientific body.” In a pithy, easy to read report, “What We Know,” the organization lays out three big conclusions:

1. Climate scientists agree: climate change is happening here and now.
2. We are at risk of pushing our climate system toward abrupt, unpredictable, and potentially irreversible changes with highly damaging impacts.
3. The sooner we act, the lower the risk and cost. And there is much we can do.

Every major scientific body in the world agrees on the basics of human-caused climate change. Here’s a list of 200 of these organizations. Also, check out out the NASA climate site or this overview of the connection between climate change and extreme weather.

If it helps, here are some other people who trust the science: basically every world leader (except one), the vast majority of large company CEOs, huge swaths of the military and security apparatus, and the pope. (His 2015 encyclical on climate and poverty is truly beautiful.)

Uncertainty and Skepticism

Again, I don’t think that many who are super skeptical will buy any of this. They can always suggest that there’s uncertainty. Well, no kidding. Science is never 100 percent certain about anything. More specifically, we can’t know precisely how rising carbon dioxide levels will play out in terms of temperature increases, or the exact effects of those increases (more storms, droughts, floods, etc.). But that uncertainty suggests we need more action, not less.

To answer the biggest category of skepticism: Of course, there are other causes of temperature and climate flux throughout the Earth’s history. But scientists have accounted for those: see this wonderful animated chart from Bloomberg. There are many other arguments that skeptics make, and it would take books to combat them all. The best resource for systematically tackling the misinformation is the website Skeptical Science.

My work is focused on business strategy and why it’s good for companies to tackle environmental and social challenges. But for years, I’ve been drawn into climate change debates. I’ve listened to attacks on the scientific method and debates over whether science relies on “consensus” versus verifiable, repeatable experiments. (It’s both.) But it’s really not worth rehashing all of that here. I’ll just say that the idea that thousands of scientists do not understand the scientific method, or that they did not consider different hypotheses, is bizarre.

So, in short, I believe what science is telling us. And it’s a dire situation — that’s not “alarmism” but realism. When the doctors tell you that you have advanced cancer, here are some reactions that are not healthy: denigrating the doctors as hacks, saying you actually know more about it than they do, calling them alarmist, or accusing them of being in it for the money.

In the end, asking why I believe in climate change is the wrong question. The one that matters is this: Why do I believe we should ACT on climate change?

The good news is that, as AAAS says, we can do something about this. And that’s why, in the end, asking why I believe in climate change is the wrong question. The one that matters for making life, policy, and economic decisions is this: Why do I believe we should act on climate change?

This one is much easier. It’s about risk and reward, regardless of my or anyone’s belief in the science. This is the “it doesn’t really matter if you buy the science entirely” argument.

Reducing Risk

Just ask yourself this: What if scientists are right about the more extreme estimates of the impacts of climate change? What are the possible outcomes for our weather, sea levels, food production, etc.?

This brings up the powerful idea of tail risk. Entire multitrillion-dollar financial markets exist to manage tail risk and so-called non-diversifiable risk. (System risk qualifies, and there’s no bigger system than the planet itself.) The financial industry and companies spend a ton to hedge against things like currency, commodity, or portfolio value fluctuations.

At the “tail” end of possible outcomes on climate change is that we make the planet uninhabitable for humans. (None of this is about “saving the Earth,” which will be fine without us.)

So, what might happen, and what’s it worth to you to reduce that risk? We buy insurance because our house might burn down or we could drop dead tomorrow. The OECD estimates that the richest countries spend about 9 percent of GDP on insurance. Isn’t ensuring a stable climate that we depend on for our existence worth some focus and investment?

Economic Rewards

But here’s the best part. The economic evidence is growing that we save money building the clean economy. When someone tells you it will “destroy the economy” to pursue clean technologies, that person is lying to you. This is the status quo argument that has never saved old technology, from the horse and buggy to the typewriter to Blockbuster.

When someone tells you it will “destroy the economy” to pursue clean technologies, that person is lying to you. This is the status quo argument that has never saved old technology, from the horse and buggy to the typewriter to Blockbuster.

Two years ago, Citibank produced a fantastic report, “Energy Darwinism II,” which compared an “action” scenario — one where the world builds out the clean energy economy — to a business-as-usual, fossil-fuel-based energy system. Citi’s key findings were:

  1. If we do not tackle climate change, by the middle of the century, it will cost the global economy tens of trillions of dollars.
  2. If we direct the vast sums we will spend on energy infrastructure and fuel toward the low-carbon action scenario, it will cost a couple trillion less.
Citi estimates of cost of action and inaction on climate from Energy Darwinism II

To repeat, Citi says we can spend trillions less to get tens of trillions of benefits. That’s an infinite ROI for those keeping score. Other reports for years have said similar things, from the monumental “Stern Review on the Economics of Climate Change” to Mayor Mike Bloomberg’s “Risky Business” report.

Since Citi’s report, the odds of the world pursuing the inaction path have only gotten lower. The economics of the clean economy have improved at near exponential rates. The costs of renewable energy, storage, and other clean techs have dropped radically over the last ten years. See this pithy chart from the U.S. Department of Energy:

Cost reductions in clean technologies, Revolution Now 2016 report, Department of Energy

The clean economy is worth trillions — huge new markets in cleaner buildings, transportation, energy, finance, and so on. And companies and countries are now racing to get their piece of it.

Winners and Losers

It’s not a trivial issue that the clean economy means some older industries disappear. There will be “losers” in the shift to the clean economy. Coal jobs are vanishing, and not just because the world wants to move to cleaner energy. Improved technology for digging up natural gas, plus automation, are killing those jobs. Some communities are losing their livelihood. We have a moral duty — based in part on what fossil fuels have meant to modern society, but also on basic human decency — to help people who are displaced.

The Inevitable

But back to the main point here. The combination of overwhelming science and the risk-reward equation has convinced the world to act. It’s why businesses wanted President Donald Trump to stay in the Paris climate accord, and why, after he rejected a historic global agreement, so many U.S. states, cities, businesses, and universities pledged to keep the commitment to the Paris agreement. (See a running list of the organizations that have declared, “we are still in.”)

Science tells us that climate change is an existential risk. Economics tells us it’s a giant opportunity. So we must act. We can debate how best to solve the climate problem, but debating the logic for action is a potentially life-threatening waste of time — time that we really don’t have anymore.

In the end, I trust the powerful combination of science and economics. Both are most definitely on the side of climate action.