The Astonishing Relationship Between Life and Temperature

I had a high school teacher who, on Earth Day, gravely declared to the whole school assembly, with a single index finger pointed up: “the earth... is a spaceship!!”. The idea was that we’re in a relatively small and fragile home in the cosmos.

For me, the smallness and fragility feels even more extreme. The earth as a whole is mostly a nightmare for us. Just a short distance below my feet it’s too hot to live. And just a short distance above my head the air is too cold and too thin to breathe. You could walk across the livable universe in your lunchtime. Our biosphere is a razor thin sheen on the surface of the planet - if the earth were a basketball, the part that could sustain life would be around the thickness of a human hair.

Yet even on that thin surface, only about 10% of it is easily habitable by humans.

And much of the reason for both boundaries on our living, is temperature. Temperature is arguably the most powerful boundary of life.

And the boundary is constrictive. Life evolves for very specific environmental niches. You get whole new species forming in just thousands of years based on what kind of food is available in an area. So life tends to evolve for a certain climate or temperature. Tropical plants and animals can’t live in temperate zones, and temperate flora and fauna can’t survive in the tundra.

Some of these constraints are hard ones that even evolution can’t crack. Life requires liquid water to metabolize. After 4 billion years of effort to adapt, there just isn’t much complex life in central Antartica, or the middle of the Sahara desert.

To take another lense on this, consider the human body, and most animal bodies. We have to maintain a fairly constant temperature within a very narrow band around 37 degrees celsius, 98 Fahrenheit. At 35 degrees you have hypothermia, at 39 you have a dangerous fever. The very specifically folded proteins that run almost everything in our bodies tend to change their shape at higher temperatures, often permanently.

One of the most surprising things I’ve learned about humans is that our absolute physical superpower may not have been the opposable thumb, but rather our capacity to perspire. We can thermoregulate by sweating. Other land animals MUST find shade, or stop running, to cool down. But we can run for days - and this was key to our triumph as a species - we couldn't outrun virtually any animal over short distances, but as the Kalahari still do, we could run any prey down over hours of midday heat. This may have even been a key advantage of walking on two legs - less sun exposure and easier thermoregulation!

We might fool ourselves that we’re quite temperature hardy. I grew up in northern Alberta, Canada where the winters often got down to minus 20 degrees or lower. But our survival across this temperature range is all about thermoregulating technology. Without clothing, you’re dead if you just open a window.

It’s the heat end of the spectrum that’s most relevant for us at the moment. The wet bulb analogy shows just how vulnerable we are to heat. Once humidity rises high enough, our superpower of sweating doesn’t work as well anymore. At 80% humidity, an outside temperature of 39 degrees celsius will kill a human in hours. Anything above 35 degrees in high humidity can qualify as a wet bulb environment, and some cities like Jacobabad in Pakistan have crossed this threshold multiple times. And no, using a fan won’t work, it actually makes it worse. The only answer is advanced technology - air conditioning.

Understanding this tremendous sensitivity of life to temperature also helps me to understand why climate change is so devastating. The climate zones of the earth are shifting constantly thorough geological history. Just 15,000 years ago the Sahara was a verdant green with flourishing human communities. But when the temperature shifts, life often can’t adapt. It just dies off. That’s why we’re losing the entire Great Barrier Reef right now. Some days the water just gets too hot, and all the coral dies.

In this sense, the constantly shifting climate has been an absolute scourge of life for billions of years. We’ve actually had a very unusually stable last 10,000 years, which may account for the rise of advanced human civilization.

But all evidence is that that stable period is coming to an end. The earth has warmed 1.5 degrees celsius, on average, since 1900. Remember that the human body can only function normally within a 4-5 degree temperature band, and that 1.5 on average means 3-4 degrees in some places. And this is just the beginning.

Of course, particularly wealthy humans have the technology to protect themselves against the immediate impacts of these shifts. But migration might not be an option for many of us. As it won’t be for our plants and animals. The reefs and forests and wetlands and agriculture that sustain ALL of humanity. These don’t move quickly. They tend to die off during climactic shifts and then slowly rebuild in new zones. Way too slowly for human civilization to survive the disruption.

So what do we do? We’ve already signed up for far more global warming than we’ve experienced so far. Most of the heat has gone into our oceans (think of how an oven heats the air before it heats the walls) but it isn’t staying there. Even if we stopped emitting greenhouse gasses today, the equilibration of the oceans with land and air will likely increase the earth’s temperature by another half a degree.

And despite the best efforts of millions of people and most of the world’s governments, we’re still pumping enormous amounts of greenhouse gas into our atmosphere.

So what do we do? Obviously, we need to stop emitting these gasses as fast as we can. But even at a high rate of cuts it won’t be enough to avoid tremendous risks to human civilization.

This is where I come back to the human superpower of thermoregulation. What if we could transfer this power to our fellow species and biosphere?

The truth is we now have the ability to warm the earth, and we may also  be able to develop the ability to cool it. Already serious scientists believe it wouldn’t be hard to just shade the earth a little by putting reflective particles in the upper atmosphere. This happens all the time when volcanoes throw dust and gas into the atmosphere, we'd just be putting it there ourselves.

Of course, giving humans the power of climate control is somewhat terrifying - what if we’re as dumb as we have been so far? If we did have a thermostat for the earth, who would control it? My wife and I often have very different ideas about the right temperature for our house. And how we exercise that control may be as important as whether we do. Doctors claimed to be able to affect the human body’s natural processes in all kinds of ways. But it was only in the last century that the presence of a doctor in a community actually decreased rather than increased the death rate. Nature has a wisdom that is often far beyond even our most advanced technologies, and arrogant human intervention often causes more problems than it solves.

But who, now, would suggest that we get rid of doctors and modern medicine? It’s still idiotic some of the time, but there’s no doubt it has changed the game for human health.

Here’s the the optimistic vision that I love to consider: what if we get as good as managing planetary health as we’ve gotten at human health? What if we, for the first time in 4 billion years, are able to stabilize the temperature and the climate? What if the human superpower of thermoregulation becomes planet earth’s superpower in the cosmos, unlocking whole new vistas of flourishing for our biosphere and our civilization. Too often we focus, understandably, on the dire catastrophic effects of climate change. But there’s also an opportunity here, to unlock something unprecedented, powerful, and explosive in the journey of life - a sustainably safe and stable climate.