It’s always difficult to peer into the past. All the proxy records we use to estimate the paleoclimate come with serious flaws and are limited to individual points on a very large planet. Many temperature reconstructions are actually proxies of proxies, for which the error bounds don’t just add but multiply.
Now we can throw bat shit onto the tapestry of tree rings and ice cores and lake sediments that climatologists have to squint at. In research published this week in Biogeosciences, a team from Canada dug through two meters of guano to construct a 4,300-year climate history for the area surrounding a Jamaican cave. Because plants and animals produce different types of sterols (like cholesterol), we can look back through these accumulated layers of bat scat to see whether the colonies were eating more fruits or insects at any given time. Insects thrive in wet conditions, so a bug-based diet is a sign of a wet period, whereas more fruit would mean drought.
Using that assumption, the team was able to find evidence that the Minoan and Medieval warm periods extended into the Caribbean. Whether these warm periods were regional or global has been a contentious question in climatology, and the more data sources we can find the better.
The assumption that the bat diet is only responding to climate conditions seems to me more than a stretch, though. Currently, there are five species of bat living in this cave, according to the paper, and there are many forces beyond climate that could punctuate the equilibrium of that local ecological balance. What if a virus or fungal infection wipes out one of the bat species that prefers insects? What if an earthquake diverts a river and changes the local hydrology? Maybe volcanic ash from a nearby eruption changes the soil pH making a new plant species thrive. Maybe human migration introduces a species of rat competing for a common fruit.
Those are just some examples off the top of my head that were likely to have happened at some point over the course of those 4,300 years, and that would each would look like climactic shifts using this methodology.
The point is that it’s impossible to accept any of these lines of evidence as proof—which is why we need so many of them.
And the point isn’t limited to paleoclimate reconstructions—it applies to everything we’re trying to call historical truth—including current events. Even in science, a very large percentage of published papers are false. And that’s using the scientific method to eliminate every sliver of bias that we can—imagine how often a news story is false, composed by a journalist on a deadline writing for clicks. And if we in the information age can’t determine what is true today, how much truth are we gleaning from the compiled historical accounts of the past?
And like the proxies of proxies, all the fake news compounds on itself. That’s why almost every post on your Facebook timeline is false. Truth is the greatest myth of the modern age—we seem to take it on faith. And it’s not because reality is subjective; it’s because we have so little access to anything objective. Everything we consume or perceive is filtered by politics and perspective and expectation.
So if you care about anything, you have to question everything. Never gather all your data from one source. That is your PSA for the day, and here’s the Sunday sciku:
found in guano
what we really know