Surprising Temperature Sensitivity: corals, man, ecosystem
A couple of degrees warmer sounds like nothing. Temperature sensitivity turns out to be one of the astounding insights from the current study of warming trends. Like so many things, when looked at with the right perspective, it actually makes sense, even if it was originally counterintuitive.
Coral reef temperature sensitivity provides a particularly enlightening example since there is a good analogy with humans, and then a larger lesson for the ecosystem.
Coral reefs are dying worldwide, with figures ranging up to 90% or more in some areas. Although the devastation is worse in some populated and highly trafficked areas, some very remote locations have also been hit. While there have been previous massive coral die-offs globally over the past hundreds of millions of years, the current phenomenon is the first in hundreds of thousands of years. There are many specific forms of coral death in the modern era, but the one that is most widespread is “coral bleaching.”
In simple terms, coral bleaching turns the hard corals white, eliminating the varied colors of the reef. It is due to the expulsion of the specialized algae, that lives in symbiotic relationship with the individual coral animals. It is a symptom of stress and usually results in a dead reef. Although it has been observed for a few decades ago, there were differing opinions among scientists as to the cause.
Now the consensus among experts is that the underlying cause is the warming of the ocean. Since the ocean has only warmed about two degrees F (1 degree C) over the last century this truly seems hard to believe. When I first heard this theory in the early 90’s, I thought ‘impossible.” Even in places like the Bahamas, ocean temperature on the shallow reefs could fluctuate from 60 – 90 degrees F during the course of a year, so how could a degree be critical.
Yet scientists have now observed and run controlled experiments showing that just an additional two degrees added to the summer maximum, and sustained for a few weeks, will cause many corals to “bleach.” At first it’s counterintuitive. Until you think of this analogy.
Humans can generally tolerate a wide range of temperatures — in fact, much wider than corals. We easily survive rather extreme cold and heat for modest periods of time. Undoubtedly you can each supply examples from tales of survival, to entertaining personal experiences––from near freezing to more than 120 are not uncommon. But those are essentially external temperatures, which our body structure and systems insulate against.
Recall that our core temperature is normally 98.6 F (37 C). If that rises by about 5 degrees F (2.5 C) for very long at all, we will almost certainly die. Thus we have a surprising temperature sensitivity when we look at it that way, quite different than what we think of as our environmental heat tolerance.
Water is so much denser than air that it has about 800 times the heat capacity. Warmer seawater has an even greater impact on the corals (as well as on the other plants and critters) than what we think of in terms of atmospheric temperature change.
The surprising temperature sensitivity of corals makes a lot more sense when we look at our temperature sensitivity. It turns out that our entire ecosystem has a similarly narrow range of sustained temperature, that we don’t recognize given the huge transient range of external environments that we can handle.
Just one final example to look at temperature sensitivity as it applies to the ecosystem. From British Columbia to Colorado and beyond, we are losing millions of acres of pine forest each year to the Pine Beetle. Literally looking at today’s headlines, the fires in Boulder Colorado are one example where unusual fire patterns are now attributed to warmer temperatures and more dead forests, similar to the fires that hit Russia last month.
The massive upsurge in Pine Beetle has now been connected to one degree temperature rise — the critical degree at the freezing point. Typical winters now are mild enough and short enough that the beetle larvae are no longer killed by the winter freeze. There is no natural predator and we do not yet have a treatment. It is the modern scourge of the west. It is just one example of how our ecosystem is temperature sensitive, like the corals, and like US.