[TL;DR: The existence and intensity of subjective consciousness in ectothermic animals probably depends heavily on their constantly fluctuating body temperature, and is therefore pretty unstable even when they are awake.]

[Epistemic status: Oh boy here we go]

Introduction

Even animals that are capable of subjective experiences are not equally conscious at all times. Naively, our own consciousness may seem like a state we inhabit more or less monotonously unless we’re fast asleep or deliberately messing with it, but sometimes it’s pretty noticeable that this is not the case. The degree to which we are conscious actually varies a lot depending of what we’re doing or experiencing at a given time; keeping track of this is difficult, though, because reflecting on your own experience often returns you to a more intensely conscious state, so that you might never properly notice you were somewhere else. Some people, notably Dennett and Drescher, even suggest that subjective awareness is more or less the result of intentional self-reflection and so does not exist at all in minds that are incapable of metacognition. I think some versions of this are totally possible, just not likely enough to justify moral indifference towards beings that demonstrate no such abilities — a more plausible alternative seems to be that there really is a magnitude or loudness to whatever we are feeling at a given time, and that probing our internal experiences mostly just makes them more intense since we attend to them more closely.

The most significant changes in the intensity of our consciousness normally occur during sleep and dreaming, though. When we’re asleep, our experiences vary from full unconsciousness to states that subjectively almost resemble wakefulness: but even though the events we go through in dreams are often bizarre enough to justify immensely strong and vivid emotional reactions, dream qualia are usually less intense and emotionally salient than what we would feel if similar situations occurred while we’re awake. (Otherwise, suffering in dreams would also be a much worse moral disaster than it currently seems to be.) When our subjective experience becomes stronger, like during particularly alarming nightmares, we tend to wake up — unless it’s trained in lucid dreaming, a sleeping brain can’t sustain very intense levels of consciousness.

There are various theories about what exactly the physiological functions of sleep are, but currently it looks like it primarily facilitates enhanced glymphatic waste clearance and energy store replenishment in the brain as well as synaptic pruning and other tasks related to connectivity regulation. Because consciousness is almost certainly dependent on extensive and metabolically costly brain activity that is incompatible with these tasks, sleeping reduces it to a fraction of its normal intensity, and at times even shuts it down completely.

Temperature as a determinant of consciousness



Even though there are many other chemical and behavioural ways in which we can somewhat intentionally modify the quality and intensity of our mental state, we — as endothermic animals with uniformly tropical internal temperatures and hence pretty stable facilities for metabolism-related molecular kinetics — practically never experience the other necessary factor that should massively affect an animal’s consciousness levels: large shifts in body temperature and their effects on metabolism and neural activity.



Ectotherms are animals that rely primarily on external warmth to maintain useful levels of body heat, and therefore tend to cycle through a wide range of temperatures depending on how thermally stable their environment is. This group includes the overwhelming majority of animals on Earth, some of which are cognitively pretty sophisticated. If we accept that these animals are directed by processes that are also experienced subjectively — which I think is likely at least when it comes to most cephalopods, reptiles, amphibians, and some fishes — their subjective life must be significantly affected by temperature, perhaps similarly to how our consciousness levels are affected by cycles of sleep and wakefulness.

Even though brain activity can probably not be allowed quite as much variability as, say, digestion or growth, many findings support the idea that an ectotherm’s brain still works very differently in cold and warm environments. Optimal cognitive performance can in some reptiles at least only be seen when tests are conducted well above room temperature: when closer to 30°C, tortoises seem to show unexpected maze solving strategies, learning by example, and the formation of long-term memories (despite historically underperforming in cooler laboratory tests requiring these skills). Interestingly, the effects of temperature on ectotherm behaviour are not limited to the immediate short-term consequences of enzyme kinetics, but can also direct development and fixed long-term behaviour. For instance, honeybees reared in higher temperatures have improved short-term memory even when the initial temperature differences during their development are equalized later on; and in another study, an increased probability to dance, earlier onset of foraging behaviour, and increased engagement in removing dead colony members. It is sometimes unclear which changes can be attributed to adaptive developmental acclimation and which ones are best understood as simple deficiencies.



So, assuming phenomenal consciousness is related to cognitive processes and supervenient on neural metabolism (which obviously is pretty plausible), a reptile or other ectotherm waking up in a cool place might experience the world in a minimally conscious, dream-like state until normal body temperature is restored, or even lack subjective experience altogether if the environment is chilly enough. Furthermore, due to differences in nervous system development, even an individual’s capacity to be conscious in the first place could be permanently increased if its development takes place in the higher tolerable end of the natural temperature variation in its habitat.



Anecdotally, my tortoise (the total cutie pictured both above and below) typically reacts in what looks like a mostly reflexive manner after spending a long time in a cooler area — for instance, automatically retracting as a response to seeing a shadow or being lifted, things that normally don’t frighten it at all anymore. It mostly shows its more personal, learned, less robotic behaviours after spending a while in warmer temperatures: thoroughly inspecting and actively following interesting objects, ignoring threats that have a history of not actually causing harm, crossing obstacles and long distances in an intentional manner, and sampling objects it figures are potential new food items (a bafflingly large category, especially in a species that naturally just relies on grass and things indistinguishable from grass). This is obviously a hunch based on my individual observations and interpretations, but I find it entirely believable that the former behaviours could be conducted in a sleepwalking state with little or no conscious experience, whereas the latter category might require more advanced cognitive processes — including the ones that bring about sentience.

Implications



I’m currently pretty confident that this principle applies to most ectotherms whose behaviour is complex enough to respond to different temperatures in interesting ways, if they are significantly conscious in the first place of course. Arthropods, which comprise the overwhelming majority of animal individuals and biomass on Earth, also show major behavioural changes in things like feeding rates, mating and communication, muscle output, and sensory perception as a response to temperature changes. I’m not confident about the picture I currently have of arthropod consciousness, but in his recent report on consciousness and moral patienthood, Luke Muehlhauser gives a 10-25% personal estimate of fruit flies being conscious in a morally relevant way depending on the definition. I would give it a slightly lower but definitely not insignificant chance.



Since consciousness is likely to be necessary or at least useful for many classes of behaviour and cognition, one could intuitively expect ectotherms in colder climates to have adjusted to their environment by systems that facilitate consciousness even when their general metabolism and growth often works very slowly, and optimal body temperatures can only be entered for a few hours each day (often by purposeful basking). This may not be the case if sentience is built on or mostly serves cognitive purposes such as enhancing attention, memory, or reactions to complex stimuli. Due to the significantly smaller number and diversity of organisms in cold climates as opposed to equatorial regions, there is just a lot less going on — so in the relative absence of previously unencountered predators, extremely diverse food items, or generally high ecological complexity, conscious responses may no longer be as crucial. Maybe a common viper only experiences a couple of hours of vaguely sentient time a day when the general buzz in its surroundings also peaks, and then gets by with reflexes the rest of the time. It just took me an hour to brew my morning coffee. I super understand that life up here in the North gets a bit sluggish.



However, it’s also possible that subjectively experienced information processing really is important enough that cold-dwelling ectotherms have developed something like cognitive cold-hardiness in order to preserve whatever processes also bring about sentience. It also seems to me that, say, the muscles of any given ectothermic species perform sufficiently well in the temperatures it is adapted to, but work even faster when the temperature rises above this (probably with tradeoffs that would be suboptimal for the organism as a whole in the long run). So is it also possible that there is a similar overshoot in consciousness levels, when an animal reaches a temperature that is higher than normally optimal but that also increases some sentience-related aspects of neural activity — so that the the animal’s consciousness actually becomes significantly more intense than it normally is? Hopefully not. This sounds pretty wild. Nevertheless, due to how little we know about sentience and its relation to metabolism in ectotherms, I don’t think it should be ruled out immediately.

Obviously the idea of temperature-dependent consciousness and its corollaries have major implications for wild-animal suffering even in the absence of such a hypersentience mechanism. It is unclear how global warming will ultimately affect animal populations and how much suffering each trajectory can be expected to cause; but if we only look at the immediate direct effects, warmer temperatures could mean that most of the animals in the biosphere will soon spend more time being sentient, or just in more intensely conscious states, which means that the sum of global suffering could increase massively without anyone ever even noticing what’s going on.

