Note: originally posted 01/05/2010 (transferred from wordpress).
I’ve started the year by studying the mechanics of how our climate operates today, and how it comes to fluctuate. Not all of this data is new to me, but as I go through it again I’m struck by an interesting dichotomy between the simplicity of the climatic system as a whole at first glance and its almost infinite complexity at finer resolutions.
The climatic system is defined very broadly by the difference between the amount of solar heat received at the equator versus that absorbed by the poles. Air expands when heated, so the atmosphere near the meteorological equator is much wider than the atmosphere over the poles. Hence, heat moves from the meteorological equator to the poles, but that movement is broadly horizontal because of the earth’s rotation. In the air this transfer is expressed through the circumpolar vortex, winds spiralling around the poles, and it is the dominant feature of our atmosphere. Eddies, waves and troughs are formed because of differences in the pressure of the air and/or geographic features – these then cause high and low pressure systems, and by extension the world’s weather. Heat transfer in the oceans is expressed through the ocean currents; the oceans hold a far greater reserve of heat than the atmosphere but the movement of the currents is driven by the circumpolar vortex, and at higher latitudes atmospheric heat transfer grows ever more important.
That all seems quite simple, but the climatic system as a whole seems to be defined by (at least) four recurring features: first, changes in one part of the system seem to balance (and be balanced by) changes elsewhere, whether that location is geographically nearby or on the other side of the world. Second, an event – often seemingly insignificant – in one part of the system can cause cascading effects through the system and ultimately major “climatic jumps;” this is a phenomenon commonly known as the “butterfly effect,” and to a degree it holds up. Third, the effects of major climatic changes can appear similar: prolonged cold weather can expand the reach of polar ice, while prolonged warm weather melts polar ice, but both phenomena usually decrease the salinity of oceanic water at high latitudes.
Fourth, the speed and violence of climatic changes is especially remarkable to me. Recent research indicates that the great ice ages – and the warmer interglacials – emerged in the space of only a few decades. This is probably at least partially a function of climatic changes being expressed most prominently at the poles, where shifts in temperature can have runaway effects. A warming trend – as we’re experiencing right now – reduces the surface area covered by ice. Because snow and ice reflect sunlight so effectively, however, the reduction of water covered by ice actually itself contributes to the warming trend. Then again, the oceanic currents themselves, while usually a check against violent climatic oscillation, can in fact influence very rapid, dramatic climatic shifts when, for example, their salinity is altered by melting ice.
Finally, I’m struck by just how little we know about our climate, and beyond that by the rather tenuous ground on which many of our scientific breakthroughs actually stand. Systems of knowledge from palaeontology to anthropology have advanced rapidly in the twentieth century because they have attached fragmentary evidence to the assumption that things in the past in some manner resembled the present, in method if not in substance. This is where much of our understanding of dinosaur behaviour comes from, for example. Similarly, we “know” about our past climate because the simplicity of the circumpolar vortex in its broad strokes – combined with its intimate relationship to weather events – allows us to reconstruct past weather from often fragmentary evidence. It’s worth noting, however, that we fail to understand how exactly our climate works now; we don’t even know exactly how many volcanoes erupt every year, or exactly how they influence our weather systems. The ways of knowing we collectively term science and so often consider sources of unquestionable truth are, of course, really paradigms resting on changing – if informed – beliefs. This does not make them necessarily less accurate or important . . . just less certain.