La Niña 2024

This week we talk about ENSO, El Niño, and attribution science. We also discuss climate change, natural disasters, and the trade winds. Recommended Book: Titanium Noir by Nick Harkaway Transcript The field of attribution science, sometimes referred to as "extreme event attribution," focuses on figuring out whether and to what degree a particular weather event—especially rare weather disasters—are attributable to climate change. Severe floods and tornadoes and hurricanes all happen from time to time, which is why such events are sometimes referred to as once in a decade or once in a century disasters: the right natural variables align in the right way, and you have a disaster that is rare to the point that it's only likely to happen once every 10 or 100 years, but such rare events still happen, and sometimes more frequently than those numbers would imply; they're not impossible. And they're not necessarily the result of climate change. Folks working in this space, which is a blend of meteorology and the rapidly evolving field of climate science, do their best to figure out what causes what, and how those odds might have been impacted by the shifts we're seeing in global average temperatures in particular, and the knock-on effects of that warming, like shifts in the global water cycle; both of which influence all sorts of other planetary variables. The most common means of achieving this end is to run simulations based on historical climate data and extrapolating those trend-lines forward, allowing for natural variation, but otherwise sticking with the range of normal fluctuations that would have been expected, had we not started to churn so much CO2 and other greenhouse gases into the atmosphere beginning with the industrial revolution. So if we hadn't done the Industrial Revolution the way we did it, what would our global climate and weather systems look like? They have a bunch of models with different assumptions baked into them that they have running, and they can simulate conditions, today, based on those models, and compare them with the reality of how things actually are in the real world, a world in which we did start to burn fossil fuels at a frantic rate, with all the pros and cons of that decision aggregating into our current climactic circumstances. This comparison, between a baseline, non-climate-change-impacted Earth, and what we see happening on real Earth, allows us to gauge the different in likelihoods for various weather systems and increasingly even specific weather events, like massive floods or hurricanes. It also allows us to ascertain what elements of a disaster or system are more or less likely, or the same, compared to that baseline Earth; so maybe we look at a regional heat wave and discover that it was a rare event made more likely by climate change, but that the intensity of the heat wasn't impacted—as was the case with a heat wave in Russia in 2010; climate change made the heat wave more likely, but had such a heat wave occurred, despite its low likelihood, in that non-industrial revolution scenario, the heat would have been roughly the same intensity as it was in real life. Both components of this system, attributing events and patterns to climate change, and confirming that they were not impacted, that they were just run of the mill bad luck, the consequence of natural systems, are arguably important, as while the former provides data for folks wanting to predict future climate change-related outcomes, and provides some degree of ammunition for the argument that climate change is making these sorts of things worse, which helps put a price tag on not moving faster to shift away from fossil fuels, it's also vital that we understand how climate and weather systems work, in general, and that we are able to set proper expectations as to what will change and how, as the atmosphere's composition continues to change, while also understanding what will remain the same, what various regions around the world need to be prepared for in a vacuum, leaving climate change out of it, and how our global weather systems work on a granular level, so that as outside influences like climate change, but not limited to climate change, act upon them, we can make better predictions about how that will adjust or overhaul the practical reality for people and ecosystems impacted by them. What I'd like to talk about today is a natural weather phenomenon that is expected to return soon, and how this phenomenon might change our latent, global weather patterns, for the better, for the worse, and for the neutral, and in turn how it might be changed by the climactic adjustments we're tracking using these simulations. — The El Niño-Southern Oscillation, or ENSO phenomenon, is the monicker we've given to a collection of sea surface temperature and wind variations in the Pacific Ocean that, largely unpredictably, tweak the patterns of these systems from time to time, influenced by and influencing a large number of other, micro- and macro-scale systems around the world. Most directly, ENSO dictates how warm it will be across the tropics and subtropics, El Niño bringing warm waters to the surface of the relevant oceans and the Southern Oscillation referring to air pressure variations spanning the ocean between Tahiti and Darwin, Australia, low pressure tending to occur over warm bodies of water, and higher pressure over colder bodies of water. When the water in this part of the Pacific, the central and east-central equatorial pacific, is warmer, on the surface, that reduces atmospheric pressure thereabouts, which in turn reduces the strength of the Pacific trade winds. That reduction, among other things, decreases rainfall over parts of Australia, India, and Indonesia, while upping the same, while also stoking additional cyclone risk, in the tropical Pacific Ocean. Fundamental to understanding why this is a big deal is understanding that this tweak in water and atmospheric conditions causes low level surface trade winds, which usually blow from east to west, to either stop blowing or barely blow, or in some cases to reverse direction. If you think about how weather patterns form, determining everything from who gets rain and how much, to what temperatures are like in a given area—because those winds pull warm or cold air along with them as they pass over warmer or cooler parts of the planet, like mountains and glaciers, but also deserts and tropical rain forests—it becomes clear why this change-up is such a big deal. There's a neutral phase of this phenomenon that typically occur between warmer and colder phases, and during that neutral phase, we usually see other, similar systems that are interconnected and predicated on still other geographic and atmospheric variables, like the Pacific-North American teleconnection pattern, and the North Atlantic Oscillation, having more of an impact on global weather and water cycle patterns. When this system is in a warmer El Niño state, though, that tends to cause a lot of heat waves throughout tropical regions in particular, while also spiking global surface temperatures for around a year, with all the secondary consequences of suddenly jolting the global thermostat higher: melting glaciers and ice caps, increasing the range of disease-carrying pests, messing with planting seasons; things like that. The opposite side of this coin, La Niña, can also be quite disruptive though, its influence defined by cooler waters rising to the surface in that part of the Pacific, warmer waters headed westward where they have less influence on this component of the world's thermostat and weather machine, and that drop in water temperature in this part of the ocean tends to reset many of the dials that are turned up by El Niño, moderating some of the weather patterns that are amplified by those warmer waters and returning the trade winds to their normal settings, while also reducing global temperatures to what we might think of as their default. But the next… This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit letsknowthings.substack.com/subscribe