While anthropogenic climate change is generally discussed in the context of gradual change (perhaps, “gradual” by standards of human lifetimes…still extremely fast by geological timescales…), there are tipping elements in the climate system which have the potential to cause very abrupt and extremely rapid shifts in climate states on regional and (more importantly) global scales. Tipping points are still somewhat controversial in the science of climate change, but there is precedence for it in the paleoclimate record; from the ice age cycles to some of the most infamous extinction-level events in Earth’s history where species simply had no chance to adapt.
I’ve discussed the concept of abrupt climate change previously and suggested that we are currently in a period of abrupt climate change. “Abrupt” defined as events occurring within less than a normal human lifetime which normally do not do so. Many scientists have studied the potential in the present or past of abrupt climate change (or quasi-“runaway” global warming which is abrupt) including Dr. James White, Dr. Jennifer Francis, Dr. Peter Wadhams, Dr. David Wasdell, and many others. Much research has looked at abrupt climate change as a function between a forcing mechanism on a system and a “breaking system” (a negative feedback) which stops the system from reaching a tipping point. However, if the forcing overcomes the breaking and forces it over the tipping point, there is the abrupt (temporally rapid and structurally changed) shift to a new climate state vastly different from the previous state (see excellent discussion on the topic by Dr. David Wasdell…a climate scientist who’s done peer review work for the Intergovernmental Panel on Climate Change of the UN).
Our current more abrupt climate change…which one may argue began in the 1980s with a more rapid rise in global air and sea surface temperatures, decrease in sea ice extent/volume, ocean acidification, land glacier retreat, among other climate change signals (noted by both the IPCC as well as the US in recent climate reports)…appears to have been caused by our rapidly increasing emissions of greenhouse gasses, including carbon dioxide in the atmosphere since the 1960s. CO2 concentration was around 315 parts per million molecules of air in 1960 (compared to 285 ppm at the end of the 19th century). We’re already near 410 ppm in 2017…twice an increase in concentration in nearly the same amount of time. Methane, a short-term (150+ times more powerful as carbon dioxide within a few years), but extremely powerful greenhouse gas has also rapidly increased because of both human and natural sources.
However, as anthropogenic climate change continues to evolve, assuming no *significant* human intervention (specifically removal of carbon dioxide and cooling of the Arctic), may lead to further tipping points being reached within the climate system which may accelerate change further. Changes which can happen over the course of just years. These more specific “sub-system” tipping points are of particular interest to some of the previous researchers mentioned. So let’s discuss a couple of interest…
Tipping Point #1: Arctic Sea Ice Sheet Collapse
Personal opinion here…I firmly believe of all the abrupt climate change tipping points, this one is likely the most imminent. Arctic sea ice has been rapidly decreasing in extent and thickness (and therefore, volume) since the 1980s. Numerical climate models in the past have attempted to predict the collapse of sea ice (what some refer too as the effective “ice free” Arctic in the warm season…roughly 10% of the Arctic Ocean Basin without ice or less). Previous predictions have called for dates such as the 2080s and more recently, the 2040s. Now there are scientists such as Dr. Paul Beckwith and Dr. Peter Wadhams and others openly giving a likelihood that the first “ice free” or “blue ocean” event will occur by or before 2020! 2017 witnessed the record low annual Arctic sea ice volume, caused by very thin tenuous ice. Where widespread, thick ice used to exist in the Arctic, tenuous thin ice only remains, ready to be destroyed by random storms and influxes of heat from the Atlantic and Pacific…a process which is already happening.
What is important about this tipping point? If most of the ice disappears from the Arctic Ocean, albedo (reflectivity) in the northern hemisphere will be significantly reduced, replacing white ice with very dark ocean, warming the Arctic Ocean column and warming and moistening the atmosphere (also clouding it, retaining heat in the polar night, making new sea ice difficult to form). Of course, this more rapid heating of the Arctic will more rapidly raise the overall average temperature of Earth as well. Note…there has not been an “ice-free” Arctic over in over 3 million years! It will also have have implications on the jet stream which depends on temperature gradients between the mid-latitudes and the Arctic for it’s strength and progression of waves around the globe – it would become much weaker, shift farther north and exhibit much greater amplitude waves with stagnant, extreme weather (see HERE and HERE).
This tipping point could set off other issues such as prolonged heat waves and droughts, leading to other tipping events such as forest diebacks (and then wildfires) and methane releases in the high tundra and methane clathrates from subsea permafrost in Arctic continental ice shelves (more on clathrates). This would release more carbon into the atmosphere. Abrupt changes in precipitation distribution (dryness or heavy precipitation) and extreme heat would pose threats to agricultural production which is very sensitive to individual weather events, let alone the climate stability which we’ve been accustomed too for the past 10,000 years since the end of the last glacial period.
Tipping Point #2: Equatorial Super Rotation
Another rather daunting tipping point is actually a common feature of several planets in our own solar system. It is called equatorial super-rotation. None of the previous scientists have dealt with this topic, but it is of interest to me as a meteorologist and is actually not a current feature of Earth’s atmosphere. It is a phenomena in which the atmosphere around the tropics and subtropics actually spins faster than the planet’s rotational velocity. This super rotational velocities occur on the terrestrial planet Venus and the Jovian planets (such as Jupiter and Saturn).
How would this occur on Earth from anthropogenic climate change and what would be the impacts on climate? Well, typically, the Earth’s tropical circulatory pattern involves structures known as Hadley Cells which features rising motion near the Equator and sinking motion in the subtropical regions. Air at the surface then flows equatorial-ward towards a convergence zone (the Intertropical Convergence Zone or Monsoon Trough) with the Coriolis force turning the air flow toward the right/left in the northern/southern Hemisphere, generating the easterly trade winds. The Hadley Cell expands and migrates north and south depending on the seasons between the two hemispheres.
With climate change however, increasingly extreme surface heating in the tropics is theorized to possibly lead to a situation where a single Hadley Cell develops, becoming extremely powerful and expansive. This would lead to the center of it straddling the equator with a strong upper-level equatorial westerly jet (the super-rotational flow). Significant areas experiencing hyper-aridity would exist over much of the mid-latitudes as far less moisture is transported from the tropics and high precipitation regions would be found much further poleward than found in the current climate regime. This tipping point in modeling isn’t expected until late century, but again, given the rate at which observed changes in the climate system are evolving relative to the limitations of modeling, it is not truly known when such a tipping point could actually be initiated.
Human Societal Tipping Points…
Of course, with anthropomorphic climate change, one of the biggest issues is humanity’s ability to deal with increasingly rapid and extreme changes and harms. Humans depend need food, water, and shelter to thrive and when repeated meteorological (hurricanes, tornadoes, floods, etc) and climatological (long-term agricultural and hydrological droughts) disasters strike, society can take very serious hits. Much of the world depends on agriculture from the US and China, for example. Freshwater resources around the world are under increasing stress from overuse by increasingly growing populations. More and more people are crowding into cities which will be under the influence of urban heat islands which may deal with hotter temperatures as the climate warms.
The ability of humanity to deal with the changes ahead will be by far the most significant challenge in the coming years ahead.
–Meteorologist Nick Humphrey