What is a hurricane? It is a tremendous pot of energy, of whirling wind and rain. It gathers the energy over water, and expends it in wind, lightning and sometimes destruction. I’m going to try to give an explanation of the processes and specific conditions involved in building such a storm.
First, let’s talk about the whirl. Why does a hurricane twist? The scientific explanation is the Coriolis effect. The atmosphere rotates with the Earth, which, if you think about it, means that the atmosphere is rotating faster closer to the equator than it is further away, since it has further to travel with every rotation.
A pitcher can cause a ball to spin as it is passing through the air using the same principle. Winding up, the pitcher imparts energy to the ball, and that energy is released when he or she lets go of the ball in the pitch. If in releasing the ball, the pitcher allows one side of it to expend at little of its energy in friction against his or her fingers, then one side of the ball has more energy than the other. This causes the ball to spin. In the same way, the Coriolis effect causes a storm to spin. The physical law of the conservation of motion requires that the differing energy levels represented in the Coriolis effect be preserved by the storm.
The Coriolis effect is not significant at or near the equator, which is why hurricanes and typhoons don’t characteristically form less than five degrees of latitude north or south of it. Also because of this effect, storms in the northern and southern hemispheres twist in opposite directions.
That explains the whirl, but what about the wind? Wind is caused by air flowing from high pressure areas to low pressure areas, like water flowing downhill. The greater the pressure differential, the steeper the fall, so to speak, and the more velocity imparted to the wind. The strongest storms are the ones characterized by the greatest air pressure differentials.
So far so good. We have a whirly wind, but we haven’t explained yet where the energy from the storm is coming from, and what produces the air pressure differential.
There are always air pressure differentials. When water evaporates it takes up more space as water vapour. Water over the oceans is evaporating all the time, here and there, in no particularly organized fashion, a process which by itself doesn’t necessarily create pressure imbalances. In evaporating, it rises, encounters the colder air higher up, and condenses again into water. Condensing into water creates a local low pressure effect, since water takes up considerably less space than water vapour, and the energy it took up in transforming from water to water vapour is released at the same time.
If these processes are happening evenly over the landscape, then nothing in particular results from it. But what if the process is not happening evenly? Then we have high pressure areas and low pressure areas and consequently air flowing from the high to the low. The air flow in passing over water imparts some of its energy to it, in the process, causing evaporation to increase slightly. This happens because the energy already present in warm ocean waters combines with wind energy and changes some liquid water to water vapour.
The ocean thus passed over by the wind is now slightly cooler because of this energy transaction. The water by evaporating has carried the energy away. When the water vapour rises and condenses, the energy it has stolen from the wind is returned to the wind system along with the additional energy it has stolen from the ocean waters. The warmer the waters were in the first place, the more vigorous the process, and the more energy the storm has to harvest.
As the process continues, eventually, if the circumstances are otherwise favourable, you have a storm, gathering more and more energy as it goes along, gaining in size as it continues and expanding the area of water it has available to steal energy from.
A snowball in harvesting potential energy sometimes becomes an avalanche. A wind storm harvesting the potential energy of a warm ocean sometimes becomes a hurricane. The higher the mountain and the wider the path, the more catastrophic the avalanche. The warmer the ocean waters over which storms form, potentially the more catastrophic the storm.
Cold northern waters don’t produce hurricanes. In those regions, storms have other causes and other characteristics. But climate change, in warming ocean waters, is gradually moving hurricanes further towards the poles. Hurricane Sandy was the strongest storm to ever hit the US north of the Carolinas.
Climate change adds juice to storms by adding to the energy being stored in the oceans.
Most of the excess heat from climate change is in fact stored in the oceans, about 90%. The amount of energy accumulating in Earth’s climate system because of the human-caused increase in heat-trapping greenhouse gases is huge, especially when added up over the whole system. Scientists estimate it to be equivalent to the heat of 2 Hiroshima bombs per second being added every second since 1961.
When storms happen some of that energy is released. With so much more energy in the system than there used to be, there is more energy for storms.
With climate change, therefore, we have entered the era of the superstorm.
Superstorms are large, are capable of winds of tremendous speed and energy. They carry massive amounts of water with them and produce air pressure differentials more extreme than humanity is used to seeing.
Air pressure differentials are relevant not only because they are capable of producing incredible wind speeds; they are also responsible for unprecedented storm surges.
What’s a storm surge? Remember that the centre of a storm is a low pressure area. As the storm passes over water, the water pushes up into the relative vacuum of this area. A storm surge rises up which travels and comes ashore with the storm. Water in the storm surge can be stacked several metres higher than it usually is, and it comes ashore as a flood. Storm surges were a major factor in the destruction caused by Superstorm Sandy last year and Typhoon Haiyan this year.
The stronger the storm, the more serious, potentially, the storm surge it creates. Add this to the fact that climate change—which because water expands and ice sheets melt in the heat—is also accompanied by sea level rise, then, when a superstorm comes calling, storm surge stacked upon sea level rise equals unprecedented disaster. Think New York City during Superstorm Sandy.
With two Hiroshima bombs of energy continuing to be added to our climate system every second, and with the amount of energy being added actually increasing over time with the continuing infusion of greenhouse gases into the atmosphere, we can expect larger and stronger superstorms in the future. Worse than Sandy or Haiyan, yes.
It’s not pretty prospect. In fact it should be hugely frightening. The world of the superstorm (and other, perhaps worse, climate disasters) is the future we are creating for our children and grandchildren, and the children of perhaps 50 to 100 generations that follow. There is really no doubt of it.
We can’t avoid disaster because it is already upon us, but we can make our prospects better if we as a species and as individuals act now and decisively.
But we live in a world where the notion of giving up coal plants, giving up tar sands, giving up fracking for natural gas, driving electric cars, taking buses, harvesting energy from wind and solar, and introducing a carbon tax is somehow even more frightening to large sectors of the population than the murderous future that climate change is preparing for human civilization.