Three Ways Global Warming Affects Weather by David Rieck

Three Ways Global Warming Affects Weather

When there has been a big storm it is often reported that it was partly due to global warming.  Not everyone understands or believes it.  I will explain the steps in the process, working from things we already know, so that everyone can be sure it is true.

Everyone can see that cloudy nights are seasonably warm and clear nights are colder.  This is because heat, as infrared light, scatters off of cloud droplets, and some of it goes back to earth.  Molecules of carbon dioxide and other greenhouse gases also send heat back, but in a different way.  They absorb the infrared light, and then radiate it back in random directions.  Some goes back to warm the earth and the lower atmosphere. 

Since some of the heat is being sent back down, less goes to the upper atmosphere, so it becomes cooler.  This twin effect of greenhouse gases, warming lower atmosphere and cooling upper atmosphere, is the key to understanding the effect of global warming on weather.

It takes the same amount of heat to evaporate water from the ocean as it would take to boil that much water on a stove.  When that water vapor turns back to liquid as cloud droplets and rain, that heat is given off again.  Warm air rises.  As warm moist air rises into the cool upper atmosphere, more water condenses out, giving off more heat, and rising again.  This is the process that forms thunderheads.    

 

Since warmer air can hold more water vapor, and greenhouse gases also make the naturally cold upper air even colder, this makes more downpours and stronger updrafts.  That is not all it takes to make a tornado, but it is a good start.

 

Like an entomologist can’t predict which flower a particular bee will land on, but he knows the swarm of bees will go to the patch of flowers, weather scientists can’t always link global warming to specific storms, but they can be absolutely certain it makes the average storm worse.  It changes whole patterns, making clouds rain out before they should.  Wet parts of the world get more floods, and dry parts get drought.  

Now think about a sink full of water.  As the water runs out the drain, at first there will be glugs and bubbles as the water falls in a disorganized fashion and the air tries to stagger out of its way.  Pretty soon, the air and water will cooperate to form a vortex, or funnel shape, and they pass each other efficiently in what engineers call laminar flow.  This is a universal fact of nature:  Nature will tend to do things the way that requires the least energy, no matter what that looks like to us.

Sub-tropical oceans get a layer of warm, moist air.  That warm layer wants to rise, and it has the same problem with the cold air above it as the air and water in the sink did.  They solve it the same way, by making an energy-efficient vortex but on a geographic scale.  This picks up more warm moist air as it slowly drifts across the Atlantic to Florida.  You may have heard of the Coriolis Effect.  That determines the direction of hurricane spin, but the warm moist air and cool upper air determine the speed.  The greater the temperature difference between upper and lower atmosphere, the stronger the storms tend to be.

 

Another important effect of global warming is weakening the polar vortex.  The vortex is formed by warm air rising through cold air at the edges of the arctic.  It moves in the same efficient manner as a hurricane, but circling the globe.  The arctic is warming faster than the rest of the planet, so now we have warm air rising through arctic air that is not quite as cold as it used to be, making the polar vortex weaker.  The polar vortex is a barrier between arctic and temperate air. The weakened vortex lets arctic air into Wisconsin more often, and lets Sahara air into Siberia.   

 

I hope this thumbnail sketch helps everyone better understand the weather now, and the weather that is coming. 

David Rieck