It's not the ground level warming so much as the upper air cooling. A little more warming on the ground coupled with a lot more cooling at extreme altitudes means thunderstorm height's rise by thousands of feet. And so become much more violent.

This is how and why it happens.

All objects, whatever their temperature might be, are constantly and simultaneously absorbing and radiating energy. The ground absorbs about eight hours of strong sunlight during the day. However it's radiating out infrared light all twenty-four hours.

The wavelength of the radiant energy depends on the objects temperature. White-hot objects radiate white light. Slightly cooler objects are red hot and radiate red light. Cooler still and infrared light is radiated. Infrared we can feel as warmth but we can't see it.

Temperatures at the centre of the sun are millions of degrees Celsius, but on the surface the temperature is only about 6000° C. To compare, the flame temperatures in an oxy-acetylene welding torch can reach 3,300° C. We see both as white hot, because both are radiating white light.

Without being too specific we can say that the air in our atmosphere is one fifth oxygen and four-fifths nitrogen. It also contains about four hundreds of one percent carbon dioxide (380 ppm). Oxygen, nitrogen and carbon dioxide gasses are transparent to white light. So sunlight goes unhindered straight through to the ground. Some of it is reflected back into space, the rest is absorbed and warms the ground.

Without some greenhouse gasses in an atmosphere, surface temperature would rise until the strong sunlight and the weak infrared radiation balanced out. Without some greenhouse gasses, on Earth the average ground temperature on the planet would settle to about minus 18° C. That's zero Fahrenheit.

Oxygen and nitrogen are totally transparent to infrared light. But carbon dioxide is not. The carbon dioxide acts like a blanket keeping the heat in and in consequence the world's average ground temperature had settled to approximately 15° C or about 60° F.

The sun shines, the ground warms up and the air near the ground, up to about tree top height, is warmed by direct ground contact and gentle mixing. As it warms it slightly expands and so becomes slightly lighter. Bubbles of warm air rise, coalesce and form rising air columns. From nearby more warm air flows in horizontally and as it joins the central column it changes direction to move vertically. This change of direction causes the air to spin, the same way as bath water develops a spin flowing into a plughole. The spinning effect results from the spinning of the planet itself. The spin is one way in the Northern Hemisphere and the opposite in the Southern Hemisphere. We see this spinning column of air as a "willy-willy" or a "dust devil".

As our warm air rises through the surrounding air there is less total air above it so it feels less pressure; so as it rises it expands. Now when a gas is allowed to expand it simultaneously cools. Inevitably, at some particular height the rising air will cool to the point where it's at the same temperature as the outer surrounding air. It's no longer buoyant, so it stops rising. Sometimes if our air is humid to start with, then at some height and with sufficient cooling, the moisture will condense out and form a small fluffy cumulous cloud.

I used to race gliders, and to be competitive you really have to understand all this stuff. In a glider you gain height by circling in these columns of rising air. They're called thermals. If you need to gain height you look for a willy-willy down near the ground, or you look for a nice fresh cumulous cloud above. You often find one first and then observe it's connected to the other. It's an axiom in gliding that the "strength" of a thermal, i.e. how fast the air is rising, depends a lot on how high the thermals are going on any particular day, and of course that makes sense as they have more time to accelerate to higher speeds. This increase in upward velocity is relevant to understanding the extreme weather phenomena we are experiencing all round the world; as we shall see.

The fundamental structures of these updrafts are all the same, although from experience the strength and form of individual thermals seem to have almost individual personalities. Thermal updraft characteristics depend on the geography and the topography of where you are. They depend on the ground cover, the ground temperature, and most notably the temperature change with height in the area on the day.

There is a wide variation in absolute power. You may get no more than just a little bit of air mixing near the ground, or the air is gently rising, or willy-willies are being formed, and they are formed sometimes with and sometimes without clouds forming above them. Variations go all the way on up to rain showers, to thunderstorms and right through to hurricanes and tornadoes. It's all merely a matter of degree and circumstances.

The same spread of thermal activity, size and ultimate violence occurs over the sea, but there ocean currents, water depth and evaporation rates affect the outcomes. But the principles are still the same.

To understand how global warming affects these phenomena we need a little poetic license.

Because the incoming sunlight is, (for all intents and purpose) unaffected by the atmosphere through which it passes, we can consider it simply as an isolated independent heating process. We can thus visualize it as a big electric blanket covering the ground surface. That then represents our solar energy input.

The carbon dioxide, because it partially blankets off the infrared heat coming off the ground (our electric blanket) we will picture as a couple of woolen blankets, one near the ground and the other a bit above it. Now the lower blanket will be warm, and the upper blanket will be cooler, but will still receive some heat that manages to pass through the lower blanket. It’s not warm but it will have some warmth.

Now spread an extra couple of blankets between our first two. These extra blankets represent the extra carbon dioxide we have been adding to the atmosphere for the last several decades.

Now two things happen. The ground itself and the blankets near the ground will get much hotter. However the upper blanket, we first put in place, now has two new blankets insulating it from the warmth from the ground and our electric blanket.

That's exactly what is happening to our atmosphere. Ground temperatures and temperatures in the lower atmosphere have risen by just under one degree Celsius as a direct result of increased atmospheric carbon dioxide levels. This is now generally acknowledged and openly discussed. But what nobody talks about, what few people are even aware of, and even those that are, are loathe to acknowledge, is the complimentary reduction in temperatures at high and very high altitudes. We have created a very chilled upper atmosphere blanket. In the Earth's upper atmosphere temperatures have dropped alarmingly.

At some heights average air temperatures have been dropping as much a full 10° Celsius, that's 18° Fahrenheit, every decade. (See Science, the journal of the American Society for the Advancement of Science. Vol 314)

Now back to thermals and thunderstorms - in simple terms with this very pronounced upper air-cooling, a rising mass of warm air will by necessity have to go much higher before it cools sufficiently to match the now cooler surrounding air. As every glider pilot knows, the vertical air velocity will in consequence be considerably higher. Also in consequence, any hail formed in these rising air columns will need to grow to king size hail stones before they become heavy enough fall back down through the rapidly rising air. And that's what we are seeing.

It will also mean large increases in wind velocities in the spinning air masses feeding the rising air columns. Category Two hurricanes grow to become Category Three. Category Three become Category Four and Fours become the once rare Category Five. Category Five wind speeds are rarely recorded as the weather stations themselves are often destroyed. As violence escalates we will have to name, define and delineate a new category; probably Category Six.

It's almost impossible to find factual articles explaining or even mentioning the phenomenon. It's even more difficult to find references that link upper air cooling to its magnifying influence on hurricane, storm and typhoon intensities. All we see reported, and almost in passing, is the vague suggestion that with global warming many weather phenomena "could become more violent". It's as if it's just some, as yet unproven, theory.

In the few references to upper air cooling I have seen in the media, the reports are almost invariably written in a way that suggests, or infers that because "here is evidence of some atmospheric cooling, maybe global warming is not happening at all." That inference is an incredibly irresponsible and dangerous misrepresentation of facts.

The build up of greenhouse gasses in the whole atmosphere is the only known and accepted explanation for high altitude atmospheric cooling. The whole phenomena and the recorded - and experienced - violence it produces is yet another frightening confirmation of our planet's dangerous over heating.

(NOTE. Nuclear radiation is a little different. There are only three important ones. Two consist of actual particles. Alpha radiation is streams of high-speed helium nuclei. Beta radiation consists of high speed, high-energy electrons. The third one is Gamma radiation, and that radiation is very similar to X-rays. Both are structured like light but have very high energies. It should be noted that the Earth itself contains a whole range of radio active materials dispersed throughout. They break down by radioactive decay and release radiation and heat. That's why the inner core is hot. This heat seeps to the surface and is radiated into space as infrared light. Surprisingly these heat flow numbers are incredibly tiny and are effectively inconsequential compared to the heat in our daily dose of sunlight.)

Allan Yeomans