The Sky Is Rising

Makarand writes "The height of the tropopause, the boundary layer between the troposphere and stratosphere and the roof of the Earth's lower atmosphere, has risen by an average of around 650 feet globally over the last 22 years according to this article in the San Francisco Chronicle. Greenhouse gases trap infrared radiation and warm the troposphere. The resulting tropospheric expansion is moving the tropopause upward. Also, the ozone depleted stratosphere is losing its ability to absorb sunlight causing it to cool and contract pulling the tropopause upward."

Comments

Re:How do you locate the tropopause?

[GodsMadClown]

The tropopause is the boundary level, between the troposphere and stratosphere, at which temperature no longer falls as you rise in altitude.

As you move beyond the tropopause, into the stratosphere, atmospheric temperature will rise because the stratosphere contains more ozone. Ozone absorbs a significant portion of the UV light from the sun, adding energy to warm the atmosphere. Because atmosphere at these altitudes is much less dense, it doesn't take nearly as much energy to make changes in temperature. Because temperature rises with altitude, the stratospheric air is stable, with little vertical mixing.

Increasing CO2 also causes stratospheric cooling!

[Anonymous Coward]

The header is correct in stating that ozone depletion leads to stratospheric cooling (i.e., through less absorption of UV).

However, the stratosphere also radiatively cools for enhanced CO2 levels.

As described in the 'Scientific Assessment of Ozone Depletion: 1998' by the World Meteorological Organization, "an increase in greenhouse gas concentration enhances the thermal infrared emissivity of a layer in the stratosphere; hence, if the radiation absorbed by this layer remains fixed and other factors remain the same, then, to achieve equilibrium, the same amount of energy has to be emitted at a lower temperature and the layer cools."

What science is this based on?

[twfry]

Also, the ozone depleted stratosphere is losing its ability to absorb sunlight causing it to cool and contract pulling the tropopause upward

Um, the tempurature of the air above another layer of air does not contract or pull air below it up or down. The stratosphere's weight would be the same causing the same amount of force to be exerted on the tropopause. The tropopause's height is only effected by 1) its own temperature and 2) the compression force of whats above it.

Not so simple

[siskbc]

That's a good analogy, but the atmosphere is a good bit more complex than that. First, the atmosphere doesn't 'pop' like a baloon would - if anything it would keep getting thinner. Second, with more surface area where the ozone layer is shifted to, more ozone will be produced, which should counteract the effect.

But ultimately, the ozone hole occurs at the south pole for two specific reasons: First, the poles get a lot less radiation that the rest of the earth, hence less ozone production there. Second, the air currents over antarctica serve to trap the CFC's and ozone there DURING WINTER, allowing the CFC's to devour the ozone without it being able to re-mix with the rest of the atmosphere.

Note that this year the ozone hole actually shrank and split in half, due to a change in the weather patterns over antarctica. So I would be extremely hesitant to use a baloon analogy to explain the ozone hole - atmospheric chemistry is so hideously complicated.

Re:Of course

[B.D.Mills]

We are talking about something like a quarter-mile increase on a sphere with a radius of about 4000 miles. The "stretch factor" on the surface area and thickness is 0.0001.

Your figures are incorrect because the earth isn't stretching along with the atmosphere.

The approximate shape of the troposphere *isn't* a sphere. It's shape is more like a solid of revolution formed by a thin annulus being rotated about its centre. (I don't know the name of this shape. But think of what shape an eggshell is if there was no egg inside it.) The troposphere is about 15-20 miles thick so an increase in thickness of 650 feet is more like a 1% increase. That's still small, but bigger than you thought.