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What is the "ozone layer"?

Ozone And Greenhouse Gases

Michael Oppenheimer (Professor, Princeton University) gives expert video advice on: How is global warming related to the hole in the ozone layer?; How far back in time can scientists measure CO2 levels?; How are humans contributing to the amount of greenhouse gases and global warming? and more...

What is the "ozone layer"?

Ozone is a form of oxygen that has three atoms in it instead of the two atoms which is the form we are used to breathing. Most of the ozone in the atmosphere lies in a layer that is centered around 2 miles above earth's surface. The ozone layer absorbs ultra-violet radiation. Were ultra-violet radiation to penetrate fully to earth's surface, it would destroy life at the surface and, in fact, a precondition for life existing was the development of the ozone layer hundreds of millions of years ago.

People often confuse global warming with the hole in the ozone layer. The most important connection is that, the gases that used to cause the ozone hole are also greenhouse gases, and contribute to the warming of the earth. Some people are under the delusion that ozone hole opens up, allows more sunlight in, and warms the earth -- this is not true.

What are "natural greenhouse gases"?

Natural greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide. These natural greenhouse gases are emitted by natural processes. For instance, when trees die and decay, because they're made of carbon, the natural greenhouse gas carbon dioxide goes up in the atmosphere. When forest fires destroy forests, they produce carbon dioxide, a natural greenhouse gas. And many forest fires are a natural phenomenon, caused, say, by lightning. Those natural greenhouse gases are a good thing, because they keep Earth about 6°F warmer than it would otherwise be. In other words, without the natural greenhouse gases, Earth would be a frozen desert. Unfortunately, humans are pumping up the levels of greenhouse gases beyond their natural level, and that's causing an unnatural warming of the Earth. And that spells real trouble for the future.

What is "carbon dioxide" or "CO2" and how does it contribute to global warming?

Carbon dioxide is the main human made greenhouse gas and it's the result of burning coal, oil and natural gas which are the major power sources in our society. The other major source of carbon dioxide is the cutting and burning of forests -- particularly to clear land for agriculture and that's an important phenomenon in developing countries like Brazil and part of Africa. The trouble is that all those carbon dioxide emissions have raised the amounts carbon dioxide in the atmosphere about 30% above what they were in pre-industrial times a couple of hundred years ago. That extra thickening of the greenhouse blanket is causing a significant warming of earth that is only going to get worse in the future if we don't stem the increase in carbon dioxide and the other greenhouse gases.

How far back in time can scientists measure CO2 levels?

The level of CO2 was measured directly by a monitor on top of a volcano in Hawaii starting in 1957 but we have other, very clever ways of measuring it from a hundred, a thousand, and 100,000 and 700,000 years ago. Scientists go to the centre of Greenland and Antarctica, and drill with a machine that looks like an oil rig. They drill down thousands of feet, pull up huge sections of ice, and segment that ice in laboratories. Ice from these cores looks just like ice in an ice cube in your refrigerator. It has air bubbles trapped in it, which are samples of the atmosphere as it was when the ice formed, as I said, as many as 700,000 years ago. So, we have a very, very solid record of carbon dioxide levels going back a very long time. Over that period, the Earth moved in and out of ice ages. We have other ways of measuring what the Earth's temperature was at the time, and there's a very, very close correlation. Every time that carbon dioxide was high for a sustained period, the Earth's temperature was high. When carbon dioxide was low for a sustained period, the Earth's temperature was low throughout that whole 700,000 years. That's very strong evidence that, as we continue to pump up carbon dioxide and the other greenhouse gases, the Earth's temperatures are going to warm significantly.

What is the "Medieval Warm Period"?

About a thousand years ago, parts of the North Atlantic Basin - Greenland, the UK, parts of Northern Europe, perhaps parts of Canada - were a little bit warmer than today. The warming was magnified around Greenland, so that areas became ice-free and could be settled. And as a result, the dominance of the Norse people spread into that area. When Earth cooled again, Greenland cooled, and the settlers were driven out. It's often argued, "if Earth was warm during the Medieval Warm Period, what are we worried about in the future?". Well, that warming was apparently restricted to a very small spot on Earth, and it was modest warming. If you look back in the indirect records we have of Earth's temperature, it turns out that the warming we saw in the last 50 years, due to the build-up of the greenhouse gases, was bigger than anything that happened in the Medieval Warm Period; the fact that Earth went through minor climate cycles in individual spots in the past really is not much of a reason to not worry about the future.

What are "climate models"?

A "climate model" is a reproduction of reality. If you collect, and combine, a number of equations, you can create a rough representation of how the world operates. If you then feed data into these equations, then you can obtain a reasonable forecast of what the future holds, with regard to climate.

What is "infrared radiation" and how does it contribute to global warming?

Infrared radiation is essentially invisible heat that radiates or comes up from hot bodies and tries to go out into space. The greenhouse gases have the property of trapping infrared radiation and it's because of that infrared trapping property that the build-up of greenhouse gases causes global warming. They act like an invisible blanket in that they trap infrared radiation near a surface.

What is "methane" and how does it contribute to global warming?

Methane is the major component of natural gas, and it is found underground. Methane is a powerful trapping agent, and contributes to global warming by holding infrared radiation near Earth's surface. The way humans add to the buildup of methane include: leaks in the methane pipeline, the decay of landfill material and certain farming methods, namely rice growing. There are many different human activities that contribute to the buildup of methane, and contribute to the buildup of the greenhouse effect.

What is "sulfur hexafluoride" and how is it created?

Sulfur hexafluoride is one of the most powerful greenhouse gases, and is created in several industrial processes, from the electronic industry. Sulfur hexafluoride is very strong, and the industry has taken various steps to limit its release.

What is "water vapor" and why is it considered a greenhouse gas?

Water vapor exists naturally in the atmosphere, because water evaporates from the oceans, forms clouds, and clouds form precipitation. In the interim stage, when it's vapor in the atmosphere, it can trap infrared radiation, heat and is a very dangerous greenhouse gas. While human beings don't have the ability to add significantly to the amount of water vapor in the atmosphere by direct emissions, there is an amplified level due to increased warming from high CO2 levels. That's called a positive feedback, "positive" because it makes the initial effect of the warming worse.

How are humans contributing to the amount of greenhouse gases and global warming?

Human beings are contributing to greenhouse gas levels, and to global warming, through the burning of fossil fuels; the cutting and burning of forests; through various agricultural processes, that lead to the build-up of methane and nitrous oxide; through some of the chemicals which are substitutes for Freons, which are now used in air conditioners and refrigerators; and through the production of smog, because smog contains ozone, which itself is a greenhouse gas.