1. Climate Change -- the scientific debate

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No, I am not going to give you the latest pronouncements from Al Gore on the subject of climate change. Al's not a scientist, let alone a geologist or a climatologist. And neither are these guys, however well-meaning they may be most environmental activists don't know schist from Shinola. And the same goes for climate prognosticators like Rush Limbaugh and Paul Harvey. This video is about science and the debate between climate scientists. I'm not going to descend into political jargon by talking about climate change believers, as if the issue depends of faith rather than a strong body of evidence. And I'm not going to talk about climate change deniers, as if there is an absolute and unassailable truth that they are deliberately refusing to see. No, there are climate scientists who are proponents of the idea that climate change is being driven by man-made causes, and there are climate scientists who are sceptics. So let's start by looking at how we've got to the current state of debate.

Our atmosphere is composed mainly of nitrogen gas, a lot of oxygen and then smaller amounts of other gases like water vapor, carbon dioxide, and methane. Most radiation from the Sun passes right through these gases because it has a short wavelength. The radiation heats up the ground and is re-emitted as long wavelength radiation, the kind of infrared heat you feel from a hot electric stove or a warm sidewalk. But although water vapor, carbon dioxide, and methane molecules allow most of this short wavelength radiation to pass right through them, they absorb the long wavelength radiation. This causes them to vibrate and, of course, vibration is heat. They radiate this heat through the atmosphere. This is the so-called greenhouse effect. But, in fact, the physics is quite different to a greenhouse, so, I dislike the term. Of the three so-called greenhouse gases, two of them are being produced by human activity, so it would be more accurate to describe these as carbon gases. If none of these three gases was there the long wavelength radiation from the ground would simply radiate into space. The Earth would be a frigid planet as cold as the moon. So, of course the opposite is true, that if these gases were abundant in the atmosphere most of the long wavelength radiation would be trapped and the Earth would heat up like a sauna. Proponents and skeptics all agree on this because it is well established basic physics. Long wavelength radiation absorption by carbon dioxide was first discovered over 150 years ago. A 100 years ago the Swedish scientist Svante Arrhenius suggested that theoretically if carbon dioxide levels were to increase drastically in the atmosphere the world would heat up. In an age of horse-drawn carriages the idea was interesting but not something to worry about. But by the 1950s there was enough concern to begin the worlds' first monitoring of carbon dioxide levels. And in the 1970s, the study conducted by the US department of energy showed that the increasing industrialization could very coon produce what's become known as the greenhouse effect. The emphasis is on the word 'could' because there were two schools of thought. One possibility was that tiny droplets of pollution in the atmosphere, so called aerosols, would reflect the Sun's radiation back into space and that would tend to overcome any warming effect from increased carbon dioxide. It could even cause the Earth to cool down, sparking another ice age. This became known as global dimming. The other possibility was that the build-up of carbon dioxide would be so great the global warming would overcome any cooling caused by reflective aerosols. By the 1980s the contest between global warming and global dimming was pretty much settled by temperature readings on the ground. The Earth wasn't getting cooler, it was getting hotter. And the 1980s turned out to be the hottest decade on record. By the way, we'll look at some of the flaws in the temperature reading in a later video.

I began reporting on this issue in 1992 when new data threw a curve ball. Crucially, although temperatures on the Earth surface were rising, satellite measurements of temperatures in the lower troposphere showed a distinct cooling. All the computer models showed that the Earth should be warming in the lower troposphere, and since it was cooling the models had to be wrong. But all the other evidence for a warming Earth was clear and compelling: ice was rapidly melting in Greenland, glaciers were retreating, and Antarctica ice sheets were braking away. By 1997 there was more than enough evidence for the world to take concerted action, or at least try to. That year I was sent to Kyoto to cover the framework convention on climate change which resulted in what become known the Kyoto protocol. Compared to the 1990s I was struck by how a lot of attitudes had changed. Most of the skeptics had become convinced by the increasing weight of evidence and the majority opinion was that climate change was real and that man-made carbon gases played a crucial role. Then in 2005 scientists in California re-analyzed the 1992 data that showed cooling in the lower troposphere and they found a crucial error. The orbit of the satellite taking the temperature readings had degraded. It had started life taking temperatures over the equator at 2 o'clock in the afternoon but by the late 1990s it was taking the readings at 5 o'clock. Hardly surprising then that the satellite had been recording a decrease in temperature over the years. The discovery knocked out the final piece of evidence that contradicted global warming. The computer models had been right all along. At last the models of how the climate should be performing with increased carbon dioxide matched how it was performing.

Even most skeptics now accepted that the Earth was warming but that didn't necessarily mean that the warming was caused by man-made carbon gases. And just as the lower troposphere anomaly was resolved, another argument arose: the 800 carbon dioxide lag time. At the Vostok station in Antarctica an ice core was drilled looking back 420,000 years in time. You can seen an explanation of how this works in my video "The Ice Age". Climatologists were able to measure both the temperature and the carbon dioxide content of the atmosphere. In his film "The inconvenient truth" Al Gore used a graph like this to show a correlation between carbon dioxide levels and increased temperatures. But he obscured the fact that the carbon dioxide increases lagged the temperature increases by 800 years. If carbon dioxide is supposed to cause global warming, as Gore claims, the lag time would suggest it's the other way around. Well, yes and ... yes. Let's look at the science, not the hype.

In my video "The Ice Age" I said there was a trigger that set off a vicious circle of events, each tipping the Earth into a cooling or a warming phase. In scientific terms, the vicious circle is called "positive feedback" and it's best explained by looking at some weights on a balanced plank. If the weights are equidistant from the pivot point the plank is in balance. A slight offset will tilt the plank but it won't offset the balance. But let's say one of the weights is round and is moved half an inch. This causes the plank to tilt slightly. But the tilt causes the weight to roll a bit and the shift in position causes the plank to tilt a bit more until soon there's a runaway event and the plank comes crushing to the ground. We know that similar positive feedback happened during the ice ages. Each cooling and warming phase is amplified so that a tiny bit of cooling ends up freezing half the planet and a tiny bit of warming ends up thawing it out again. But each time something had to act as that initial trigger, something had to nudge the round weight just a fraction. A strong contender has always been regular cyclical deviation in the Earth position or orbit changing the amount of the sunlight the Earth received. Whatever it was, in the depths (?) of ice age this change melted a tiny part of ice sheet and released carbon gases from the soil and from the warmer oceans. The carbon gases that were released trapped more long wavelength radiation and warmed the planet a bit more and that released more carbon gases and so on. Climate change proponents have never suggested that the carbon dioxide increase was the trigger for past warming, only that the trigger released carbon gases which set off this vicious circle of heating. So, the lag time shown in the Vostok ice core isn't disputed, and the reasons for it are a part of the global warming model. But without a trigger, this positive feedback wouldn't even begin. So, if the trigger was the cyclical variation in the Earth's position then we don't have anything to worry about, right? Because as we saw in the video "The Ice Age" the Earth's orbit will remain steady for another 16,000 years. The problem is, anything that causes a tiny increase in temperature can trigger this vicious circle. And the premise of the climate change proponents is that our industrial output of carbon dioxide itself is now the trigger. The calculate that the dramatic rise we've seen in carbon dioxide levels over the last 100 years will increase temperatures just enough to trigger a positive feedback loop that will result in more greenhouse gases, causing more warming, causing the release of more greenhouse gases, and so on. This is already being seen. For example, in Siberia melting ice is thawing out millions of square miles of marsh producing tons of methane gas. Methane is a more potent greenhouse gas than carbon dioxide but it's much less abundant in the atmosphere. Even so, the methane that goes in the atmosphere adds to global warming creating more marshland which releases more methane.

The 800 year lag time may be a wonderful debating point in an ideological war but it barely touches the real discussion going on among climate scientists. So what is the debate going on in that field? To say that there's no debate is nonsense. There's always a debate about every scientific issue. But to claim there's no consensus is equally false. There are many ways to measure the views of climate scientists and, as we will see in a later video, it's clear that overwhelming majority accept the role of man-made gases in global warming. But however unequal the debate might be, there are still dissenting views of qualified skeptics. In the next video I want to look at some scientific papers that suggest two alternative hypotheses on climate change, neither of which has anything to do with carbon gases.

Author's description [hide]
A basic look at how climate scientists infer that man-made carbon gases are changing the climate, and how this view is contradicted by other climate scientists who are skeptics.
   I am a former science correspondent with an interest in reporting the facts, not the media hype. My thanks to 9thgate for checking my script for errors.
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