Are humans causing global warming?
There is a clear correlation in the ice record: high CO2 and high temperature go together. The presumption is made that high CO2 causes high temperature. But what if it was the other way around? What if higher temperature causes higher CO2? The ice record shows a lag: CO2 starts rising 800 years after warming starts. Perhaps the climate change lobby have got it all wrong.
Remember in the 1970s an ice age was said to be just around the corner? The world had been cooling for the previous 35 years (yes, cooling) and 'obviously' if that continued northern latitudes would before too long be under huge ice sheets and the end of civilisation would be upon us. If anyone had stood up in the seventies and said the world was in danger of getting too warm they would have been laughed out of court!
Some think that world temperature is predominantly driven by the sun, not by mankind. In the Middle Ages it was as warm as it is today and there weren't too many cars around in those days. Indeed, world temperature has always changed over time. Over the past few thousand years it has at times been warmer than now and at other times cooler than now.
Some claim that change in world temperature correlates closely to change in solar activity. Solar activity was exceptionally high in the 20th century - lots of sun spots. [Sun climate effects.] Cosmic rays (subatomic particles that bombard the earth from space) cause water vapour in the earth's atmosphere to condense and form clouds, and these clouds cause cooling. More cosmic rays, more clouds, cooler planet. Fewer cosmic rays, less cloud, warmer world.
But when the sun is very active, as it is now, the so-called solar wind - radiation from the sun - becomes stronger and blows some of those cosmic rays away, preventing them reaching the earth. Result? Fewer clouds and thus higher world temperature. Higher temperatures gradually warm the oceans. Warmer oceans absorb less CO2. Result? More CO2 in the atmosphere. In other words raised CO2 levels are primarily a consequence of temperature rise, not the cause of it. Though, of course, the higher CO2 levels do then themselves cause even more warming, creating a snowball effect. But a natural snowball not a man-made one. Only when solar activity reduces does the world begin to cool.
Though low clouds cool the climate, high clouds warm it. But global warming means warmer clouds which tend to condense faster to form rain. As a result there is less thick, watery cloud to reflect radiation back into space and also less icy cloud remaining. Icy clouds are very good at reducing the release of infrared energy into space, so less of them means more heat escaping.
In other words high cirrus clouds act as a regulator: high temperature, less high cloud, more heat escapes into space.
So take your pick:
How long will it be before the orthodox belief becomes, once again, that we are heading for another ice age and
we must do something about it?
So the global warming lobby have got it all wrong. The current observed rises in global temperatures and sea levels are a natural, cyclical phenomenon and nothing to do with human activity. Indeed, do some clever sums factoring in sun spots, water vapour and naturally occurring CO2 and assume "diminishing returns" from adding more CO2 and you can prove that mankind is not contributing to global warming in any significant way.
If global warming is a vicious circle (more warming --> naturally more greenhouse gases --> more warming --->...) how does this cycle ever end? Why doesn't the world just go on getting hotter and hotter until it disappears in a puff of smoke?
In the very long term the relative position of the sun and earth determine whether the earth will be warm or cool. On a shorter time horizon solar activity is a significant factor. When solar activity declines the earth starts to cool, levels of greenhouse gases (water vapour, CO2, etc.) naturally reduce which causes even more cooling. Perhaps most important is that infrared radiation emitted by Earth increases exponentially with temperature, so as long as some infrared can escape from the atmosphere at some point heat loss will equal heat retention.
Meteorite strikes too can end warm periods. A large meteorite striking the earth can throw large quantities of
dust into the upper atmosphere causing sudden and dramatic cooling. [And very large ones, say a mile across,
can have very dramatic consequences: huge amounts of dust thrown into space then re-entering the atmosphere creating so
many shooting stars that they act like a grill, toasting the earth below; the ozone layer is destroyed;
atmospheric nitrogen ionises resulting in acid rain which wipes out crops;
dust remaining in the atmosphere reduces sunlight so much that new crops do not grow.
Climatic disaster, chaos, mass starvation, the end of civilisation as we know it... But that's another story.
Spaceguard Near Earth Object Tracking]
Periods of warming may also be brought to a sudden end by cometary dust. When the earth passes through a comet's tail dust enters the earth's atmosphere. Usually the volume isn't great and apart from a fine display of shooting stars there is little or no effect. However, sometimes a huge amount of dust ends up in the atmosphere significantly reducing the amount of solar energy that gets through which results in considerable cooling.
In late 2007 the Holmes comet might dump enough dust into the atmosphere to cause noticeable cooling. At the time of writing it doesn't look likely that it will, but it could - as might any other passing comet.
Indeed, had an accommodating comet dumped enough dust into our atmosphere a few years ago the world would not be warming now.
If, tomorrow, solar activity declined we might stop worrying about the warming effects of anthropogenic CO2. But there's nothing to suggest the sun is about to take a breather.
And what of the idea that higher temperature causes higher CO2 rather than the other way around? The ice record shows that at the end of a cold period first it gets warmer and then atmospheric CO2 levels rise. True, but this is what happens: Some initial warming, perhaps due to a change in the position of the earth relative to the sun, causes CO2 to enter the atmosphere. This CO2 then itself causes warming which causes more CO2 to enter the atmosphere and so the warming cycle begins. The level of CO2 may well lag behind at the start of the cycle but then takes over and drives further warming.
An alternative way would be artificially to pump large amounts of CO2
(or better still methane) into the atmosphere of a frigid planet and get the cycle going that way.
Indeed, such an approach has been suggested to "terraform" Mars to warm it up for human habitation.
The notion that mankind is not causing global warming is a minority view. A majority of scientific opinion recognises that solar activity affects weather patterns but believes it is not the primary driver of the global warming we are currently observing.
The debate will no doubt rage ever more ferociously until something - a major volcanic eruption or a
meteorite or a comet or a reduction in solar activity - cools both the earth and the argument.
Copyright MR 2005 2006 2007 2008 2009 2010
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