Monday, September 3, 2007

The Sky Isn't Falling

Stephen McIntyre, a Canadian mining executive and amateur climatologist has pointed out a flaw in the way NASA is measuring temperatures. Apparently NASA changed the way temperatures were recorded after the year 2000. So when NASA went back and recallibrated everything before 2000 they discovered that, in the United States, the year 1934 was 1/50th of a degree Centrigade warmer than the year 1998. In fact, in the U.S.A. six of the warmest years in the twentieth century were in the “dirty thirties”. What gives?

Why would the Great Depression with its drastic fall in production, have a warming effect? Wouldn't the resultant lower levels of CO2 emissions cause the temperature to fall? Rush Limbaugh is having a field day with this. Lorne Gunter writing in the National Post August 13, in a piece called “Global Warming? Look at the Numbers,” positively crows. “There is no discernable trend, no obvious warming of late.” he says triumphantly.

Those wildfires in Greece, Spain, Portugal, and California – that's not a trend. Record flooding in North America and India – that's not a trend either. Or the first time since records began, the Canadian Northwest Passage is open to shipping. Don't worry, it isn't a trend.

A year ago PBS showed a documentary called “Dimming the Sun”.
What the scientists in this documentary said was that the global output of soot and particulate matter has increased and this has caused clouds to reflect more sunlight. The reason is that the particles in these polluted clouds have ten times as many water droplets attached to them as particles in unpolluted clouds. Thus the polluted clouds act like giant mirrors. This trend of the rise in particulates in the atmosphere is caused by humans.

Human produced carbon dioxide is accumulating in the atmosphere. But particulates usually drop out of the atmosphere in a matter of weeks if they are not continually replenished. In the thirties when U.S. production nosedived, U.S. emissions of CO2 and particulates must have fallen considerably. The decrease in CO2 emmisions wouldn't have effected the CO2 that was already in the atmosphere. But the decrease in particulates would have had an immediate effect. It could have led to the uncharacteristically higher temperatures in the United States in the thirties.

This business of global dimming has complicated the global warming picture. Even environmentalists have tried to ignore the evidence in order to keep the explanation of climate change simple. These two forces oppose one another. In the short term they are comparable in strength but in the medium to long term global warming is vastly more powerful because of positive feedback effects which are only now coming into play. But the danger is, that by ignoring global dimming we may be seriously underestimating global warming.

Contrary to what the climate change deniers are arguing, many of the climate change models have underestimated the strength of global warming because they have not included these positive feedbacks in their computer models. What are these effects? Think of the oceans and forests as huge carbon sinks. Unfortunately, as the temperature of the oceans rises the amount of CO2 that gets absorbed declines because CO2 is less soluble in warm water. So as the temperature rises the oceans will begin to emit more CO2 than they absorb and this will accelerate global warming. As the temperature on land rises and more water evaporates from the soil, forest fires become more common. Fires destroy trees that absorb CO2 and they release more CO2 into the atmosphere as they burn.
Ice reflects light so that it has a cooling effect . But the more ice that melts the more the heat of the sun is absorbed instead. As the Arctic Ocean becomes more ice free, it warms up faster because the open water absorbs heat. At the bottom of the Arctic Ocean are frozen deposits of methane. Once the temperature of the oceans increase enough these deposits could melt releasing billions of tons of methane into the atmosphere. Methane is a much stronger greenhouse gas than CO2.

The permafrost in the arctic and mountainous regions is starting to melt. There are billions of tons of carbon locked away in the permafrost. Once melted the carbon will start to decay, releasing CO2 and methane into the atmosphere. All these positive feedback effects I have mentioned will work to accelerate global warming. Once they come into play there is nothing we can do to stop them. However there is one thing we can do that will make a difference and that is to lower human emissions of greenhouse gases by conserving energy, by reducing our use of fossil fuels and by embracing renewable sources of energy.


1 comment:

  1. Good points on "Particles drops, but CO2 doen't drop" and "positive feedbacks".