There are some indications today that global warming has reached the threshold where the thermohaline circulation could start to be significantly impacted. These indications include observations documenting that the North Atlantic is increasingly being freshened by melting glaciers, increased precipitation, and fresh water runoff making it substantially less salty over the past 40 years. (reference)
The cold reality is that WE PRESENTLY HAVE NO BACKDOOR if the environment we are thriving on becomes miserable. The only option we have is to be cautious and prudent and surely not bold and ignorant. Are we simply playing ostrich with our SUVs?
Research commissioned by The Independent reveals that the accumulation of greenhouse gases in the atmosphere has now crossed a threshold beyond which really dangerous climate change is likely to be unstoppable. The implication is that some of global warming's worst predicted effects, from destruction of ecosystems to increased hunger and water shortages for billions of people, cannot now be avoided, whatever we do. The danger point we are now firmly on course for is a rise in global mean temperatures to 2 degrees above the level before the Industrial Revolution in the late 18th century.(reference)
At the moment, global mean temperatures have risen to about 0.6 degrees above the pre-industrial era and worrying signs of climate change, such as the rapid melting of the Arctic ice in summer, are already increasingly evident. But a rise to 2 degrees would be far more serious.
By that point it is likely that the Greenland ice sheet will already have begun irreversible melting, threatening the world with a sea-level rise of several meters. Agricultural yields will have started to fall, not only in Africa but also in Europe, the US and Russia, putting up to 200 million more people at risk from hunger, and up to 2.8 billion additional people at risk of water shortages for both drinking and irrigation.
A clear threshold in the accumulation of greenhouse gases in the atmosphere, which should not be surpassed if the 2 degree point was to be avoided with relatively high certainty is that the total concentration of these gases would stay below 400 ppm (parts per million) in 'equivalent greenhouse concentration' of carbon dioxide (for example, methane has 20 times the greenhouse impact of carbon dioxide, so 1 ppm of methane is the greenhouse equivalent of 20 ppm of carbon dioxide). However, the carbon dioxide equivalent concentration has now risen beyond this threshold.(reference)
According to a world's leading expert on the effects of greenhouse gases on climate, Professor Keith Shine, head of the meteorology department at the University of Reading, the equivalent concentration of carbon dioxide, taking in the effects of methane and nitrous oxide at 2004 levels, is now 425 ppm. This is made up of carbon dioxide itself, at 379 ppm plus the global warming effect of methane in the atmosphere, equivalent to another 40 ppm of carbon dioxide itself and the effect of nitrous oxide (the famous gas responsible for smog), equivalent to another 6 ppm of carbon dioxide itself.
The passing of this threshold is of the most enormous significance. It means we have actually entered a new of dangerous climate change. We have passed the point where we can be confident of staying below the 2 degree rise set as the threshold for danger. What this tells us is that we have already reached the point where our children can no longer count on a safe climate.
Some scientists have been reluctant to talk about the overall global warming effect of all the greenhouses gases taken together, because there is another consideration the fact that the 'aerosol', or band of dust in the atmosphere from industrial pollution, actually reduces the warming causing GLOBAL DIMMING.
There is enormous uncertainty about the degree to which this is happening, so making calculation of the overall warming effect problematic. However, in the event of an industrial downturn, the aerosol could fall out of the atmosphere in a matter of weeks, and then the effect of all the greenhouse gases taken together would suddenly be fully felt.
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