Monday, December 7, 2009
550 ppm (parts per million) carbon dioxide equivalents explained; potentially dangerous despite best efforts.
Stabilizing at 550 ppm CO2e may not be enough to protect against the worst effects of climate change & global warming. To clarify further, if there were in total 1,000,000 'balls' of atmosphere, of the 1,000,000, 550 balls would be carbon dioxide balls (standard unit of greenhouse gases is CO2e - carbon dioxide equivalents). For the Copenhagen climate summit, 550 ppm is the target by 2050; the goal is to have no additional balls of carbon added to the atmosphere. Why? Because at 550 ppm the temperature has a 76% chance of not exceeding 5 degrees C. Good odds of getting to a dangerous temperature, but still avoiding catastrophe.
Currently the world is at 430 ppm CO2e (or 430 balls of carbon dioxide for every 1,000,000 balls of atmosphere). In pre-industrial times, around the 1850s, the world had 280 ppm of CO2e in the atmosphere (280 balls per 1,000,000 atmospheric balls). Every year the planet adds 3 balls into the air, or adds 3 ppm of CO2e into the atmosphere. In four decades the planet is extremely likely to get to 550 ppm CO2e. The likely outcome would be global warming temperature increase of 5C.
But that is just an estimate; it is reasonable to go beyond 5C at 550 ppm. Computer simulations consistently point to stabilization of carbon in the atmosphere to 550 ppm because it is extremely likely to occur by 2050, under "business as usual" (often abbreviated to 'BAU' in technical papers). By stabilizing at 550 ppm we hope to stop throwing balls of carbon into the atmosphere all together. By then we'll wait and see how much hotter the planet will get. Box 8.1 taken from the Stern Review (2007) reveals humbling percentages pertaining to carbon emissions levels. Once at 550 ppm there is a 7% chance of exceeding temperatures greater than 5 degrees C; there's a 2% chance of exceeding 6 degrees C; and a 1% chance of exceeding 7 degrees C. Humans have never experienced a temperature past 5 degrees C than what it is now.
So what’s the big deal with 5 degrees C? To compare a temperature change of 5 degrees C: 10,000 years ago the climate was 5 degrees colder than it was today and ice sheets extended from the North Pole down latitudes of present day New York. Doing nothing about climate change, the path of least resistance, may see us past a 7-degree increase of temperature. The consensus in science is that each year the likelihood of shooting past 550 ppm (and therefore 5 degrees C) by 2050 is growing. As Stern has suggested, if we limit throwing carbon dioxide balls into the sky now, the cost of success will be 1% of global GDP. As we've covered in the Justmeans American Climate Change Policy Series it would cost the USA $444B to cover it’s own losses under BAU, which equates to 3.7% US GDP. It's smarter and cheaper to act now; collective strength spreads the costs thin.
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