Atmosphere weight, emissions, half life in the atmosphere and residence time

The earths atmosphere weight in tons is 5.8 X 10^15 US tons (5.3 x 10^15 metric tons).

The atomic mass of carbon is 12, while the atomic mass of CO2 is 44. Therefore, to convert from gigatonnes carbon to gigatonnes of carbon dioxide, you simply multiply 44 over 12. In other words, 1 gigatonne of carbon equals 3.67 gigatonnes of carbon dioxide.

[From Skeptical Science] Atmospheric CO2 levels are expressed in parts per million by volume (ppm). To convert from ppm to gigatonne of carbon, the conversion tables of the Carbon Dioxide Information Analysis Center advise that 1 part per million of atmospheric CO2 is equivalent to 2.13 Gigatonnes Carbon. Using our 44 over 12 rule, this means 1ppm = 7.81 Gigatonnes of Carbon Dioxide. [This part per million is different from the 5.3 billion tons from the atmospheric weight]

Stopping the upward addition of manmade carbon dioxide would mean getting rid of all usage of coal (currently the world is using 7 billion tons per year and is adding hundreds of millions of tons of increased usage), oil (in cars and other uses) and natural gas. Roughly halving the use of carbon dioxide would be easier because natural gas usage could be increased to displace coal. This was done in the USA for 20% of its electrical energy over about 3-5 years.

The world added roughly 100 billion tonnes of carbon to the atmosphere between 2000 and 2010. That is about a quarter of all the CO₂ put there by humanity since 1750. And yet, as James Hansen, the head of NASA’s Goddard Institute for Space Studies, observes, “the five-year mean global temperature has been flat for a decade.”

The IPCC claim

Carbon dioxide itself absorbs infra-red at a consistent rate. For each doubling of CO₂ levels you get roughly 1°C of warming. A rise in concentrations from preindustrial levels of 280 parts per million (ppm) to 560ppm would thus warm the Earth by 1°C. If that were all there was to worry about, there would, as it were, be nothing to worry about. A 1°C rise could be shrugged off. But things are not that simple, for two reasons. One is that rising CO₂ levels directly influence phenomena such as the amount of water vapor (also a greenhouse gas) and clouds that amplify or diminish the temperature rise. This affects equilibrium sensitivity directly, meaning doubling carbon concentrations would produce more than a 1°C rise in temperature.

The Intergovernmental Panel on Climate Change (IPCC) believes the answer is about 3°C, plus or minus a degree or so. In its most recent assessment (in 2007), it wrote that “the equilibrium climate sensitivity…is likely to be in the range 2°C to 4.5°C with a best estimate of about 3°C and is very unlikely to be less than 1.5°C. Values higher than 4.5°C cannot be excluded.”

[from Skeptical Science] Individual carbon dioxide molecules have a short life time of around 5 years in the atmosphere. However, when they leave the atmosphere, they’re simply swapping places with carbon dioxide in the ocean. The final amount of extra CO2 that remains in the atmosphere stays there on a time scale of centuries.

A little quick counting shows that about 200 Gt C leaves and enters the atmosphere each year. As a first approximation then, given the reservoir size of 750 Gt, we can work out that the residence time of a given molecule of CO2 is 750 Gt C / 200 Gt C y-1 = about 3-4 years. (However, careful counting up of the sources (supply) and sinks (removal) shows that there is a net imbalance; carbon in the atmosphere is increasing by about 3.3 Gt per year).

It is true that an individual molecule of CO2 has a short residence time in the atmosphere. However, in most cases when a molecule of CO2 leaves the atmosphere it is simply swapping places with one in the ocean. Thus, the warming potential of CO2 has very little to do with the residence time of CO2.

What really governs the warming potential is how long the extra CO2 remains in the atmosphere. CO2 is essentially chemically inert in the atmosphere and is only removed by biological uptake and by dissolving into the ocean. Biological uptake (with the exception of fossil fuel formation) is carbon neutral: Every tree that grows will eventually die and decompose, thereby releasing CO2. (Yes, there are maybe some gains to be made from reforestation but they are probably minor compared to fossil fuel releases).

Dissolution of CO2 into the oceans is fast but the problem is that the top of the ocean is “getting full” and the bottleneck is thus the transfer of carbon from surface waters to the deep ocean. This transfer largely occurs by the slow ocean basin circulation and turn over. This turnover takes 500-1000ish years

Particulates and Soot

Particulate air pollution from incomplete combustion is affecting climate over East Asia more than carbon dioxide and cause premature deaths of over half a million annually in China alone, yet its sources have been poorly understood. Scientists have now used a powerful carbon-14 method to show that four-fifths of the soot particle air pollution are from fossil fuel combustion such as household cooking with coal briquettes and city traffic, drastically changing the view on sources and guiding efforts to mitigate emissions.

In Environmental Science and Technology (journal of the American Chemical Society) a research team from China, Sweden, USA and South Korea use a powerful carbon-14 method to show that four-fifths of the soot particle air pollution are from fossil fuel combustion such as household cooking with coal briquettes and city traffic, drastically changing the view on sources and guiding efforts to mitigate emissions.

Severe air pollution, covering large parts of South and East Asia as Atmospheric Brown Clouds (ABC), originate from incomplete combustion such as household burning of coal and wood fuel, agricultural residue burning, industrial processes and massive traffic. Previous studies, based on uncertain emission factors, spans a wide range but have all suggested a larger role for biomass combustion than what is shown by the now published source-diagnostic characterization of soot in the actual atmosphere over East Asia.

The rewards of decreasing soot emissions from fossil fuel combustion in China, the World’s largest emitter, may be rapid and sizeable. Globally, soot accounts for roughly half the warming potential of carbon dioxide. Ke Du, a professor at the Chinese Academy of Science Institute of Urban Environment in Xiamen and co-leader of the study, says that while carbon dioxide is the key target for fighting climate change, its levels in the atmosphere respond on a sluggish 100-1000 yr timescale to reductions in emissions. “In contrast, Brown Cloud soot particles only reside in the atmosphere for days-weeks raising the hope for a rapid response of the climate system” explains Du.

Örjan Gustafsson, a professor at Stockholm University and co-leader of the study, says that understanding the sources of the soot air pollution is central to current international efforts to fight such short-lived climate pollutants. “Efficiently addressing the key sources of Chinese soot emissions will lead to rapid and multiple co-benefits to the quality of the air people breathe, the regional climate and its secondary effects such as on freshwater availability” says Gustafsson.

Mitigating soot would cost about $6 per ton of CO2 equivalent. CO2 mitigation costs about $100 per ton. Nextbigfuture has frequently written that soot is the most cost effective emission target for managing climate. It is also the one with the fastest results. Carbon dioxide mitigation does not impact temperatures for 50-80 years. Fully mitigating soot can also save 1-2 million lives by avoiding the disease from soot pollution.

Bending the temperature curve is cheaper and faster by dealing with soot and their is the other benefit of saving millions of lives a year and reducing medical costs which would improve national economies and government budgets

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