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> Methane clathrates on the deep sea floor will not be releasing their methane. That is possible only where temperature is changing and pressure is low, neither

> Methane clathrates on the deep sea floor will not be releasing their methane. That is possible only where temperature is changing and pressure is low, neither of which will happen without surface changes catastrophic enough to make methane irrelevent. Methane ice forms under certain temperature and pressure. See the phase diagram at [1]. When methane ice forms on a sloping ocean floor, there is a boundary where the methane ice formation stops. The boundary depends on the temperature and pressure (depth). When water warms, this boundary moves deeper and all methane ice above it will convert to gas and eventually leave the ocean. How much deeper does the boundary move per 1C of temperature rise? I examined the phase diagram in Figure 6 of [1]. I found two points: (20 MPa, 275 K) and (40 MPa, 278 K). A change of 10.06 m increases pressure by 1 atm [2] or 101325 Pa [3], about 10 kPa per m or 1 MPa per 100m. So a 3 K increase in temperature results in the boundary pressure increasing 20 MPa or 2 km of ocean depth, a 1.5 K increase moves the boundary down 1000 m. The world's CO2 pollution is expected to raise surface temps by 1.5K. Given that methane is 70x more warming than CO2, if we were to convert most of the world's CO2 to methane and then release 1/70 or 1.4% of it, we would have the same amount of warming and could expect a similar 1.5 K temp rise. What percentage of methane ice will form near the boundary? To answer that, we would need to analyze ocean floor topography. I searched for a chart of depth to area and found none. Do you think the top-most 1km of methane ice forming areas would hold 1.4% of the ocean's recently-formed methane ice? The deepest part of the ocean is 10km deep. If the top-most 1km holds much more than 1.4% then there is the risk of runaway warming. Another risk is a change in ocean currents. Currents keep large areas of the ocean floor cold. If a current is disrupted, even for a short time, the clathrates in that region could release their methane, triggering runaway warming. > You are reaching. It is not a good look. Personal insults are boring and against the site guidelines [4]. Please don't write them any more on this site. [0] https://en.wikipedia.org/wiki/Methane_clathrate#Natural_deposits https://en.wikipedia.org/wiki/Methane_clathrate#Natural_depo... [1] https://doi.org/10.1021/acs.jpcb.7b10581 https://doi.org/10.1021/acs.jpcb.7b10581 [2] https://oceanservice.noaa.gov/facts/pressure.html https://oceanservice.noaa.gov/facts/pressure.html [3] https://en.wikipedia.org/wiki/Pascal_(unit) https://en.wikipedia.org/wiki/Pascal_(unit) [4] https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html

ncmncm 5y ago
Air temperature rising 1.5 degrees does not mean a corresponding increase in temperature at depth -- or anything close to it, and that not for centuries. Meanwhile, sea level rises as glaciers melt, so pressure increases. The line will move up, not down. The only substantial changes in temperature at depth would be effects of changes in current, e.g. a warm current diverted to where clathrates have accumulated over eons. These are local, affecting only isolated deposits. Methane escaping dissolves in water until it saturates, and is made available to microbes to metabolize. Methane only saturates, bubbling out, when melting is fast enough. The deeper it is, the more opportunity it has to dissolve before it gets to the surface. Only methane breaching the surface contributes to warming. And, CO2 inserted at middling depth still needs eons for some trace of it to be incorporated into methane clathrates. It takes a lot of energy to get oxygen unstuck from carbon, and most life would rather stick some back on than let the carbon float off as methane. So, you are still reaching. Why?
- mleonhard 5y ago
  We can presume that humans will stop making new CO2 pollution in the next 100 years. It will take hundreds or thousands of years for the CO2 to convert to methane clathrates. I worry about creating a problem for people far in the future. It's like setting a climate bomb with a timer of 2,000 years. > Methane escaping dissolves in water This is a good point. Let's see if the ocean can hold enough methane. Methane dissolves 0.04g/l in pure water at 0C ant 1atm [0]. Seawater has about 35g salt per L [1], or about 3.5% NaCl by weight. Methane has slightly lower solubility in salt water than in pure water (see tables starting on page 11 of [2]). Ocean pressure increases 10 kPa per m, or 1.45 psi per m [3]. At 25C, increasing pressure from 1,000 psi (700m depth) to 2,500 psi (1700m depth) increases the solubility of methane in salt water by 2x, and 5x at 15,000 psi (10km depth). I couldn't find data for lower temperatures. Methane ice forms in mud starting at 300m depth [4]. Humans have burned fossil fuels and released about 380 GtC [5]. Converting this carbon into methane yields about 500 Gt methane. Let's assume that the ocean slopes linearly down to 10,000m depth. Then the ocean floor from 300m-1300m is 10% of the ocean floor and contains approximately 10% of the methane ice, about 50 Gt of methane. The volume of water above it is (300m + 0.5 x 1000m) x 0.10 x 361,900,000 km-km (the area of the ocean [6]), about 29,000,000 km-km-km or 2.9x10^22 l. About 1.160x10^21 g or 1,600,000 Gt methane can dissolve in this water. Let's assume that the average solubility in the ocean is 2x the solubility at the surface, or 0.08g/l of methane in sea water. Then the entire 1.335x10^9 km-km-km ocean could dissolve about 1.068x10^23 g or 100,000,000 Gt methane. You are right. The ocean could dissolve all of man's fossil fuel CO2 pollution as methane. Since the methane would probably not bubble up, the rate of methane escaping into the air would be very low. I think it would be slow enough that the methane would stay in the ocean's carbon cycle and not escape fast enough to trigger runaway warming. I feel relieved. > So, you are still reaching. Why? Describing my analysis as "reaching" is incorrect. I think you mean it as a personal attack, which breaks the site's guidelines [7]. Removing the insult yields "Why do you care about this issue?" The reason is that I think it is interesting and important. [0] https://www.engineeringtoolbox.com/gases-solubility-water-d_1148.html https://www.engineeringtoolbox.com/gases-solubility-water-d_... [1] https://en.wikipedia.org/wiki/Seawater https://en.wikipedia.org/wiki/Seawater [2] https://doi.org/10.3133/ofr80371 https://doi.org/10.3133/ofr80371 [3] https://en.wikipedia.org/wiki/Pound_per_square_inch https://en.wikipedia.org/wiki/Pound_per_square_inch [4] https://en.wikipedia.org/wiki/Methane_clathrate https://en.wikipedia.org/wiki/Methane_clathrate [5] https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere#Anthropogenic_CO2_emissions https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_at... [6] https://en.wikipedia.org/wiki/Ocean#Geography https://en.wikipedia.org/wiki/Ocean#Geography [7] https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html

ncmncm 5y ago

Air temperature rising 1.5 degrees does not mean a corresponding increase in temperature at depth -- or anything close to it, and that not for centuries. Meanwhile, sea level rises as glaciers melt, so pressure increases. The line will move up, not down. The only substantial changes in temperature at depth would be effects of changes in current, e.g. a warm current diverted to where clathrates have accumulated over eons. These are local, affecting only isolated deposits. Methane escaping dissolves in water until it saturates, and is made available to microbes to metabolize. Methane only saturates, bubbling out, when melting is fast enough. The deeper it is, the more opportunity it has to dissolve before it gets to the surface. Only methane breaching the surface contributes to warming. And, CO2 inserted at middling depth still needs eons for some trace of it to be incorporated into methane clathrates. It takes a lot of energy to get oxygen unstuck from carbon, and most life would rather stick some back on than let the carbon float off as methane. So, you are still reaching. Why?

mleonhard 5y ago
We can presume that humans will stop making new CO2 pollution in the next 100 years. It will take hundreds or thousands of years for the CO2 to convert to methane clathrates. I worry about creating a problem for people far in the future. It's like setting a climate bomb with a timer of 2,000 years. > Methane escaping dissolves in water This is a good point. Let's see if the ocean can hold enough methane. Methane dissolves 0.04g/l in pure water at 0C ant 1atm [0]. Seawater has about 35g salt per L [1], or about 3.5% NaCl by weight. Methane has slightly lower solubility in salt water than in pure water (see tables starting on page 11 of [2]). Ocean pressure increases 10 kPa per m, or 1.45 psi per m [3]. At 25C, increasing pressure from 1,000 psi (700m depth) to 2,500 psi (1700m depth) increases the solubility of methane in salt water by 2x, and 5x at 15,000 psi (10km depth). I couldn't find data for lower temperatures. Methane ice forms in mud starting at 300m depth [4]. Humans have burned fossil fuels and released about 380 GtC [5]. Converting this carbon into methane yields about 500 Gt methane. Let's assume that the ocean slopes linearly down to 10,000m depth. Then the ocean floor from 300m-1300m is 10% of the ocean floor and contains approximately 10% of the methane ice, about 50 Gt of methane. The volume of water above it is (300m + 0.5 x 1000m) x 0.10 x 361,900,000 km-km (the area of the ocean [6]), about 29,000,000 km-km-km or 2.9x10^22 l. About 1.160x10^21 g or 1,600,000 Gt methane can dissolve in this water. Let's assume that the average solubility in the ocean is 2x the solubility at the surface, or 0.08g/l of methane in sea water. Then the entire 1.335x10^9 km-km-km ocean could dissolve about 1.068x10^23 g or 100,000,000 Gt methane. You are right. The ocean could dissolve all of man's fossil fuel CO2 pollution as methane. Since the methane would probably not bubble up, the rate of methane escaping into the air would be very low. I think it would be slow enough that the methane would stay in the ocean's carbon cycle and not escape fast enough to trigger runaway warming. I feel relieved. > So, you are still reaching. Why? Describing my analysis as "reaching" is incorrect. I think you mean it as a personal attack, which breaks the site's guidelines [7]. Removing the insult yields "Why do you care about this issue?" The reason is that I think it is interesting and important. [0] https://www.engineeringtoolbox.com/gases-solubility-water-d_1148.html https://www.engineeringtoolbox.com/gases-solubility-water-d_... [1] https://en.wikipedia.org/wiki/Seawater https://en.wikipedia.org/wiki/Seawater [2] https://doi.org/10.3133/ofr80371 https://doi.org/10.3133/ofr80371 [3] https://en.wikipedia.org/wiki/Pound_per_square_inch https://en.wikipedia.org/wiki/Pound_per_square_inch [4] https://en.wikipedia.org/wiki/Methane_clathrate https://en.wikipedia.org/wiki/Methane_clathrate [5] https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere#Anthropogenic_CO2_emissions https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_at... [6] https://en.wikipedia.org/wiki/Ocean#Geography https://en.wikipedia.org/wiki/Ocean#Geography [7] https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html