2 00:00:07,513 --> 00:00:15,290 For atmospheric methane a greenhouse gas, we got to recycle the 3 00:00:15,290 --> 00:00:20,580 kitchen sink analogy yet again. But for CO2, it's more complicated. 4 00:00:20,580 --> 00:00:22,540 If we're going to use the kitchen sink analogy to 5 00:00:22,540 --> 00:00:27,040 understand, we have to do some construction work here. 6 00:00:27,040 --> 00:00:29,470 This is what it would look like. 7 00:00:29,470 --> 00:00:32,050 The atmosphere would be a sink. 8 00:00:32,050 --> 00:00:32,780 And there'd be 9 00:00:32,780 --> 00:00:37,540 a line coming into it as before. 10 00:00:37,540 --> 00:00:41,400 But then there are those other sinks that are kind of connected to it 11 00:00:41,400 --> 00:00:46,890 by these tubes that run from one to the next, sideways. 12 00:00:47,910 --> 00:00:53,160 The fossil fuel, carbon is a source 13 00:00:53,160 --> 00:00:57,940 to the atmosphere there. And it raises the water level 14 00:00:57,940 --> 00:01:02,800 in this atmosphere sink way up. And the first thing that will happen is 15 00:01:02,800 --> 00:01:08,250 that the water will run from this middle sink into those two other sinks. 16 00:01:08,250 --> 00:01:11,450 I've drawn these other sinks as much bigger than the atmosphere sink. 17 00:01:11,450 --> 00:01:13,860 Because that's the way it is in the real world. 18 00:01:13,860 --> 00:01:17,890 What happens then is that the amount of carbon in the land reservoir, maybe 19 00:01:17,890 --> 00:01:23,960 and in the ocean reservoir certainly, will rise as a result of this 20 00:01:23,960 --> 00:01:27,840 fossil fuel carbon spreading out to those other reservoirs. 21 00:01:27,840 --> 00:01:35,140 And then there is also the steady drip, drip of water coming into this 22 00:01:35,140 --> 00:01:40,920 sink which would represent the volcanic degassing of the earth and this is the 23 00:01:43,270 --> 00:01:47,410 consumption of CO2 back to the solid earth 24 00:01:47,410 --> 00:01:52,480 by the weathering reaction, and so when this all of these 25 00:01:52,480 --> 00:01:56,340 sinks have a water level which is raised up compared to what it 26 00:01:56,340 --> 00:01:58,820 used to be, because we dumped a bunch of water into the center 27 00:01:58,820 --> 00:02:05,730 sink, they will eventually all settle back to the original equilibrium water level. 28 00:02:05,730 --> 00:02:09,090 In a very long time so there's different stages 29 00:02:09,090 --> 00:02:12,810 to the response to a CO2 edition here. 30 00:02:12,810 --> 00:02:15,710 First it spreads out and the whole 31 00:02:15,710 --> 00:02:18,900 thing relaxes back to an equilibrium. 32 00:02:22,250 --> 00:02:27,450 If we look at the airborne fraction of 33 00:02:27,450 --> 00:02:32,740 a slug of carbon that's added to the atmosphere it starts out at at zero. 34 00:02:34,420 --> 00:02:39,910 And then we'll call this the fossil fuel era when the CO2 is rising, and 35 00:02:42,690 --> 00:02:46,540 at the peak, about half of the CO2 36 00:02:46,540 --> 00:02:48,870 that had been emitted would be in the atmosphere. 37 00:02:48,870 --> 00:02:50,620 That's where we are today actually. 38 00:02:50,620 --> 00:02:54,220 If we were to stop emitting carbon dioxide to the atmosphere today, we would 39 00:02:54,220 --> 00:02:58,770 be right here, with about half of the carbon we ever put, in the atmosphere. 40 00:02:58,770 --> 00:03:02,200 Or if we stop in the year 2100, or whenever, it'll 41 00:03:02,200 --> 00:03:07,420 be about 50%, given how quickly we're adding the CO2. 42 00:03:07,420 --> 00:03:14,040 Then the recovery can commence. There will be a fairly fast 44 00:03:14,040 --> 00:03:19,910 draw down of the atmosphere CO2 on a time scale of centuries 45 00:03:19,910 --> 00:03:25,310 governed by the thousand year circulation time scale of the ocean. 46 00:03:25,310 --> 00:03:30,220 And that will draw the CO2 down fairly fairly far. 47 00:03:30,220 --> 00:03:34,180 It won't recover all the way to the 48 00:03:34,180 --> 00:03:38,570 original atmospheric C02 concentration, 49 00:03:38,570 --> 00:03:41,880 because this sink is bigger than that, but it's not infinitely bigger than that. 50 00:03:41,880 --> 00:03:48,440 And so the atmosphere still gets some. The next stage is when calcium 51 00:03:48,440 --> 00:03:55,260 carbonate dissolves to make carbonate ion, 52 00:03:55,260 --> 00:03:59,140 which essentially replenishes the carbonate ion stock 53 00:03:59,140 --> 00:04:03,148 in the ocean. This is a neutralization stage. 54 00:04:03,148 --> 00:04:06,890 This calcium carbonate is an antacid, and 55 00:04:06,890 --> 00:04:10,410 it's neutralizing the acid of the CO2, and 56 00:04:10,410 --> 00:04:12,590 when it does that it replenishes the carbonate 57 00:04:12,590 --> 00:04:16,950 ion, which as the reaction partner of CO2. 58 00:04:16,950 --> 00:04:19,570 It's like anti-CO2. 59 00:04:19,570 --> 00:04:24,240 when you replenish that carbonate ion, you allow the ocean to take up more, a little 60 00:04:24,240 --> 00:04:25,770 bit more CO2. 61 00:04:25,770 --> 00:04:30,140 Because you're restoring the chemical buffer of the ocean. 62 00:04:31,420 --> 00:04:35,650 This process takes a few thousand years. 63 00:04:35,650 --> 00:04:41,960 And it draws the CO2 down a little further, still not all the way to 64 00:04:41,960 --> 00:04:47,420 the initial value, but down to 10% or so of the CO2. 65 00:04:47,420 --> 00:04:49,910 And the last bit 66 00:04:49,910 --> 00:04:55,680 is this very long recovery due to the CO2 weathering thermostat, 67 00:04:55,680 --> 00:05:01,430 which because the fluxes are so low, 0.1 gigatons per year is the weathering rate 68 00:05:01,430 --> 00:05:08,200 of igneous rocks, it will take a very long time for the ultimate recovery. 69 00:05:08,200 --> 00:05:13,860 There's kind of a peak and a long tail to the CO2. 70 00:05:13,860 --> 00:05:15,160 As opposed 71 00:05:15,160 --> 00:05:19,360 to methane, which is just a simple single exponential decay, 72 00:05:19,360 --> 00:05:24,134 this is mathematically, you would describe this as the sum 73 00:05:24,134 --> 00:05:28,301 of several exponential terms, if that makes any sense to you. 74 00:05:28,301 --> 00:05:32,060 If not, you can just look at the artwork.