Not sure if this is strictly factual, or where to put it so I put it here.
Is there a linear relationship between CO2 concentration in PPM and how much the temperature will go up, or is it more complex? Does every increase of 1 in the PPM of CO2 cause the temperature to go up by ~.0X degrees C, or is the relationship a lot more complex? Or as the concentration of CO2 goes up, does the temperature growth speed up or slow down instead of follow a linear relationship?
Has the amount of CO2 being released stabilized at about 2 PPM per year? Looking it up, I think the world has been adding about 2 PPM per year for the last few decades. Some nations are producing more, some are producing less and it seems to balance out (my understanding is that the US, pre-covid, was at CO2 production rates from the early 90s and our emissions peaked around 2005). So if that the predicted rate of increase, if we’re at 410 ppm now are we expected to be at around 570 ppm in 2100, or will the rate of how much CO2 we add grow, slow or stay the same?
If we are on track to be at about ~600ppm in 2100, what temperature increase would that be?
If the methane clathrate hypothesis is true and we end up dumping large amounts of methane into the atmosphere due to increased ocean temperatures, can we intentionally ignite the methane to turn it into CO2 which has less greenhouse effects?
What large scale geoengineering programs are possible to combat climate change? I know that planting large amounts of trees (or certain kinds of plants and weeds) to absorb CO2, or adding iron to the ocean to increase plankton levels, or using boats to create clouds over the oceans are being looked into.
Short answer because it’s late but we have to consider that global climate change is not only influenced by the direct effects of human emissions release but also by the feedback loop that we create. If we release enough greenhouse gases to melt permafrost, that in turn will also release methane by amounts we might even be able to accurately account for, and methane is an even stronger greenhouse gas than carbon.
What worries me now is ocean acidification. The oceans absorb the greenhouse gases but at a cost. I fear we’re about to observe (possibly in our lifetimes) a cataclysmic die off of marine life.
The key question is not about whether it’s linear or not, but precisely what the function is that relates CO2 increase to temperature rise. There are several versions of that equation, the most important of which is framed as “expected temperature rise at equilibrium after a doubling of CO2”. This is called equilibrium climate sensitivity (ECS) and modeling exercises over many decades have pinned it down to between 1.5 and 4.5 degrees Celsius. It was formerly stated to have a “most probable” value of about 3 deg C, but the IPCC no longer states a “most probable” value. This is still a pretty wide range, and all the uncertainties come about because of the relatively uncertain nature of climate feedbacks, such as reduced albedo from the melting of Arctic ice, and of course things like the methane emissions you mention, not just from undersea clathrates, but also from thawing permafrost.
While planting more trees and other such initiatives are a good idea, this is not what is typically meant by climate geoengineering. Most such schemes are in the “crackpot” category and many – like intentionally polluting the atmosphere with sulphate aerosols or whatever else – are downright dangerous. The IPCC scientific assessment on climate mitigation strategies doesn’t take them seriously.
There are a couple geo-engineering methods mentioned in the IPCC summary for policy makers as options for Carbon Dioxide Removal (CDR) - enhanced weathering and ocean alkalinization. For example, Project Vesta is proposing to mine and crush olivine rock and spread along warm coastal beaches to capture CO2 via ocean alkalinization. The chemistry behind it seems pretty sound, and a nice benefit is that it also helps offset ocean acidification, so IMO its viability largely comes down to cost and efficiency - on the face of it, mining, crushing and transporting rock to spread on beaches doesn’t particularly cheap, and the emissions associated with those processes also has to be taken into account. I think the project is targeting $20/tonne CO2e removed, but other estimates for enhanced weathering were looking more at the $60-200/tonne range (some of it is for terrestrial application/soil enhancement though, which may require more grinding than applying on beaches). Their goal also appears to be to have carbon removal in the range of 100+ Mt/yr when rolled out at full scale, so it would at best be a thin slice of the pie of overall carbon reductions required, though I have read some papers estimating the overall potential for enhanced weathering could be in the range of a few Gt/yr.
Yeah, there are various ideas being tossed around and experiments being done, some of which are non-crazy (but others, like injecting particulates into the atmosphere, are insanely dangerous). Another example is a company out in BC called Carbon Engineering that’s been experimentally making synthetic fuels from direct air capture of CO2 and hopes that the process will eventually be net carbon negative. Most of those projects are not likely to scale anywhere close to the extent necessary, and most of the serious science and engineering attention is still being directed to the elephant in the room, emissions reductions.
I might perhaps add to this, for the sake of clarity, that there is no uncertainty about the amount of heat energy that various greenhouse gases add to the atmosphere, and for CO2 it is indeed approximately linear over a fairly broad range around current levels. Indeed, for every GHG, there is a parameter that associates this thermal contribution to its atmospheric concentration, frequently referred to as the GHG’s radiative transfer code, which is a first-order approximation. The quantitative value of this thermal contribution is referred to as climate forcing, and is a measure of the thermal imbalance it creates in the earth’s energy budget.
However, this still doesn’t quantitively tell us what temperature rise will result from any given increase in CO2 or any other GHG concentrations, because of the vast myriad of climate feedbacks that also occur, both positive and negative (but mostly positive – that is, they amplify the warming effects of the GHG).
That can only work if you’re getting the energy needed to do that from a non-carbon source, and to work on a large scale, you’d need a large-scale non-carbon energy source. It would be much more productive to just use whatever that energy source is to replace current fossil fuel energy sources. Only after you’ve replaced almost all of the existing energy sources would direct capture into fuel start to make sense.
I don’t know if it’s always that straightforward. Being able to use the energy source directly still requires the ability to transport it to where the energy is needed, and match up the energy produced with the energy demand, timing wise. Since many renewable energy sources are highly variable, and often require significant land footprint that may be far away from large population centres, there can be significant cost to building storage and transmission to adapt the electrical grid to a high % of renewables. CO2 to fuels can be looked at as just another form of energy storage - so compared to batteries, electrolyzed hydrogen, pumped hydropower, compressed air storage, etc. It may, for example, be more efficient and cost-effective to put a big solar farm out in the middle of the desert, using the electricity to convert CO2 to fuels and transport that fuel via pipeline or truck, than to build a battery farm and new high-voltage transmission system. Or, perhaps, a tidal power plant on some remote rocky coast, where building transmission lines across difficult terrain would be prohibitively expensive but shipping liquid fuels would be economical. In its current state, its applications may be pretty niche, but there is no fundamental reason that atmospheric CO2 capture couldn’t be a good option to help deal with renewable energy sources with high amounts of variability.
@wolfpup basically answered this, so let me be slightly more pithy: no, it’s not linear. It’s almost certainly logarithmic. The first doubling (to ~560 ppm) will add x degrees temperation, and then the second doubling (to ~1120 ppm) will add x more degrees. X is likely to be around 3 degrees Celsius.
That said, it’s also more complex, because there are other greenhouse gases (methane, nitrous oxide, etc) in the mix and blah blah blah. But roughly logarithmic.
This one is too complicated to answer. To add one ppm to the atmosphere, you need to add 7.8 gigatons of CO2. We added 33.4 gigatons of CO2 (not to be confused with CO2e) to the atmosphere in 2019, and then a little over half of that was absorbed by ‘sinks’, primarily the oceans and terrestrial plants. So about 15 or so gigatons stayed in the atmosphere, which is why the concentration increased by ~2 ppm.
Will it stay at 2 ppm / year? It depends on how much we emit, which will hopefully peak soonish and not too much higher than where it is today. But no one really knows for sure. But it also depends on whether those sinks can keep absorbing at their current rates, or if they get saturated. The science on that question is very uncertain.
600ppm in 2100 is a little less than RCP 6, so you’d probably expect the heating to be a little less. Maybe a touch under 3 degrees C? But even if the CO2 concentration completely leveled out there, it would still continue to increase for some decades afterwards.
Yes, but in my clarification I was saying that the climate forcing associated with increases in CO2 is approximately linear (at least, within certain ranges), whereas you’re describing the temperature increase defined by climate sensitivity. It should also be noted the climate sensitivity is almost certainly not a constant, but very likely changes as the climate dynamics change. For example, it’s been conjectured that climate sensitivity will be a lot higher if there is a loss of the majority of polar ice cover.
There is, in fact, also a logarithm involved in computing a first-order approximation of climate forcing, but it’s the natural log of the ratio of the new CO2 concentration to a reference concentration. If you compare the resultant forcings from 600 ppm CO2 and 1200 ppm, over a reference value of 300 ppm, the doubled concentration results in almost exactly doubled forcing.
Understood. The OP’s question was specifically around the relationship between CO2 concentration and temperature - not forcing. Excluding other greenhouse gases, the first-order effect there is a logarithmic relationship. But - particularly as you go past the 1.5-2 degree zone - the real world could be much more complex, particularly if something like the clathrate gun fires, or there is a major change in albedo, or for a number of other potential reasons.
No, it’ll be too dilute. It will be reduced to CO2 naturally in the the atmosphere over time, which is why it has a much shorter lifetime in the atmosphere than CO2, but the only way to speed that up would be to have an ignition source ready over each bubble of methane popping on the ocean surface, which seems like an unrealistic approach.