2024 Global Carbon Budget

The 2024 Global Carbon Budget has been out for a while now, but I thought it would be helpful to show the results of this update now along with the 2024 "year in review" type posts. The data included in the report goes from 1750 to 2023, since the report was published before the end of 2024. Below FFI stans for fossil fuels and industry and LUC stands for land use change. I'm not including uncertainties in my graphs below for the sake of keeping the graphs readable, but the uncertainties are discussed in the report linked at the bottom of this post.

Carbon emissions continue to increase, though rates have flattened over the last decade or so. The bad news is that 2023 experienced record high emissions, so we haven't reversed the trend towards decreasing emissions yet. Here are graphs showing this from 1850 and 1958 (when the Keeling Curve begins.

Human carbon emissions are mirrored by the land and ocean sinks plus atmospheric growth, such that on average, human emissions equals equals the growth of carbon in the ocean, land and atmosphere. This can be shown graphically below. I took the atmospheric growth in GtC (blue) and plotted it with the total land/ocean sinks subtracted from human emissions (red). As you can see, sometimes red is higher than blue and sometimes blue is higher than red, but they are both following roughly the same trend. In other words, natural and seasonal variability can affect the balance for any given year, but overall, human emissions is causing the increase in CO2.

Here's the budget's accounting for cumulative human emissions and sinks + atmospheric growth. Total human emissions are 718.3 GtC (494.6 GtC FFI and 223.7 GtC LUC) and sinks total 438.3 GtC (194.3 GtC Ocean and 244.0 GtC land). Atmospheric growth totaled 304.1 GtC. This means that human sources totaled ~720 GtC and sinks + atmosphere totaled ~740 GtC, with a budget imbalance of 23 GtC, so the budget nearly balances.

And since studies show warming increases linearly with cumulative emissions, I plotted HadCRUT5 with cumulative emissions below and found a slope of 1.8°C per 1000 GTC. This is consistent with teh IPCC: "the AR6 reports the TCRE likely range as 1.0°C to 2.3°C per 1000 PgC in the underlying report, with a best estimate of 1.65°C."[1] To be clear, 1000 PgC = 1000 GtC = 1 TtC. This implies a warming rate of 0.018°C per 10 GtC, which is roughly equivalent to our annual emissions. Since we're currently at a long term mean of ~1.31°C above 1850-1900, this means we're on track to hit 1.5°C in about 10 years with continued emissions of 10 GtC/yr. 

When debunking a ridiculous paper published a few years ago, I decided to try to quantify changes in carbon sinks and the airborne fraction as CO2 increases. This is hard to do from the carbon budget data because the data is given annually, and in the early years of the record, CO2 remains the same concentration for multiple years while in recent decades, CO2 increases multiple ppm per year. This added a bias to a graph produced in that paper. To correct for this, I binned CO2 values in 10 ppm increments and plotted the change in those bins. There's probably a better way to do this, but I think it was a good, simple way to show that the land and ocean sinks are becoming less efficient and the airborne fraction is increasing as atmospheric CO2 increases.

References:

[1] Friedlingstein, P., O'Sullivan, M., Jones, M. W., Andrew, R. M., Hauck, J., Landschützer, P., Le Quéré, C., Li, H., Luijkx, I. T., Olsen, A., Peters, G. P., Peters, W., Pongratz, J., Schwingshackl, C., Sitch, S., Canadell, J. G., Ciais, P., Jackson, R. B., Alin, S. R., Arneth, A., Arora, V., Bates, N. R., Becker, M., Bellouin, N., Berghoff, C. F., Bittig, H. C., Bopp, L., Cadule, P., Campbell, K., Chamberlain, M. A., Chandra, N., Chevallier, F., Chini, L. P., Colligan, T., Decayeux, J., Djeutchouang, L., Dou, X., Duran Rojas, C., Enyo, K., Evans, W., Fay, A., Feely, R. A., Ford, D. J., Foster, A., Gasser, T., Gehlen, M., Gkritzalis, T., Grassi, G., Gregor, L., Gruber, N., Gürses, Ö., Harris, I., Hefner, M., Heinke, J., Hurtt, G. C., Iida, Y., Ilyina, T., Jacobson, A. R., Jain, A., Jarníková, T., Jersild, A., Jiang, F., Jin, Z., Kato, E., Keeling, R. F., Klein Goldewijk, K., Knauer, J., Korsbakken, J. I., Lauvset, S. K., Lefèvre, N., Liu, Z., Liu, J., Ma, L., Maksyutov, S., Marland, G., Mayot, N., McGuire, P., Metzl, N., Monacci, N. M., Morgan, E. J., Nakaoka, S.-I., Neill, C., Niwa, Y., Nützel, T., Olivier, L., Ono, T., Palmer, P. I., Pierrot, D., Qin, Z., Resplandy, L., Roobaert, A., Rosan, T. M., Rödenbeck, C., Schwinger, J., Smallman, T. L., Smith, S., Sospedra-Alfonso, R., Steinhoff, T., Sun, Q., Sutton, A. J., Séférian, R., Takao, S., Tatebe, H., Tian, H., Tilbrook, B., Torres, O., Tourigny, E., Tsujino, H., Tubiello, F., van der Werf, G., Wanninkhof, R., Wang, X., Yang, D., Yang, X., Yu, Z., Yuan, W., Yue, X., Zaehle, S., Zeng, N., and Zeng, J.: Global Carbon Budget 2024, Earth Syst. Sci. Data Discuss. [preprint], https://doi.org/10.5194/essd-2024-519, in review, 2024.
https://essd.copernicus.org/preprints/essd-2024-519/