Thread by @hausfath

Big news: recent CO2 emissions have been revised notably downward in the just-released @gcarbonproject dataset. The revisions – due to a major reassessment of land-use – suggest emissions have likely been flat rather than increasing over past decade: carbonbrief.org/global-co2-emi… 1/19

Global CO2 emissions come from a combination of fossil fuel emissions (~90% in recent years) and land use change (LUC) emissions (~10%) from deforestation and soil carbon loss. While fossil emissions have an uncertainty of +/- 5%, LUC emissions are much more uncertain. 2/

The Global Carbon Project (GCP) substantially revised their best estimate of LUC emissions in their newly released dataset. Rather than a 35% increase in LUC emissions since 2000 – as the data previously showed – the new version has a roughly 35% decrease instead. 3/

The GCB uses the average of three different bookkeeping models – H&N, BLUE, and OSCAR – to estimate LUC emissions. Previously these showed large disagreements, with BLUE showing large increases in net LUC emissions since 2000, OSCAR moderate increases and H&N moderate declines 4/

The new versions of these three datasets – which now use more accurate land-use data from satellite observations – have come into greater agreement, and all now show similar declines in recent years (though still differ in the absolute magnitude of LUC emissions): 5/

Despite these updates, large uncertainties remain. While the different datasets no longer disagree, there are still gaps and some factors (increased forest degradation, recent changes in deforestation rates in Brazil) might not be reflected well in the data. 6/

The researchers at the GCP caution that “It is too early to infer robust trends. More regional analysis is needed and accurate, high-resolution monitoring of land-use dynamics. Only then can we reduce the uncertainty around land-use emissions and their trends.” 7/

Past estimate of fossil CO2 emissions, by contrast, are mostly unchanged in the new GCP dataset. Emissions estimates were actually slightly increased by ~0.3 GtCO2 over the past few years, and were 0.7 GtCO2 greater than initial estimates of 2020 emissions. 8/

The GCP shows that fossil CO2 emissions have largely rebounded in 2021 from their pandemic-related lows in 2020, and will end up just 0.8% below the record highs of 2019. This rebound was much larger than many were predicting, driven by rapid and fossil-intensive growth 9/

While all major emitting countries and regions increased their emissions in 2021 compared to 2020, only China and India set new records – surpassing their 2019 emissions: 10/

This figure shows drivers of declining emissions between 2019 and 2020, and increasing emissions between 2020 and 2021 by country. While many countries had a similar increase in emissions in 2021, China actually increased its emissions in 2020 while others showed declines. 11/

We can also look at fuels – rather than countries – responsible for CO2 emissions over time. Here coal is the single largest source of emissions, followed by oil and gas. However, gas emissions have grown much more than oil or coal over the past decade (coal has declined): 12/

Here is how each fuel contributed to declines in 2020 and increases in 2021 emissions. While coal and gas have already returned to above 2019 emissions levels, oil is still well below pre-pandemic emissions, reflecting residual impacts on transportation. 13/

This means that if oil recovers to its pre-pandemic highs, we could see record global fossil CO2 emissions next year in 2022 even if coal and gas emissions remain flat. 14/

Finally, here is the full updated carbon budget, including both sources of emissions (fossil and LUC) and sinks (land, oceans, and atmosphere): 15/

The GCP projects that atmospheric CO2 concentrations will increase by around 2 ppm in 2021, from 413 ppm to 415 ppm. Around 47% of total CO2 emissions have remained in the atmosphere each year over the past decade, with the remainder being taken up by ocean and land sinks. 16/

The new updates to global CO2 emissions in the GCP substantially revise scientists’ understanding of global emissions trajectories over the past decade. The new data shows that global CO2 emissions have been flat – if not slightly declining – over the past 10 years. 17/

However, falling land-use emissions have counterbalanced rising fossil CO2 emissions, and there is no guarantee this will continue. These updates do not fundamentally change our climate picture; large declines in emissions – not just flattening – is needed to meet Paris goals 18/

For more details, see our coverage of the new @gcarbonproject report over at @CarbonBrief: carbonbrief.org/global-co2-emi… 19/

A quick reminder of what flat CO2 emissions mean for the climate:

https://twitter.com/hausfath/status/1456275917462917134