Thread by @DrSimEvans

Last week for @CarbonBrief I estimated UK emissions fell 10.7% last yr, taking them to 51% below 1990 levels

Today, BEIS says it was an 8.9% drop in 2020, bringing us to 49% below 1990 levels

Why are these numbers (slightly) different?

THREAD 🧵

carbonbrief.org/analysis-uk-is…

TL;DR most of the difference between my estimate of UK emissions in 2020 & the official BEIS figure is due to revisions in the underlying energy & emissions data

For more detail, read on…

carbonbrief.org/analysis-uk-is…

Overall, our estimates are similar. We both said the drop last year was the fastest in at least 30yrs, due to Covid

And I'd say 49% still counts as "halfway" (per our headline last week) – splitting hairs to say otherwise

carbonbrief.org/analysis-uk-is…

(My analysis sparked vigorous debate about whether the UK target of net-zero by 2050 – & progress toward that goal – is meaningful or ambitious, given it excludes emissions from intl shipping / aviation & from imported goods & services. I won't revisit that debate here.)

Returning to my analysis, the difference between the CB and BEIS estimates was larger than in previous years, at 1.8 percentage points

(vs an average difference over the previous 10yrs of data of just 0.4 percentage points)

carbonbrief.org/analysis-uk-is…

In my piece last week I said one major source of uncertainty is the underlying energy & emissions data from BEIS, which is subject to revision…

…and there have, in fact, been some fairly significant changes to the latest emissions inventory (see chart)

gov.uk/government/sta…

Looking closer at those UK inventory changes, the biggest revisions are for land use & forestry, which in the new data is now barely considered a CO2 "sink"

🌲🌳🐄🚜🐑🌄

This alone accounts for most of the difference between old vs new UK emissions data

gov.uk/government/sta…

I'm trying to find out why estimated emissions from UK land use & forestry have changed so much

I don't *think* it's the big expected update to peatland methodology, as I'd understood that was going to make an even bigger difference

Could be wrong tho

carbonbrief.org/ccc-uk-must-cu…

There are also some notable changes in the inventory for "other GHGs" ie methane, nitrous oxide etc

I haven't got to the bottom of this either but NB the changes are not consistent, so are not to do with updating GWPs ("AR5 adjustment" due to come later)

gov.uk/government/sta…

Finally, there have been the usual revisions to the provisional 2020 vs latest BEIS energy use data

These changes were pretty small but noted here for completeness

Taken together, the energy & emissions data revisions account for most of the difference between my initial estimate (-10.7% in 2020) vs BEIS (-8.9%)

⏩Applying my original method to the revised data gives an updated CB estimate of -9.5%

I'll take that!

carbonbrief.org/analysis-uk-is…

Finally, one interesting nugget from BEIS is that residential emissions went up 7% last year, after accounting for the fact it was warmer than average

This big jump presumably reflects the increase in home working due to Covid, meaning more gas for heat

gov.uk/government/sta…