We've done a major update of our @CarbonBrief CMIP6 explainer to include the latest ScenarioMIP results; up to 36 different CMIP6 models included now, with between 28 and 35 models available in each of the "Tier 1" scenarios (2.6, 4.5, 7.0, and 8.5): carbonbrief.org/cmip6-the-next… 1/8
Here are the latest warming projections (late 21st century vs preindustrial) from CMIP6 models. Note that SSP1-1.9 is included as it has 12 models available, but others (3.4, 6.0) are not shown as they still have very few (< 10) models reporting. 2/8
Some notable changes: the SSP1-1.9 scenario which was designed to limit warming to 1.5C actually succeeds in doing that in the multimodel mean (which was not the case when we had fewer model runs in our initial analysis). Similarly, SSP1-2.6 MMM (barely) limits warming to 2C. 3/8
Its illustrative to compare the CMIP6 model results to similar scenarios run in CMIP5. Note that SSP4-6.0 results are not shown here due to the very small number of models reporting so far: 4/8
Generally speaking, there is a lot of overlap in the model ranges, but the CMIP6 multimodel mean is around 0.3C to 0.4C warmer by 2100, reflecting the higher sensitivity of some of the new models. 5/8
Turning to historical runs, here is the updated hindcast plot, showing quite similar overall performance to CMIP5. 6/8
That said, the CMIP6 multimodel mean does project a bit faster warming over the last 30 years on average than CMIP5, and around 16% faster than whats been observed: 7/8
Finally, here are the equilibrium climate sensitivities of the CMIP6 models; those in yellow are higher than the IPCC AR5 "likely" range of 1.5C to 4.5C per doubling CO2: 8/8

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More from @hausfath

4 Nov
Ambitious climate policy is going to be a major challenge in a divided government with a conservative court. But that doesn't mean we can't make real progress over the next four years.

A short thread: 1/7
We can continue to make clean energy cheap. There is a strong bipartisan consensus for things like ARPA-E and more spending on RD&D, which is particularly important outside the power sector where clean energy alternatives are less readily available. 2/7
We can still likely pass some big infrastructure bills, modernizing our power grid, enhancing our resiliency to climate change, and create jobs in the process. 3/7
Read 8 tweets
20 Oct
We (@Peters_Glen and I) have a new letter in the Proceedings of the National Academy of Sciences responding to a recent article by Schwalm et al on whether or not the RCP8.5 scenario is appropriate to use for near-term emissions (through 2050): pnas.org/content/early/… 1/15
Their original article suggested that RCP8.5 best matched historical emissions and what they identified as likely future emissions based on the IEA WEO fossil emission data and their own land use assumptions, at least through 2030 (and still reasonably close through 2050): 2/15
We point out that when you only look at fossil emissions (e.g. fossil fuels and industry) this is not the case; IEA projections are much more in line with RCP4.5 or RCP6.0: 3/15
Read 16 tweets
19 Oct
Today I published an op-ed in Politico with @atrembath on why @JoeBiden and @KamalaHarris are right to be skeptical of a fracking ban. It risks reviving coal when we need to phase it out ASAP and could perversely slow clean energy if not done carefully politico.com/news/agenda/20… 1/
As an aside, I really wish op-ed departments would stop rewriting headlines to make them more edgy without your permission. The title we submitted "Why Biden and Harris Are Right to Be Skeptical of a Fracking Ban"... 1.5/13
The op-ed is in part a distillation of this exceedingly long twitter thread the other week, so I'd suggest checking that out for details if you haven't seen it yet: 2/13
Read 14 tweets
14 Oct
So, this new paper in Nature has a rather misleading statement in the abstract. It says ecosystem restoration could "sequester 299 gigatonnes of CO2—30% of the total CO2 increase in the atmosphere since the Industrial Revolution". 1/3
However, 299 GtCO2 is only ~15% of human emissions (~2000 GtCO2) since the industrial revolution.

Sequestering 299 GtCO2 would only reduce atmospheric CO2 concentrations by 15%, not 30%. The airborne fraction that applies to our emissions also applies to negative emissions. 2/
This is the same mistake that the Bastien et al paper in Science made last year, conflating sequestration potential with the perturbation of atmospheric CO2 without accounting for sinks. 3/3
Read 5 tweets
9 Oct
A lot of the climate section of the VP debate focused on hydraulic fracturing (e.g. fracking). Its a complex subject – one that I've published a few papers about – and worthy of an exceedingly long twitter thread.

For more, read on! 1/
First, a bit of background about the debate. Fracking primarily occurs on privately owned land, and states rather than the federal gov't have primary jurisdiction over it. That said, the fed gov't can regulate it in some ways (e.g. rules around flaring or fugitive methane). 2/
Fracking is used to produce both oil and natural gas by fracturing shale rocks deep underground. When combined with horizontal drilling it allows for cost-effective extraction of both. 3/
Read 30 tweets
29 Sep
Lets talk a bit about forest management. There is growing acknowledgement among (some) policymakers that we need to tackle the combination of climate change, fuel buildup in our forests, and development in high-risk wildland urban interface areas.

A thread: 1/15
First of all, we all acknowledge that climate change has played a major role in making wildfires worse. Human emissions of greenhouse gases have increased spring and summer temperatures by around 2C in the Western U.S. over the past century. 2/15
This has extended both the area and time periods in which forests burn; in parts of California, fire season is now 50 days longer. The recent NCA4 suggested that about half the increase in burned area in the Western U.S. since 1980s can be attributed to a changing climate. 3/15
Read 15 tweets

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