@PatrickTBrown31 Hi Patrick, those IPCC WG2 figures of mine show the range of outcomes, but do not show the extent of model agreement on the sign of change. Working Group 1 Ch 11 Fig 11.1 shows that even at +2°C, there's ≥80% agreement on increased extreme precip over most land areas in CMIP6 @PatrickTBrown31 Link to WG1 chapter 11 "Weather and Climate Extreme Events in a Changing Climate" ipcc.ch/report/ar6/wg1…

Excellent article by @hausfath et al

When are fastest-warming climate models useful?

1. risk assessment
2. for Global Warming Levels if timing not important

When not? If you're interested in the more likely rates of warming

Thread on this and GWLs ⤵️

nature.com/articles/d4158… IPCC no longer considers all models as equal

In AR6, other lines of evidence were used to assess likelihoods of different rates of future warming for each scenario of greenhouse gas increase

While many models project likely warming rates, several warm at unlikely fast rates

2/

What will the iconic @Keeling_curve graph of atmospheric CO2 concentrations need to look like in future if we're to limit global warming to 1.5°C?

The build-up of CO2 in the air has been accelerating

This build-up needs to slow within a few years, then stop & reverse

Thread⤵️ Our extended version of the Keeling Curve is based on the SSP1-1.9 scenario

With this scenario (light blue) the IPCC central estimate has warming reaching 1.5°C on average over 2021-2040, overshooting but returning below 1.5°C by the end of the century

ipcc.ch/report/ar6/wg1…

@flimsin @Peters_Glen @ClimateAdam @MichaelEMann @FrediOtto Yes, I was going to mention that more generally there is a misunderstanding that the political goals for limiting warming to round(fish) numbers (1.5C, 2C) represent some sort of physical threshold, beyond which feedbacks suddenly kick in or all is lost in some other way > @flimsin @Peters_Glen @ClimateAdam @MichaelEMann @FrediOtto And as a variant on that, some folk seem to think that there is some sort of physical significance to warming of 1.5C, 2C at smaller scales, eg. individual countries. These numbers were established as targets to keep *global* warming below (+2C) or to try to limit to (+1.5C)

@clivehbest @HG54 @Leigh_Phillips @CC_NoThanks @XRebellionUK @ziontree @afneil @ScientistsX 4C global warming by 2100 seems to be much more likely than a lot of people realise

It doesn't even need one of the highest emissions scenarios. RCP6.0 (considered likely with current policies) gives that much warming fairly near the middle of the range in our latest projections @clivehbest @HG54 @Leigh_Phillips @CC_NoThanks @XRebellionUK @ziontree @afneil @ScientistsX For RCP6.0 and current policies, see this from the Hausfather & Peters Nature comment

They label it 3C but that's the central estimate, & I don't think it accounts for uncertainties in carbon cycle feedbacks like the UKCP18 probabilistic projections do

nature.com/articles/d4158…

Are we on track to cause mass extinction of other species?

Yes

Huge numbers of species to be lost if we don't act now to change course

This includes improving conservation efforts and stopping global heating

Short thread⤵️ prompted by this new study

bbc.co.uk/news/science-e… Here's this week's paper by Andermann et al on human impacts on mammal extinctions

"Based on current trends, we predict for the near future a rate escalation of unprecedented magnitude"

"still a window of opportunity to prevent many species extinctions"

advances.sciencemag.org/content/6/36/e…

@PlanB_earth @IlanKelman @thetimes @bwebster135 I read the emails

Yes global warming of 4˚C this century is quite possible, & would bring massive risks to life & society (heatwaves, coastal & river flooding, drought etc)

Ilan does not seem to dispute that - he just says (correctly) that societal outcomes can't be predicted > @PlanB_earth @IlanKelman @thetimes @bwebster135 Ilan's right that the DARA claim of 400,000 deaths per year due to climate change can't be verified - they don't give the source. It's possible that they have mis-typed a reference as there's a similar one in their bibliography, but even that doesn't seem to support the number >

The latest forecast from the World Meteorological Organization @WMO, led by @metoffice, suggests that over the next five years there is a 24% chance of the global average temperature exceeding 1.5C above pre-industrial levels for at least one year

carbonbrief.org/guest-post-glo… This is a reminder of rising temperatures, but it would not mean that the long-term Paris goal to limit warming to 1.5C will have been breached

The 1.5C limit refers specifically to long-term human-caused warming and not the added effect of natural fluctuations in the climate

Extremely important to note the caution by the @metoffice scientist who actually led the development of this model:

“my first response is: why has the model done that? We are still in the stage of evaluating the processes driving the different response.”

theguardian.com/environment/20… I see that this scientist (Cath Senior, our Head of Understanding Climate Change) is not quoted until paragraph 16 of the article, whereas Johan Rockström (not a climate modeller, and not involved in developing, evaluating or using this model in any way) is quoted in paragraph 5

Good @edyong209 piece on science advice to UK govt:

"actual goal is same as that of other countries:

flatten the curve by staggering the onset of infections.

As a *consequence*, the nation may achieve herd immunity;

it’s a side effect, not an aim"

theatlantic.com/health/archive… The Coronavirus action plan, published on 3rd March, never even mentioned "herd immunity"

gov.uk/government/pub…

.@hausfath & @Peters_Glen correctly highlight that RCP8.5 *emissions* are not "business-as-usual"

BUT it's important to note that in Earth System models, the RCP8.5 CO2 *concentration pathway* can still arise from a lower emissions scenario (eg. SRES A1B) if feedbacks are strong @hausfath @Peters_Glen This is a very important point (which Zeke and Glen do make, but it seems to get overlooked)

Any particular emissions scenario can give rise to many different future concentration pathways, some rising faster and some slower, depending on the strength of carbon cycle feedbacks

We predict that in 2019, the annual mean CO2 concentration at Mauna Loa will be 411.3 ± 0.6 ppm

This is 2.75 ± 0.58 ppm higher than 2018 - a larger rise than most years in the record including the last two years, but not as large as 2015-2016

metoffice.gov.uk/news/releases/… The relatively large rise is due to record high anthropogenic CO2 emissions and a temporary weakening of land carbon sinks due to climate variability.

The record rise in 2015-2016 was due to the sinks being particularly weakened by the large El Nino event at that time.

This is the "Hothouse Earth" paper that was all over the news yesterday. pnas.org/content/early/… It is a "perspective" piece - basically an essay rather than new modelling or data analysis, in which the authors present an argument supported by existing literature. (Thread) The authors draw on a very diverse set of literature to paint a holistic picture of how a chain of feedback processes or events could *potentially* take place and lead to very large climate warming once a threshold is passed, and also how the risks of this could still be avoided.