[Last Glacial Maximum pattern effects reduce climate sensitivity estimates]

Abstract

Here, we show that the Last Glacial Maximum (LGM) provides a stronger constraint on equilibrium climate sensitivity (ECS), the global warming from increasing greenhouse gases, after accounting for temperature patterns. Feedbacks governing ECS depend on spatial patterns of surface temperature (“pattern effects”); hence, using the LGM to constrain future warming requires quantifying how temperature patterns produce different feedbacks during LGM cooling versus modern-day warming. Combining data assimilation reconstructions with atmospheric models, we show that the climate is more sensitive to LGM forcing because ice sheets amplify extratropical cooling where feedbacks are destabilizing. Accounting for LGM pattern effects yields a median modern-day ECS of 2.4°C, 66% range 1.7° to 3.5°C (1.4° to 5.0°C, 5 to 95%), from LGM evidence alone. Combining the LGM with other lines of evidence, the best estimate becomes 2.9°C, 66% range 2.4° to 3.5°C (2.1° to 4.1°C, 5 to 95%), substantially narrowing uncertainty compared to recent assessments.

https://www.science.org/doi/10.1126/sciadv.adk9461

[Is the Atlantic Overturning Circulation Approaching a Tipping Point?]

Article Abstract

The Atlantic Meridional Overturning Circulation has a major impact on climate, not just in the northern Atlantic but globally. Paleoclimatic data show it has been unstable in the past, leading to some of the most dramatic and abrupt climate shifts known. These instabilities are due to two different types of tipping points, one linked to amplifying feedbacks in the large-scale salt transport and the other in the convective mixing that drives the flow. These tipping points present a major risk of abrupt ocean circulation and climate shifts as we push our planet further out of the stable Holocene climate into uncharted waters.

https://tos.org/oceanography/article/is-the-atlantic-overturning-circulation-approaching-a-tipping-point

[Model Output Discussion - Spring Has Sprung]

A good example of evaporative cooling over Devon yesterday

[Autumn & Winter 2023---2024 Stratospheric Polar Vortex. Events, Analysis, Discussions AND Outlooks]

The current warming at 10mb illustrated on the 00 at Orland in Norway

[Moans, ramps and banter]

I think serious consideration should be given to the possible temporary closure of the mod. thread as a humane gesture to end the suffering. 

[Model Output Discussion - Spring Has Sprung]

 Addicks Fan 1981 Signals do not lead the models and to say this rather makes a mockery of 70 odd years of model development. The sun drives the models via Atmospheric/ Oceanic interactions  using mathematical and physical equations and the teleconnections are part of this complex evolution. And of course forecasting. This is of course a very short and simplistic explanation.

[Moans, ramps and banter]

I notice that over in the mod. thread a relative newcomer to the thread has made the rhetorical comment , "Seriously how can any model promoting cold weather now be a good thing". There is of course no intelligent answer to this.

[Model Output Discussion - Spring Has Sprung]

 Met4Cast I wasn't aware that I was suggesting that knowledge in itself is a bad thing. What I was suggesting is that posting comments on teleconnections, Stratosphere/Troposphere interactions and synoptic meteorology all in the model discussion thread, is in my humble opinion operation overload and asking a lot from many punters, including myself.. And there really is no need for the separate threads in that case. I will leave it there as I realise my opinion is not welcome in here

[Model Output Discussion - Spring Has Sprung]

Why should this thread become even more filled with teleconnections and Stratosphere talk? There are separates threads for those subjects. It is almost as if synoptic meteorology, and all the interesting complexities of that, is a no go area. Without this being addressed adequately I am not sure how punters relatively new to interpretating models can possible get to grips with it. 

[Moans, ramps and banter]

I am very saddened to note the the air of despair and desperation that has crept into the Mod thread over the last few days. 

[Model banter and emotions]

Climate Change would appear to be hastening the redundancy of the chasing cold thread............it just doesn't bear thinking about  

[Model Output Discussion - Spring Has Sprung]

 Flub136 I do not think this a true representation of the warming

An important character of sudden warming is its downward propagation from 45 km into the lower stratosphere. This feature is not zonal in character, but has nonzonal structure, with a planetary wave tilting westward with height. In the middle latitudes, warming in the stratosphere (40 km) is followed by cooling in the mesosphere (65 km). Simultaneously, the opposite occurs in low latitudes, with stratospheric cooling and mesospheric warming, but the magnitude of the changes in the lower latitudes is one order less compared to that noted in higher latitudes

[Model Output Discussion - Spring Has Sprung]

 Neilsouth There is a problem with pinning down the detail at this range as it the start of pattern change. All one can say at the moment is it is likely to be cool and breezy (depending on where the dig is)  and with a wave on the front crossing the south late on the 24th according to the gfs. Not very helpful I'm afraid

[Model Output Discussion - Spring Has Sprung]

 Weatherman_93 That's a bit like expecting a vegetarian to salivate over a fillet steak

[Model Output Discussion - Spring Has Sprung]

Not that the my opinion is worth diddly squat in here but the development of yet another Nor'easter  and it's subsequent track is having ramifications downstream regarding HP amplification.

[Moans, ramps and banter]

A touch of Nat this morning

 

[Moans, ramps and banter]

I've just noticed that there is new 'Post Mortem' thread. and I came quite faint for a moment assuming it was the last rites of the mod thread 

[Moans, ramps and banter]

I have to say there is an awful whiff of desperation in the air.............time to break out the Prozac 

[Model Output Discussion - Spring Has Sprung]

Good to see that the mid Feb. amplification eases appreciably by the beginning of March.

[Model Output Discussion - Spring Has Sprung]

 johncam Well I have no idea on the altitude variations but suffice it to say the snow is along the leading edge of the front so obviously dependant on the position/orientation of it

 

 

[Model Output Discussion - Spring Has Sprung]

Not for the first time, and I'm sure it wont be the last, but I sometime wonder what the punters in here want

[Moans, ramps and banter]

 RJBingham Totally irrelevant it it's not following the party line. 

[Moans, ramps and banter]

I see the UKMO has gone from favourite son to tosspot in 24 hours. 

[Moans, ramps and banter]

Interesting to note that we are only on page 30 in the mod thread after a week. During periods of mass hysteria this landmark would be reached whilst making a cup of coffee. I'm taking this, perhaps wrongly, that this is a signal that winter is over. Oh my..................................

[Model banter and emotions]

  @SLEETY

I can't believe winters over...........I'm totally gutted