Bishop Hill Tail wind
Feb 10, 2016 Climate: Models Climate: WG2 
I once faced off against Paul Williams of Reading University in a radio debate. He came across as a pretty rational kind of guy and we had a nice exchange of emails afterwards. But I have to say that his most recent paper is one of those ones that make you despair with their sheer futility. Here's the BBC take on it.
Flights from the UK to the US could take longer due to the changes in the climate, according to a new study.
Global warming is likely to speed up the jet stream, say researchers, and slow down aeroplanes heading for the US.
While eastbound flights from the US will be quicker, roundtrip journeys will "significantly lengthen".
It's published in Environmental Research Letters, which is usually not a good sign. The authors apparently fed "synthetic atmospheric wind fields generated from climate model simulations into a routing algorithm of the type used operationally by flight planners" and deduced that westbound transatlantic flights were going to take longer while eastbound flights will be faster. But, almost inevitably, the losses are expected to outweight the gains.
I wonder what evidence there is that GCMs can predict, or even hindcast, changes in wind speeds in a warming world?
Reader Comments (109)
ATTP:
'Probably that they're based on some pretty fundamental laws of physics'.
Beware the words 'based on'
As weaselly as you can get.
Is it really this bad where they have to lump everything in to a single big scary number???
BTW, I used to hold my PPL in NZ (having passed the CPL law, navigation and weather exams back in the bad old days of the 1% rule).
So are these clowns suggesting that the increase of 1m35s per flight is from the moment engines are turned on to the moment they are turned off or is it the moment it's wheels up to wheels down?
How the hell do you even measure such an a small amount of time in a flight given there are so many fecking variables that can and do alter flight times??
So what if they are claiming 3 gazillion extra hours of flight per aircraft. At the end if the day it is still only a claimed extra 90 seconds per ENTIRE round trip! Correct me if I'm wrong but there really are more important things we should be dealing with in this world (like rampant Islamic terrorism).
Mailman
"A major limiting factor is likely to be computational resources.."
Of course it is. Computers are just so slow nowadays, aren't they..?
Others have pointed out that total journey time is what counts (in terms of time) and, of course, stupid Green taxes and Chancellors' kleptomania have huge impacts on costs.
But let's take some fairly well reported demographic statistics and wildly extrapolate.
So by 2090, we 'might' be living under Sharia law both in the UK and USA. Noting also the Islamic disregard for Elfen Safety, Inshallah, we won't need security and all sorts of other tedious time wastes.
So much, much quicker if a little more exciting.
But few on here will be much bothered either way.
Certainly, arrogant psyentists with their grant applications will be very much an endangered species.
Apologies if someone has already made this point, but is this research or just algebra?
An object moving along a distance L and back again at a constant velocity v (disregarding sign) will take a total time 2L/v. Whereas an object moving along a distance L at velocity v+a, and then back at a velocity v-a, will take a total time L/(v+a) + L/(v-a). With a bit of algebra this can be expressed as 2L/v(1 - a^2/v^2). Since for real values a^2/v^2 is always positive, v(1 - a^2/v^2) is always smaller than v, and the time taken is therefore longer. If a stronger jetstream accelerates and retards flights by roughly the same amount, it will therefore tend to increase 2-way flight times. Though this is slightly counter-intuitive, you can't argue with algebra.
DavidB -
Yes, the results can be largely predicted by algebra. The authors' equation 3 is much the same as what you wrote, except they expanded in a power series, writing t = 2 d/U * (1 + w^2/U^2 + ...). [Your L = their d = distance; your v = their U = airspeed; your a = their w = windspeed.] Their next equation expresses the fractional sensitivity to windspeed as:
dt/t = 2 w dw /U^2.
Their study is a little more sophisticated than mere algebra, though. They calculated the least-time paths based on wind fields at altitude, so distance and windspeed are not precisely constant, nor identical on the eastbound & westbound legs. Then assessed the expected future changes in windspeed (dw) according to GCMs, including the seasonal variation of w. When w is small (boreal spring & summer), there is a smaller effect, as one would expect from the equation above. In the end, they note that the average change in round-trip time is 1 min 35 sec using the simple algebraic equation, and 1 min 6 sec (0:33 to 1:51 by season) using the more sophisticated optimum routes.
Bish asked: "I wonder what evidence there is that GCMs can predict, or even hindcast, changes in wind speeds in a warming world?"
Isaac Held has a post showing how well the GFDL model agrees with observed wind speeds - particularly the difference between winter and summer. (The observations are from re-analysis and I don't know how much the re-analysis process makes observations of the jet streams look like model predictions, but the Figures are quite convincing.
I think a better response would be that these differences are trivial and a total waste of research dollars.
http://www.gfdl.noaa.gov/blog/isaac-held/2015/06/07/60-the-quality-of-the-large-scale-flow-simulated-in-gcms/
IIRC global warming is supposed to warm the high latitudes more than the tropics which should lead overall to less pressure differentials that drive the jet streams. So global warming should be less wind, not more.
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