In the Times yesterday, we read the following:

The jet stream — the powerful transatlantic wind that dominates British weather — is being shrunk by climate change, scientists say.

Climate change shrinks many things: the US economy, fisheries, fish, chips, Salamanders, wasps, tropical moths, plankton (could they get much smaller?), mountain goats, the Winter snowpack, the Sahara Desert, oyster habitat in California, the ranges of Adelie Penguins and bumble bees and Sweden’s tallest mountain. In fact, probably the only thing which climate change doesn’t shrink is hurricanes, which are becoming ginormous and threatening to gobble up huge areas of the US. Note also how climate change obligingly shrinks mountain goats and mountains – meaning the poor dimininutive critters won’t feel so overwhelmed by their environment because as they shrink, it shrinks also. How sweet. I guess that’s what you call #ClimateJustice for small(er) furries. But anyway, we can now add the Jet Stream to that long list above, courtesy of research scientist Tim Woollings:

Tim Woollings, associate professor of atmospheric physics at Oxford University, who has published a new book, Jet Stream, said: “The planet is warming rapidly due to humanity’s greenhouse gases. It means the whole of the Earth’s tropical belt is likely to expand, pushing the jet stream north so it shrinks in size and accelerates.”

The warning comes as greenhouse gas levels in the atmosphere hit a new high, keeping Earth on track for global temperature rises of 4C-5C by 2100. This weekend CO 2 levels reached 410 parts per million (ppm) at one global reference laboratory in Mauna Loa, Hawaii, and 414ppm at another in Alaska. Such figures are a huge rise on the 350ppm seen in 1990.

Apparently, this “means that Britain is at growing risk of more violent storms in winter and searing heatwaves in summer”.

Woollings suggests that, as the world warms, the jet stream will spend more of the winter across the British Isles and go further into Europe, letting storms keep their power as they reach the UK.

In summer it is likely to shift further to the north than now, opening Britain to hot air from the tropics.

Scientists have long been reluctant to link weather events to climate change but, said Woollings, the number of extremes means connections can be made. He cited the stormy winter of 2013-14 as the first evidence that the jet stream was altering.

Reluctant? Who is he kidding? They’re falling over themselves to attribute extreme weather to climate change. They can’t get in there quick enough!

Now this is all very well but what the Times doesn’t tell you in its eagerness to convince readers that heatwaves in summer and storms in winter are heading their way is that this is just another hypothesis about what might happen to the jet stream due to GHG warming and it is a hypothesis which relies upon a predicted consequence of GHG warming which has not been observed, despite the best efforts of scientists to torture the data in order to claim that it has been observed. The predicted consequence is accelerated warming in the tropical troposphere, the so called tropospheric tropical ‘hot spot’, which has remained annoyingly elusive.

Woolings explains his hypothesis in more detail at the Nonversation:

Scientists are however increasingly confident that important changes are afoot in the tropics. Driven by the vast quantities of energy pouring in from the Sun directly overhead, these are the great powerhouses of Earth’s climate.

Over the past few years, it has become apparent that at high altitudes, the Earth’s tropical regions are heating up more quickly than the rest of the world. At least partly because of this, the tropical regions of the atmosphere have been widening, expanding ever so slightly away from the equator, and impinging more on the jet stream.

Woolings’ link which he uses to justify his claim that the tropical atmosphere is heating faster than the rest of the world goes to a 2013 paper entitled ‘Revisiting the controversial issue of tropical tropospheric temperature trends‘ by four authors including Stott of the Met. He gets around does Peter Stott. Popping up here, there and everywhere in scientific defence of the climate worrier culture. The abstract says:

Controversy remains over a discrepancy between modeled and observed tropical upper tropospheric temperature trends. This discrepancy is reassessed using simulations from the Coupled Climate Model Inter‐comparison Project phase 5 (CMIP 5) together with radiosonde and surface observations that provide multiple realizations of possible “observed” temperatures given various methods of homogenizing the data. Over the 1979–2008 period, tropical temperature trends are not consistent with observations throughout the depth of the troposphere, and this primarily stems from a poor simulation of the surface temperature trends. This discrepancy is substantially reduced when (1) atmosphere‐only simulations are examined or (2) the trends are considered as an amplification of the surface temperature trend with height. Using these approaches, it is shown that within observational uncertainty, the 5–95 percentile range of temperature trends from both coupled‐ocean and atmosphere‐only models are consistent with the analyzed observations at all but the upper most tropospheric level (150 hPa), and models with ultra‐high horizontal resolution (≤ 0.5° × 0.5°) perform particularly well. Other than model resolution, it is hypothesized that this remaining discrepancy could be due to a poor representation of stratospheric ozone or remaining observational uncertainty.

They tortured the data. Alas, the discrepancy between observed tropospheric warming vs. that predicted by models is still apparent as shown by Christy and by McKitrick and Vogelsang. This means that Woolings’ idea is an interesting hypothesis not currently backed up by data. Indeed, not only this, but the fact that the jet stream, in contrast to becoming more powerful and straighter (zonal) has apparently given rise to an increase in extreme weather events in the 21st century precisely because it has tended to be weaker and more meridional. This has been much remarked upon by climate activists, scientists and the alarmist press and presented as evidence for the correctness of Jennifer Francis’ hypothesis that Arctic warming has weakened the jet stream. Woolings is not convinced by this alternative hypothesis.

Some have suggested that the rapidly warming Arctic is weakening the jet, by reducing the temperature contrast between the tropical and polar air to either side of it. As a result, the jet meanders more to the north and south, and these meanders can remain fixed over one location for longer – as happened when the “Beast from the East” placed much of Northern Europe under a bitter chill.

There are certainly some interesting ideas here, but many still do not find the logic compelling, and more convincing evidence from observations and computer models will be needed for these theories to become widely accepted.

Personally, I’m not convinced by either. There certainly is a battle for the jet stream but it’s not raging overhead, as suggested by Woolings at the Con, it’s raging in climate alarmist world to see who can ‘prove’ first that global warming is altering the jet stream ‘dangerously’ to give us more frequent and severe extreme weather, in both winter and summer.