Claim: “The jet stream forms a boundary between the cold north and the warmer south, but the lower temperature difference means the winds are now weaker.

Relevance (1 = gold evidence, 0 = mined hard negative): 1
Passage: As the temperature difference between the Arctic and the equator decreases, ocean currents that are driven by that temperature difference, like the Gulf Stream, are weakening.

Relevance (1 = gold evidence, 0 = mined hard negative): 1
Passage: This in turn reduces the temperature gradient that drives jet stream winds, which may eventually cause the jet stream to become weaker and more variable in its course.

Relevance (1 = gold evidence, 0 = mined hard negative): 1
Passage: If two air masses, one cold and dense to the North and the other hot and less dense to the South, are separated by a vertical boundary and that boundary should be removed, the difference in densities will result in the cold air mass slipping under the hotter and less dense air mass.

Relevance (1 = gold evidence, 0 = mined hard negative): 1
Passage: Therefore, the strong eastward moving jet streams are in part a simple consequence of the fact that the Equator is warmer than the North and South poles.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: The polar vortex is a whirlwind of especially cold, dense air forming near the poles that is contained by the jet stream, a belt of fast-flowing winds that serves as a boundary between cold polar air and the warmer air of other hemispheres.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: This jet stream instability brings warm air north as well as cold air south.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: Because the power of the polar vortex and jet stream is derived partly from the temperature contrast between cold polar air and warmer tropical air, it is at risk of becoming severely diminished as this contrast is eroded by the effects of melting sea ice.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: Model simulation suggest diminished Arctic sea ice may have been a contributing driver of recent wet summers over northern Europe, because of a weakened jet stream, which dives further south.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: More specifically, D-O cold events, and their associated influx of meltwater, reduce the strength of the North Atlantic Deep Water current (NADW), weakening the northern-hemisphere circulation and therefore resulting in an increased transfer of heat polewards in the southern hemisphere.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: Enhanced warming over north Eurasia is partly linked to the Northern Annular Mode, while in the southern hemisphere the trend toward stronger westerlies over the Southern ocean favoured a cooling over much of Antarctica with the exception of the Antarctic Peninsula where strong westerlies decrease cold air outbreaks from the south.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: A northwards branch of the Gulf Stream, the North Atlantic Drift, is part of the thermohaline circulation (THC), transporting warmth further north to the North Atlantic, where its effect in warming the atmosphere contributes to warming Europe.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: As the vortex becomes weaker, it is more likely to allow cold arctic air to escape from the confines of the jet stream and spill over into other hemispheres.