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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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What on Earth is up with Heatwaves?

Posted on 10 August 2022 by Guest Author

Extreme heat and wildfires are battering the entire globe - one of the most obvious symptoms that climate change is here, today. Europe has roasted, while the UK topped 40 degrees Celsius for the first time in history. Meanwhile wildfires rage across the planet.

So why is global warming turbo charging extreme heat just so much? Why is only a 'small' amount of climate change causing heatwaves to sometimes become hundreds or thousands of times more likely? And what can we do protect ourselves, as heat waves continue to heat up?

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  1. The video is a nice example of why even the experts loose the oversight and do not anymore understand what's going on or what's causing this heat to become so much more likely as you have to understand Earth for the complex answer!

    (1) higher mean temperatures - so much is clear!

    (2) non-linear increase in marine heat waves - neighboring landmasses get cut off from moisture and neighboring warm waters lead to higher temperatures over coastal areas.

    (3) the drying out of the atmosphere - relative moisture values decline over the land masses leading to higher temperature increases as evaporation is not buffering temperature increases what is supercharging the drying out of the vegetation what is again reinforcing the drying out of the atmosphere - vicious cycle!

    (4) early snow melt leads to dryer springs and summers which become warmer. And receding snow cover now in all seasons.

    (5) drying our of rivers which is increasing the drying out of the vegetation and atmosphere. Here the smaller glaciers that are vanishing are important, as many small streams are now vanishing.

    (6) higher water vapor content in the tropics leads via extreme convection in the tropics over the expanding warm water surfaces to an increased release of latent heat - condensation - and when the dry but extreme energetic air descends it gets extremely warm again on its way down (gets compressed again) where it causes extreme heat waves - across the subtropics where the air of the tropics normally descends. Further, the dry air descends into drier air thus no clouds forming.

    (7) the meridional heat transfer in the Earth system in speeding up thus warmer waters and warmer air masses move farther away from the poles which are then contributing to extreme heat waves.

    (8) As the tropical oceans are warming fast - e.g. indo-pacific warm water pool is expanding fast - extreme convection is intensified thus the brian dobson circulation in the stratosphere is enhanced - the air raises from the surface oceans ou into the stratosphere from where i risies further up on its way to the poles only to come down again in the mid to high latitudes. And where the air from the stratosphere descends it can reinforce heat waves (high pressure systems) across the mid and high latitudes. Further, the descending air from the stratosphere brings high Ozone loads to the surface what is also contributing to the heat at the surface.

    (9) then we have a changing planetary circulation - the meridional direction (north/south) is increasing and the zonal direction (east/west) is weakening. The main cause is here that the zonal air flows are increasingly disturbed and redirected into a meridional direction by blocking systems.

    (10) the increasing transport of cold air equatorward and warm air poleward leads to increasing zonal temperature differences which reinforce north/south air movements. And tropical/subtropical air moving poleward causes more heat waves.

    (11) vanishing sea ice disturbs the jet around the Arctic and Antarctic now which is meandering more thus also contributing to an increasing meridional air transport leading to more heat waves.

    (12) next dryer air leads to lesser clouds - and as we observe now large areas of the continents drying out the cloud feedback in heatwave-affected areas is getting stronger. Further, we observe now over heatwave regions and marine heat wave regions a decline of cloud cover thus we have here also a vicious cycle.

    As a concluding remark: the emergence of large-scale exceptional heat waves is in many aspects a vicious cycle that will have an extreme impact on the carbon cycle and its subcycle the methane cycle now becoming an important driver for global warming - in short: we have now entered self-amplifying warming!

     And sorry for the mistakes i have made, but this was only a short improvised oversight of the factors driving the recent emergence of extreme heat waves long before we anticipated them!

     

     

     

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  2. The video is perhaps more a bit of engaging fun and less an attempt to explain why extreme weather events are far more extreme than the averaged level of AGW would suggest.
    (And the video comment about Germans being taller than Brits - well there is evidence for this:-
    Giant German surrenders at Calais
    The midget is photographer Eddie Worth (5'7") who was apparently a few inches taller than some in the Canadian unit that captured this lanky German - Jakob Nackem - 7'3".)

    On a more serious note...

    The NOAA Global Time Series page provides the following numbers.
    While OLS 1980-2021 of global average SAT shows a rise of +0.175ºC/decade, the global land average SAT is rising at +0.30ºC/decade, a difference mentioned in the video. But these are averages.
    The land average SAT for Europe shown by NOAA is rising at +0.46ºC/decade. And just taking the summer months JJA, these are rising at +0.52ºC/decade, although this is a few points higher than the Jul-Aug rise of +0.51ºC/decade, this because June is the 'warmiest' of these 3 months. Mind, July showed more wobbliness in this regression.
    A repeat for North America rather than Europe gives less dramatic results with JJA rising +0.29ºC/decade.
    It would be possible to dig deeper using maximum daily temperatures but I cannot see such breaking down of average would lead to finding less extreme events.

    One thing the video did mention (@5.29) was global circulations although not in any detail and not very clearly - "...shifts in the motion of as (sic) atmosphere and ocean swell as the dryness of soils can also dial up the heat." I think the Arctic jetstream is a big factor in the NH extra-tropics experiencing more extreme weather events and the shifting of that jetstream and its bendy blocking events are in turn attributed to AGW, as this Bloomberg OP explains..

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