Tuesday, July 29, 2014

More than 2.5m Sea Level Rise by 2040?

A warming period more than 400,000 years ago pushed the Greenland ice sheet past its stability threshold (which may have been no more than several degrees above pre-industrial temperatures). This resulted in a nearly complete deglaciation of southern Greenland, raising global sea levels some 4.5-6 meters, found a recent study by Reyes et al. Due to melting elsewhere, global mean sea level then was 6 to 13 metres above the present level. Indeed, melting of the entire West Antarctic Ice Sheet can add a further 6-meter rise in sea levels. If the East Antarctic Ice Sheet (EAIS) were to melt as well, sea levels would rise by around 70 metres.

Sea level is now rising by 3.1mm (0.122 inch) per year. Much of this rise is due to rising temperatures, but there are also other factors. One quarter of the rise results from groundwater depletion, while run off from melting ice and glaciers adds another quarter and the remainder is attributed to thermal expansion of sea water. Furthermore, as temperatures rise, feedbacks start to kick in, e.g. the kinetic energy from stronger waves and more intense storms can speed things up.

Clearly, a rapid multi-meter rise would be devastating as it would flood many coastal cities, as well as much of the land now used to grow food. By how much have sea levels been rising recently and how fast can they be expected to rise in the near future?
NASA image, data by the JPL PODAAC, in support of the NASA's MEaSUREs program.
Sea levels have risen by some 60 mm over the past 20 years, as above NASA image shows, which has a linear trendline added. The question is whether a linear trendline is the most appropriate trendline, given that it suggests that a similar rise could be expected over the next 20 years. A polynomial trendline appears to fit the data better, as the animation below shows.

Such a polynomial trendline, however, points at a similar rise (of some 50 mm) in just four years time, with an even more steeper rise to follow, as illustrated by the image below.

And indeed, such a rise doesn't slow down there. A polynomial trendline applied to the data points at a sea level rise of more than 2.5 m (8.2 ft) by the year 2040.

The image below gives an idea of what a sea level rise of six feet (1.829 m) would do to the City of New York. Of course, this is only the sea level rise. Storm surge would come on top of this, as discussed at Ten Dangers of Global Warming.

So, what would be more appropriate, to expect sea levels to continue to rise in a linear way, or to take into account feedbacks that could speed things up? Where such feedbacks could lead to is illustrated by the image below.
[ from: How many deaths could result from failure to act on climate change? click on image to enlarge ]
This calls for comprehensive and effective action, as discussed at the Climate Plan blog.


- South Greenland ice-sheet collapse during Marine Isotope Stage 11, Reyes et al. (2014)

- Nonsustainable groundwater sustaining irrigation: A global assessment, Yoshihide Wada et al. (2012)

- Groundwater Depletion Linked to Rising Sea Levels

- Assessment of the Jason-2 Extension to the TOPEX/Poseidon, Jason-1 Sea-Surface Height Time Series for Global Mean Sea Level Monitoring, Beckley et al. (2010)

- Feedbacks in the Arctic

- How many deaths could result from failure to act on climate change? (2014)

Monday, July 21, 2014

Methane rising through fractures

by Harold Hensel

Methane is colorless and odorless and it is right above us in the atmosphere.

In addition to other sources, methane has traveled from the Arctic and has blanketed most of the Northern Hemisphere.

The well-known sources are methane hydrates from the Arctic Ocean floor and methane coming from thawing permafrost.

There is also another less well-known source. During the geologic history of the Arctic area, tectonic plates have spread, crashed into each other and subducted under one another. Geologists call the Arctic a tectonic plate junkyard. There are numerous fractures in the earth's crust there.

A quote from earth scientist Malcolm Light: ‘Mantle methane formed from the reduction of oceanic carbonates by water in the presence of iron (II) oxides buried to depths of 100 km to 300 km in the Asthenosphere and at temperatures above 1200°C.’ This is a nonorganic source of methane formed near the earth's mantel. Katey Walter Anthony from the University of Alaska calls it geologic methane.

Vast reservoirs of methane have been created by chemical reactions and stored near the mantle under a lot of pressure for millennia.

The methane has had a route to the surface through the fractures in the earth's crust, but the fractures have been sealed over by ice. Now for the first time in human history, the ice sealing the fractures is thawing. Methane is rising through the fractures and into the atmo­sphere. This methane has migrated to the United States and is over us.

Harold Hensel, 
Cedar Rapids.
Earlier published as 
Letter to the Editor 
Cedar Rapids Gazette 
(without images)


- Study: Geologic methane seeping from thawing cryosphere - by Marmian Grimes

- Focus on Methane - by Malcolm Light

- Arctic Atmospheric Methane Global Warming Veil - by Malcolm Light, Harold Hensel and Sam Carana

- Mantle Methane - by Malcolm Light

Friday, July 18, 2014

Smoke Blankets North America

A thick layer of smoke blankets large parts of North America, as also illustrated by the animation below based on images from July 15 to 18, 2014, from Wunderground.com.

[ note that this animation is a 2.3MB file that may take some time to fully load ]
The are also extensive wildfires throughout the boreal forest and tundra zones of Central Siberia in Russia.

Such wildfires can send huge amounts of carbon dioxide, methane, soot, dust and volatile organic compounds into the atmosphere. Much of this gets deposited at higher latitudes, discoloring land, snow and ice, and thus speeding up warming by absorbing more sunlight that was previously reflected back into space.

Soils at higher latitudes can contain huge amounts of carbon in the form of peat, as described in the earlier post The Threat of Wildfires in the North. There are further conditions that make the situation in the Arctic so dangerous.
Temperature anomaly March-April-May-June 2014 (JMA)

The Arctic is particularly vulnerable to warming due to geographics. Seas in the Arctic Ocean are often shallow and covered by sea ice that is disappearing rapidly. Largely surrounded by land that is also rapidly losing its snow and ice cover, the Arctic Ocean acts like a trap capturing heat carried in by the Gulf Stream, which brings in ever warmer water. Of all the heat trapped on Earth by greenhouse gases, 90% goes into oceans, while a large part of the remaining 10% goes into melting the snow and ice cover in the Arctic, as described in an earlier post. Such basic conditions make that the Arctic is prone to warming.

Then, there are huge amounts of methane held in sediments under the Arctic Ocean, in the form of hydrates and free gas. Unlike methane releases from biological sources elsewhere on Earth, methane can be released from the seafloor of the Arctic Ocean in large quantities, in sudden eruptions that are concentrated in one area.

Until now, permafrost and the sea ice have acted as a seal, preventing heat from penetrating these methane hydrates and causing further destabilization. As long as there is ice, additional energy will go into melting the ice, and temperatures will not rise. The ice also acts as a glue, keeping the soil together and preventing hydrate destabilization from pressure changes and shockwaves resulting from seismic activity. Once the ice is gone, sediments become prone to destabilization and heat can more easily move down along fractures in the sediment, reaching hydrates that had until then remained stable.
Temperature anomaly March-April-May 2014 (NASA)
When methane escapes from the seafloor of the Arctic Ocean and travels through waters that are only shallow, there is little opportunity for this methane to be broken down in the water, so a lot of it will enter the atmosphere over the Arctic Ocean. The Coriolis effect will spread the methane sideways, but latitudes over the Arctic are relatively short, making the methane return at the same spot relatively quickly, while the polar jet stream acts as a barrier keeping much of the methane within the Arctic atmosphere. In case of large methane eruptions, the atmosphere over the Arctic will quickly become supersaturated with methane that has a huge initial local warming potential.

Hydroxyl levels in the atmosphere over the Arctic are very low, extending the lifetime of methane and other precursors of stratospheric ozone and water vapor, each of which have a strong short-term local warming potential. In June/July, insolation in the Arctic is higher than anywhere else on Earth, with the potential to quickly warm up shallow waters, making that heat can penetrate deep into sediments under the seafloor.

created by Sam Carana, part of AGU 2011 poster
The initial impact of this methane will be felt most severely in the Arctic itself, given the concentrated and abrupt nature of such releases, with the danger that even relatively small releases of methane from the seafloor of the Arctic can trigger further destabilization of hydrates and further methane releases, escalating into runaway warming.

This danger is depicted in the image on the right, showing how albedo changes and methane releases act as feedbacks that further accelerate warming in the Arctic, eventually spiraling into runaway global warming.

The currently very high sea surface temperature anomalies are illustrated by the two images below.

As the image below right shows, sea surface temperatures as high as 18 degrees Celsius (64.4 degrees Fahrenheit) are currently recorded in the Arctic.

Albedo changes and methane releases are only two out of numerous feedbacks that are accelerating warming in the Arctic.

Also included must be the fact that Earth is in a state of energy imbalance. Earth is receiving more heat from sunlight than it is emitting back into space. Over the past 50 years, the oceans have absorbed about 90% of the total heat added to the climate system, while the rest goes to melting sea and land ice, warming the land surface and warming and moistening the atmosphere.

In a 2005 paper, James Hansen et al. estimated that it would take 25 to 50 years for Earth’s surface temperature to reach 60% of its equilibrium response, in case there would be no further change of atmospheric composition. The authors added that the delay could be as short as ten years.

Earth's waters act as a buffer, delaying the rise in land surface temperatures that would otherwise occur, but this delay could be shortened. Much of that extra ocean heat may enter the atmosphere much sooner, e.g. as part of an El Niño event. Another buffer, Arctic sea ice, could collapse within years, as illustrated by the image below.

[ click on image to enlarge ]
The demise of sea ice comes with huge albedo changes, resulting in more heat getting absorbed by the Arctic Ocean, in turn speeding up warming of the often shallow waters of the Arctic Ocean. This threatens to make heat penetrate subsea sediments containing huge amounts of methane. Abrupt release of large amounts of methane would warm up the Arctic even more, triggering even further methane releases in a spiral of runaway warming.

Particularly worrying is the currently very warm water that is penetrating the Arctic Ocean from the Atlantic Ocean and also from the Pacific Ocean, as illustrated by the image further above and the image on the right.

The danger is that the Arctic will warm rapidly with decline of the snow and ice cover that until now has acted as a buffer absorbing heat, with more sunlight gets absorbed due to albedo changes and as with additional emissions, particularly methane, resulting from accelerating warming in the Arctic.

The numerous feedbacks that accelerate warming in the Arctic are pictured in the image below.

[ from: climateplan.blogspot.com/p/feedbacks.html ]
Furthermore, the necessary shift to clean energy will also remove the current masking effect of aerosols emitted when burning fuel. One study finds that a 35% – 80% cut in people's emission of aerosols and their precursors will result in about 1°C of additional global warming.

In the video below and the video further down below, Guy McPherson discusses Climate Change and Human Extinction.

This is further illustrated by the image below, showing how surface temperature rises are accelerating in the Arctic compared to global rises, with trendlines added including one for runaway global warming, from How many deaths could result from failure to act on climate change?
[ click on image to enlarge ]
The situation is dire and calls for comprehensive and effective action, as discussed at the Climate Plan blog.

Hat tip to Jim Kirkcaldy for pointing at the wildfire development at an early stage.

Monday, July 14, 2014

Focus on Methane

by Malcolm Light

Methane formed by organisms in the water becomes trapped in the fabric of water ice crystals when it freezes and is stable below about 300 metres depth in the Arctic Ocean.

There are such massive methane reserves below the Arctic Ocean floor that they represent around 100 times the amount that is required to cause a Permian style major extinction event, should the methane be released into the atmosphere.

There are also giant reservoirs of mantle methane, originally sealed in by shallow methane hydrate plugs in fractures cutting the Arctic seafloor.

Unfortunately for us, global warming has heated up the oceanic currents fed by the Gulf Stream flowing into the Arctic, causing massive destabilization of the subsea methane hydrates and fault seals and releasing increasing volumes of methane directly into the atmosphere.

Screenshot from Perdue University's Vulcan animation, which
shows pollution from North America spreading over the North
Atlantic, from Warming of the Arctic Fueling Extreme Weather
The volume transport of the Gulf Stream has increased by three times since the 1940s due to the rising atmospheric pressure difference set up between the polluted, greenhouse gas rich air above North America and the marine Atlantic air.

The increasingly heated Gulf Stream, with its associated high winds and energy rich weather systems, flows NE to Europe where it recently pummelled Great Britain with catastrophic storms. Other branches of the Gulf Stream then enter the Arctic and heat up the Arctic methane hydrate seals on subsea and deep high - pressure mantle methane reservoirs below the Eurasian Basin- Laptev Sea transition.

This is releasing increasing amounts of methane into the atmosphere contributing to anomalous temperatures, greater than 20 degree C above average. Over very short time periods of a few days to a few months the atmospheric methane has a warming potential from 1000 to 100 times that of carbon dioxide.

The amount of carbon stored in hydrates globally
was in 1992 estimated to be 10,000 Gt (USGS),
while a later source gives a figure of 63,400 Gt C
for the Klauda & Sandler (2005) estimate of marine
hydrates. A warming Gulf Stream causes methane
 off the North American coast. Methane also
appears to be erupting from hydrates on Antarctica,
on the Qinghai-Tibetan Plateau and on Greenland.
In just one part of the Arctic Ocean alone, the East
Siberian Arctic Shelf (ESAS), up to 1700 Gt of
methane is contained in sediments in the form of
methane hydrates and free gas. A sudden release
of just 3% of this amount could add over 50 Gt of
methane to the atmosphere, i.e. some seven times
what is in the atmosphere now, and experts consider
such an amount to be ready for release at any time.
From: Will the Anthropocene last for only 100 years?
There are such massive reserves of methane in the subsea Arctic methane hydrates, that if only a few percent of them are released, they will lead to a jump in the average temperature of the Earth's atmosphere of 10 degrees C and produce a "Permian" style major extinction event which will kill us all.

The whole northern hemisphere is now covered by a thickening atmospheric methane veil that is spreading southwards at about 1 km a day and it already totally envelopes the United States.

A giant hole in the equatorial ozone layer has also been discovered in the west Pacific, which acts like an elevator transferring methane from lower altitudes to the stratosphere, where it already forms a dense equatorial global warming stratospheric band that is spreading into the Polar regions.

The spreading atmospheric methane global warming veil is raising the temperature of the lower atmosphere many times faster than carbon dioxide does, causing the extreme summer temperatures in Australia and the US.

During the last winter, the high Arctic winter temperatures and pressures displaced the normal freezing Arctic air south into Canada and the United States, producing never before seen, freezing winter storms and massive power failures.

When the Arctic ice cap finally melts towards the end of next year, the Arctic sea will be aggressively heated by the sun and the Gulf Stream. The cold Arctic air will then be confined to the Greenland Ice cap and the hot Arctic air with its methane will flow south to the United States to further heat up the Gulf Stream, setting up an anticlockwise circulation around Greenland.

Under these circumstances Great Britain and Europe must expect even more catastrophic storm systems, hurricane force winds and massive flooding after the end of next year, due to a further acceleration in the energy transport of the Gulf Stream. If this process continues unchecked the mean temperature of the atmosphere will rise a further 8 degrees centigrade and we will be facing global deglaciation, a more than 200 feet rise in sea level rise and a major terminal extinction event by the 2050s.

The US and Canada must cut their global emissions of carbon dioxide by 90% in the next 10 to 15 years, otherwise they will be become an instrument of mass destruction of the Earth and its entire human population. Recovery of the United States economy from the financial crisis has been very unsoundly based by the present administration on an extremely hazardous "all of the above" energy policy that has allowed continent wide gas fracking, coal and oil sand mining and the return of widespread drilling to the Gulf Coast. This large amount of fossil fuel has to be transported and sold which has caused extensive spills, explosions and confrontations with US citizens over fracking and the Keystone XL pipeline. Gas fracking is in the process of destroying the entire aquifer systems of the United States and causing widespread earthquakes. The oil spills are doing the same to the surface river run off.

We are now facing a devastating final show down with Mother Nature, which is being massively accelerated by the filthy extraction of fossil fuels by US and Canada by gas fracking, coal and tar sand mining and continent wide bitumen transport. The United States and other developed nations made a fatal mistake by refusing to sign the original Kyoto protocols. The United States and Canada must now cease all their fossil fuel extraction and go entirely onto renewable energy in the next 10 to 15 years otherwise they will be guilty of planetary ecocide - genocide by the 2050's. There must also be a world-wide effort to capture methane in the oceans and eradicate the quantities accumulating in the atmosphere.

Friday, July 4, 2014

The Threat of Storms Wreaking Havoc in the Arctic Ocean

Arctic sea ice extent is close to a record low for the time of the year, as the image below shows.

Furthermore, the current decline in sea ice extent is much steeper than it used to be for this time of the year, raising the specter of sea ice hitting an absolute record low later this year. Moreover, a total collapse of sea ice may occur if storms continue to develop that push the remaining ice out of the Arctic Ocean into the Atlantic Ocean.

The threat posed by storms is illustrated by the track projected to be followed by Hurricane Arthur (above NOAA image, July 4), renamed as Post-Tropical Cyclone Arthur (NOAA image below, July 5).

The path followed by Arthur is influenced by the current shape of the jet stream. As the animation below illustrates, the jet stream looks set to prevent Hurrican Arthur from moving to the east and instead make it move into the Labrador Sea to the west of Greenland and - partly due to the high mountains on Greenland - continue to wreak havoc in Baffin Bay further north.

[ Note: this animation is a 1.87 MB file that may take some time to fully load ]
As described in an earlier post, post-tropical cyclone Leslie made landfall with hurricane-force winds in Newfoundland in September 2012. The large extratropical low pressure system continued to move rapidly northeastward across eastern Newfoundland at a forward speed of near 45 kt, and merged with a much larger extratropical low over the Labrador Sea.

Recent research by NOAA-affiliated scientists suggests that - over the years - the latitude where hurricanes, typhoons, and cyclones reach their maximum intensity on the Northern Hemisphere has shifted closer to the North Pole.

Such storms can bring lots of heat and moisture into the Arctic, and they can also increase the height of waves. All this can have devastating impact on the sea ice. The many ways in which storms can increase the dangerous situation in the Arctic is described in the post Feedbacks in the Arctic.

Last month, the June heat record broke in Greenland. Very high temperatures are currently recorded all over North America, as the image below shows.

Furthermore, sea surface temperature anomalies in the Arctic are currently very high, as the image below shows.

Additionally, the sea ice is currently very thin, as shown by the Naval Research Laboratory animation below.

The above animation further shows that there now is very little sea ice left in Baffin Bay, making it easier for storms to cause very high waves that could enter the Arctic Ocean and break the sea ice north of Greenland and Canada.

Arctic sea ice volume minimum is typically reached around halfway into September. This is still months away, but the prospect of an El Niño event striking this year now is 90%, according to predictions by the European Centre for Medium-range Weather Forecasts.

All this combines into a growing threat that hydrates contained in sediments will destabilize and that huge quantities of methane will be released abruptly from the seafloor of the Arctic Ocean. The risk that this will eventuate is intolerable and calls for parallel lines of action as pictured in the image below.

Climate Plan, July 7, 2014 version, as discussed at this Climate Plan post and at the Climate Plan blog


- Storm enters Arctic region

- Huge cyclone batters Arctic sea ice

- Hurricane Sandy moving inland

- Feedbacks in the Arctic

Climate Plan

This image sums up the lines of action, to be implemented in parallel and as soon as possible, and targets of the Climate Plan, in order to avoid climate catastrophe.

The Climate Plan and its various parts have been discussed in many post at Arctic-news blog over the years.

Now is the time to support the Climate Plan and to make sure that it will be considered at many forums, such as the Climate Summit, to be held September 23, 2014, at the U.N. Headquarters in New York, and preparations for the UNFCCC Climate Change Conference in Paris in 2015.

Please show your support by sharing this text and the image widely!

Emission cuts

In nations with both federal and state governments such as the U.S., the President (or Head of State or Cabinet, basically where executive powers are held) can direct:
  • federal departments and agencies to reduce their emissions for each type of pollutant annually by a set percentage, say, CO2 and CH4 by 10%, and HFCs, N2O and soot by higher percentages.
  • the federal Environmental Protection Agency (EPA) to make states each achieve those same reductions. 
  • Target: 80% cut everywhere for each type of pollutant
    by 2020 (to be managed locally provided targets are met)
  • the EPA to monitor progress by states and to step in with more effective action in case a state looks set to miss one or more targets.
    (More effective action in such a case would be to impose (federal) fees on applicable polluting products sold in the respective state, with revenues used for federal benefits. Such federal benefits could include building interstate High-Speed Rail tracks, adaptation and conservation measures, management of national parks, R&D into batteries, ways to vegetate deserts and other land use measurements, all at the discretion of the EPA. Fees can be roughly calculated as the average of fees that other states impose in successful efforts to meet their targets.)
Similar policies could be adopted elsewhere in the world, and each nation could similarly delegate responsibilities to states, provinces and further down to local communities.

Carbon dioxide removal and storage
Target: restore atmosphere and ocean to long term average
by 2100 (with each nation's annual contributions to reflect
its past emissions)

Energy feebates can best clean up energy, while other feebates (such as pictured in the above diagram) can best raise revenue for carbon dioxide removal. Energy feebates can phase themselves out, completing the necessary shift to clean energy within a decade. Carbon dioxide removal will need to continue for much longer, so funding will need to be raised from other sources, such as sales of livestock products, nitrogen fertilizers and Portland cement.

A range of methods to remove carbon dioxide would be eligible for funding under such feebates. To be eligible for rebates, methods merely need to be safe and remove carbon dioxide.

There are methods to remove carbon dioxide from the atmosphere and/or from the oceans. Rebates favor methods that also have commercial viability. In case of enhanced weathering, this will favor production of building materials, road pavement, etc. Such methods could include water desalination and pumping of water into deserts, in efforts to achieve more vegetation growth. Selling a forest where once was a desert could similarly attract rebates.

Some methods will be immediately viable, such as afforestation and biochar. It may take some time for methods such as enhanced weathering to become economically viable, but when they do, they can take over where afforestation has exhausted its potential to get carbon dioxide back to 280ppm.

Additionally, conservation and land use measures could help increase carbon storage in ecosystems.

Solar radiation management

Target: prevent Arctic Ocean from warming by more
than 1°C above long term average (U.N. supervised)
Apart from action to move to a more sustainable economy, additional lines of action are necessary to reduce the danger of runaway global warming.

Extra fees on international commercial aviation could provide funding for ways to avoid that the temperature of the atmosphere or the oceans will rise by more than 1°C above long term average.

Due to their potential impact across borders, these additional lines of action will need ongoing research, international agreement and cooperation.

Land, clouds, wind, water, snow and ice management

Target: increase Arctic snow and ice cover (U.N.
supervised) and restore it to its long term average 
Apart from action to move to a more sustainable economy, additional lines of action are necessary to reduce the danger of runaway global warming.

Extra fees on international commercial aviation could also provide funding for ways to cool the Arctic and restore the snow and ice cover to its long term average extent.

As said, due to their potential impact across borders, these additional lines of action will need ongoing research, international agreement and cooperation.

Methane management and further action

Target: relocate vulnerable Arctic clathrates (U.N. supervised)
and restore mean atmospheric CH4 level to long term average
by 2100 (with each nation's annual contributions to reflect its
past emissions.
Further action is needed to avoid that huge quantities of methane will abruptly erupt from the seafloor of the Arctic Ocean.

Vulnerable hydrates should be considered to be relocated under U.N. supervision.

Besides this, local action can be taken to reduce methane levels in the atmosphere with each nation's annual contributions to reflect its past emissions.

Adaptation, conservation and land use measures could further improve the situation.

The comprehensive and effective action of the Climate Plan will reduce the threat of runaway warming, and this will have obvious benefits for the environment and for species threatened with extinction.

Additionally this will also save people money, will improve people's health and safety, will increase security of food and fresh water supply, will make energy supply and the electric grid more efficient, safe, robust and reliable, will reduce perceived needs for military forces to police fuel supply lines globally, and will create numerous local job and investment opportunities.

Please support, follow and discuss the Climate Plan at facebook.com/ClimatePlan and at Arctic-news

Wednesday, July 2, 2014

What's wrong with the weather?

Above map shows temperatures in NewFoundland and Labrador close to 30°C (86°F), compared to temperatures in Albuquerque, New Mexico of only 20°C (68°F), while temperatures seem to be even lower in Mexico City. What's happening with the weather?

Jet Streams are changing

World climate zones used to be kept well apart by jet streams. On the northern hemisphere, the polar jet stream was working hard to separate the Tundra and Boreal climate zones' colder air in the north from the Temperate climate and the Subtropical climate zones' warmer air in the south.

As the Arctic is warming even faster than the Equator, the falling temperature difference between the two reduces the speed at which warm air is moving from the Equator to the North Pole. This in turn slows the speed at which the jet streams are circumnavigating the globe on the Northern hemisphere and it is deforming the jet streams in other ways as well.

NOAA image ]
As above image shows, the polar jet stream is typically located at about 60°N and the subtropical jet stream at about 30°N. The polar jet stream's altitude typically is near the 250 hPa pressure level, or 7 to 12 kilometres (4.3 to 7.5 mi) above sea level, while the weaker subtropical jet stream's altitude is higher, between 10 and 16 kilometres (6.2 and 9.9 mi) above sea level.

NOAA image
The polar jet stream used to travel at speeds of up to 140 miles per hour, while following a relatively straight track that was meandering only slightly, i.e. with waves that go up and down only a little bit. This fast and relatively straight jet stream kept climate zones well apart. Accordingly, the Northern Temperate Zone used to experience only mild differences between summer and winter weather, rather than the extremely hot or cold temperatures that we're increasingly experiencing now.

Polar jet stream (blue) & subtropical
jet stream (red) - NOAA image
Loss of snow and ice cover in the north is accelerating warming in the Arctic. This is decreasing the difference in temperature between the Arctic and the Northern Temperate Zone, in turn causing the polar jet to slow down and become more wavy, i.e. with larger loops, as illustrated by the animation below.

Imagine a river that at first rapidly runs down a narrow and straight path when its waters fall down from the top of a high mountain. Once that river flows through flat land, though, it becomes slow and curvy.

Similarly, the polar jet stream is now circumnavigating the globe at slower speed and along a wavier tracks. Its waves are now more elongated, more stretched out vertically, making that cold air can move more easily down from the Arctic, e.g. through the middle of North America, as illustrated by the animation below.

At the same time, warm air can move up more easily from the South into the Arctic. This is creating huge temperature anomalies in many places, as also illustrated by the animation below.