dohboi wrote:Thanks for this dis and T. (T, you must have missed my intended understatement--when I said "I doubt...smoothly linear" I meant, "There's essentially no conceivable way it could be smooth or linear" especially as it is experienced locally.
But maybe dis could chime in on the physics of these patterns. Any idea of how many possible formations are possible? Will the Hadley cell just keep expanding steadily? Is there a point when it necessarily will break into some other pattern. How long can the three-cell-per-hemisphere hold up? What is likely to go first? Are two-cell structures even physically possible?
(Sorry to pepper with questions. Take any one that seems remotely interesting or move on to other things, as you wish. Thank ahead of time for any light anyone can throw on this. My understanding is that modeling wave patterns even in fairly straightforward contained simple structures can be devilishly difficult. Butterflies and all that...)
Coffee And Climate Change: In Brazil, A Disaster Is Brewing
dohboi wrote:Thanks, dis.
"there are fundamental dynamical limits on how far it can expand. This is imposed by rotation of the planet and baroclinic instability."
That's what I had heard elsewhere. I don't pretend to completely grok the physics behind this, but about how far can the Hadley expand till it bumps up against these physical limits. Do we know with any precision? And can we estimate when this halt in expansion will happen based on how fast it is expanding now?
It seems like such questions would be of vital interest to those trying to make preparations for these now pretty much inevitable events...oh, I forgot...pretty much no one in charge shows much sign of giving a sh!t about any of these developments...oh well. :/
The tropics are widening rapidly, but humans may not be entirely to blame — yet
An uptick in tropical expansion the past few decades would seem to suggest that some unknown factor, perhaps as a result of human activities, is driving the widening of the tropics. But a study led by Paul Staten, an atmospheric sciences professor and researcher at Indiana University Bloomington in the United States, finds that that is not necessarily the case.
Staten and his colleagues determined that the tropics have been widening at an average rate of about 17 miles, or 0.2 degrees latitude, per decade in both the Northern and Southern hemispheres, which is not outside of what climate models predict.
Staten and team state in the study that no hidden forcing is required in order to explain the tropical expansion we’ve already observed — our current models, which take into account natural variation and man made global warming, can account for the 0.2 degree-per-decade expansion rate they established.
Scientists have observed the tropics expanding toward Earth’s poles in recent decades, which was projected to happen as increasing concentrations of greenhouse gases in the atmosphere continue to heat up the planet. Some observational studies have found that the tropics are widening much faster than climate models predicted, however.
Any widening of the tropics can have significant impacts for the roughly half of the global population who live there — from shifting rain belts and growing desertification to more severe and frequent droughts and wildfires. So it’s an important question: Is anthropogenic climate change causing even more rapid poleward expansion of the tropics than expected? And if so, why?
An uptick in tropical expansion the past few decades would seem to suggest that some unknown factor, perhaps as a result of human activities, is driving the widening of the tropics. But a study led by Paul Staten, an atmospheric sciences professor and researcher at Indiana University Bloomington in the United States, finds that that is not necessarily the case.
“[S]ome studies claim that the observed tropical widening outpaces that expected from modern climate change, suggesting that some ‘hidden forcing’ may be unaccounted for. Here we strive to resolve this apparent mystery by synthesizing results from the growing body of literature on the quantification, attribution and underlying processes of tropical widening,” Staten and team write in a paper detailing their findings, published in the journal Nature Climate Change late last month. “We review metrics, causes, observations and simulations of tropical widening, and find that the widening of the global mean tropical belt may not be predominantly human-induced.”
In contrast to previous estimates of tropical widening made since the beginning of the satellite era in the late 1970s, which ranged from 0.25 to 3 degrees of latitude per decade, Staten and his colleagues determined that the tropics have been widening at an average rate of about 17 miles, or 0.2 degrees latitude, per decade in both the Northern and Southern hemispheres — though they add that the rate can vary significantly from year to year and location to location.
“If we compare the observed trends of how the tropics have widened to modeling trends, it’s actually not outside of what the models predict,” Staten said in a statement.
Staten and team state in the study that no hidden forcing is required in order to explain the tropical expansion we’ve already observed — our current models, which take into account natural variation and manmade global warming, can account for the 0.2 degree-per-decade expansion rate they established. “Including recent evidence, it is fair to assert that the natural swings in decadal atmospheric and oceanic variability may have driven at least as much of the observed expansion as human activity,” the researchers write.
Staten said that this should give us more confidence in predictions based on current climate models. “Climate change should continue to expand the tropics over the next several decades,” he said, adding: “But the expansion may not continue at the rapid rate we’ve seen; at times it may even temporarily contract.”
The researchers focused on five factors that influence the widening of the tropics, including increasing greenhouse gas emissions; ozone depletion in the stratosphere over the South Pole; aerosols from volcanic eruptions; pollution like soot and ozone in the troposphere; and natural variation, such as changes in sea surface temperatures due to El Niño and La Niña events.
Due to how complex these factors are, the researchers note, it’s actually quite difficult to discern between natural and manmade causes of tropical widening. But if we don’t do something soon to rein in greenhouse gas (GHG) emissions and pollution, the human factor will become much more readily apparent.
“Although discerning a forced signal in the observational record is challenging, the detection of such a signal in the future is not so much a question of if, but when, if humanity continues on the business-as-usual path of GHG emissions,” the researchers write in the study. “In the near term, natural variability muddles the widening signal of increasing GHG concentrations. But models project that the forced tropical widening will break out of the envelope of natural year-to-year variability some time in the middle of this century.”
Alfred Tennyson wrote:We are not now that strength which in old days
Moved earth and heaven, that which we are, we are;
One equal temper of heroic hearts,
Made weak by time and fate, but strong in will
To strive, to seek, to find, and not to yield.
Tropics Expanding with Climate Change
The tropics are expanding outward from the Equator due to the various factors causing climate change, according to a new study.
The thermal patterns since the late 1970s have gradually pushed the arid and semi-arid regions of the tropics by about 17 miles per decade, according to the paper in the journal Nature Climate Change.
“Our synthesis shows strong evidence that the tropics have widened by about 0.5 degrees per decade since the beginning of the satellite era (1979),” write the authors. “Since no one has a crystal ball to tell when the (Pacific decadal oscillation) will switch phases (as decadal prediction remains a major challenge to the climate community), it is impossible to predict whether or not the Earth’s tropical belt is going to continue bulging in the coming decade.”
The estimations have nothing to do with the Tropic of Cancer and Tropic of Capricorn, at 23 degree 27 minutes north and south, respectively. Instead, the estimations were based on observations of the climate patterns established by the Hadley cells, cycles that circulate heat and thermal energy and weather patterns from the Equator outward to the subtropics, and back again, like a natural pump.
The dynamics have been reaching ever outward toward the temperate zones since the advent of satellite observations, the researchers conclude.
The team identifies various factors including greenhouse gas emission, ozone depletion at the South Pole, volcanic aerosols, pollution and natural variation, which may play a part in the changes. The balance between naturally-driven and human-caused changes have yet to be better understood.
One upside: according to their models, the recent “bulge” in the tropics will slow down somewhat, partly perhaps because the ozone depletion over Antarctica has been largely reversed.
But even with fluctuations, the larger trend is clear, the researchers add.
“Climate change should continue to expand the tropics over the next several decades,” said Paul Staten, one of the authors, from Indiana University-Bloomington. “But the expansion may not continue at the rapid rate we’ve seen; at times it may even temporarily contract.”
“Considering that about half of the world’s population either lives in or near these subtropical semi-arid climate zones, the implications of tropical widening are potentially significant,” the paper adds.
Alfred Tennyson wrote:We are not now that strength which in old days
Moved earth and heaven, that which we are, we are;
One equal temper of heroic hearts,
Made weak by time and fate, but strong in will
To strive, to seek, to find, and not to yield.
Cid_Yama wrote:“THE PROMISE of food lies in the tropics,” the UN Food and Agriculture Organization director general said at the University of the Philippines. “Here in this sun-drenched belt of land, temperature is benign and rainfall abundant. These could be the food granaries for the world of our children.”
Not anymore. Rising temperatures have widened the “Tropical Belt,” notes Nature Geoscience. Since the FAO official delivered his address in Los Baños in May 1979, the tropics expanded by between 2 and 4.8 degrees latitude. As the world warms, edges of the “Belt”—outer boundaries of the subtropical dry zones—drift toward the poles.
Temperature and rainfall changes are altering yields. Affected are politically volatile crops like corn and rice. “In the Philippines, rice yields drop by 10 percent for every one degree centigrade increase in night-time temperature,” BBC’s environment correspondent Richard Black writes.
The slump is region-wide. As droughts dry reservoirs, yields have fallen by 10 to 20 percent over the last 25 years. More declines are ahead.
“We found that as the daily minimum temperature increases, or as nights get hotter, rice yields drop,” researcher Jarrod Welch said. “Where temperature increases more than 3 °C, impacts are stressful to all crops and in all regions,” the Intergovernmental Panel on Climate Change (IPCC) concluded.
There are biological limits to what can be done. “We can’t just move all our crops north or south because a lot of crops are photosensitive,” notes Dr. Geoff Hawtin at the International Center for Tropical Agriculture. “Flowering is triggered by day length.”
We don’t know where the tipping points are,” Hawtin adds. “They could come quite quickly.”
Atlas reveals birds pushed further north
Data from 120,000 birdwatchers in 48 countries shows forest birds have expanded their range while area occupied by farmland birds has shrunk
Europe’s breeding bird populations have shifted on average one kilometre north every year for the past three decades, likely driven by the climate crisis, according to one of the world’s largest citizen science projects on biodiversity.
The European Breeding Bird Atlas (Ebba2) provides the most detailed picture yet of the distribution of the continent’s birds after 120,000 volunteers and fieldworkers surveyed 11m square kilometres, from the Azores in the west to the Russian Urals in the east.
The book documents changes in the range of Europe’s 539 native bird species in the 30 years since the first Ebba, which was published in 1997 but was based on observations from the 1980s. It shows that since the first study, each population can be found around 28km further north.
Mediterranean species such as the European bee-eater and little egret are now reaching the UK, France and the Netherlands, mainly due to milder winters. Eurasian bittern, pied avocet and red kites have also expanded their range, probably in response to better protection of habitats coupled with laws banning persecution.
Overall, 35% of birds increased their breeding range, 25% contracted their breeding range and the rest did not show any change, or the trend is unknown. Forest birds and those protected by international legislation have generally expanded their range, while farmland birds occupy a smaller total area.
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Generally, if a species is present in more areas it is less likely to go extinct, but it could be spreading out because of habitat deterioration, and not because the population has increased. “The results are confirmation that the major driving forces are climate change and land-use change. At the same time, the situation is really very complex, and that’s why we will provide this dataset for further exploration and investigation,” said Dr Petr Voříšek from the Czech Society for Ornithology.
r Iván Ramírez, senior head of conservation at BirdLife Europe and central Asia, said: “Those birds that have been legally protected have been doing better than those which are not protected. This is a really important message within the European Union. We have one of the oldest policies – the Birds Directive – and we can prove that it works.” Birds protected by the Bern Convention, such as white-tailed eagles, are also doing better.
As the climate warms, forests are stretching into boreal and Arctic regions. In parts of northern Europe there has also been tree planting (mainly for wood and paper) and land abandonment (specifically in Mediterranean areas) which have damaged farmland birds but benefited many woodland species such as woodpeckers and warblers.
Alpine species are also losing out as scrubby trees and vegetation colonise higher mountain slopes, shrinking the range of mountain grassland specialists such as wallcreepers and water pipits.
Generally, farmland birds are big losers, suffering overall declines in population and reduced distribution because agricultural intensification means there is less food, such as insects and residue from harvesting. The State of Nature in the EU 2013-2018 assessment showed 80% of key habitats were in poor or bad condition, and intensive farming is a major driver of decline. The UK’s farmland birds have declined by 55% since 1970.
Alfred Tennyson wrote:We are not now that strength which in old days
Moved earth and heaven, that which we are, we are;
One equal temper of heroic hearts,
Made weak by time and fate, but strong in will
To strive, to seek, to find, and not to yield.
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