The climate change debate continues.

[octave]

1 hour ago, spacesailor said:

My take on what I read, was,

Your solar system will be switched off, so it Does Not supply your house, making you pay for all of your power !.

spacesailor

 

 

Here is an article from "Solarquotes".  This is a website that has a vested interest in rooftop solar installations   https://www.solarquotes.com.au/blog/solar-inverter-control/

 

If anyone would be concerned about solar becoming less economically attractive it would be these folks. The above link explains the issue quite well and dispels the myths 

 

 

 

Space I am assuming you do not have rooftop solar. i am wondering how you would feel if you had a power a cut because your neighbours were pouring  excess power into the grid when demand was low. 

 

As an enthusiastic advocate for solar and as someone who has a rooftop system this does not overly concern me.

 

 

 

 

 

 

 

[Marty_d]

3 hours ago, spacesailor said:

My take on what I read, was,

Your solar system will be switched off, so it Does Not supply your house, making you pay for all of your power !.

spacesailor

That would be an act of complete bastardry, if it were so.

 

However they'd have a hard time explaining how cutting the solar supply off to your house, instead of just stopping the component going back to the grid, would help stabilize the grid.

The idea with solar is that you use it first and anything left over is returned to the grid.

[Old Koreelah]

There are lots of ways being developed to adapt the grid to renewable energy; here is one from Newcastle Uni:

 

https://www.abc.net.au/news/2020-09-08/thermal-blocks-technology-to-convert-coal-fired-power-station/12638462

[Yenn]

Why would I do as Marty  suggests. I get paid 44c per kW for my solar and buy from the grid at 23c per kW. I know it is stupid but that is what the government was pushing to get people to install solar.

[nomadpete]

Grid stability requires control over grid inputs. While rooftop solar was a minor input, it didn't affect grid stability. Now, however, rooftop solar is a major input to the grid, so there will be times when rooftop solar will have to be limited - at low demand times.

Don't worry, all power generator companies have to do this, too.

Anyway, remember that unless you have a battery and a home system that can cutover from grid to battery, and back when the battery is low, your normal standard grid feed inverter will automatically disconnect your solar energy from the grid whenever your local supply rises above about 245 volts (ish). They have always done this. So, at times when your rooftop grid feed system might upset grid stability, all the distributor has to do is allow the street distribution system to rise above that critical voltage, and hey presto! All rooftop solar will cease to feed into the grid (or supply what your house is using at the time. Remember, your 240volts street supply is 'nominal 240v' and can normally vary by 10%.

[Marty_d]

3 hours ago, Yenn said:

Why would I do as Marty  suggests. I get paid 44c per kW for my solar and buy from the grid at 23c per kW. I know it is stupid but that is what the government was pushing to get people to install solar.

You're one of the lucky ones.  We get about 6 cents back and pay about 26 cents for power from the grid.  In your case it'd be better to switch it somehow so everything you generate goes straight back to the grid.

[onetrack]

I must say I'm a little surprised to see Victoria and NSW have a 10% overvoltage allowance (at a nominal 240V) - making for 264V.

 

The Australian Standard is a nominal 230V, and has been since the early 2000's. This is to bring us into line with European trading partners. But here in W.A., we have the Australian Standard of 230V supply, and a maximum voltage of 253V.

 

https://ewh.ieee.org/r10/nsw/subpages/history/Australian-AC-Line-Voltages.pdf

[Jerry_Atrick]

Meanwhile, Western suburbs of Sydney, with their over-development, are resulting in developing human slow-cookers for houses: https://www.bloomberg.com/news/features/2020-09-15/sydney-s-new-suburbs-get-so-hot-that-people-could-die-there

[old man emu]

Well, there you have it. These young pups with their university degrees and research funding have identified the same thing that a silly Old Man Emu spoke about on these very pages quite some time ago. The Southwest Sydney area is a cool air reservoir that is an integral part of the climate of the Sydney Basin. This http://www.condellpark.com/bear/smogbasin.htm#Figure7 is a bit dated, and off topic but it is the best illustration of the air circulation system as it was at the start of the 21st Century. The caption for Figure 2 is now out of date. The V-shaped area between the indicated roads and the top of the map are now filling with houses, or are planned to be filled.

 

 

These housing developments consist of very small block sizes with dark-roofed houses covering them to the exclusion of anything else.

 

This is what is happening in Sydney's southwest. Similar crowded development is occurring in the northwest of the Basin. 

 

It won't be long before those who fly from Camden to Bankstown will be able to put a tourist sticker on their plane "I Flew the Nullabor" 

[Yenn]

Dark roofs are going to heat up the atmosphere, but architects made them popular. I have just come back from two weeks away travelling in N Qld. I notice all the new subdivisons, all with Victorian style houses, brick or other solid walls and minimal eaves. Everyone of them air conditioned. That must cost an arm and a leg and is so stupid as the old Queenslander was a very comfortable house in Summer. Of course the local governments do not help as they practically insist that houses must be air conditioned. They have only recently allowed water tanks and even then they must not be plumbed into anywhere where somaone could drink the water. I thimnk the main reason is to force people to drink town water, which is so foul tasting that they prefer soft drinks.

Our illustrious leader sems to be hell bent on promoting coal, to the detriment of the environment, now he wants to steal the money for renewables and use it to promote caol.

I really don't think excess solar electricity can be responsible for raising the voltage and therefore shutting down the PV electricity being fed into the grid. THe other day my system said it was overvoltage and the sun was hardly over the horizon. Something else does it as well.

[Bruce Tuncks]

Do we have any real hairy-chested denier on the forum?  If so, here's my question.. Is there ANY bit of evidence that you will accept and change your mind?

In real life, I do know a couple of real deniers, one of whom is a real well scientifically educated guy. But I notice that they refuse to look at the total evidence and instead focus on the odd tiny bits of contrary evidence. 

For example, as climate change proceeds, there are a couple of small areas where the temperature has fallen, due to changing wind patterns.  Further, some years ago, there were papers published about how a new ice age was upon us. Also, the current  forecasts have not been correct to the fraction of a degree.

So I repeat my question... what ( if anything ) will convince them?

[Old Koreelah]

Bruce I fear many are like Trump's rusted-on supporters and nothing will sway them, even though their own kids will have to deal with the developing mess. Too many climate change predictions are coming true, some decades ahead of schedule. 

Most ominous is permafrost thawing in Siberia, releasing masses of methane- a greenhouse gas many times worse than CO2.

 

Even a small rise in sea level displaces hundreds of millions, who will join the multitudes already flocking to the rich countries that caused this mess. How can Australia stop them? 

[pmccarthy]

OK, I'll bite. I am not convinced that (a) there is significant climate change that is not part of natural variation and (b) that humans are causing a runaway climate disaster. I am happy to concede that burning all that fossil fuel has had some effect, but not that it is responsible for major climate change. I am happy that we will transition to other sources of energy and have no reason to oppose it as long as we do not leave people dying of heat exhaustion in summer or freezing to death in winter due to lack of electricity. Or in long term unemployment with all the mental effects of that.

 

I have posted extensively about this previously in this thread but have concluded that I am wasting my time putting up references, charts and data. People believe what they want to believe.

 

I have a Bachelor of Science degree from  the University of NSW and a Master of Science degree in Geological Science from Macquarie University. They don't make me any sort of an expert, but I am not stupid either. I am not a climate change denier whatever that is but am certainly a skeptic.

[Yenn]

Climate change will depend upon where you are. There is a theory that if the climate warms up and the North polar waters thaw, then the gulf stream will stop running and the UK will become much colder. Still climate change but not warming.

[old man emu]

Not as fully understood, but I'd say that if the Antarctic melts, the water circulating in the Pacific Ocean will become colder as well. Maybe that will increase rainfall over the west of the South America and turn deserts there into habitable areas. The opposite seems to have happened in the past.

[Old Koreelah]

18 hours ago, pmccarthy said:

OK, I'll bite. I am not convinced that (a) there is significant climate change that is not part of natural variation and (b) that humans are causing a runaway climate disaster.

Good to hear from you, PM.  You and I might be seeing the world thru different eyes.  To me the evidence for climate change is obvious and very concerning; some of the changes are unprecedented in human history. The thawing of Siberian permafrost alone could cause a catastrophic rise in temperature.

Quote

I am happy that we will transition to other sources of energy and have no reason to oppose it as long as we do not leave people dying of heat exhaustion in summer or freezing to death in winter due to lack of electricity. Or in long term unemployment with all the mental effects of that.

The fossil fuel lobby has ran an insidious fear campaign. They blamed power outages and rising electricity prices on renewables; what hypocrisy! Storms caused the SA outages, some of our coal burners are quite unreliable and rising prices have more to do with dodgy industry management than the shift to renewables.

 

Renewables already employ as many people as the coal industry.

Quote

I have posted extensively about this previously in this thread but have concluded that I am wasting my time putting up references, charts and data. People believe what they want to believe.

I have read most of your posts and haven’t yet been convinced of your point of view.

 

There are several good reasons for Australia to phase out fossil fuels and embrace the rapidly advancing renewable revolution.  

 

Renewables are already cheaper than the heritage fuels we used to rely on.

Global financiers can see that renewables are our future and are dropping fossil fuel projects like hot potatoes; they are rapidly becoming stranded assets.

 

Preventing this country becoming an international pariah state (as was Apartheid South Africa) is more than enough reason in itself.

If we don’t, the global community will expect Australia (perceived as a rich, developed country with lots of spare room) to take in vast numbers of refugees displaced by rising seas, storms, floods and droughts...

and I doubt we’d get to pick and choose.

Don’t doubt this could happen; Australia’s human rights reputation has taken a battering in the last decade or so; we have rapidly alienated many international allies.

[old man emu]

Not too many years ago, Sydney used to experience very strong westerly winds in August, with the winds continuing to blow for several days in a row. This August the winds were not noticeably strong. However, here we are at the end of September and we have been getting strong winds (gust up to 62 kts) from the NNW.

 

It makes me wonder if that is a sign of change to the usual weather patterns.

[onetrack]

As a climate change skeptic, and as I've previously stated, my argument is that the climate on this planet is vastly older than mankinds inhabitation of the Earth - and it runs in major recurrent time cycles, with large variations in weather conditions over extended periods.

As an indicator of these extremes, we have engineering and planning measurements, known as "1 in 100 year," "1 in 250 year", and "1 in 500 year" calculated extremes in wind strength and flood levels, that have a major bearing on how strong man--made structures have to be built, or how high or low those structures can be positioned.

Those weather extremes, related to engineering and planning design, show that there are regular extremes in wind and water levels, that can seriously affect structures and planning. Accordingly, there must be extremes of low wind strength periods and low water levels (drought).

Extended droughts (Mega-droughts)  have been recorded regularly as long as Mankind has kept written records that have survived. It's a shame that many accurate records from the past have not survived, due to upheaval of civilisations, poor recording materials, and simple vandalism and destructive acts by humans.

 

The weather extremities cycles are often in periods that are not even. There has been talk of steady cycles of extremes, but I believe they are not always steady periods, because of the vast number of inputs that affect our climate and our weather.

In addition, the weather cycles that have run for hundreds of millions of years, have only been measured with a degree of global accuracy, for the last 30 years. Then highly educated people promptly make claims that they can see major and massive changes to the worlds climate, based on measurements, that in a time span, is equal to about 0.000000001% of the climate length on Earth.

Based on any other scientific proof standard, this is the equivalent of claiming to be able to identify an animal, its habitat, its breeding methods, and its characteristics, simply by examining a hair follicle found from that animal. 

 

I have no tertiary qualifications of any kind to back up my position or my ruminations as regards climate change - it's just that I have spent a very large part of my working life (55 years) studying weather on a practical basis as it constantly affected my business operations and income.

We are most certainly suffering from an extended period of lower-than-normal annual rainfall levels across Australia, as well as some variations in other climatic conditions. The ice sheet and glacier shrinkage are certainly real and visible events, but I would opine that this has happened before, in previous centuries, without the massive "calculated" sea level rises, that experts have predicted. This is all part of climate cycles, and I believe we have periods where various climate cycles overlap, creating extremes in weather events.

 

In addition, I have serious reservations about a U.N. division formed to examine and continually produce reams of reports about climate change - which major bureaucratic structure must continually increase in size and importance, and continually justify its existence, by promoting the principle of climate change, to ensure continued funding. And as we all know, once bureaucracies are established, they need to continually grow, and become more important in exercising control over our lives.

Edited September 26, 2020 by onetrack

[old man emu]

The recorded climate has seen a warm periods followed by a cold period in the 2000 years from 250 BCE.

 

The Roman Warm Period, or Roman Climatic Optimum, was a period of unusually warm weather in Europe and the North Atlantic that ran from approximately 250 BC to AD 400. Theophrastus (371 – c. 287 BC) wrote that date trees could grow in Greece if they were planted, but that they could not set fruit there. That is the case today, implying that South Aegean mean summer temperatures in the 4th and 5th centuries BC were within a degree of modern ones. That and other literary fragments from the time confirm that the Greek climate then was basically the same as it was around AD 2000. Tree rings from the Italian Peninsula in the late 3rd century BC indicate a time of mild conditions there at the time of Hannibal's crossing of the Alps with imported elephants (218 BC). Dendrochronological evidence from wood found at the Parthenon shows variability of climate in the 5th century BC, which resembles the modern pattern of variation.

 

The Medieval Warm Period (MWP) also known as the Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region lasting from c. 950 to c. 1250. It is thought that between c.  950 and c. 1100 was the Northern Hemisphere's warmest period since the Roman Warm Period. It was likely related to warming elsewhere while some other regions were colder, such as the tropical Pacific. Average global mean temperatures have been calculated to be similar to early-mid-20th-century warming. Possible causes  include increased solar activity, decreased volcanic activity, and changes to ocean circulation.

 

The Little Ice Age (LIA) was a period of cooling that occurred after the Medieval Warm Period. Although it was not a true ice age, the term was introduced into scientific literature by François E. Matthes in 1939. It has been conventionally defined as a period extending from the 16th to the 19th centuries, but some experts prefer an alternative time span from about 1300 to about 1850. Several causes have been proposed: cyclical lows in solar radiation, heightened volcanic activity, changes in the ocean circulation, variations in Earth's orbit and axial tilt (orbital forcing), inherent variability in global climate, and decreases in the human population (for example from the Black Death and the colonization of the Americas).

 

Based on the number of years between these climate extremes, one could speculate that between 450 CE and 900 CE there was a cool period, which could be shown by tree-ring analysis and pollen counts from buried material. Likewise one hundred and fifty years from the end of the Little Ice Age to the beginning of the 21st Century seems a reasonable period before the start of another warm period.

[Marty_d]

Science is in folks.  The amount of scientific consensus over this is overwhelming.  Saying anthropomorphic climate change isn't real is kind of like saying cancer isn't real (and trusting the fossil fuel to solve it is like trying to cure that cancer with the power of prayer).

 

Reading Malcolm Turnbull's book at the moment and it's enlightening to hear from someone who dealt one on one with the conservative rump of the LNP.  Idiots like Canavan, Abbott and their ilk have an awful lot to answer for.

 

To be fair, so do the Greens.  If they'd voted with Rudd on the ETS we'd have had a proper mechanism to price carbon for over a decade now.  

[Bruce Tuncks]

what all this proves to me is that the earth's temp is a very sensitive thing. This should be no surprise... between -270 and +5800 degrees, what is a 2 degree difference?

( the -270 is interstellar gas temp, while the 5800 it the sun's radiation temp.)

[spacesailor]

BUT

the Earth has been Frozen then Scorched over and over for eons.

Now,  the New date of 450 million years ago. The temperature knocked-out a lot of marine life and gave rise to the Dinosaurs.

spacesailor

[Jerry_Atrick]

I don't thin'k climate change "deniers" deny that the climate is changing, not the climate change proponents are not saying all climate change is the result of human activity (or endeavour). it is accepted over the ages (eons, even), there has been gradual shift in weather patterns. Australia had a giant inland sea, for example, which dried out over a very long time due to global weather changes.

 

The question is how is the impact on human activity disproportionately affecting the planet? In what direction? What will be the impact? and if it is an existential threat, what can we do about it?

 

There are many myths and misinformation/agendas propagated by the extremeties on both sides of the argument.. Unfortunately, as has been laid to bare in the current global political climate (pardon the pun) and the ease with which technology allows news and views to be permeated through society, these extremities are gathering traction - we all like to believe what we hear that confirm our bias.. I don't exempt myself from that, however, I have often swallowed the bitter pill that my belief or intuition has been trumped (pardon the other pun) by the facts - and I stress all the facts at the time. Because, when we are in denial based on accepting something that confronts our beliefs, the bar to change our mind is a lot higher than the facts we use to reinforce our beliefs...

 

So, believe me when I say this, I want - I really want it to be that the earth's climate is changing at a rate that is alarming all by itself, of course including effect of man's endeavours beyond sustaining life clad in bear skins and dragging our women by the hair while holding a roughly molded baseball bat or club. It would mean I could fire up the avgas burner in the smug knowledge I am having  fun at no-one's climate changing expense.

 

But the reality is the science currently doesn't bear this out. @pmccarthy - I have seen and responded to many of the facts and figures you have presented. I can see where you are coming from, but to be honest, statements such as

On 25/09/2020 at 3:55 AM, pmccarthy said:

but have concluded that I am wasting my time putting up references, charts and data. People believe what they want to believe

Is sort of reflective, I think.  As mentioned, I (Octave, Marty_d, OK, and others) have responded to much of what you have previously written. I recall your last post was, from memory about the marginal impact human activity has on the total amount of CO2 (ot may have been something else but I don't have the time to look things up at the moment). I was shocked at how little it was and it did challenge my current analysis/assessment (I use this term because I prefer this to blind faith belief, which seems to be the charge laid at us). However, as a trained scientist, you would understand that the numbers showing the materiality of the change in a variable, by itself, is not enough to draw a conclusion of the argument - in this case, the assumption being made is a tiny change results in a tiny effect, therefore, carry on. We have to assess/observe how the change of the variable (delta) affects the system.. so I did some digging, and yes, the impact is quite material as the system is naturally at capacity (which makes sense, otherwise we wouldn't have a natural weather cycle because otherwise the system would have capacity to absorb most shocks). I found and presented the credible data/facts to show that the small change in CO2 (I think it was) was enough to tip the scales. I used the analogy of pouring water into a glass that was already full - it will spill over.. The analogy isn't 100% correct as the earth processes CO2 to allow for more to be produced - the real analogy is that there is a glass of water that remains full because there is a small hole at the bottom that drains the existing stuff, while more stuff is added - volume in roughly equals volume out.. A small increase in the volume in will cause the glass to spill over... the rate of increase over time will dictate the rate of increase of the spillage - we also have an exponential risk because as permafrost thaws, more greenhouse gases are released into the atmosphere, etc I have not had a response to that, yet the same old "putting up references, charts and data... people believe what they want to believe".

 

@onetrack - It's an interesting analogy, but using historial weather records to look for outliers that are likely to occur in the lifetime of an asset that may be affected by the weather is not indicative of the weather cycles itself nor the impact man is having on the weather cycles. If you build a building to withstand the massive flood that historically comes once in 250 years, the fact it now comes once, say,  every 50 years will not affect the defence of the building to it (except possibly for remedial repairs after such a flood). The CSIRO has observed the IDP and SAM are deviating from their norms far more frequently and at larger quantums with predictions it will continue over time more or less in an incremental way.  There are once in a lifetime (or other time span) events, however, these appear to be occuring more frequently and hanging around longer... The earth's climate (and environment in general) is a fine balance; things such as climate gradually change over time - long times generally - except where there is an event that stimulates a rapid and monumental shift (normally - but once in a period of time are the exception). Things like large meteroites that impact earth and send dust clouds, etc... will cause rapid, but longer term effects... It can be argued human endeavour is analgous to one of those events.. given the evidence today.

 

Whilst, just because everyone says something is, doesn't mean it is, the vast majority of the scientific community  have drawn a similar conclusion and more of the ranks from the climate change "denier" fraternity join it in the face of what is reported to be overwhelming evidence. The difference between now and Copernicus' times is that there is an erosion (in many rational civilisations anyway) of the belief system over evidential science... and therefore we can have a greater level of confidence (not absolute) in the science.. It doesn't always get it right... so, say it is wrong and there is no impact. Shouldn't we deploy our vast collective technological resources to delay or push back the onset if we can rather than keep sailing the ship to oblivion? (of course, if we are not having an impact now, then you could argue that whatever we try will not have an impact on delaying the inevitable).

 

The other thing is that people allege science has an agenda - I would love to know what that agenda is? Are they financed by renewable energy companies? Nope. Do they just want to get a bigger slice of the research pie? Maybe, but it would be a hell of a coordinated effort across many nations with different funding models, etc. Seems unlikely.. What else would they want to do.. create a distraction? For what? For whom? It just doesn't add up.

 

Do they want us to have a reduced standard of living or return to a primitve way of life? Doubt it, though no doubt, there will be some of the extremists (such as vegan extremism) that will want us to give up eating meat (at least from methane producing animals) etc., but they are the fringe. Many are calling for small personal adjustments, but a massive adjustment to the energy mix..

 

And will this bring on economic ruin? Doubtful; the world changes, technology changes, there are relics of bygone industries and eras everywhere.. today, your bricks and mortar retail companies are under threat, but do we do anything to save them from the eCommerce onslaught? Not really (there may be token gestures, here and there). The reality, is that industries rise and die, and the working population adapt (some do get caught out). Instead of looking back to the fossil fuel lobby, we could have been looking forward and  developing the capability in renewables - not many countries have the same idyllic conditions to do so. Netherlands, I think, are the worlds largest windmill producers - they have higher structural costs than Australia, yet can do it because it solves a problem and provides high value. China has overtaken PV cell manufacture - why weren't we in these? Because we look back.. and we will become dinosaurs as we refuse to innovate. I read the other day that ScoMo will order the government build a gas-fired power station near Newcastle, I think, if private enterprise don't build one. So far, there are no takers because they know renewables is coming, it is cleaner, its economies of scale are starting to bite so the cost of building is lower and ROI is quicker. There will still be central planning engineers, but the maintenance workforce will be required to be more distributed. Mining will still go on as well, so it is win-win.. But we decide to play a win (for the producers) and lose (for the consumers - Australia).. more lost opportunity.

 

Our economy is already dichtomous  - Mining and the rest.. and the rest hasn't fared to well of late. Provate enterprise is starting to snub its nose at fossils and they would only do that if a) they had to by law;; or b) the ROI over the asset lifetime for renewables is going to be better. I believe SA has proved it can work.. there were teething problems; there were external problems, but they have taken the lead; proven it, so we should follow..

 

Hopefully, before long, we won't have to feel (or have other people attempt to make us feel) guilty when we go flying. Pipestrel already have electric planes; others are working on them, and there is hydrogen powered and hybrids being developed both for regional commerical and GA... Clear skies so we reduce our carbon footprint and reduce the lead and other poisons we put into the atmosphere. Again.. .

 

Bring it on!

 

Edited September 26, 2020 by Jerry_Atrick

[nomadpete]

Jerry, thanks for a great post. I'd love to have you drop in for dinner and debate, any time. But I warn you, it might be a long debate. Don't worry, in spite of us sharing many views, I'm pretty sure we'd keep it lively but harmless.

 

[old man emu]

The year 1816 is known as the Year Without a Summer  because of severe climate abnormalities that caused average global temperatures to decrease by 0.4–0.7 °C (0.72–1.3 °F). Summer temperatures in Europe were the coldest on record between the years of 1766–2000. This resulted in major food shortages across the Northern Hemisphere.

 

Evidence suggests that the anomaly was predominantly a volcanic winter event caused by the massive 1815 eruption of Mount Tambora in April in the Dutch East Indies (known today as Indonesia). This eruption was the largest in at least 1,300 years (after the hypothesized eruption causing the extreme weather events of 535–536), and perhaps exacerbated by the 1814 eruption of Mayon in the Philippines.

 

This period also occurred during the Dalton Minimum (a period of relatively low solar activity), specifically Solar Cycle 6, which ran from December 1810 to May 1823. May 1816 in particular had the lowest sunspot number (0.1) to date since record keeping on solar activity began. The lack of solar irradiance during this period was exacerbated by atmospheric opacity from volcanic dust.

 

Solar activity also affects our climate. The solar cycle or solar magnetic activity cycle is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the solar surface. Solar activity, driven both by the sunspot cycle and transient aperiodic processes govern the environment of the Solar System planets by creating space weather and impact space- and ground-based technologies as well as the Earth's atmosphere and also possibly climate fluctuations on scales of centuries and longer.

 

With all these things going on, it makes one wonder how significant is Mankind's contribution. As for methane production, how much methane would a large population of herbivorous dinosaurs have produced during the life span of one of the herd?