How Many People Can Live on Planet Earth?

[WoodDragon]

[Deleted - double post]

Edited February 18, 2011 by WoodDragon

[WoodDragon]

WD- We will discuss this further in a more suitable thread. Oh how much better this would be in person ....... Maybe one day

In person would be much easier in many ways, as it doesn't take nearly as long to get a point across as a blog conversation does, and digressions can be made instantly.

Thankyou for the calc of 1/4 of a second, it did have me thinking.

Be careful not to underestimate the extra time per day if all the ice melts - it's 2/3 of a second, which is 2 and 2/3 times more than 1/4 of a second... That's a whole lot longer to wait between birthdays if we melt the poles!

On another note, you mentioned about the legitimacy of when the data is collected in the south pacific, but what makes your figures anymore reliable.

If you're referring to my comment at the 3rd paragraph of post #214, I was actually talking about the rate of sea level increase over recent decades, compared with the rate of increase at the beginning of the 20th century. My point there was that the rate of sea level rise is increasing with time, as ever-increasing warming of the ocean leads to thermal expansion of water, and to the beginnings of ice melt.

On your point, however, recent (i.e., the latter half of the 20th century) data is likely to be more precise, as technology is better now compared with earlier measurements, and because there are more measuring stations. The precision of older measurements though is sufficient to still easily discern the rise of sea level - have a look at the confidence intervals of the first graph here, or on page 12 here (note that the second graph depicts the change in the rate of SL increase). In each of the graphs you will see that precision tightens with time, but not remarkably so, because it was already quite tight to begin with. Contrary to what many people seem to think, scientists and engineers in the centuries prior to the electronics age actually knew how to make precision instruments and measurements - just look at some of the chronometers that were used on ocean tallship voyages to monitor longitude: they are exquisite examples of instrumentation.

We are both basing our ideas on work by someone else, so I don't know what makes your facts any more special.

It's not a matter of my facts or your facts, really. It's a matter of the validity of the facts (and their explanations) that have been passed to you, and of those that I have tested myself.

In my work as a scientist I have read many of the relevant sea level rise articles (and as an aside, in this Australia is lucky to have a world-renowned scientist in the discipline in John Church) and I have even contacted oceanographers directly to corroborate methodologies and to get raw data for analysis. I do have some idea about how to check the reliability of the major statements made by other scientists. Often the statements made by people claiming no sea level rise are based on data used by scientists themselves, but the data are not properly explained or faithfully interpreted.

Which leads me to:

The graphs I posted above are just as reliable as any of the tidal graphs or computer models by the CSIRO

If you're referring to the graphs at #207, then these graphs are actually an interesting thing to raise, because they serve as a small case history to exemplify the manner in which data needs to be considered.

There are a number of things that need to be taken into account when referring to specific data sets. The first I've mentioned before, which is that over short periods of time (say, 30 or 40 years) the natural tidal variation can swamp the underlying sea level rise, and there is essentially no visible trend. Linear regression may tease it out, but the variability of the data on this time scale may swamp the real trend if the data from the station is not of top quality.

Which leads to the next point. There are many stations out there for which there are datasets available. It doesn't mean that the data is applicable to sea level rise analysis though... Often tide gauges are located in estuaries where there is dredging; damming upstream; riverbank alterations/constrictions/etc; mouth modification; and/or local subsidence or uprising. It's quite valid to have gauges in such locations, even if they do not accurately reflect global sea level trends, because their primary functions are not to monitor global sea level, but to monitor local tide trends and local waterway navigability. Many people new to the sea level rise kerfuffle are surprised to learn this, but it is actually the case.

To determine global trends marine hydrologists are careful to use only the best data, from the best stations, and to correct for known biases - for example if a gauge is moved - using the best calibration techniques. Of course, there is always error in measurement (it's the first lab lesson that new science students learn in first year uni), and professional hydrologists know what the uncertainty intervals around the data are. Personally, what I find interesting is how well tide gauge measurement do agree with satellite measurement - the two methods are completely independent of each other and yet they track remarkably closely, as the inset on figure 3a of the Church et al paper shows.

So yes, your graphs are actually quite reliable - you just need to know what they show and what they don't show, and to ask the right questions, based on the correct provisos, when you are using their data.

Edited February 18, 2011 by WoodDragon

[random]

Was that just the longest post in the history of the forum or what?

Nevertheless still interesting to read both sides ..

[ThunderIdeal]

not by a long shot.

[7baz]

curiosity question...

if we were to triple the population say in the next ten years...

are we not going to start starving off oxygen in the air ?

because to fit say 30 billion people on the planet.. then that means more trees have to come down to make communities etc etc.

trees play a big part in our oxygen levels.

Edited February 18, 2011 by 7baz

[ThunderIdeal]

it mainly comes from the ocean, and as i think has been discussed there is a useful thing happening where increased carbon dioxide causes increased growth for oxygen producers. surely the last of our worries.

[WoodDragon]

Arghhh!!!

This is my second attempt at typing this, after I lost a post about double the size of my last one because I hit the 'refresh' button rather than the tab scroll.

And then my broadband died...

Anyway, the brief version...

I used to think that most oxygen was produced by marine photosynthesis, exactly as ThunderIdeal suggested, but when I looked for the numbers, I found that terrestrial sources are apparently greater, if table 2 here is reliable. I was a little surprised by this, as I had heard figures of up to 70%, but there you go. What's not in doubt is that oxygen was originally produced in the oceans when life arose on the planet, even if the marine environment is not the largest source today. If anyone is really interested I can try to corroborate the figures, but I won't have time for a while to do this.

In terms of human population increase and oxygen depletion, there are a couple of factors to consider. First, the day-to-day oxygen use by respiration is fairly quickly turned over by photosynthetic CO₂ photolysis during carbon fixation, ans so the overall use and recovery of oxygen balances out. Secondly, the use of oxygen by a tripling human population would also be balanced out by a concurrent reduction in biomass elsewhere in the biosphere, as we use the carbon/energy flux that would otherwise have been used by other species.

If one wants to see some numbers though, consider these...

A tripling of the human population would result in an additional 14 billion people. Given that the human body is 65% oxygen by mass, and assuming that the average human weighs 60 kg, that represents 0.65 x 60 x 14 x 10⁹ = 5.5 x 10¹¹ kg.

That seems like a lot, doesn't it?

Be aware though that the total mass of oxygen in the atmosphere is around 1 x 10¹⁸ kg. This means that there is 1 x 10¹⁸/5.5 x 10¹¹ = 1.83 x 10⁶ times more oxygen in the atmosphere than there would be in 14 billion humans.

In other words, there is more than 1.83 million times as much oxygen in the atmosphere as would be embodied in 14 billion extra humans.

Therefore tripling the population of the planet is not going to make any significant difference to the atmospheric concentration of oxygen, even if the oxygen weren't simply being moved from other parts of the biospheric biomass.

This is not to say though that humans don't have an impact on atmospheric oxygen concentration. We certainly do, both by our direct and indirect impacts on the functioning of the photosynthetic component of the biosphere, and by our burning of fossil fuels. When we oxidise carbon, or carbon compounds, oxygen is bound up in the combustion products. Consider the following oxidation reactions:

1) C + O₂ -> CO₂

2) CH₄ + 2O₂ -> CO₂ + 2H₂O

3) 2C₄H₁₀ + 13O₂ -> 8CO₂ + 10H₂O

4) 2C₈H₁₈ + 25O₂ -> 16CO₂ + 18H₂O

The oxidation of carbon (Eq. 1,) such as coal/peat, results in one atom of carbon causing the binding of 2 atoms of oxygen.

The oxidation of one molecule of methane (Eq. 2), results in one atom of carbon causing the binding of 4 atoms of oxygen.

The oxidation of one molecule of butane (Eq. 3), results in four atoms of carbon causing the binding of 13 atoms of oxygen.

The oxidation of one molecule of octane (Eq. 4), results in eight atoms of carbon causing the binding of 25 atoms of oxygen.

The oxidation of aromatic hydrocarbons, and of hydrated, halogenated, and other substituted hydrocarbons, is much more complex. And then there is the complication of non-complete oxidation. However, the overall effect of the combustion of fossil fuels on the oxygen concentration in the atmosphere can be calculated, and it apparently works out to about a 0.07% to 0.09% reduction of the total atmospheric oxygen content. When the biospheric photolysis of, and the hydrolithospheric sequestration of, CO2 is accounted for, the amount of oxygen lost from the atmosphere is closely reflected in the stoichiometry of fossil fuel burning (see the oxygen slides here: warning - 8 mB in size).

This is not a lot proportion-wise, although it is still an appreciable amount - to frame it differently, humans have to date caused to be removed, a little under one one-thousandth of the oxygen from the atmosphere. It's impressive that we have reduced it even this much, but seriously, oxygen depletion at this rate, by fossil carbon burning, is not a significant concern.

Although we're unlikely to remove any serious proportion of oxygen by burning fossil fuels, we could easily alter the oxygen balance by our potential impacts on photosynthesis. Our pollution and habitat destructions/modifications could quite conceivably worsen in the future, and have a much more profound effect than they do now.

To put a context on the issue of oxygen, about 20.95% of the atmosphere is oxygen. Humans require a range of 19% to 23% oxygen: we don't do well with more, and below 19% we start to go wobbly. Below about 15% and we die fairly quickly.

A more serious matter in the future than oxygen depletion is CO₂ increase. One of the things that's not often mentioned is that CO₂ competes with oxygen for binding sites on haemoglobin, and when the external (atmospheric) concentration of CO₂ increases, the capacity to unload it from the lungs decreases. We won't see detectable effects in our lifetimes, but if humans keep burning fossil fuels for a few more human lifetimes then our decendants will live in a world where taking a lungful of air is a different experience to the one that we enjoy.

From Wikipedia:

...the U.S. Occupational Safety and Health Administration says that average exposure for healthy adults during an eight-hour work day should not exceed 5,000 ppm (0.5%). The maximum safe level for infants, children, the elderly and individuals with cardio-pulmonary health issues is significantly less.

Several points... The 'significantly less" can be anything up to half (or more) of the 0.5% limit. And the limit is based on 8 hours of exposure per day. No-one really knows what the safe upper limit is for permanent exposure to CO₂, but it will be less than the occupational exposure limit.

We're currently at 390 ppm CO₂ (0.039%) in the atmosphere, from a starting point of around 280 ppm. The cur

ane clathrates, then this level could be easily achieved.

Of course, it's unlikely that we could c

uts things into a perspective...

[Edit: just noticed that I lost some of the last two paragraphs in an earlier edit. I'm too buggered now to fix them, so I'll come back later]

Edited February 19, 2011 by WoodDragon

[Guest svarg26]

we need a carbon tax to save us all. it is the only way. thank you woody, you have made me realize that paying more tax will stop the sea level from rising and the sun from getting too damn hot. we need a system in place that only benefits the elite. the mass production of useless plastic crap from the corporations at inflated prices with carbon offsets is definitely the only way to save the planet. we need to cull the population through poisoning the food and water supply. we need to fabricate a drought through mismanagement of the river systems and tax private dams into oblivion to force farmers who don't grow gmo crops off of the land and reduce local food production, so that we can say that there is not enough food to go around. we need more excuses from corporate shills like woody to usher in the new world order.

How Many People Can Live on Planet Earth?

just enough people needed to serve the ruling elite. how does 300 million sound?

look about right to you? woody.

[WoodDragon]

Svarg26:

...we need a system in place that only benefits the elite. the mass production of useless plastic crap from the corporations at inflated prices with carbon offsets is definitely the only way to save the planet. we need to cull the population through poisoning the food and water supply. we need to fabricate a drought through mismanagement of the river systems and tax private dams into oblivion to force farmers who don't grow gmo crops off of the land and reduce local food production, so that we can say that there is not enough food to go around. we need more excuses from corporate shills like woody to usher in the new world order.

How Many People Can Live on Planet Earth?

just enough people needed to serve the ruling elite. how does 300 million sound?

When did I say any of that rubbish? Times and dates and links, please. And if you actually knew me you'd know that I am about as far from being a coroporate shill as anyone could be.

You are putting words into my mouth, and quite inappropriately.

I don't know what that makes you, buy I do know that it's not a very nice thing to do.

Your mother must be so proud.

Edited February 21, 2011 by WoodDragon

[The Dude]

To be fair, he didn't say you said any of that. Just called you a corporate shill. Which is pretty mean, like calling someone an idiot I guess.

Edited February 22, 2011 by The Dude

[Slybacon]

Svarg26:

When did I say any of that rubbish? Times and dates and links, please. And if you actually knew me you'd know that I am about as far from being a coroporate shill as anyone could be.

You are putting words into my mouth, and quite inappropriately.

I don't know what that makes you, buy I do know that it's not a very nice thing to do.

Your mother must be so proud.

 

I'd have to agree with the dude here. Getting offended only lends to your situation.

[Teotzlcoatl]

We are supposed to reach 7 billion by 2012... let's have a big party

[synchromesh]

Is that with or without aliens?

[Guest svarg26]

and jesus will pop in to put his stamp of approval on the ruling elite.