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Science communication is important in today's technologically advanced society. A good part of the adult community is not science saavy and lacks the background to make sense of rapidly changing technology. My blog attempts to help by publishing articles of general interest in an easy to read and understand format without using mathematics. I also give free lectures in community events - you can arrange these by writing to me.

Monday, 21 January 2019

Global Greenhouse-Gas (GHG) Emissions by Humans and Animals - An Outreach Feature

Who am I?  Blog Index

Nothing will benefit health and increase chances for survival of life on Earth as much as the evolution to a vegetarian diet.          ...Albert Einstein (quoted)

Greenhouse gases (GHG - mostly carbon dioxide CO2, methane CH4 and nitrous oxide N2O) in the atmosphere trap heat radiated from the Earth and keep it at a comfortable temperature of 14C . Without GHG the Earth will be  about 32 degrees colder with an average temperature of -18C - life would be impossible. During an ice age, the average global temperature only falls by about 7 to 10 degrees.

Since the first industrial revolution, humans have been putting more CO2 and other GHGs in the atmosphere with a sharp increase in the 20th century.  Population numbers have gone up too; the following slides show the steep rise in GHG over the past 100 years.  This has resulted in the Earth warming by about 1C over this period. 

In 2017, total CO2 emissions from fossil fuel and industry were 36.8 billion tons; CO2 stays in the atmosphere for over 100 years. 
Total annual methane emissions had reached 623 million tons in 2016. 
The residency time of methane in the atmosphere is about 12 years.

(Click on a slide to see its full page image, press ESC to return to text

Methane is a potent GHG.  Over a 20 year period, methane has 86 times greater global  warming potential than carbon dioxide. Many publications quote a global warming potential of methane as 26 over a 100 year period. 

We normally attribute the rise in GHGs to increased industrial,  transport and agricultural activity based around the burning of fossil fuels (coal, oil and natural gas).  Most publications do not discuss GHG emissions due to metabolic activity in humans and their livestock, both have increased fourfolds in the past 100 years. 

I shall estimate such metabolic contributions using 'back of the envelope' calculations.  The simple calculations give surprisingly realistic results and help the non-specialist general population to understand this aspect of the science behind global warming.

GHG Emission by Humans and Animals: 
Are we heating the planet as we breathe?

Many news articles mention the role of cattle in emission of the greenhouse gas methane, but it is not widely appreciated that humans and animals also emit significant amounts of CO2 which contributes to the GHG budget and to global warming. I shall estimate these numbers in the following: 

Carbon dioxide emission by humans:  Humans inhale atmospheric air containing CO2 at 0.0004% concentration but exhale air with CO2 at 5% concentration. (I shall use rounded numbers for ease of calculation).
The following slide provides more details:
CO2 is a product of metabolic activity (respiration).  While it is possible to calculate the amount of CO2 emitted by using volume of exhaled air and breathing rate (I have described the calculation at the end of this blog), it is easier (and probably more accurate) to work out the amount of CO2 produced per day by the aerobic respiration reaction in which glucose uses oxygen to produce energy, water and CO2.  
For our purpose, it suffices to say that carbohydrates in the food are broken down to glucose molecules and the reaction may be written as

     Glucose   +   Oxygen    ->    Water  +  Carbon dioxide  +   2886 kJ Energy
    C6H12O6  +   6 O2      →        6 H2+  6 CO2                +       heat 

Essentially, one molecule of glucose uses 6 molecules of oxygen to produce 6 molecules of CO2.  The molar weight of glucose is (calculated from its formula) 180 and that of CO2 is 44.  
This means that 180 gram of glucose burns to produce 6 x 44 = 264 gram of CO2.  
Assuming that we consume 2000 Calories per day and carbohydrates produce 4 Calories per gram, we are burning equivalent of 500 gm of glucose per day in aerobic respiration. 
This will produce 500 x 264 /180 = 733 grams of CO2 per day or 268 kg/year.
Each of us produces this amount of CO2 per year.  The world population is over 7 billion and will produce 1.87 Billion Tonnes of CO2 per year.  This is 5.2% of the total CO2 put into the atmosphere by human activity.

What about Animals?  The main population of animals is comprised of those reared for human consumption - cattle, sheep, pigs, poultry etc.  Their numbers have sharply increased in response to increasing human population and higher demand of meat over the past 50 years or so.

Additionally, there were about 23 billion poultry in the world in 2014.  
Livestock animals exhale CO2 generated in the respiration process - most amount is exhaled by cattle which are much bigger in size than other livestock animals. 

The metabolic energy requirements of a mammal vary as  0.75 power of the body mass, we can calculate for a given body mass how much CO2 per day an animal will produce.  The table shows the amount of CO2 exhaled by livestock animals.  The emissionn of methane is also given.

In conclusion, humans and livestock release 
1.87 + 6.65  = 8.52 billion tons of CO2 in the atmosphere per year. This number has increased fourfold in the past 100 years. Only China emits more CO2 than humans and animals exhale (2015 figures in billion tons per year: China 10.6 and USA 5.2)!

Methane Exhaled by Livestock:   The table above 
gives methane emisssions from various livestock animals.  Meat cattle are the main source of methane.  Exhalation represents about 96% of total methane put into the atmosphere by the cattle - there is a common misunderstanding that cattle emit methane by farting but that only contributes a tiny %.  Most exhaled methane is produced in rumination.

Wiki explains: Ruminants are mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The process, which takes place in the front part of the digestive system and therefore is called foregut fermentation, typically requires the fermented ingesta (known as cud) to be regurgitated and chewed again. The process of rechewing the cud to further break down plant matter and stimulate digestion is  called rumination.   

Currently, we are putting in 623 million tons of methane in the atmosphere every year.  Of this 110.7 million tons ( ~ 18% is emitted by livestock rumination - enteric fermentation or EF).  These numbers have been revised upwards by 11% in 2017 by Wolf et al.  In 2010, EF accounted for 43% of all GHG emission from agricutural activity in the world. 

Remember that biggest increase in methane emissions is due to meat cows and pigs (their numbers have gone up fivefold over the last century); more people are consuming meat that will only make the situation worse.  

Manure Treatment is a serious source of Methane too:
It is not only that livestock exhale methane (product of the rumination process in cattle) but the storage and treatment of manure from the livestock is also a serious source of methane.

Manure is stored in tanks, lagoons where microbial activity causes its deacy.  Anaerobic breakdown produces greater amount of methane and a switch to aerobic decay will reduce the emission of methane.

Final Word:  In this blog, I have used the population numbers and emission of carbon di-oxide and methane by individual animals to calculate the total contribution to GHG emossions that humans and their livestock make.  Additional emission will also come from other animals that I have not considered.  

The warming of the world due to GHG emissions is predicted to reach at least 2 degrees centigrade by the end of the century.  Human and Livestock emissions can be most effectively reduced by population control - while the human population is supposed to stabilise around the 10 billion mark in the next 50 years, livestock population can only decrease if we change our emphasis to eating meat - this is a trend that has a lot of mementum and is unlikely to change in the near future.

Better manure management (using aerobic storage tanks) will help but that is not the major contribution.  Pasture grazed cattle emit less methane but again it is not a practical solution if we all insist on eating meat-rich diet.  


Thanks for reading...

Friday, 11 January 2019

SLEEP (Part 1): Why Do We Need to Sleep Eight Hours per Day? Malaise caused by Impaired, Insufficient Sleep: A Community Education Feature

Who am I?  Blog Index

Sleep is the 3rd pillar of good health, alongside diet and exercise

Early to bed and early to rise, makes a man healthy, wealthy and wise (ref)
Sleep is the best meditation                         ...Dalai Lama

Humans spend about a third of their lives sleeping.  
There has to be an evolutionary reason.  

Why do we need to sleep so much and what advantages we derive from it?  
Or one can turn the question around and ask 
what happens if we do not sleep enough or sleep poorly?

Historically, most people thought of sleep as a dormant, switched-off state of the body - an unproductive time. However, recent research has established the relevance of sleep for humans and animals with the clear message that sufficient sleep (7 to 8 hours) is not only important for our physical and mental health/welfare, but a lack of sleep has many unwelcome serious consequences. 

(Click on a slide to see its full page image. Press ESC to return to text)

It is not only that many adults do not get enough sleep, the quality and regularity of sleep in lot of people is relatively poorMany adults are curtailing their sleep or obtain 'low-quality' sleep  in response to increasing demands and lifestyle changes, such as prolonged working hours, increased environmental lighting, introduction of new communication technologies, which enable living 'round the clock'.  A National Sleep Foundation Survey in five OECD countries found that 20% of the working population sleeps less than 6 hours per 24-hour day. (see also and also).  

In the following sections, I shall present some disturbing findings as to how sleep deprivation (length or irregularity or both) affects our health and well-being. 

Sleep and Productivity:  Rand Corporation Report (2017) estimates that sleep deprivation of workers has serious impact on a country's GDP:

   Country                          GDP Loss 
                              billion US $        % GDP
    USA                         411             2.28
    UK                             50             1.86
    Japan                       138             2.92
    Germany                    60             1.15
    Canada                      21             1.35

Sleep and Mortality:  One might think that sleeping longer than 8 hours or using drugs to help you sleep (hypnotic medication) will be the solution.  That will be a big mistake.  Both choices have been shown to be extremely harmful and significantly increase the odds of premature death. 

Sleep and Traffic Accidents/Sports Injuries: 

Sleeping less than the recommended amount adversely affects neuro-cognitive performance; verbal and visual memory, co-ordination, reaction time are seriously affected. The impairment in these abilities is higher for greater sleep deprivation.  
In adults, sleep deprivation manifests itself as slower than normal reaction time, reduced alertness/concentration, shortened attention span, forgetfulness, poorer memory, involuntary sleeping (microsleep) lasting from a few seconds to a few minutes etc. 

I discuss two examples in the following:

In their 2016/17 report, AAA has published a detailed analysis of police-reported serious vehicle crashes in the USA during the 2005-2007 period. The study indicates that there is a significantly higher crash risk for drivers who slept for less than 7 hours in the past 24 hours; and also for drivers who slept 1 or more hours less than they usually sleep. 

A similar effect of sleep deprivation is observed in incidences of sport injuries in teenagers.

A recent study (March 2019) found that moderate-to-severe insomnia more than tripled the college athletes' risk of concussion, and excessive daytime sleepiness - even just a few days a month - more than doubled it.  The chance of getting a sports-related concussion during the next year was 14.6 times higher for those with both insomnia and excessive daytime sleepiness than for those who were well rested. See also.  See here and here.

Insufficient/poor quality sleep seriously affects the elderly who tend to sleep 6 hours or less.  It is not correct that old people can manage with less sleep  - they also need 7 to 8 hours sleep per day but for various reasons are unable to do so.  This has serious health consequences as we shall discuss in the following sections.

The modern society puts lot of obstacles in young childrens' sleeping patterns.  Using electronic screens (TV and smart phones) near bedtime disturbs the circadian rhythm and can cause difficulty in falling asleep.  To attend school at 9 am, most children wake up by 7 or 8 am - leaving insufficient time to get the recommended sleep of 10 to 11 hours for primary school pupils.  

Physiological Effects of Sleep Deprivation:  The quantity and quality of sleep is important for our physiological health. Sleep deprivation has been linked to many health problems like obesity, cardiovascular disease (CVD),  depression, type-2 diabetes mellitus (DM), ADHD and Alzheimer disease (AD).  I shall discuss some of the evidence in the following:

Sleep and Obesity:  Many studies in animals and humans have found good correlation between sleep deprivation and weight gain.  Essentially, lack of sleep slows the metabolic rate - even a couple of hours loss of sleep can reduce metabolism by 5 to 20%.  Sleep-deprived humans also show increased appetite - particularly, for calorie-rich carbohydrates. When you are sleep deprived, you have more grehlin (hormone that tells you when to eat) and less leptin (hormone that tells you when to stop eating).  More grehlin and less leptin equals weight gain that can lead to obesity. 

Sleep and Diabetes:  Weight gain and obesity are implicated in the rising number of diabetics.  Sleep deprivation increases the likelihood of gaining weight leading to diabetic condition.  
In a study, healthy young men were sleep deprived for 4 hours on six consecutive nights.  Their average blood glucose level increased by 270 mmol/L (or 15 mg/dl) and insulin response to glucose was 30% lower – essentially they became prediabetics (thankfully reversible) after just six days of sleep deprivation. Changes in metabolic and endocrine (hormone production) functions, driven by impaired sleep, predisposes individuals to clinical diabetes.

The following slide suggests that sleep deprivation may be an independent risk factor in the development of diabetes.

Sleep and Hypertension:  Restricting sleep durations has been shown to raise blood pressure and heart rate.  Chronic sleep deprivation can raise the average 24-hour blood pressure with the result that the cardiovascular system operates at a higher blood pressure, thus increasing the risk of hypertension.

Timing of sleep can also disrupt your body-clock (circadian rhythm) and lead to increased blood pressure by disturbing heart function.  

Sleep and CVD:  Current data indicates that people with impaired sleep are at higher risk for cardiovascular (CVD) and cerebrovascular disease (strokes) - regardless of age, weight, smoking and exercise habits. 
The slide shows the situation for adult population:
The association between long duration (9+ hours) and CVD may be explained by other factors - for example, depression, low socio-economic status, unemployment, low level of physical activity and undiagnosed health conditions have been shown to be associated with long duration of sleep. The association between long sleep hours and CVD may be reflecting the role of long sleep as a marker, rather than a cause. A 7-year study of weight reduction, healthy diet and increased physical activity supports the view that long sleep may be an indicator of risk that can be successfully managed.
Sleep is equally important for the young as well.  Adolescents who do not sleep well are at greater risk of developing ailments related to CVD.  Sleep deprived teenagers were observed to have higher cholesterol levels, higher BMI, higher blood pressure  - all indicators of major health issues in later life. 
For a recent review click here

Sleep and Cancer:  Evidence on the association between sleep duration and cancer risk is controversial, with findings showing inverse, positive, and null effects.  A recent (2018) review of the available information indicated that neither short nor long sleep duration was significantly associated with cancer risk. I refer you to this very extensive study, available online, for more details. 

Sleep and Mental Health:  Sleep and mental health are closely connected. Sleep deprivation affects one's psychological/emotional state and can lead to mental health problems; conversely, people with mental health issues find it difficult to get good quality sleep (Likelihood of  a psychiatric patient to suffer from sleep problems is about 5 times greater than somebody without mental health issues).

The most common sleep problems are insomnia (difficulty in falling or/and staying asleep), sleep apnea (waking up frequently due to disordered breathing like snoring etc) and nacrolepsy (falling asleep suddenly during the day).  Studies have found that, in both adults and children, lack of good quality sleep can directly contribute to  mental health illnesses like depression, anxiety etc. 

The brain basis of a mutual relationship between sleep and mental health is not well understood. Studies suggest that a good night's sleep helps mental and emotional resilience, while chronic sleep disruptions set the stage for negative thinking and emotional vulnerability.

Sleep and Alzheimer Disease (AD):  Incidence of AD, and dementia in general, has increased in the past few decades and the projections do not make comfortable reading.  AD is an irreversible, progressive brain disorder that slowly destroys memory and thinking skills, and eventually the ability to carry out the simplest tasks.
At present, there is no cure for AD and the burden of care of AD patients puts large demands on the society.  The infographic from the World Alzheimer Society is quite revealing about the seriousness of the dementia epidemic.  (Click here for the full report). 
The brain of AD patients is found to have many abnormal clumps of proteins (amyloid plaques), tangled bundles of fibrous proteins (tau tangles) and severe loss of connections between nerve cells (dead neurons). 

Hippocampus (essential in forming memories) is affected first.  As neurons die, other parts of brain are affected and by the final stages of AD, the brain tissue has shrunk significantly.  Genetics, lifestyle and environmental factors play a role in AD but the detailed mechanisms are still not well understood.

There are 47 million people living with dementia worldwide with numbers projected to nearly double every 20 years, increasing to 75 million by 2030 and 131 million by 2050!  The cost of dementia is huge - in 2018, the global cost of dementia is estimated at US$1 trillion rising to $2trillion by 2030.

There is mounting belief among research scientists that sleep problems and Alzheimer's pathology may be connected. Multiple studies have shown that people with dementia often experience sleep disturbances, and other studies, using positron emission tomography (PET), have shown build-up of amyloid plaques in the brains of adults and animals who slept poorly or had inadequate sleep. The following shows the possible connections:

The glymphatic system (brain's sewage network) is responsible for removing the metabolic debris that is produced in a functioning brain.  Amyloid protein molecules are part of the debris.  The cleansing of this debris is done in the night when you are deeply asleep. During the non-rapid eye movement (NREM) sleep (more on it in Part 2), glial cell size is reduced by 60% allowing the cerebro-spinal fluid (CSF) to efficiently flush out the amyloid and tau proteins and other stress molecules produced by neurons.  
In sleep deprivation, the cleansing process is inefficient with the result that amyloid proteins collect and form sticky plaques around the neurons and cause them to die.  

In this Part 1, I have listed some of the health implications of sleep deprivation.  There are other issues, e.g. effect on reproductive system, infection rates, immune system etc. where sleep deprivation can have serious negative effects.  A good reference to learn more about this subject is the book entitled 'Why We Sleep' by Matthew Walker.

In part 2, I intend to look at the nature and science of sleep and its relation to the body clock (circadian rhythm). We shall discover that it is not only the duration of the sleep that matters but also the time of the day that we sleep.

Final Word:  In the '24-hour' world, sleep is a precious commodity.  Long distance travel, shift work, school start times, smart phones, TV in bedrooms, long work and commuting hours disturb the body clock and distort the sleep/wake cycles.  Ever stayed in a hospital overnight? The constant traffic in the wards and check-ups make it impossible for the patients to get rest - not helpful for their recovery.  The relevance of sleep in the maintenance and promotion of good health is not appreciated/acknowledged by the modern society  - even health professionals never discuss this issue.  

Collectively, the modern society is sleep-walking into the vicious circle of sleep deprivation and poor physical and mental health. 

A footnote about the studies referred to in this blog.  Most data on sleep duration was self reported by those taking part in the study - this may be problematic sometimes.  Wrist-worn actigraphy bracelets are non-invasive and provide much more reliable information about sleep.

I would love to receive your comments - please send them to ektalks@yahoo.co.uk 
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