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Monday, November 13, 2017

Computer Sentience

The great ethical debate in the year 2100 will be about the civil rights of sentient machines. 
The great ethical debate in the year 2200 will be about the civil rights of sentient humans.  
OK, that’s supposed to be a joke.  But let’s think a bit about the possibility of sentient machines.

Life is immaterial and ephemeral.   One moment after death, a being has all of the same solids and fluids, all of the same atoms and molecules as at a moment before death.   But something mysterious has departed.  Life exists as a collection of electrical impulses and chemical changes.  The idea of a living, immaterial, non-physical spirit is a powerful one, and most people throughout history subscribe to the idea that all living creatures are endowed with such a spirit.   But no such spirit has ever been reliably observed.  On a scientific basis, we must presume that life consists solely of the electrical and chemical interactions that animate our muscles and minds.

Consciousness, too, must be a matter of electrical and chemical physical properties.  It should not be a surprise. We can influence consciousness with as chemicals diverse as caffeine, TCP, or LSD; and we can stimulate memories with electrical impulses to the brain.  Is there any reason, then, why machines using complicated patterns of electrical connections could not become as conscious and aware as humans? 

Examples from Science Fiction
Science fiction and science fiction authors have proved to be remarkably prescient about future technology and social issue, and there are innumerable examples of computer consciousness in science fiction.   Considering the remarkable consensus of science fiction authors about the possibility of computer consciousness, I am inclined to believe that it is a real possibility.   I think it is time to consider in what form it may occur, and what implications it will have for mankind.

Here are a few sentient machines from some of my favorite science fiction stories.

Character            Type                  Book or Show                                              Author
Mycroft              Mainframe           The Moon is a Harsh Mistress                     Robert Heinlein
Daneel Olivaw   Android                The Caves of Steel                                       Isaac Asimov
Colossus             Mainframe           The Forbin Project                                        Michael Crichton
Data                    Android                Star Trek, Next Generation                          Various
Samantha           AI Program          Her                                                               Spike Jonze
Marvin                Robot                    Life, the Universe and Everything              Douglas Adams
Bender                Robot                   Futurama                                                     Matt Groening
Jay Score            Robot                   Jay Score                                                      Eric Russell
Einstein               AI Program          Beyond the Blue Event Horizon                  Fredrick Pohl
Tardis                  Time-Ship            Dr. Who Series                                             Various

There are dozens of other examples in science fiction. What makes these stories interesting is the range of thoughts and behaviors exhibited by the sentient machines.  And in a way, the stories are explorations of what it means to be human and sentient.  In some of the stories, machines threaten mankind; in some stories they save mankind.  Sometimes they bond as friends with human characters; sometimes they question their own lack of humanity.  But as drawn by the authors, they are unquestionably alive.
Image from the film "I, Robot", screenplay by J. Vintar and A. Goldsman, 
after a collection of stories by Isaac Asimove. 

Today, artificial intelligence is one of the fastest developing fields of technology.  Artificial Intelligence is expected to understand our spoken speech, speak meaningfully in response, act as clerks or servants, interpret our instructions from gestures, render judgments and decisions in complex fields such as medicine, recognize and appropriately classify images and scenes, drive our cars, work in our factories.  Ultimately, artificial intelligence may design and improve its own replacements.  At this time, there are no known limits to what artificial intelligence can do.

But all of this is less than what we see in science fiction.  Few computer specialists would believe that today’s artificial intelligence is anything living.  AI programs execute instructions from programmers, and in some cases, can adapt that programming based on input from the external environment.  But even then, the program is simply performing as it was designed, without motivation or will.  It isn’t alive.

What, then, would be the hallmarks of a sentient machine?  What qualities would it have that differ from today’s artificial intelligence?  Would we recognize a sentient machine if we saw one?

Here is a list of the qualities that I think are necessary to the definition of sentience.
Consciousness – Awareness of the surrounding environment.
Self-awareness – The ability to say “I am”, without being asked.
Personal Memory – The ability to remember former analyses (thoughts) and actions.
Thought -- the ability to think in processes, make forecasts and predictions based on processes, rather than pattern recognition.
Will – The deliberate decision to perform or not perform an action according to self-determined reasons.
Empathy – The ability to recognize other beings as sentient.

Consciousness is hard to define.  In the biological world, I think that consciousness is a gradational quality, rather than a discrete property.  No one would suggest that a virus is conscious, and yet it has some property of life which is greater than that of a piece of rock.   But most would agree that a worm is more conscious than a virus, and a dog is more conscious than a clam.   And perhaps a colony of bees is more conscious than an individual bee. 

Both computer programs and flatworms can respond to external stimuli.  Flatworms can be trained to avoid stimuli associated with pain, and seek stimuli associate with food.  Perhaps these actions demonstrate the emotions of fear and pleasure.  But it is unclear if the responses of either flatworms or computers are aware and knowing responses, or simply the results of chemical and physical programming.

Definitions of consciousness include awareness of exterior and/or interior things.  But the definition and observation of awareness is difficult, even in humans who have suffered brain damage.  The identification of consciousness, separate from the qualities of self-awareness and free will, will be very difficult to recognize in computer intelligence. 

Personal Memory
Personal memory is a critical part of human personality.  I define personal memory as the memory of prior thoughts (analyses) and actions.  Personal memory is distinctly different than computer memory which is used to hold data for processing.  It is the memory of performing previous processes, and the memory of those results.  This kind of memory allows people to learn, and to develop preferences which reflect personality.  Without personal memory, a machine could never develop self-awareness or will.

When we wake up in the morning, personal memory is what allows us to know that we are the same person who went to bed the night before.  Or more directly, personal memory informs us that we are the same person from moment to moment. 

Machine learning algorithms must have some kind of personal memory, recording and comparing previous analyses to new ones.  The type of memory probably depends on the type of machine learning algorithm.  Some kind of personal memory, perhaps developed from machine learning, will be a necessity for a sentient machine. 

My son gave me the simplest definition of self-awareness: The ability to say “I am”, without being asked.  But perhaps this is a little too glib.  Like consciousness, living creatures span the range from clearly not self-aware, to fully aware. 

A test performed with some creatures uses a mirror.  A parakeet can be kept company by a mirror, never realizing that the parakeet in the mirror is not a companion.  A cat is initially mystified by a mirror, but may eventually realize that the cat in the mirror is not another cat.  A great ape will almost immediately realize that the image in the mirror is itself. 

It seems to me that for a digital entity, self-awareness implies a recognition of external reality and the separation of the self from that reality. 

How could self-awareness be recognized?  In biology, creatures have reward systems, seeking food and sex.  Rewarding oneself is a demonstration of self-awareness.  Self-aware creatures also pass the mirror test, recognizing a patch of paint visible only in the mirror.  If a computer could be observed treating itself differently than external reality, it might demonstrate self-awareness.  Perhaps a self-diagnosis problem might show that the computer would treat an internal problem differently than an external problem.  But computers lack inborn desires, fears or survival instinct.  It might be difficult to observe self-awareness in a computer, even when it exists.

Will is the ability to perform independent actions.  This will be easier to recognize than consciousness or self-awareness.  Actions independent of programming would be evidence of some measure of sentience in a computer.  Nevertheless, machine-learning algorithms allow computers to make independent judgments and perform actions.  Machines can play chess, diagnose medical conditions, connect electronic traffic in efficient ways, answer questions, and perform many functions similar to humans.  But at what point does a computer exhibit free will?  How can we tell? 

Computer AIs do unexpected things all the time.  Chatbots are a good example, offering spectacularly bad examples of conversations, based on some learning algorithm applied to real human conversations.   Microsoft’s experimental chatbot “Tay” became notorious after only a few hours of exposure to interaction with real humans.  Of course, a number of users were deliberately trolling Tay, and succeeding in turning the na├»ve chatbot into a bigoted and sexually aggressive delinquent.  Within 16 hours, the chatbot’s personality was hopelessly corrupted, and Microsoft took Tay offline, ending the experiment.  In a second, accidental public release of the chatbot, the bot became stuck in a repetitive and poignant loop, tweeting “You are too fast, please take a rest” several times a second to 200,000 followers. 

It is still unclear how we could recognize free will in a machine, as opposed to an apparent malfunction.  (Once again, I recall episodes of Star Trek which explored that very dilemma.)  Perhaps behaviors that were clearly in the best interest of the machine would be noticed, but how could we expect such behaviors, when machines have not evolved to pursue their own best interest?  Once again, recognition of sentience seems difficult or impossible.

It seems to me that thought is a property of sentience.  I believe that the empirical learning performed by AI programs is not thought.  (I have similar views about empiricism in science, e.g.,  Actual thought involves something more than the correlation of previous patterns.  Thought requires the recognition of processes which change reality (even a digital reality).  When an AI program can recognize causation, rather than correlation, I would acknowledge that the machine is thinking.  And thinking is one component of sentience.

There might be a test which could reveal how a computer was solving problems, whether by empirical correlation, or by understanding processes (thought).  Understanding processes allows something that physicist David Deutsch calls “reach”.  Processes can be extrapolated to situations which are far beyond the range of input data.  For example, a computer might draw empirical data on how apples fall from many trees, and describe how other apples fall from trees.  But understanding the process of Newtonian gravity allows the computer to describe the orbits of planets, far beyond the bounds of what could be achieved by any empirical program.

My wife suggested that empathy should be a component of sentience, and I agree.  A sentient machine must have the qualities already discussed: Consciousness, Self-awareness, Will, and Thought.  But just as self-awareness requires the recognition of external things (which are “not-self”), full sentience requires the recognition of other sentient beings. 

As I would define sentience, it consists of several components: Consciousness, Personal Memory, Self-awareness, Will, Thought and Empathy.  If sentience does emerge in machines, I expect it will be gradual, and will not appear as the full-blown sentient beings of science fiction.  Recognition of sentience may be very difficult, particularly in machines which are already performing independent machine learning. 

In the biological world, four billion years of evolution has been necessary for the development of sentience.  Computers lack that evolutionary background.  Computers have no innate instinct for survival or self-interest.  Computers, even if they have the glimmerings of consciousness and self-awareness, may not demonstrate self-oriented behavior that would reveal their progress toward sentience.  Some period of evolution, by design or by accident, will probably be necessary for computers to develop sentience.  

I am not sure what form computer sentience might take when it appears.  It seems to me that sentience could appear in many different guises, and may surprise us by the form that it takes.   It may be a single machine, running specialized machine learning programs, and designed to develop sentience.  It may be a network of computers, or it may be the entire Internet.  The latter would echo an old story by Arthur C. Clarke, in which a global telephone system developed sentience.  Sentience may develop out of computer viruses, which have considerable evolutionary pressure placed upon them already.  Sentience may exist as software, jumping from device to device as new hosts.  In most science fiction stories, sentience develops in a single, unique machine, but it may not happen that way.  My daughter suggested that each of many small devices – cell phones, smart TVs, home security systems – may become sentient at the same time.  Alternatively, it is worth remembering that the human brain (as well as the human body) is a colony of smaller cells, each capable of performing some of the basic functions of life independently.  Cells in the brain each perform some analytical function, but it is only the total network of the brain that we consider sentient. 

A number of futurists, including Elon Musk and Stephen Hawking, have spoken strongly about the risks that artificial intelligence (whether sentient or not) poses to mankind.  I would not presume to contradict them.  When artificial intelligence reaches the point that it becomes self-designing, producing improved replicas without human design, it will exceed our capacity to understand or predict the capabilities of those machines.  But I nevertheless think that the development of sentient machines will occur.  

If I am correct that human sentience is strictly a matter of physical chemistry and electricity, then I believe that machine sentience is ultimately inevitable, provided that humanity survives long enough.  When it happens, it will challenge our place in the world, the meaning of our goals, and the meaning of humanity.  It may be the most important thing that has happened to mankind since the emergence of our own species as sentient beings.

Thursday, October 12, 2017

Seven Ways Climate Change Makes Hurricanes Worse

As I’m writing this post, Hurricane Ophelia is forecast to hit Ireland, the first full-strength hurricane to hit the island since 1961, and the tenth consecutive storm this season to reach hurricane strength.  The year 2017 has already been a tragic and record-setting Atlantic hurricane season.  Hurricane Harvey hit Texas as a 1000-year rainstorm, dropping about 11 cubic miles of rain on Houston with enough weight to depress the earth’s crust by a measured 2 centimeters.  And within a period of two weeks, Hurricanes Irma and Maria struck the Caribbean Islands as category 5 hurricanes – the strongest measure on the Saffir-Simpson scale, setting a record for the duration of category 5 storms in one season. 

The obvious question is whether climate change is causing an increase in the frequency or intensity of these storms. 
Hurricanes and Climate Change
A hurricane is a convection engine.  Warm tropical waters convey heat and humidity to the air over the water.  The warm, humid air is light, and begins to rise at random spots over the ocean.  The warm air cools as it rises, dropping below the dew point.  Water vapor condenses to form clouds and rain.  The condensation of water vapor reduces air pressure, further lowering the air density.  The low-pressure center draws warm air from the ocean surface toward itself, which feeds the rising convection column.

The converging air currents are affected by the Coriolis force, and begin to spin as they approach the growing low-pressure center.  As the storm develops structure, a downward current of air forms as the eye in the center of the storm, returning dry air from high altitude.  The hurricane eyewall of clouds, rain and ferocious winds spins around the central eye.  Surrounding the eye, spiral rain bands develop as subsidiary convection systems, with upward air flow in the rain bands and downward flow between those bands. 

The strength of a hurricane is often limited by high-level winds blowing across the top of the hurricane.  Strong high-level winds effectively decapitate a hurricane by blowing the top off of the convection column.  Hurricanes tend to drift westward in equatorial waters, as the globe spins eastward beneath them; and to drift toward the poles in temperate latitudes.  Areas of surrounding high and low pressure form steering currents, which modify the path of the hurricane as it drifts across the globe.

Climate change is expected to increase the intensity of hurricanes in a number of ways. Here are seven ways in which climate change is expected to make hurricanes worse.
Modified after image by Thompson Higher Education.

1)  Average surface air temperature has risen around the globe by about one degree Celsius since 1980.  The particular warming is variable at different times and places, and may be greater over tropical waters at times.  Warmer surface air creates a greater tendency to form thermal convection currents.
Average annual global surface temperature, 1880 - 2016.  Image credit NASA.

2)  Average temperature in the upper 100 meters of the ocean has risen by ½ degree Celsius since 1980.  As with air, temperatures in the ocean vary seasonally and in complex patterns of time and space.  At times, tropical waters will be warmer by more than the average ½ degree Celsius global average.  A warmer ocean surface contributes more heat and humidity to a hurricane.

Average water temperature, 0-100 meters, 1955-2017.  Image credit NOAA.

3)  The average temperature of the ocean water at depth has also risen.  The average temperature of waters from the surface to 700 meters has risen by 1/10 of a degree Celsius since 1980.  Waters from 100 to 200 meters have warmed nearly as much as surface waters.  Hurricane waves churn up deeper water, bringing cooler water to the surface.  In the past, this stirring of deeper water cooled the ocean surface, and acted as a buffer on the intensity of a hurricane.  But now that deeper waters are also warmer, there is less tendency for wave action to moderate the strength of a hurricane. 
Average water temperature, 0 - 700 meters, 1955 - 2107.  Image credit NOAA.

The principles of physics mean that higher air temperatures and higher water temperatures mean that more humidity is carried in tropical air before the formation of a tropical storm.  Warmer air raises the water-carrying capacity according to the principle of relative humidity, and higher water temperatures raise the humidity of the air according to the Clausius-Clapeyron equation.  Higher humidity acts in three ways to increase the intensity of a hurricane.

4)  Higher humidity lowers the density of the air, because the water molecule is lighter than the average molecular weight of air.  Intuitively, we tend to think that moist air is “heavy”, perhaps because liquid water seems heavy.  But the molecular weight of water is 20, while the molecular weight of nitrogen is 28, and oxygen is 32, giving dry air a molecular weight of about 29.  Molecules of water vapor occupy just as much space as gaseous molecules of nitrogen or oxygen, thus lowering the density of air.  [If we had a bucket of liquid water and a bucket of liquid air, the liquid air would be heavier.]   Lighter air contributes to stronger convection, which strengthens the hurricane.

5) Air with higher humidity has more moisture to condense, causing a stronger drop in air pressure.  This can lead to stronger winds and more rapid intensification of a hurricane.

6) Higher humidity raises the water-carrying capacity of the hurricane, and contributes to higher volumes of rainfall and flooding when a hurricane makes landfall.  The unusual volumes of rainfall associated with hurricanes Harvey and Maria probably reflect higher humidity caused by climate change.

7) Finally, it is possible that climate change has reduced the strength of high-level winds, reducing the tendency for these winds to blow the tops off of hurricanes.  Some scientists have observed a decline in the strength of high-level winds in recent years, and tentatively suggest that this may be a result of climate change.  However, the mechanisms by which climate change would affect these winds is unclear, and the proposal is still controversial. 

I wrote to “Ask a Climate Scientist” on Facebook, and asked whether satellite data from NASA’s GOES satellites documented higher humidity over the Atlantic since the 1980s, either in actual hurricanes or in general background humidity.  I wanted to know if the data supported the idea that climate change is making hurricanes worse.  Here’s the answer I received:

"The GOES imager series involve technology upgrades and are not well calibrated, and so are not well suited for measuring changes in water vapour over time. 
However, the HIRS instrument aboard the NOAA polar orbiter series which began about the same time is fairly well calibrated, and does show increases in humidity. 
More recently the microwave radiometers on board the AMSU series of satellites also show the increases, as does the global radiosonde and surface-observing networks.  The increases are in line with expectations from thermodynamic principles (the Clausius-Clapeyron equation) and climate models. 
We are pretty confident that these increases are indeed causing a storm to dump more rain now than it would have a few decades ago, all other things being equal.”
Professor Steve Sherwood, Climate Change Research Center, UNSW Australia

I made a brief attempt to quantify changes in the hurricane system in the Gulf of Mexico that are due to climate change.  Assuming a 1.5 degree rise in sea surface temperature, humidity will rise by about 5 percent, from about 75% relative humidity to 80%, at an average daily temperature of 80 degrees F.  Along with rising humidity, air temperatures have risen by about 2 degrees F (global average).  Air density will fall, but not very much, only about ½ of one percent.  This will result in stronger convective activity, but I do not have the knowledge or modeling ability to translate that change into hurricane intensity. 

When water vapor in the air is converted to rain, air pressure drops.  Higher initial humidity will lower air pressure in the center of the hurricane.  This means stronger rotation and stronger winds.  Hurricanes are incredibly efficient at removing humidity from the air.  Almost all of the surface humidity in a hurricane is converted to rain, as convection drops the temperature of the air from 80 degrees Fahrenheit at the surface to minus 130 degrees F at the cloud tops.  But the initial saturation pressure of water in air is fairly small.  At 86 degrees F and 80 percent humidity, air contains only 3.3 percent water vapor.  Although climate change has raised the humidity by 5 percent, this means that the surface air in a hurricane now contains 3.5 percent water vapor.  When the vapor is converted to rain, the difference in air pressure is 0.2 percent. 

So, temperature and humidity reduce the air density in a hurricane by 0.5%; additional rain reduces the air pressure by another 0.2 %, for a total climate-change reduction in air pressure of 0.7%. 

Climate change produces higher temperature and humidity.  Those changes push the physical processes of a hurricane toward stronger convection, more rapid intensification, higher wind speeds, and greater rainfall. 

Quantifying those changes is difficult.  Without sophisticated modeling, it is impossible to say whether the small changes in air density and water vapor can result in a major change to a storm system.  But it is important to note that hurricanes are feedback systems.  Hurricanes start as a mild swirl of air over the water, or a rain squall no different than any other rain squall.  But like the proverbial “butterfly effect”, a small change in the initial conditions of the hurricane may result in profound changes in the ultimate intensity of the storm.  Feedback mechanisms in the convection system create the hurricane; it would not be surprising if those same feedback mechanisms amplify the small changes due to climate change to create monster storms. 

I am generally critical of strictly empirical reasoning in science.  Science is about providing explanations, identifying, observing and measuring processes which change the world.  But empirical evidence can support scientific reasoning, and give a clue that an explanation is on the right track.  Currently, the remarkable 2017 hurricane season is supporting the notion that Climate Change is producing stronger, more frequent storms, with more rapid intensification and heavier rain.
Temperature of cloud tops -90 degrees C.

Chart showing mass of water contained in air at 50% and 100% humidity, as a function of temperature.
Air with 80% humidity at 86 degrees Fahrenheit contains about 21 grams of water per kilogram of air.

Tells us there is a roughly 3 percent increase in average atmospheric moisture content for each 0.5 degrees Celsius of warming

Air density calculator

Average annual humidity for places in Texas.

Average annual humidity for places in Florida.

Temperature change for mid-Gulf surface waters, 1975 to the present.  Average temperatures have increased by 1.5 degrees F; high temperatures have increased by about 3 degrees F.

Average Gulf of Mexico air temperatures, by month.

Mass of water in air at 50% and 100% humidity, as a function of temperature.

Hurricane facts. 

Cloud top temperatures for hurricane Ingrid, 2013.

Partial pressure of water in saturated air, as a function of temperature.

Standard Air Pressure
14.70 psi
1013.25 millibars
Air Density @ 80 F & 75% humidity:  1.166 kg/m3
Air Density @ 82 F & 80% humidity:   1.16 kg/m3

Personal Communication from Profesoor Steve Sherwood, Climate Change Research Center, UNSW, Australia:
"The GOES imager series involve technology upgrades and are not well calibrated, and so are not well suited for measuring changes in water vapour over time.  

However, the HIRS instrument aboard the NOAA polar orbiter series which began about the same time is fairly well calibrated, and does show increases in humidity. 

More recently the microwave radiometers on board the AMSU series of satellites also show the increases, as does the global radiosonde and surface-observing networks.  The increases are in line with expectations from thermodynamic principles (the Clausius-Clapeyron equation, and climate models. 

We are pretty confident that these increases are indeed causing a storm to dump more rain now than it would have a few decades ago, all other things being equal."

Real time and archived statistics on global cyclone energy.

Friday, September 22, 2017

Flooding in Houston: Hurricane Harvey and Climate Change

September 2017 has been an active and violent hurricane season in the Atlantic tropical zone.  Most of this post was written following Hurricane Harvey, and before Hurricanes Irma and Maria.  Hurricane Harvey dumped record-setting volumes of rain on the south Texas coast.  Hurricanes Irma and Maria, occurring in a two-week period, were the strongest hurricanes on record in the open Atlantic Ocean.  For many years, researchers have warned that climate change would produce stronger hurricanes -- it seems that the future has arrived.

In the simplest analysis, I would ask the following question.  Is it more likely that Hurricane Harvey was a completely natural, unlikely event with a probability of 1:1000, or is it more likely that the storm was made worse by climate change, according to well-understood physical principles and predicted by scientists for over two decades? 

In August 2017, Houston Texas became the face of climate change.   More than 20 inches of rain fell over an area of 28,949 square miles; > 30 inches over 11,492 square miles; and > 40 inches over 3643 square miles.  The maximum rainfall of 52 inches broke the record for rainfall from a single storm in the contiguous United States.  The intensely flooded area received 11 ½ cubic miles of water.  Within a few days, over 300,000 people had already filed claims for federal disaster assistance, and many more are likely to require assistance in the future.  The immediate death toll from the storm was 82, and illnesses relating to the storm are expected to persist for years.
Total Rainfall from Hurricane Harvey, August 30, 2017 

Climate change is often represented in terms of polar bear on melting ice; of changing migration patterns for wildlife; of seemingly trivial changes in long-term average temperatures; of higher sea level in the next century.  All of those are true and real.  But for many Americans, these issues do not impact their lives.  None of this matters in terms of day-to-day living. 

Hurricane Harvey is different.  It has been called a 1000-year flood by scientists.  This is an expression of the probability of an event of this magnitude in a given year, based on statistics of smaller events.  The storm dropped an awe-inspiring quantity of water on the earth, and America’s fourth-largest city was totally disrupted.  There was certainly no economic productivity from the city for a week, and the damages are considerable.  When floodwaters threatened to destroy Houston's earthen flood-control dams, emergency managers opened the floodgates, deliberately flooding neighborhoods downstream of the dams, to save other neighborhoods in a kind of triage.  An estimated 100,000 homes were flooded or damaged by the storm.  Many of them will be totally destroyed after sitting in flood waters for a month.  The human toll in lives and economic loss is huge. 

The damage is personal to me; two of my three former houses in Houston almost certainly flooded. Old friends and former neighbors are dealing with the loss of their homes, cars, and lifelong possessions. A number of deaths occurred in familiar neighborhoods
Image credit Joe Raedle/Getty Images
Image credit: David J. Phillip, AP
Image Credit: T.B. Shea, AFP/Getty
Image credit: AP

Climate Change: Prediction and Consequences

The Intergovernmental Panel on Climate Change (IPCC) 2014 Report includes this statement: “It is very likely that heat waves will occur more often and last longer, and that extreme precipitation events will become more intense and frequent in many regions.”

On August 27, 2017, the National Weather Service tweeted this statement regarding Hurricane Harvey: “This event is unprecedented & all impacts are unknown & beyond anything experienced. Follow orders from officials to ensure safety.  #Harvey”.   [Emphasis mine.] 

These statements are not unrelated. 

Scientific Analysis
The full scientific analysis of Hurricane Harvey will not be known for a long time, probably years.  And uncertainties will remain after the full analysis of all available data.  There are a number of known factors relating to climate change which will increase hurricane severity – it is simply physics.  These factors include higher temperatures at the ocean surface, higher temperatures in the upper 200 meters of the ocean, and higher humidity.  The factors are well-established -- the changing temperature of ocean waters have been observed by NOAA’s ARGO system of buoys since 2004, and by satellite since the 1980s.  Some scientists have also suggested that climate change is reducing the strength of upper level winds, though this proposal is not yet considered proved.

Higher temperatures at the ocean surface are believed to have caused a rapid, late intensification of the storm from category 2 to category 4 immediately before landfall. 

Higher temperatures in the water column are believed to have reduced the tendency of wave action to bring cooler water to the surface, weakening the hurricane.  

Higher humidity, relating to higher water temperatures and higher air temperatures, allowed the storm to carry more water than other storms.  Higher humidity and higher temperatures also lower air density, contributing to the strength of convection and wind speed.

At this time, it is unknown how much wind systems have changed due to climate change, or how much these changes might have affected Hurricane Harvey.  Hurricane Harvey stalled after moving onshore, caught between stationary high-pressure systems.   High-level winds, which sometimes reduce convection through wind shear, were also weak through the hurricane.  Quantifying these impacts using new observations and modeling is the job ahead for scientists. 

The specific magnitude of these changes is unknown, but the known factors contributing to the severity of the hurricane are clear.  According to one preliminary estimate, factors relating to climate change increased the volume of rainfall from Hurricane Harvey by 30%.   While this may seem to be only a moderate increment, thirty percent of extra water is what exceeded the capacity of flood-control reservoirs, caused neighborhoods to flood, and caused a number of deaths.

The earliest warning that climate change could result in more frequent and severe hurricanes was published in 1992, and incorporated into the IPCC Second Assessment Report.  At that time, there was sparse statistical evidence that hurricanes were becoming worse.  In 2017, statistical evidence is still weak.  However, science is not all about empiricism.  Explanations matter.  We understand the physical processes of hurricane convection, the Coriolis effect, and the importance of water temperature, air temperature, humidity and air density.  We have observed that these factors are changing due to accumulating greenhouse heat, and will increase the frequency and intensity of hurricanes.

At this time, we do not know the specific amount that climate change contributed to the Hurricane Harvey disaster.  But there is a simple, shortcut analysis that we can do now.  Simply consider which possibility is more likely: whether Hurricane Harvey was an extreme event with a probability of 1:1000, or whether climate change intensified an ordinary storm, as predicted by scientists for over twenty years?

 Graphical Representation of 1:1000 Probability Event

Long-term temperature is about one degree higher than a few decades ago.    Local conditions were 2.7 degrees to 7.2 degrees F higher than usual.   Humidity rises at about 3 percent per degree C., so humidity during Harvey was 3% to 5% higher than usual.
High level winds that typically steer tropical storms collapsed in 2010.  Although a meteorologist expects the winds to return in a few years, long-term climate modeling suggests that collapse of steering currents may become more common.    

Speech by Mike Pence

Immediately prior to landfall, and during the time of intensification to category 4, Harvey over water 4 degrees F warmer than average.

Waters off South Texas were 5 degrees warmer than usual during Hurricane Harvey.

Warm water extended deeper into the water column.

Atlantic Decadal Oscillation is trending to cooler temperatures, which may bring cooler waters to the tropics and weaken storms in coming years.   Another researcher suggests that GHG warming may keep the ADO positive for the coming decade.

Background conditions were about 2 degrees warmer than average, and then warmed further by an eddy of the Gulf Stream Loop Current.

“The human contribution can be up to 30 percent or so of the total rainfall coming out of the storm”.  Hurricane waves usually bring cooler water to the surface, which acts as a buffer to moderate the strength of the storm.  But Hurricane Harvey churned up water 100 m to 200 m below the ocean surface, but this water was still warm. 

Graphics representing 27 trillion gallons (about 25 cubic miles) of water. 

Probability of Hurricane Harvey, based on historical statistics, is 1:1000.

Immediate death toll from Hurricane Harvey was 82.  A number of serious health effects could persist for years. 

Daniel Huber, Jay Gulledge, Center for Climate and Energy Solutions, Extreme Weather and Climate Change, 2011.
“There is a physical basis for expecting hurricanes to have stronger winds and produce more rainfall due to global warming, and models with enhanced greenhouse gas levels show an increase in the number of such storms….However, observational evidence is insufficient to confirm that such a response has already begun.”

IPCC Second Assessment Report, 1995.
"Direct impacts on infrastructure would most likely occur as a result of changes in the frequency and intensity of extreme events. These include coastal storm surges, floods and landslides induced by local downpours, windstorms, rapid snowmelt, tropical cyclones and hurricanes, and forest and brush fires made possible in part by more intense or lengthier droughts."
“It is presently uncertain whether the frequency and severity of tropical cyclones will increase due to climate change.”

O'Brien, S.T., B.P Hayden, and H.H. Shugart, 1992: Global climatic change, hurricanes, and a tropical forest. Climatic Change , 22 , 1750-1790.

Monday, August 28, 2017

Where is the Dark Matter in the Earth's Core?

I just finished reading “Dark Matter and the Dinosaurs” by Harvard University physicist Lisa Randall.   Dr. Randall is an excellent popular science writer, as well as being a top-flight theoretical physicist.   Her exposition on dark matter gave me most of my exposure to this arcane topic in modern physics.  

My understanding of the topic is shallow, but I think some common-sense observations provide constraints on the distribution of dark matter, which need to be recognized in models of dark matter and experiments to find it.

My biggest question about dark matter is: Where is the dark matter in the earth's core?  

The Nature of Dark Matter
Dark matter is a form of matter that does not interact with ordinary matter or energy, except through the force of gravity.  A better name for dark matter might be “ghost matter”, as the lack of interaction with ordinary matter means the dark matter can occupy the same space as ordinary matter, or pass right through it, undetected. 

Lisa Randall writes: “Dark matter passes right through our bodies, and resides in the outside world as well…. Every cubic centimeter around you contains about a proton’s mass worth of [dark] matter….if those particles travel at the velocity we expect based on well-understood dynamics, billions of dark matter particles pass through each of us every second.  Yet no one notices that they are there.”

It is unknown whether dark matter can interact with ordinary matter at all, except through gravity.  Nevertheless, some theoretical results suggest there may be very weak interactions, and experiments are in progress seeking to detect dark matter, either directly or indirectly, through some kind of interaction with ordinary matter.  According to Dr. Randall, it is also unknown whether dark-matter interacts with itself. 

It seems to me that dark matter is necessarily self-interacting.  Evidence (the lack of a distinct dark matter core in the earth) indicates that dark matter has a very low maximum density.   Dark matter must exclude other dark matter from occupying the same space.  The density of dark matter is much, much lower than regular matter.  Dr. Randall states that every cubic centimeter around you contains about 1 proton’s worth of dark matter.  Accordingly, the density of dark matter at the surface of the earth is only 1.7 x 10-24 gm/cc, or 1.7/1,000,000,000,000,000,000,000,000th of the density of water.

Evidence of Dark Matter
Dark matter is known through its influence on ordinary matter, via the force of gravity.  It is observed only on the scale of galaxies or larger structures.  Observed gravitational effects suggest that dark matter actually comprises 85% of the matter in the universe.  The evidence for dark matter is mostly derived from deep-space astronomy and cosmology, as follows.
  1. The orbital velocities of stars in galaxies are much too high, given the quantity of ordinary matter in the galaxy.  Additional mass, in the form of dark matter, is required to explain the cohesion of galaxies.
  2. The gravitational lensing of light around galaxies indicates a much greater mass in the galaxy than can be seen in ordinary matter.
  3. The background radiation of the universe which formed shortly after the Big Bang shows an irregular distribution, which can only be explained by gravitational accumulation, requiring more mass than is known to exist as ordinary matter.
  4. Modeling the development of the universe since the Big Bang shows that the gravitational influence of dark matter is necessary to create galaxies in the primordial universe. 
  5. Evidence of dark matter can also be seen in the gravitational lensing of distant objects near colliding galaxies, such as the spectacular Bullet Cluster.  In such events, dark matter becomes separated from ordinary matter, and is revealed by observations of separate patches of magnification by gravity lensing.

Bullet-Cluster Galaxy.  Image credit: NASA

Local Dark Matter and Self-Interaction of Dark Matter
Dark matter reveals itself through the force of gravity on a very large scale – the scale of galaxies or larger structures.  But what about smaller settings?  What can we deduce about dark matter by its small-scale behavior?

Black Holes of Dark Matter
If there was no exclusionary force to dark matter, particles of dark matter (which do interact through gravity) would fall together, presumably to a very high or infinite density.  Without an exclusionary force, dark matter would be particularly prone to forming black holes from small quantities of dark matter, collapsing to very high density.  [Despite the similarity in names and difficulty of observation, dark matter and black holes are quite different things, and should not be confused.]  But we don’t observe the gravitational influence of lots of small black holes, within the galaxy.  If they existed we would notice their presence by abnormalities in the velocities of stars in the Milky Way, by gravitational lensing of distant starlight, and by deflections in clouds of interstellar gas.  We don’t see those things, so there must be an exclusionary force prohibiting the close association of particles of dark matter. 

Dark Matter at the Center of the Earth
Also, since dark matter interacts with normal matter only through gravity, we might expect all of the dark matter in the neighborhood (that is traveling at less than escape velocity) to fall through the crust and mantle of the earth, and accumulate in the earth’s center.  Since dark matter comprises 80% of the matter in the universe, we ought to find a substantial gravity anomaly in the earth’s core, unexplained by the density of normal matter in the core. 

We don’t.

The Earth’s Structure and Core
We have a very good understanding of the structure and composition of the earth’s core.  The structure of the core is revealed by the behavior of earthquake seismic energy as it is transmitted through the earth.  Seismic waves generated by earthquakes travel through the earth, and can be recorded at most places around the earth following a major earthquake.  Compression waves and shear waves travel at different speeds, and behave differently depending on the nature of the transmitting media, whether solid or liquid.   The speed of the waves depends mostly on density, and interfaces between materials of different composition produce both reflections and refraction of the waves.  All of this information allows us to construct the specific solution of layers, mineral composition, and phase (liquid or solid) of the interior of the earth.
Image credit: Charles Sturt University, via Ethan on

The interior of the earth consists of a number of concentric shells of varying composition and consistency.  Below the atmosphere and oceans, there is the earth’s crust, which occurs as oceanic and continental components.   Below the crust, the upper mantle is divided into the lithosphere and asthenosphere.  The crust and mantle are composed of silicate minerals.  The crust and lithosphere are rigid, and move as plates on the ductile asthenosphere.  The lower mantle is also ductile, and deforms plastically to form convection cells, driving the motions of the shallower plates. 

Image Credit:

The earth’s core is primarily composed of iron and nickel, with a small amount of lighter elements.  A huge clue to the composition of the core exists in form of iron-nickel meteorites, which are derived from some proto-planet in the early solar system.  Iron-nickel meteorites typically contain nickel in concentrations of about 6% to 10%.  Gravity shows that the density of the core is about 3% lighter than pure iron, implying about 10% of lighter constituents, probably silicon, oxygen and sulfur.   Nickel is slightly denser than iron, so higher nickel concentrations would imply correspondingly higher concentrations of light elements to compensate in overall density.

Seismic studies show that the inner core is solid, and the outer core is liquid.  Convection in the liquid outer core accounts for the earth’s magnetic field.  The mineral composition of the inner core can be replicated and studied using high-pressure tools in the laboratory.  The combination of seismic studies, gravity studies, mineral composition studies, meteorite studies, and magnetic studies yields a model that fully explains all observations about the earth’s core.  No dark matter is indicated by the observations; rather, the introduction of dark matter would require unreasonable changes to the most logical interpretation for the composition of the core.  

Model of the Earth's density from the center to the surface.  Image credit Wikipedia.
Model of the Earth's gravity from the center to outer space.  Image credit: Wikipedia

Dark Matter in the Cores of Stars
The sun is a delicately balanced fusion engine.  The heat generated by hydrogen fusion produces an expansion force, which is balanced by the gravity of the star.  When the balance is disrupted by the exhaustion of nuclear fuel, the star becomes unstable, exploding as a nova or supernova, or collapsing into a white dwarf, a neutron star or a black hole.  The processes of nuclear fusion are known and well-quantified as a result of nuclear weapons research and super-collider experiments. 

Any gravitational anomaly in the sun or in the theoretical models of other stars would surely be noticed, and would be glaringly apparent to scientists studying stars.  We have to conclude that there is no dark matter accumulated in the cores of stars.  

Evidence from Spacecraft
Dark matter may exist as a “soup” of uniform density larger than the solar system, so that there is equal gravitational attraction in all directions.  In this case, no anomaly could be detected, because the gravitational influence of dark matter would be the same in all directions.  By analogy, a point at the exact center of the earth would be weightless, subject to equal gravity in all directions.  But even in this case, as objects move in some direction through the soup, differential gravity should be detectable if there are heterogeneities or nearby limits to the dark matter soup. 

Our best experiments to find dark matter in the Solar System are the Pioneer 10, Pioneer 11, Voyager 1 and Voyager 2 spacecraft.  Data from the Pioneer spacecraft was last received in 2002 and 1995, respectively, but the probes lasted long enough to identify a potential gravity anomaly in the solar system, the Pioneer Anomaly.  As I read Lisa Randall’s book about Dark Matter, I initially thought that the Pioneer Anomaly might be the expression of dark matter in the solar system, but subsequent reading revealed that the anomaly was robustly explained in 2012 as a thermal recoil phenomenon relating to the spacecraft itself. 

The Voyager spacecraft are now the most distant man-made objects from earth.  Both are still transmitting, at distances of 12.9 billion miles (19 light-hours) away, and 10.7 billion miles (16 light-hours) away, respectively.  The craft are traveling at roughly a right angle to each other, providing two long baselines to measure any gravity anomalies in those directions, revealed by an unaccounted-for acceleration of the spacecraft.  None have been detected.


Any theory of dark matter must account for the lack of detectable dark matter in the cores of planets and stars.  The lack of a detectable dark matter core in these places is strong evidence that dark matter is self-interacting.  There must be a property of dark matter that prevents dark matter from accumulating at high density.  This exclusionary force must act on at least the scale of a planet, and probably on the scale of the solar system. 

The exclusionary force places a limit on the maximum density of dark matter.  To the best we can now recognize, that limit is the detectable limit of density anomalies in the sun or the earth.  It is a very small density compared to the density of ordinary matter.

The lack of acceleration anomalies in distant spacecraft shows the large-scale homogeneity of dark matter surrounding the solar system.  At this time, I don’t know the limits of velocity determinations of the Voyager spacecraft, but I think that these long-distance measurements would be quite sensitive to a local density anomaly.  It would be a worthwhile exercise to calculate the effect of a dark-matter accumulation (such as Dr. Randall’s posited dark-matter disk within the Milky Way) on the velocities of the spacecraft, and see if the results would be within the tolerance of the spacecraft velocity measurements. 

If not for the robust evidence of dark matter in cosmology, it would be tempting to dismiss the idea of dark matter entirely.  But perhaps the finding that there is an exclusionary force limiting the density of dark matter can be a clue to identifying the true nature of dark matter. 

Maybe dark matter doesn’t fit the particle model of matter at all.  At this time, all we know is that it is very sparsely dispersed gravity.  But the particle theory of matter has proven very useful at explaining most of our reality.  We shouldn’t give up on it too easily.  We should think for a moment about what constraints our observations put on a particle theory of dark matter.

Ordinary matter and dark matter are clearly different in scale.  A proton excludes other protons on the scale of 0.8414 x 10-15 linear meters.  If we assume a particle of dark matter has the same density as a proton, each dark matter particle must exclude other dark particles on the scale of 0.02 linear meters.  The ordinary proton occupies a volume of about 3 x 10-46 cubic meters, and a dark matter particle of the same mass would occupy a volume of 1 x 10-6 cubic meters, a difference of 40 orders of magnitude.

Perhaps the difference in size between ordinary matter and dark matter is the sole reason for the undetectability of dark matter.  It seems to me that electrical and other interactions between normal particles occur because the wave properties of the particles have similar wavelengths.  The waves can interfere, and therefore interact.  With wave properties of vastly different sizes, there is no interference, and therefore no interaction.

I am not optimistic about the present round of experiments looking for dark matter, as described by Dr. Randall.  If you are looking for an elephant with an electron microscope, you are likely to be unsuccessful. 

What kind of experiments could reveal particles which exist at a scale many orders of magnitude larger than ordinary matter?  I don’t know.  The electromagnetic spectrum is well-explored on that scale, and reveals nothing.  Perhaps other forces need to be synthesized, and examined at larger scales.  There may be practical technological benefits if instruments can be developed that directly detect dark matter.  Perhaps, such instruments could provide the ability to manipulate other forces, such as a way to generate, shape and manipulate artificial gravitational fields, in the way that artificial magnetic fields have been generated and used for almost 200 years.

That would be a real advance for mankind.

Lisa Randall, Dark Matter and the Dinosaurs; The Astonishing Interconnectedness of the Universe, 2015, 432p.

Density of the Outer Core (liquid):  9.9 to 12.2 gm/cc
Density of the Inner Core (solid):  12.6 to 13.0 gm/cc

Thickness (km)
Density (g/cm3)
Types of rock found
Silicic rocks
Andesite, basalt at base
Upper mantle
Peridotite, eclogite, olivine, spinel, garnet, pyroxene
Perovskite, oxides
Lower mantle
Magnesium and silicon oxides
Outer core
Iron + oxygen, sulfur, nickel alloy
Inner core
Iron + oxygen, sulfur, nickel alloy

Composition of the earth’s core.

The core is about 3% lighter than pure iron, implying about 10% of lighter constituents, probably silicon, oxygen, and sulfur.

Voyager 2: 10.7 billion miles (16 light-hours) away.

The last data received from Pioneer 10 was in 2002.  The last data received from Pioneer 11 was in 1995.

[The new] measurement measured [a proton] to be 0.8418±0.0007 fm.  A femtometer is 10-15 meters