Global Warming: Natural Drivers, Ice Ages, Humans, and Science

In his February 15, 2014 editorial titled “Global Warming in the deep freeze,” Keith Dasher states, “The Earth has gone through at least nine ice ages and warming cycles since day one.  Do you really think man can stop it or be responsible?”  His editorial attacks climate scientists as “alarmists” and “liars” who “have a huge political agenda.”

Mr. Dasher is in-part correct, and in-part confused.  I will begin with the part where he is correct.

Natural Climate Change Drivers and Ice Ages

There are two primary natural drivers of climate change that are not the result of human activity.  These drivers are solar variation and volcanic eruptions.

Solar radiation is the main power source for our climate system.  It is well documented that variations in Earth’s orbit have driven the ice age cycles.  Earth’s orbit is not round; our path around the Sun is actually elliptical, and the shape of that ellipse changes with time.  Earth also tilts on its axis as it rotates, and it wobbles like a top.  Throughout geological time periods, complex variations in Earth’s orbit, tilt, and wobble have converged in cycles that altered the balance and distribution of solar radiation on the surface of our planet.  These cycles (called Milankovitch Cycles) can be calculated with precision, and there is strong scientific evidence to link the cycles with periodic glaciations beginning with the ice ages.  These calculations show that we will not enter another ice age for 30,000 years.

Now, I will address some areas of confusion in Mr. Dasher’s article as well as provide some background information.

Solar variation also affects our climate on the short-term.  The Sun’s solar output is not constant.  It varies between a maximum and minimum over an 11 year cycle by about 0.1%.  The contribution of this short-term varying solar irradiance as a natural driver is relatively small.

Volcanic eruptions can cause our planet to cool by spewing ash and gases into the atmosphere.  Ash settles out in about 3 to 4 months.  Gases blown into the stratosphere are converted into aerosols and begin to settle from the atmosphere in about twelve to fourteen months.  The ash and aerosols from volcanic eruptions can cause measurable planetary cooling for up to 2 years.

Human Impacts

Solar variation and volcanic eruptions alone cannot explain the observed global warming of recent decades.  Human activity has clearly emerged as the primary driver of recent warming, especially since the 1960’s.  When I was a 10-year-old boy, a young scientist named Dave Keeling obtained the first high accuracy, high precision measurement of carbon dioxide in our atmosphere at 313 ppm (parts per million).  We will pass the 400 ppm mark in April or May of this year.  (Note:  Media outlets prematurely reported that we passed the 400 ppm park last year based on preliminary data.)

During 10,000 years of human history, the carbon dioxide (CO2) concentration in our atmosphere was relatively constant.  Since the beginning of the industrial era, atmospheric CO2 has been rising rapidly.  Since I was a 10-year-old boy, it has increased by more than 27%.

It is the trace amount of CO2 in our atmosphere that creates a natural greenhouse effect and keeps our planet warm.  In the absence of CO2, Earth would be a cold, lifeless third-rock-from-the-Sun.  The rapid short-term increase of CO2 in our atmosphere is creating an enhanced greenhouse effect causing our planet to warm.

Sophisticated scientific models clearly show that humans are responsible for contributing this excess CO2 which results in the enhanced greenhouse effect (dubbed “global warming”).  Yes Mr. Dasher, “Man…[is]…responsible.”

On Science and Politics

In our approach to understanding how nature works, we as scientists employ a methodology often referred to as the scientific method.  To begin, scientists make observations.  This is the foundation of scientific thinking.

But, scientists also want to know why nature works the way it does.  The scientist will set forth a proposal called a hypothesis which is a testable explanation for an observable phenomenon.   A hypothesis must be falsifiable.  This means that scientists must be able to test the hypothesis.  If it can’t be tested, it isn’t a scientific hypothesis—this is what distinguishes science from speculation or belief.

A hypothesis that has been tested and supported by experiments over and over again may result in a scientific theory.  A theory is a concept that unifies a broad range of observations within the natural world.  The theory explaining the warming of our planet is robust and strongly supported by independently collected and analyzed data from around the globe.

Scientists are not “alarmists”.  The very nature of scientific inquiry requires a conservative approach.  Politics, ideologies, and belief systems on the other hand cannot be falsified—they just need to be convincing.

There is no grand global conspiracy of scientists to promote a “belief” in global warming and a “political agenda”.  Scientists observe, collect data, hypothesize (it must be a falsifiable), test, and correct.

Nearly all current peer-reviewed scientific articles converge on the same conclusion; humans are responsible for the current warming we are observing.  Media and others have coined this “consensus.”  It is not a vote.  It is scientists independently arriving at the same conclusion.


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