Farming for Better or Worse
Here on Marco Island, February and March are the peak months
of “the season”, the time when the snowbirds in Florida number
in the zillions. At least it seems that way when one ventures out
on the main roads and highways. A safe weather forecast that
would be correct 90 percent of the time here would be “sunny
and warm”. There are exceptions, as was the case Sunday, when
our Venetian friends (from Venice, Florida) were to come down
for a visit. Venice is about a two-hour drive from here and they
called to say they were not coming because of predictions of
heavy rain and possible tornadoes! Fortunately, the latter did not
materialize but in Venice it did rain all day with 5 inches total.
Here on Marco, it was relatively sunny without a drop of rain.
Why does Florida have “the season” and why does New Jersey
have winter and summer, not to mention spring and fall seasons?
Let’s examine how the earth orbits the sun and pretend that the
earth’s axis is perfectly perpendicular to the plane of the earth’s
orbit. In other words, if you drew a straight line between the
earth and the sun and you had a rod through the earth that passed
through the North and South Poles, the rod would be at right
angles to that line. If that were the situation, as the earth made
its yearly orbit around the sun, the northern and southern
hemispheres would receive the same amount of radiation from
the sun. No seasons.
We know that’s not true. When it’s winter in the Northern
Hemisphere it’s summer in the Southern Hemisphere. The axis
of the earth is tilted, not perpendicular to that line we drew form
the sun to the earth. It’s now winter in New Jersey. The earth is
tilted so that New Jersey in the Northern Hemisphere is tilted
away from the sun while Australia in the Southern hemisphere is
tilted towards the sun. Australia gets more of the sun’s rays than
New Jersey. Six months from now, the earth will be at the
opposite point in its orbit and the situation and the Northern
Hemisphere is tilted towards the sun and it will be summer.
I’ve left out two important facts. First, the earth spins around its
axis like a top slowing down and starting to wobble. What this
means is that the ends of that imaginary rod through the poles are
tracing circles as the earth wobbles. But this a very slow wobble.
It takes some 22,000 years for the ends of that rod to trace
complete circles. Let’s take the point on the earth’s orbit around
the sun where we are today. The earth is tilted at a certain angle
to the sun. It will be 22,000 years from now when the earth is
once again at precisely the same angle at this point in its orbit.
I also neglected to say that the earth doesn’t literally “circle” the
sun. Its orbit is not a circle, but an ellipse; there are opposite
points where the earth is closest to and farthest from the sun.
Combine this fact with our 22,000-year tilt cycle and we get an
interesting situation. If we start at a time when the earth is
closest to the sun and the tilt is such that the Northern
Hemisphere is most exposed to the sun’s rays, what does that
mean? This is the situation under which the Northern
Hemisphere receives the most solar radiation and hence should
be the time of the warmest northern summer. This won’t happen
again for 22,000 years. But, 11,000 years later, when the earth is
tilted in the opposite direction, summer will occur when the earth
is at the farthest point in its orbit around the sun, and this should
be a time of the coolest northern summer.
If you plot the solar radiation in the Northern Hemisphere over
the years, it rises and falls with the peaks and valleys 11,000
years apart and the distance between peaks of 22,000 years.
Why am I taking you through all this? It has to do with what
may be a major misconception about when and what started
global warming and a radical claim that global warming began
much earlier and for a different reason than the common wisdom
would have it. The claim is detailed in an article by William
Ruddiman titled “How Did Humans First Alter Global Climate?”
in the March Scientific American. Ruddiman is a marine
geologist, former chair of the department of environmental
sciences at the University of Virginia and experience as an
oceanographer and research scientist at the U.S. Naval
Oceanographic Office and Columbia’s Lamont-Doherty Earth
Ruddiman claims that global warming began, not with the
industrial revolution in the 1800s, but thousands of years earlier.
In fact, he claims that humans have been affecting global climate
for at least 8,000 years! There were no cars or smokestacks
pouring out greenhouse gases, but Ruddiman cites some very
intriguing histories of two greenhouse gases, carbon dioxide
(CO2) and methane in the atmosphere.
Let’s concentrate on the history of methane in the atmosphere
over a period of hundreds of thousands of years. How do we get
such a history? Let’s go down to Antarctica, where the ice has
been laid down over millennia and piled up to amazing depths.
Intrepid researchers have managed to drill down deep enough to
obtain a core of ice 3 kilometers (almost two miles) long. (I
don’t know if this was one long core or a bunch of cores
covering a total depth of 3 kilometers. Either is impressive!)
When the ice in the core was laid down over a 400,000-year
period, it trapped tiny bubbles of air. By analyzing the bubbles
for methane and CO2, scientists obtained plots of the amounts of
these gases over these 400,000 years. They found that the
concentrations of both gases rose and fell in regular patterns over
this time. Ruddiman presents a plot over the past 250,000 years
or so and the concentration of methane cycles up and down
within a range of about 400 and 700 parts per billion (ppb).
And, what do you know? The methane peaks and bottoms out
along with the solar radiation, the time between peaks being
22,000 years! The correlation is remarkable. The plots in the
article cover 10 peak-to-peak cycles, with the last peak occurring
11,000 years ago; this means we should now be at or near the
coolest northern summer period.
The methane content at the last peak was over 700 parts per
billion (ppb). Sure enough, for the next 6,000 years the methane
content fell along a normal curve to below 600 ppb. Then, 5,000
years ago, something happened. The methane departed from the
normal curve and started increasing, as it has to this day, when
it’s back up over 700 ppb. Without going into detail, the carbon
dioxide in the atmosphere also took off from its normal curve
3,000 years earlier than for methane, or 8,000 years ago.
What happened? Ruddiman proposes that it was a new human
endeavor – farming! Farming started about 11,000 years ago in
Mesopotamia and China. About 8,000 years ago, our Stone Age
counterparts started clearing forests in Europe to plant crops.
Did this burning of forest and additional farming fuel the rise in
CO2? And the methane? It was 5,000 years ago that Chinese
farmers started flooding land near rivers to grow rice. A big
source of methane is the decay of vegetation and the stagnant
water in rice paddies promotes such decay.
With more deforestation and farming, the CO2 and methane
concentrations continued to rise. But in the past 1,500 years or
so, the CO2 levels fell markedly on some occasions. Ruddiman
points out that three episodes of falling CO2 happened at times
when there were major plagues that killed off significant
numbers of people. For example, there was a long period of
plagues that culminated in about 500-600 AD with the deaths of
25 to 40 percent of all Europeans. The CO2 rose after that only
to fall again, when the Black Death killed about the same
percentage of Europeans. Another, more precipitous fall in CO2
happened in the period of 1500 to 1700 when diseases introduced
by the Europeans killed 90 percent of native populations in the
Each of these incidents would have reduced the amount of
farming activity in the affected areas and the abandoned farms
would be headed back to their natural forested state before the
population recovered and farming commenced in earnest once
again. A few weeks ago, we talked about global dimming of the
sunlight reaching the ground and its possible holding back of
global warming. Ruddiman suggests that greenhouse gases from
farming counteracted the normal cooling trend expected from the
fact we’re in the bottoming out phase of the 22,000-year solar
radiation cycle. Could the farmers be responsible for preventing
a new ice age?
As for me, I’m more confused than ever and will concentrate on
whether to wear my heavy or light sweatshirt on tomorrow
morning’s beach walk here on Marco Island. It’s supposed to be
in the 40s and a brisk day for sunny Florida.
Allen F. Bortrum