Some things to think about concerning life on earth and climate change.
Approximately 2.3 billion years ago, Earth could have been easily mistaken for a hostile alien planet. Methane spewed into the atmosphere by constant volcanic activity, and fatal UV radiation bombarded the surface without the protection of an ozone layer. The primordial seas were blood red, a hue caused by the massive amounts of suspended iron in the water. It is beneath these red waves in which almost all life on the planet survived, most of which would require a microscope to view. Anaerobic single celled organisms were the dominant life form on earth at the time; they lived in the hostile chemical make up of the primordial sea without the need of oxygen. However just one of these single celled organisms may have caused the greatest extinction event on planet Earth: the Cyanobacteria.
What was formerly known as blue-green algae, the Cyanobacteria
are actually bacteria that have the unique ability of photosynthesis.
This single-celled organism had emerged only a few hundred millions
years before, at a time where all other organisms relied on methods
of anaerobic respiration. By creating its own energy from the sun,
this bacterium was able to generate up to 16 times more energy than
its counterparts, which allowed it to outcompete and explode in
reproduction. This seemingly innocent organism would spell doom
for most of life on the planet, as photosynthesis produced
free oxygen molecules as a byproduct.
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In a relatively short amount of time, Earth went from having very
little oxygen to what may be the highest levels of atmospheric
oxygen it has ever had. This event had wiped out most of life
on the planet to which the oxygen was poisonous. Some of these
anaerobic organisms were though to have survived by burrowing into
the earth where oxygen levels were survivable. What may have the
biggest change is that when oxygen accumulated in the methane rich
atmosphere, the concentration of this greenhouse gas dwindled,
causing temperature levels to drop. They dropped so low in fact,
that this oxygen event is thought to have triggered the Huronian
glaciation, the longest snowball Earth period.
Chemical reactions on early Earth could have created all four building blocks of RNA molecules, triggering the beginning of life.
Now, chemists have identified simple reactions that, using the raw materials on early Earth, can synthesize close cousins of all four building blocks. The resemblance isn't perfect, but it suggests scientists may be closing in on a plausible scenario for how life on Earth began.
If projections about the future of climate change are prone to considerable potential error, we must allow for that error to go in both directions. There is nothing necessarily reassuring about climate change uncertainty; those error bars encompass a space in which our worst nightmares find refuge.
The moment we concede the uncertainty about climate change projections - magnitude, pace, impact - that Mr. Stephens asks of us, we are obligated to allow for the entire expanse of that potential error. That's what scares me most.