Chapter 1


The Latin meaning of Homo sapiens is “wise man” or “rational man.” We are the only
surviving species of hominids and are characterized by large well‐developed brains that
provide capabilities for tool use, reasoning, problem solving, advanced communication
and the creation of complex social structures. Evidence of anatomically distinct Homo
sapiens date back 200,000 years to the plains of Africa. For the first 199,900 years of
existence, the lives of Homo sapiens, like all other animal species, had no significant
effect on the atmosphere and climate of Earth. By the year 1750, the capabilities
and circumstance of man lead to the onset of the Industrial Revolution whereby raw
materials were extracted from the Earth in volume and combusted for energy to drive
mechanical processes. By 1900, the core inventions of the Industrial Revolution and
other advances in science and agriculture had placed mankind on a path toward a
future of intensive fossil fuel use and other activities that would release substantial
quantities of greenhouse gases into the atmosphere. Over the past 117 years, the
activities of man have led to an accumulation of these gases at sufficient concentrations
to elevate surface temperatures. Future surface warming is dependent on the extent
of continued release and atmospheric accumulation of anthropogenic (man‐made)
greenhouse gases.

Over the 4.5 billion year history of Earth, the climate has fluctuated between extremes
of “hot house earths”, where average surface temperatures were 14°C warmer than our
current climate to “snowball earths” where the entire surface of the planet was covered
in snow and ice. An assessment of the triggers and processes involved in naturally
occurring climate change provides an understanding of how we have transitioned to
a new geological age where human activity has become the dominant influence on
climate and the environment.

Our solar system began as a pre‐solar nebula localized in a cold molecular cloud of
hydrogen and helium gases sprinkled with particles of cosmic dust.1 The mass of the
nebula would have been slightly more than the mass of the sun, and the composition
would be identical to that of the current solar system (73% hydrogen, 25% helium
and 2% heavier elements). The nebula began to spin faster as material condensed
and, eventually, a hot dense protostar formed at the center of a protoplanetary disk.

  1. Encrenaz, T., Bibring, J. P., Blanc, M., Barucci, M. A., Roques, F., & Zarka, P. (2004). The Solar System (3rd Edition). Berlin. Springer.