Copenhagen: a warning from the history of Earth

The history of the Earth’s atmosphere indicates the extreme sensitivity of climate to even minor compositional changes of the greenhouse gases (CO2, methane, nitric oxide, ozone), which affect the carbon cycle and oxygen cycle which, in turn, control life.

Major changes in the CO2 and methane composition of the atmosphere since the 18th century threaten to shift the state of the Earth’s atmosphere to conditions similar to those of 2.8 million years ago (mid-Pliocene) and 18 million years ago (mid-Miocene) thermal peaks.

The cumulative nature and centuries to millennia-scale atmospheric residence time of CO2 is tracking towards the natural boundary between the current interglacial climate state and a transient greenhouse climate state, defined by paleoclimate history above a level equivalent to 500ppm CO2 (Zachos et al. 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science). The effects of this rise are evidenced by contemporaneous melting of mountain glaciers, Arctic Sea ice, Greenland and West and East Antarctica ice sheets and the increasing rate of sea level rise.

Figure 1. Greenland, west Antarctica and East Antarctica ice melt rates and glacier thinning in metres per year (ma-1). British Antarctic Survey. The red and purple areas represent ice melting at rates larger than 0.5 metres per year. Grey areas have no ice melt data.

Global warming by +0.8 degrees C since 1750, plus +0.5 degrees C currently masked by sulphur aerosols, with further effects of ice albedo (reflection) loss not yet accounted for, has surpassed the temperature rise associated with the last interglacial (Emian: 124,000 years ago; ~ +1 degree C; ~ +4 to 6 metre sea level rise) (Figs 2 - 4).

At 460ppm CO2-e (a value including the CO2-equivalent radiative forcing of methane) the energy level of the atmosphere exceeds that of the mid-Pliocene (2.8 million years ago; CO2 ~400ppm, +2 to +3 degrees C; sea levels +25±12 metres). As CO2 and temperatures rise they track towards levels reached in the mid-Miocene ~13-15 million years ago (CO2 levels near-500ppm; deep sea temperature 4.0 - 4.4 degrees C) and the Oligocene (CO2 ~650ppm; deep sea temperatures ~5 degrees C; sea levels tens of metres higher than at present).

Figure 2. Variations in Oxygen and CO2 through the last 600 million years of Earth evolution. Note the concomitant decline in CO2 and increase in O2 during ice ages, and the opposite relations during greenhouse phases of Earth history. Oxygen plot after Berner et al. 2007 [6]. CO2 plot after Royer 2004. The blue bars represent glacial periods, with heights corresponding to the latitudes the ice sheets reached.

Figure 3. Paleo-CO2 and paleo-temperature plots for the periods 400 million year to the present and 65 million years to the present. Note the upper ~500ppm CO2 boundary between glacial and greenhouse Earth climate conditions. IPCC-2007 Chapter 6.

Top: Atmospheric CO2 and continental glaciation 400 Ma to present. Vertical blue bars mark the timing and paleo-latitudinal extent of ice sheets. Plotted CO2 records four major proxies.
Middle: Global compilation of deep-sea temperatures based on 18O of fossil plankton from 40 Deep Sea Drilling Program and Ocean Drilling Program sites.
Bottom: Detailed record of CO2 for the last 65 Million years. Estimates based on soil nodules have high uncertainty

Figure 4. Atmospheric CO2 and ocean bottom temperatures for the period 25 - 10 million years ago (Oligocene-Miocene). Paleo-temperatures are based on 18O and Ca/Mg ratios; Paleo CO2 levels are based on Stomata (fossil leaves pores), carbon isotopes and boron isotopes. Royer, 2008. PNAS, 105, 407-408, January 15, 2008.

Trends in atmospheric CO2, temperatures, ice age phases and greenhouse phases in Earth history demonstrate close relations between atmospheric CO2 levels of below 500ppm and glaciations (Figs 2-4).

There is no known precedence in the recent history of Earth for a rise in CO2 as fast as the current rate of 2ppm/year. With an upper stability limit of the Antarctic ice sheet at about 500ppm (Royer D. 2008. Linkages between CO2, climate, and evolution in deep time. PNAS), the onset of ice melt at the margins of East Antarctica raises the possibility Earth may be tracking toward ice-free conditions analogous to those of the late Eocene (>500ppm CO2; +5 degrees C; +70 metres sea level).

There is no knowing the time table towards an ice-free Earth, the current “experiment” by Homo sapiens being unique in the history of the planet.

The history of the Pleistocene (1.8-0.01 million years-ago) glacial-interglacial era is dominated by abrupt shifts in the state of the climate (Alley R. B. 2000. Ice-core evidence of abrupt climate changes. Proceedings of the Natural Academy of Science). During this time gradual climate changes were repeatedly interrupted by abrupt tipping points, involving temperature shifts of several degrees over a few centuries, a few decades and even a few years (Steffensen et al., 2008. High-resolution Greenland ice core data show abrupt climate change happens in few years. Science Express). The implications for an unstable, highly reactive, nature of the atmosphere are clear.

Having placed a man on the moon, split the atom, coded the DNA and created a World Wide Web, science and technology possess the ingenuity required for 11th hour attempts at climate change mitigation and adaptation, including bio-sequestration and CO2 down-draw techniques. However, the $-trillion-scale funding needed to implement these methods continues to be poured into the military, casinos and games.

A medieval state of mind appears to be manifest through a resistance to enlightenment and to science. Much like the grieving cycle of Helen Kubler-Ross, denial, resistance, anger and finally resignation alternate. Vested interests embark on massive well financed disinformation campaigns, using mouthpieces who defy the basic laws of physics and often fabricate climate data.

Governments undertake merely symbolic actions out of step with scientific projections of looming climate tipping points. None of the targets discussed in Copenhagen get near the minimum effort required to reduce the increasing carbon emissions and deforestation.

What is referred to as climate change represents, in terms of Earth’s history, a Great Oxidation Event perpetrated by a Prometheans who assumed the mastery of fire. We may never understand the natural rationale for a species to cut and burn the forests from which it descended, proceed to dig and burn the fossil remnants of past biospheres and unconsciously render the atmosphere, the lungs of the Earth, unsuitable for its own future.

The atmosphere is not waiting for a human decision.