You won’t find it in the headlines, but last month measurements of CO2 concentrations over the Arctic topped 400 parts per million (ppm) — a level not seen for 2.6 million years.

Measurements at Hawaii’s long-running Mauna Loa site reached 395.77 ppm. These kinds of numbers have not been seen since the end of the Pliocene period (5.3-2.6 million years ago).

Current CO2 rates are rising at around 2 ppm a year (2005 — 2.52; 2006 — 1.76; 2007 — 2.22; 2008 — 1.59; 2009 — 1.89; 2010 — 2.42; 2011 — 1.88 ppm per year, see Figure 1), which is a rate that exceeds any recorded since 65 million years ago. The rapid change in the state of the atmosphere is shifting the climate at a pace to which many species can hardly adapt.

Figure 1. Atmospheric CO2 variations at Mauna Loa

During the Pliocene (5.3-2.6 million years ago), mean global temperatures were 2-3 degrees higher and sea levels 25 metres (plus or minus 12 metres) higher than in the 18th century. Since 1880 the rise in temperature of about 0.8 degrees  is compounded by a further rise of approximately 1.2 degrees, currently masked by emitted industrial sulphur oxide aerosols and sulphuric acid (see Figure 2).

Figure 2. The main frame indicates the sharp rise in CO2 since the 18th century. The inner boxes indicate the rise in greenhouse gas-forced energy levels (+3.2 Watt/m2) and sulphur dioxide forced aerosol cooling by about -1.6 Watt/m2. (1 Watt/m2 ~ ¾ degrees). After Hansen, et al, 2011. Earth’s Energy Imbalance and Implications. [PDF]

Mean global temperatures have continued to rise (see Figures 3 and 4), notably in polar and sub-polar latitudes, where in May 2012 mean Greenland temperatures reached an all-time high of 24.8 degrees.

Figure 3. Global surface temperatures anomalies from (deviations from normal values) four independent sources, showing nearly identical warming trends. Sources: NASA, NOAA, Met Office, Japanese Met Agency


Figure 4. Global annual temperature map for 2002-2011 relative to 1951-1980.

In accord with the basic laws of physics and chemistry of the atmosphere, paleoclimate proxy-based calibrations and direct measurements, the rising levels of greenhouse gases (CO2, methane, ozone) are shifting the energy state (radiative forcing) of the atmosphere beyond that which allowed relatively stable climate conditions in the past 10,000 years, which made possible the development of agriculture and civilisation.

As a result of rising energy levels in the atmosphere-ocean system, the frequency and intensity of heat waves, droughts and floods increased since about 1980, as confirmed by Hadley, NOAA, CSIRO, BOM and other climate research organisations.

Ongoing emissions driving about 2 ppm CO2 per year rise would lead to a level of 576 ppm by the end of this century, well above the  about 500 ppm stability limit of the Antarctic ice sheet. That’s not even considering further rises due to positive feedbacks from ice and permafrost melt, warming water, droughts and fires. In other areas, rising ocean water temperatures intensify the hydrological cycle, leading to the intensification of hurricanes and severe floods.

So what was the climate like during the Pliocene, 5.3-2.6 million years ago, a climate towards which we are now heading with increasing certainty?Research has found that 3 million years ago CO2 levels were about 380 ppm and temperatures about 3.5 degrees warmer than at present. Enhancement of the North Atlantic Thermohaline current, acting as a conveyor belt, resulted in retreat of sea ice, with consequent positive feedback to global warming.

Researchers have also determined that the mid-Pliocene was a period of sustained global warmth as a result of elevated CO2, lowered orography (mountain relief), and vegetation and ice sheet changes. Salzmann, et al, (2009) observe that in the mid-Pliocene, there was a generally warmer and wetter climate, a northward shift of the taiga  (boreal forest, is a biome characterised by coniferous forests) and tundra (sub-polar regions where tree growth is hindered by low temperatures and short growing seasons) — boundary and a spread of tropical savannahs and woodland in Africa and Australia at the expense of deserts.

Estimates of carbon reserves indicate that there are enough coal, oil and gas reserves to emit more than 2000 billion tonnes of carbon and raise CO2 levels above 1000 ppm (Figure 5). Kiehl 2011 states states:

“Consider one example when CO2 was about 1000 parts per million at ~35 million years ago (Ma). Temperature data for this time period indicates that tropical to subtropical sea surface temperatures were in the range of 35 to 40 degrees (versus present-day temperatures of about 30 degrees) and that sea surface temperatures at polar latitudes in the South Pacific were 20 to 25 degrees (versus modern temperatures of about 5 degrees).”


Figure 5. Fossil fuel: emitted, reserves and recoverable resources versus derived CO2 equivalents

As established by Earth and climate science, planetary climates are determined by factors including solar radiation, greenhouse gases and volcanic activity. Major changes in any one of these parameters leads to transient to long-term shift in the state of the climate.

The increase since the onset of the industrial age in the atmospheric CO2 and methane concentration by more than 40% (from 280 to 400 ppm CO2) poses a major threat to the Earth’s biosphere. According to Hans Joachim Schellnhuber, director of the Potsdam Climate Impacts Institute and climate adviser to the German government, “we’re simply talking about the very life support system of this planet”.

Peter Fray

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