Earth tracking toward climate conditions of 3 million year ago?

by Prof. Andrew Glickson and Dr Graeme Pearman

   Andrew is Associate Professor at Department of Earth and Marine Science, Australian National University. Graeme is former Chief, CSIRO Division of Atmospheric Research, and now heads a consulting group at Monash University. Both have impeccable academic credentials.

   Andrew has sent me a series of papers, some intended for a scientific audience, some for the lay public. I have selected this one, because it very briefly summarises the relevant information. Because this paper is too important to be buried in the Archives of 'bobbing around', I have posted it here in its own right.

   Although I am not a climate scientist, I have been studying these issues since 1972, and consider these sober, cautious, scientific forecasts way too optimistic. For one thing, they cannot include consideration of sudden cataclysmic events such as a global tidal wave caused by a huge piece of ice breaking off at the Antarctic (see Sleeper, Awake), or immense volcanic activity in areas freed of the weight of ice. Andrew and Graeme do mention effects on the Gulf Stream, but what happens to Western Europe if it stops, reverses or moves out to sea?

   Three million years ago, during a period referred to by geologists as the Mid-Pliocene, average global temperatures were between 2 and 3 degrees C warmer than at present, the Arctic Sea was free of ice and much of the Greenland ice sheet melted, with sea levels higher by between 13 and 37 metres. In reports by the UN Intergovernmental Panel on Climate Change earlier this year, scientists have warned of the high probability that warming by similar amounts is expected through this century due to the release of greenhouse gases into the atmosphere. This, together with recent observations of a changing climate, leads us to pose the questions, could the Earth be rapidly returning to such conditions and if so, what does this mean for humanity?

melting ice -- drowning coastal cities   Observations of changes to the global climate systems include the advanced summer melting of the Arctic Sea ice growing by 23 percent over the last 2 years and an increase in spring melt area of the Greenland ice sheet by 16 percent between 1979 and 2002. These may be short-term aberrations or they may indicate that global warming is crossing a new threshold since the mid-1980s, since which mean global temperature rose by about 0.6 degrees C.

   Two principal factors are together pushing the Earth's atmosphere from the relatively stable conditions which existed for the last 10,000 years (the Holocene) toward conditions analogous to the interglacial peak at 130-125 thousand years-ago and beyond toward conditions more like those of the mid-Pliocene about 3.3-3.0 million years ago.

   burning of coal -- burning the futureThese factors include the combustion of coal, oil and natural gas containing more than 300 billion tonnes of carbon, continuing at a current rate of about 8 billion tonnes per year, with more than half remaining in the atmosphere as the greenhouse gas, carbon dioxide. This is compounded by extensive land clearing, which despite new growth and re-fertilization of soil and vegetation by carbon, sulphur and nitrogen, results in net reduction in the capacity of vegetation to sequester carbon dioxide and minimise its impact on climate.

   With rising water temperatures and lowered pH (higher acidity), the carbon dioxide absorption capacity of ocean surface water and of marine life are reduced. The capacity of the oceans to transport carbon dioxide into the deep oceans, where it is semi permanently out of the atmospheric system, is about 2 thousand million tonnes of carbon per year; that is, much less than what we are releasing into the atmosphere. Hence carbon dioxide concentrations are increasing in the atmosphere and will continue to do so until we reduce emissions to at least these levels. But this capacity is expected to decrease, particularly as warming of the surface oceans leads to even greater stabilisation of the ocean circulation and thus overturning of these waters. Recent evidence suggests this process has already commenced.

   Consequently, atmospheric carbon dioxide levels are rising at more than 2.5 parts per million per year, one thousand times faster than at pre-industrial rates (about 0.002 ppm/year) and one hundred times faster than during the end of previous glacial (ice age) periods. The temperature rise from 1990 to 2005 of 0.022 degrees C/year exceed the 1850-1970 rate of 0.004 degrees C/year by five fold.

   The 2007 projections of the Intergovernmental Panel on Climate Change for global temperature by 2100 of about 2 - 6 degrees C are consistent with mid-Pliocene conditions. On the other hand, sea-level rises projected by the IPCC of 18-59 cm by 2100 are at least 10 times less than those of mid-Pliocene levels. The relationships between sea-level rise and temperature rise observed over geological time suggest that a 2 - 6 degrees C rise will result in rise of sea level by many metres, given enough time.

   Studies of the past and projections from modern climate science suggest that multiple consequences flow from a transition from current (Holocene) climate conditions to peak Pliocene-like conditions, including:

(A)deserts are growing Poleward shift of climate zones, with increased temperature and fire conditions in tropical and subtropical latitudes, desertification in low-mid latitudes, and extensive mountain and polar ice melting. In Australia, contraction of the Antarctic wind vortex results in reduction of rainfall in mid-latitudinal wheat belts;

(B) Melting of Greenland ice, causing retardation of the Gulf Stream. This results in sharp reduction of temperatures to freezing levels in Western Europe and northeast America, and elevated sea temperatures in tropical oceans, with consequent increase in the frequency and intensity of hurricanes;

(C) Melting of mountain glaciers and thereby reduction of major river valley agricultural systems;

(D) Rising sea levels. Total Greenland and west Antarctic melt lead to about 14 metres sea level rise, with consequent flooding over coastal zones and lower river valleys world-wide.

   About 3 million years ago, Hominoids survived abrupt climate upheavals by migrating between climate zones. By contrast, present civilization may hardly be able to cope with a more rapid collapse of agricultural food-production systems, coastal habitats, harbours and sea transport networks and fuel supply lines, severely eroding the basis of current world populations; these in a world of much larger population and political segmentation.

   Current climate trends can hardly be halted, although long-term stabilization for the next several centuries may be achieved through urgent and abrupt reduction in the emissions of greenhouse gases from energy production and extensive forest regrowth campaign. The economic cost of transformation from fossil fuel-based technologies to alternative energy sources (solar thermal, photovoltaic, geothermal, wind, hydrogen) is estimated at around 0.1% of GDP (IPPC 3rd working group, the Stern Report, Australian Business Roundtable, AGL-WWF study). This contrasts with the trillions of dollars of world resources currently used for destructive purposes, funds required for long-term restoration and re-vegetation of degraded regions of the biosphere.

   These considerations, drawn from both geological and modern evidence, make it clear that addressing climate change is urgent. This has been stressed by 150 global business leaders recently, charging the UN discussions in Bali with a responsibility to be bold in seeking aggressive and immediate targets for controlling future emissions thus substantially avoiding the prognosis of a Mid-Pliocene scenario for our children and their children.

   We thank Barrie Pittock, Barry Brook and Jim McNamara for their comments.