Climate change, a geologist’s view

Materials World magazine
,
1 Mar 2009


Professor Ian Plimer of the University of Adelaide, Australia, presents his conclusions on climate change.

Climate change is blamed for almost every weather event on Earth, but, as most geologists know from studying Earth processes, climate has always changed. Over 200 years ago, James Hutton, one of the founders of geological science, unraveled the history of rock formations near Edinburgh, UK, by recognising the long periods of time required to lay down sediments. It was obvious to Hutton that overlying rocks had been put down in different climates.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Modern geology and planetary science has revealed a constant cycle of events that change climate. These include a 143m-year galactic cycle; 100,000, 41,000 and 23,000-year Earth orbital cycles; 1,500, 210, 87, 22, and 11-year solar cycles, and an 18.6-year tidal cycle, all of which effect the amount of radiation that reaches Earth. Today, anthropogenic carbon dioxide is cited as the cause of global warming, and various measures have been put in place, mainly by developed countries, to moderate carbon dioxide output. This includes including complicated carbon trading.

However, there were periods in the geological past when carbon dioxide levels were considerably higher than they are today. Atmospheric carbon dioxide is absorbed by organisms and captured in sediments, and from these, past concentrations can be determined. They reveal that during the first stage of life on Earth, in the Cambrian era (some 550 million years ago), carbon dioxide levels were up to 7,000ppm, which gradually fell to levels similar to today in the Permian (300 million years ago), only to rise in the age of the dinosaurs to 2,000ppm. There is however no correlation with temperature during these geological periods, and there was no runaway global average with high carbon dioxide. In fact, during some periods of high CO2 levels, there is geological evidence of glaciations.

Changing temperature

Between 400,000 and 100,000 years ago, carbon dioxide levels were around 200-300ppm with approximately 100,000-year cycles between peaks. Average Earth temperatures had similar cycles, but some 800 years in advance of those of carbon dioxide. These temperatures have always varied – 16,000 years ago the northern hemisphere saw the onset of glaciations that covered most of the UK in thick ice. Annual average temperatures then were fluctuating rapidly from +15ºC to -10ºC as the ice sheets waxed and waned, but since the end of the last glaciation, these changes have slowed to around +/-3ºC.

Within recorded history temperatures have changed, independent of carbon dioxide levels, alternating between cooler and warmer periods. What is next in the cycle is a cooler period that may end the interglacial period in which we now live.

Since the 1850s, temperatures have been taken at measuring stations in the USA. Many of those were in towns that have been increasingly urbanised, and unsurprisingly showed small average temperature gains, for example New York has risen from 51ºC to 54ºC since 1840. In rural areas such as Harrisburg, Pennsylvania, a fall from 54ºC to 52ºC has been measured over the same period. In Siberia, Russia, temperature increases have been recorded since the end of the Soviet subsidy for diesel and vodka, which was triggered by -10ºC temperatures. The lack of consistency in measuring temperatures and the effects of urban heat islands, different station heights and human bias does question the veracity of results, especially as they do not correlate with satellite and radiosonde measurements.

When the past 28 years of high-quality satellite data is examined only a slight (<0.5ºC) increase is recorded for average annual temperatures in the northern hemisphere, and none in the southern.

Sunny outlook

The heat source for the surface of the Earth and atmosphere is the sun. Its radiation is not constant and follows well defined cycles. These can be measured by sunspot activity, and their number and length have been recorded for over 150 years. Cosmic radiation creates low level clouds that reflect light, as well as new chemicals in the upper atmosphere, such as Carbon-14, that eventually accumulate in geological sediments where they can be measured and dated.

From the 15th-19th centuries, during the UK’s Thames frost fairs, sunspot activity was low. It is also low now, where the end of a 23-year cycle is overdue. There are also strong correlations with precipitation, and historical data indicates the relation of sunspot activity to temperature. Data compiled by the economist Adam Smith positively correlated high grain prices (reflecting poor harvests) with low sunspot activity.

Heat and ice

The high carbon dioxide levels in the Cambrian era fell away over a few hundred million years as life on Earth evolved. A resurgence in values in the Mesozoic period came from volcanoes. The Permo-Triassic boundary is marked by Siberian flood basalts, the Earth’s largest subaerial volcanic event and, coincidentally, a rise in carbon dioxide.

Water vapour and CO2 comprise the majority of volcanic gases. The International Panel on Climate Change (IPCC) has set aside an estimate for carbon dioxide from subaerial volcanoes, but 85% of volcanoes are found on the 64,000km of mid-ocean ridges that provide new basaltic ocean crust. These eruptions have a high carbon dioxide output, which is recycled through seawater (some 10,000km3 of cooling water) and sea floor sediments. Submarine volcanoes are also responsible for affecting ice sheets. In Antarctica, numerous active subglacial volcanoes are actively accelerating normal glacier accumulation and movement of ice to the sea. Over the majority of the continent, ice is thickening, with decreases only in the western part. Overall sea ice has increased over the period 1978-2006.

In the Arctic, the mass balance of ice over Greenland has also increased, as has that of the Artic sea ice, despite eruptions of 13% carbon dioxide from submarine volcanoes.

Opening up the debate

Carbon dioxide is undoubtedly a greenhouse gas, however, this research, (based on over 500 references) indicates that water vapour is the main greenhouse gas. These findings extend the focus beyond the current debate. I believe the indisputable evidence of past carbon dioxide at levels much greater than at present, and the fact that at times they correlated with cooler periods warrants consideration.

The present baseline of 280ppm set by IPCC as a pre-industrial level, a level noted in 1880, is the lowest in the past 200 years. The first few ppm atmospheric carbon dioxide do have a profound effect on Earth temperatures, but after 40ppm, the effect declines continually. This is supported by the geological, archaelogical, historical and present day observations.