The Hindu Business Line : Precarious irreversibility of climate change

The British Prime Minister, Mr Tony Blair, terms climate change the "world's greatest environmental challenge". `Avoiding Dangerous Climate Change,' summarises the proceedings of an international symposium on the subject held a year ago. Also interesting, is William F. Ruddiman's new book, `Plows, Plagues and Petroleum.' The author, says D. Murali, pushes the debate of climate change beyond the usual two centuries of industrial development to 8,000 years!

ANTARCTICA. Earth's `highest, windiest, coldest, and driest landmass.' Its 99.7 per cent of surface is covered by a vast ice sheet with an average thickness of about 2 km. "Were it to melt, global sea level would rise about 57 metres." Thus cautions a 406-page book titled, Avoiding Dangerous Climate Change, and released on January 30 by the Department for Environment, Food and Rural Affairs (DEFRA) of the UK (www.defra.gov.uk).

The book has been edited by Hans Joachim Schellnhuber, and `typeset by Charon Tec Ltd, Chennai, India.' While the latter fact should warm the hearts of the publishing outsourcing industry, the dismal news is that "Sea level is reported to have risen during the 20th century by between 1 and 2 mm per year and model predictions suggest the rise in global-mean sea level during the 21st century is likely to be in the range of 9-88 cm." The book has more than 40 chapters, summarising the proceedings of `The International Symposium on Stabilisation of Greenhouse Gas Concentrations, Avoiding Dangerous Climate Change (ADCC),' held a year ago; the symposium drew about 200 participants from 30 countries.

To set the tone, the UK Prime Minister, Tony Blair, declares in his Foreword to the book that climate change is the world's greatest environmental challenge. The first chapter is by Rajendra Pachauri, on `Avoiding dangerous climate change'. He cites Norman Myers, for the ominous forecast of "150 million environmental refugees by the year 2050". What follow are chapters on the Antarctic ice sheet, Greenland ice sheet, risk of a collapse of the `Atlantic Thermohaline Circulation', and the impact of increased atmospheric CO{-2} on oceanic pH and the marine ecosystem.

Whole sections have been devoted to broad themes such as perspectives on dangerous impacts, vulnerabilities of ecosystems and biodiversity, emission pathways, and technological options. The final chapter, titled `the technology of two degrees,' looks at the implications of limiting the change in global mean surface temperature (GMST) to two degrees Celsius (2{+0}C) relative to pre-industrial temperatures. "While the technical and economic challenges of the emissions trajectory between 2005 and 2050 are daunting under the assumption of a 2.5{+0}C climate sensitivity, they are far more modest than the challenges of the 2050 to 2095 period," postulates the report. By 2095, global population would have reached close to 10 billion; global GDP increased from $30 trillion (2002) to more than $250 trillion; and the global energy demand risen from about "375 exajoules per year (EJ/y) in 1990 to more than 1200 EJ/y by 2095." No joyous news, but there's more.

Humans are beating nature at climate control

One of the references in the ADCC report is to Ruddiman, W.F. for his article "The Anthropogenic Greenhouse Era Began Thousands of Years Ago", in Climatic Change (2003). You can download the 33-page file on http://courses.eas.ualberta.ca.Of greater interest is William F. Ruddiman's new book, Plows, Plagues & Petroleum, from Princeton University Press (pup.Princeton.edu). Because the author pushes the debate of climate changed beyond the usual two centuries of industrial development to 8,000 years!

In part one of the book, Ruddiman asks, `What has controlled earth's climate?' He argues that till the discovery of agriculture, about 12,000 years ago, we didn't affect climate. "If you could watch a time-lapse film showing Earth's surface since agriculture began, you would see a subtle but important change spread across southern Eurasia during the last several thousand years," he writes. "In China, India, southern Europe, and northernmost Africa, you would see darker shades of green slowly turning a lighter green or a greenish brown," indicating the conversion of forests into pastures and croplands. Ruddiman uses the analogy of the tortoise in the fable, to explain how agriculture has overtaken the damage caused by the hare, that is, industrialisation.

Part two of the book, titled `nature in control', begins with the story of how the 4.6 billion-year old Earth became oxygen-rich about 2.2 billion years ago. "India broke loose from Antarctica about 70 million years ago and began slowly crunching into Asia 20 million years later, heaving up the Tibetan Plateau and the Himalayas." It was all `slow going for a few million years', when our predecessors acquired their food "from scavenging, gathering, and hunting small animals", till about 12,000 years ago.

Ruddiman cites research to show that over the last 9 lakh years, up to nine 1,00,000-year glacial cycles can be counted. The Northern Hemisphere, and the planet as a whole, has been gradually drifting toward a more refrigerated state for the last 3 million years, notes the book. Before 2.7 million years, no large ice sheets existed in the North. "From then and until 0.9 million years ago, ice sheets appeared in cycles but then melted away completely." In Ruddiman's view, therefore, "the ice-free condition in the Northern Hemisphere today (excluding Greenland) is part of a very short break in a mostly glaciated world." Thus, as if to remind you of `The Day After Tomorrow, northern Canada and Scandinavia could reach a condition akin to Antarctica if the long-term cooling trend were to continue!

The 22,000-year monsoon cycle

"Tropical monsoons are driven by changes in summer solar radiation at the 22,000-year orbital cycle," explains a chapter on monsoon cycles, citing the work of John Kutzbach. He'd noted that solar radiation levels were considerably higher than those today at regular intervals of 22,000 years, with the last such time occurring just 10,000 years ago. It seems Kutzbach's theory found support in "ancient air bubbles trapped in the Antarctic ice sheet," as discovered by Russian engineers working at station Vostok "for years in the warmth of Antarctic summers (-20{+0}F)".

The bubbles told the story of methane changes. The mantra is `more Sun, more monsoon, more methane,' explains Ruddiman. How so? "When strong monsoon rains fall on tropical wetlands, they flood them with water during the summer season when plants grow. As plants die, they decompose in stagnant water lacking oxygen. Bacteria attack the decaying plant matter and convert its carbon to several products, including methane gas."

Half of Earth's surface lies between 30{+0}N and 30{+0}S, and monsoon changes are the primary orbital-scale control of climate across this vast region, writes Ruddiman. "Most of the world's population lives at these latitudes today and has done so since humans evolved. We have lived with these monsoon fluctuations for several million years."

Irrigation, the culprit!

Part three is where `humans begin to take control', where the author pursues the major theme of his `detective story'. Like methane levels, the long-term concentration of CO{-2} is controlled by orbital cycles, though the CO{-2} system is more complex. Ruddiman's hypothesis is that the departures of atmospheric CO{-2} values from their natural trend are because of human influence. "Had nature remained in full control, Earth's climate would naturally have grown substantially cooler," postulates the author.

Greenhouse gases produced by humans have contributed to warming, counteracting nature's cooling, and thus rivalling nature "as a force in the climate system". The chapter on `early agriculture and civilisation' narrates how the first evidence of permanent settlements emerged about 10,500 years ago, with "populations in the hundreds".

One learns that "the earliest remains are mud-brick houses, surrounded by animal bones that indicate year-round butchering at the same location".

With dependable food sources, populations began to rise. For the abrupt rise in the levels of methane 5000 years ago, contrary to the natural cycle, `the most likely culprit' was irrigation, suggests the author. Other factors such as human waste, livestock emissions, and biomass burning, were closely tied to the population, he explains.

Unaccounted methane and CO_-2

"The full methane anomaly must be close to 250 parts per billion, considerably more than the observed rise of 100 parts per billion." But climate scientists are "wrestling with the problem of accounting for the 200 billion tons of CO{-2} that was removed from the atmosphere during major glaciations". A disturbing graph plots CO{-2}, to show how the observed level is far high compared to the natural trend and the `natural CO{-2} peak'. The grim message of Ruddiman is that humans are in control now. Worryingly, our impact has exceeded that of nature. "A millennium or so from now, the fossil-fuel era will largely have ended, and the climate system will be slowly returning toward its natural (cooler) state," he predicts.

"The single most effective thing that can be done about global warming is to invest in technologies that will reduce carbon emissions, especially those that will come from the 200-year supply of coal we will eventually burn."

To Ruddiman global warming isn't as great an environmental problem as the depletion of key resources. The final chapter, titled `consuming Earth's gifts' deplores the enormous spending on fertilisers, produced from petrochemical sources, and therefore accelerating depletion.

"It will be a very long wait indeed until nature gets around to making more topsoil, probably 50,000 to 1,00,000 years until the next ice sheet bulldozes the next rich load southward." Right reads to cool this weekend with!

Economics@TheHindu.co.in

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