Words Of Warming  

The Guardian has an essay from Tim Flannery on the current state of play for global warming - Words Of Warming.

A sophisticated understanding of the great climatic cycles has permitted a new approach to the climate problem that finds its closest parallel in the "wiggle matching" used by stock-market analysis. William Ruddiman is a climatic historian whose book Ploughs, Plagues and Petroleum, published by Princeton in 2005, uses this approach to identify evidence of human impact on the climate system, by identifying precisely where we are in the current cycle and comparing the trend with earlier ones. We are, he explains, 12,000 years into a cooling phase which, judging from previous cycles, should continue for tens of thousands of years more. Instead the world is warming. But what is most remarkable about Ruddiman's work is the evidence it provides for an initial disruption to the climate system that occurred long before the industrial revolution - around 8,000 years ago.

It was then, at the dawn of agriculture, that the "wiggle" of the current cycle first departed from earlier patterns - for instead of cooling, Earth's average temperature remained remarkably stable. Ruddiman thinks that this was caused by carbon and methane being released into the atmosphere from early agriculture and the destruction of forests. In his account, human activity and the great cycles struck a delicate balance that allowed the flowering of civilisations. He also sees evidence in the ice cores for the consequences of the Black Death (a drop of around two parts per million of CO2 as forests grew over abandoned fields, absorbing carbon from the atmosphere), as well as other historic events. Aspects of his work remain highly contentious, yet I believe that Ruddiman's realisation that the gaseous composition of Earth's atmosphere is an exquisitely sensitive barometer of changes to life itself represents a great breakthrough.

Now that the majority of politicians, industry leaders and the public are convinced there is a climate problem, the focus is on what to do. The most influential assessments of the problem's scale are doubtless those of the IPCC, whose projections of various outcomes form the basis of global negotiations and national action plans. One of the most influential of these projections concerns the extent to which Earth's surface will warm over the next century. The lower bound is 1.4°C; the upper bound is 5.8°C. This is an extraordinary range of possible impacts - 1.4°C poses some threat, but 5.8°C is widely recognised as sufficient to induce a Lovelockian Ragnarok. The chance of either outcome, according to the IPCC, is small - less than 10%, and so political dialogue has come to concentrate on the mid-range of the projections.

The moment of truth will arrive in December 2009, in Copenhagen, when the world's political leaders will come together to decide the basis of a new global treaty to replace the Kyoto protocol. It's no overstatement to say that the Copenhagen protocol, as it may well come to be known, will play a large role in deciding the fate of humanity. It will come into force in 2012, and if it fails to deliver we'll have to wait until 2020 for a replacement. That will be too late. ...

In his analysis, Nordhaus does identify one economically effective strategy worth pursuing. Called the "low-cost backstop", it revolves around identifying and developing some as yet unknown technology to combat the problem. Possible candidates include "low-cost solar power, geothermal energy, some non-intrusive climatic engineering or genetically engineered carbon-eating trees".

Writing in the New York Review of Books, Freeman Dyson has explored the unappealing option of such trees. The graph that first alerted humanity to the climate problem - drawn up by Charles David Keeling to show the CO2 increase from 1956 to the present - might, Dyson argues, hold the key to the solution. The graph has a generally rising line, with jags, like saw teeth, along it, which indicate a spike in CO2 each autumn in the northern hemisphere and a dip each spring. The difference between the minimum and maximum each year is around six parts per million, and it is due to the growth, then leaf fall, of the forests that grow across North America, Europe and Asia. It turns out, Dyson says, "that about 8% of the carbon dioxide in the atmosphere is absorbed by vegetation and returned to the atmosphere every year".

If only a way could be found, he muses, to permanently sequester that carbon, we would go a long way towards solving the climate crisis - hence the genetically modified trees. But the truth is that all trees are carbon eaters. They grow from the air by drawing CO2 into their leaves, and there solidifying it to build their wood, bark and leaf tissues. Trees are congealed CO2. What we need is a way of transforming the carbon they capture into an inert state. It turns out that humanity has had the capacity to do this for thousands of years, and is now on the brink of doing it on a very large scale.

The process of charcoal-making is called pyrolysis, and involves the heating of any biological matter in the absence of oxygen. The result is the generation of a synthetic gas, or a crude-oil like material, and charcoal. If the gas or oily matter is captured, it can be used to generate electricity or power transport. The charcoal is largely carbon (representing one-third to half of the carbon in the biomass) and it is inert. Indeed, the tenacity with which charcoal resists rotting, even when buried in the soil, is clear from C14-dating, which uses ancient charcoal from hearths or fires as much as 60,000 years old.

Modern pyrolysis involves machinery that captures flue gas or oil, and needs no external inputs to run the machine (some of the gas being used to heat the biomass). It's already being used on a small scale on farms, for urban garbage disposal (where 1,000-tonne units are deployed) and in forestry. On farms it has multiple benefits, for the charcoal can be ploughed back into the soil, where it balances acid soils, aids soil moisture retention, adds nutrients and acts as a habitat for soil fungi and bacteria. A farmer pyrolysing crop waste gains four benefits: 1) as usual, he gets to sell the commercial part of his crop; 2) he gets to generate electricity or transport fuel; 3) where carbon is traded, he can potentially sell the carbon he sequesters; and 4) by adding charcoal to his soil, he will increase the chances of getting a better crop the following year.

With so many benefits, why is pyrolysis not more widely used? Because pyrolysis machines are expensive, and farms are mostly still family businesses. If farmers are ever to be able to afford the machines, they'll need to be paid around $37 per tonne for the carbon they create. They'll also need to be living in areas with carbon trading schemes that allow charcoal as a recognised method of carbon sequestration.