Tag: thermohaline

Wallace Broecker is a distinguished scientist in the field of climate history, and he’s been at it for over 50 years. He was one of the first scientists to warn of the dangers of global warming, as long ago as 1975. In a book published last year he teamed up with science journalist Robert Kunzig.  Fixing Climate: The Story of Climate Science – and How to Stop Global Warming is a highly readable narrative of how the modern scientific understanding of climate change has developed since it dawned on a few 19^th century observers that there was evidence in the Swiss mountains of vast areas of past glaciation.  The book makes it very apparent that understanding climate in the past is the key to realising what is happening in the present and what it will lead to.

It’s a packed book, though it rarely seems so in the reading.  It ranges from relaxed stories about the scientists at work to closely explained accounts of the processes they investigate or uncover. The work of Broecker himself is often of considerable significance.  He was early engaged in the field of carbon dating, which proved a useful tool in establishing the abrupt (geologically speaking) end of the last ice age. He did recalculations of Milankovich’s theories on the earth’s orbital cycles and established their importance in affecting ice age climates, but only as part of the explanation – feedbacks must also be at work. He is known for his idea that ocean currents might rapidly change climate by switching on and off, and he came up with the name of conveyor belt to describe the ocean’s globe-spanning thermohaline circulation which transports heat into the North Atlantic and salt out. The section of the book explaining this is a model of clarity and interest for the general reader.  As indeed are many other sections like those on CO₂ and on what portion of the carbon in the atmosphere goes into the sea or is taken up on land – so far at least.

New Zealand is there. A six-page section of the book begins with the words: “Outside the little town of Methven…”  George Denton and his team have spent a decade identifying and dating moraines all over the Southern Alps and recording their results on detailed maps.  Denton had spent decades working in Antarctica and Alaska when Broeckner convinced him to move his fieldwork into mid-latitude New Zealand.

Do we need to worry about what is happening?  The authors think so. They dissociate themselves, albeit respectfully, from the arguments of Al Gore and other environmentalists that it is a threat to western civilisation, considering that western civilisation is more resilient than that and that such “grandiose rhetoric” converts many reasonable people into sceptics. Their logic escapes me here, but never mind, for they go on to identify two dangers which strike them as particularly urgent – prolonged, catastrophic drought in some regions, and a rising sea level. Both dangers are explained in illuminating detail.

The last fifty pages of the book swing between pessimism and hope.  Although the authors recognise that we need to stop the increase in atmospheric CO₂, they see no sign that we are capable of weaning ourselves from fossil fuels and are pessimistic of that obvious solution being applied. They sympathetically canvass the various green technologies but dismiss them as inadequate to the magnitude of the task and as too expensive in relation to cheap fossil fuels. For some time adaptation seemed the only option.  But then Broecker met Klaus Lackner, a theoretical physicist who considered that it was possible to scrub CO₂out of the atmosphere, not just capture it in the industrial settings where it is produced. By 2001 Lackner was on the staff at Colombia, Broecker’s university. He has worked with engineer partner Allen Wright on designing a carbon scrubber which can work anywhere taking CO₂ from the air for sequestration.  The process is described in some detail and estimates made of the number of extractors required to have a substantial effect on the levels of CO₂ in the atmosphere. It would be a large undertaking but by no means beyond our capacity.

Scrubbing the carbon is one matter, but how is it to be disposed of?  The book covers a range of possibilities for sequestration: deep in the ocean; old oil wells; saline aquifers; layers of volcanic basalt; and eventually, because Lackner does not consider these forms adequate in the long term, mineral sequestration – accelerated geochemical weathering made possible by reducing immense quantities of igneous rock to a fine powder and reacting it with CO₂.

Scrubbing CO₂ from the air would not supplant capturing emissions from stationary sources, such as power plants, directly at the smokestack. It is an additional means of capture. It has the great advantage of being able to be carried out close to the intended place of sequestration.

The authors are very serious about the prospects for this technology. One can almost hear their sigh of relief that it has turned up. I notice they have just published an article in New Scientist further exploring it not only in relation to Lackner but also to teams working on lab-scale units at the University of Calgary in Alberta and at the Swiss Federal Institute of Technology in Zurich. In this article they allow themselves a little more room for hope in alternatives — solar, wind or nuclear — than is apparent in their book. But if we can’t avert a climate crisis through a massive switch to those means then air scrubbers could be the last-ditch lifeline.  I was mollified by the New Scientist article because I thought their book’s assertion that green technologies wouldn’t be adequate was reached too quickly, as was their belief that humankind would not turn from fossil fuel use while it remained available. At this point they had moved from science to politics and policy where it seems to me premature to declare failure — though of course it looms as a possible outcome.  But in any case the technology of removing CO₂ directly from the atmosphere could meanwhile have a very useful function as one of the means by which we battle climate change and which can be rapidly scaled up if necessary. If it is a feasible process it must surely have a significant part to play.

In the final section of the book, Broecker and Kunzig examine some of the more drastic geo-engineering possibilities, such as putting sulfur dioxide in the atmosphere or iron in the ocean, and express reservations about them. The process of  taking CO₂out of the atmosphere they do not see as geo-engineering. It is much more conservative. It is merely cleaning up after ourselves. They conclude, sounding something of a recurrent theme in recent writing, that the planet has become ours to run, and we can’t retreat from the responsibility to run it wisely. This might seem an overweening claim: nature has hardly surrendered the reins.  But there is at least a metaphorical truth to it. It highlights the immensity of the effect on Earth’s climate of our releasing so much extra CO₂ into the atmosphere, and the concomitant responsibility we bear for managing that. Sequestration schemes seem a sensibly modest approach which respects the natural cycles.  The authors are too respectful of the complexities of the Earth’s systems to want to go further than that.