Are all environmentalists hypocrites?

Maybe, but it's better to be hypocritically active than honestly inactive

Hypocrisy is a useful tool for environmentalists. Show the world that Shell is tearing up the sands of Alberta and the world shrugs. Show the world that Shell is tearing up the sands of Alberta, and at the same time advertising themselves as a green company, and the world pricks up its ears. Dishonest wrong-doing carries more weight than mere wrong-doing.

But hypocrisy is one of those tools that can easily turn on its users. Those who make moral claims are expected, on pain of hypocrisy, to back them up with unambiguous action -- environmentalists included.

This is fair enough, but sometimes it seems to go too far. Tell someone you've quit meat to reduce carbon emissions, and friends and foes alike will wonder aloud why you are still driving a car, buying imported fruit, etc. etc. Spend a year living cashfree and a mob of commenters will call you a hypocrite for submitting a blog post by broadband. It seems that people who try to do good, and succeed imperfectly, are more guilty than people who don't try at all. Is this fair?

The hypocrisy of some actions is indisputable, and indisputably a vice. Shell's hypocrisy is worse than mere wrong-doing because it is a lie designed to downplay the extent of their wrong-doing. Is it just as bad to be a selective environmentalist, one who picks and chooses their good works depending on what is convenient for them (assuming that leaving a Western-sized carbon footprint is a wrong-doing)?

There has been a lot of scholarly ink spilt on the nature of lying and on whether or not wrong-doers forfeit their right to complain about the actions of others. Which is to say that it would be easy to get one's knickers in a philosophical twist on the topic of hypocrisy.

But the following points seem to me salient, obvious, and within the grasp of people (like me) who want to think about this issue but do not want to think too hard.

Firstly, it is not a good thing for an individual to be deluded about the extent of the harm he inflicts on the world, for the simple reason that such an individual is less likely to reduce the harm they inflict.

Secondly, in at least some cases it is wrong for an individual to deceive others about the extent of his wrongdoing. If I put it about among Ethiopians that I was down to 1.2 tonnes of CO2 a year when in fact I was not, then I would be a lot like Shell when they put it about among Britons that they are a clean company when in fact they are pumping Alberta's dirt into the atmosphere.

Thirdly, a person who takes some action to reduce their carbon footprint, but not all possible action, does not automatically deceive himself or anyone else. It might be perfectly clear in his mind that his actions are of real but limited use, and he may never lead anyone to believe otherwise.

Fourthly, it is better to take some good action on climate change, and be a bit deluded or dishonest about the value of those actions, than to take no action at all now or in the future. A population of frank and knowing individuals is not much use if none of them reduce emissions.

Fifthly, and finally, the fear of being called a hypocrite should not stop people from making incremental changes to their lives in the interests of the environment (or in the interests of any other worthwhile cause). The fear of being a selective environmentalist should not turn people into timid environmentalists. The alternative is damaging, absurd, and selfish.

It would be damaging because most environmentally-friendly action by individuals will be step-by-step action. Wipe out incremental action and you wipe out most action.

It would be absurd because the charge of hypocrisy assumes that the accused party has some wrong-doing to hide: I would be a lier, but not a hypocrite, if I said I would do five handstands but only did three. So if the fear of being hypocritical has any bite, it should urge us to take more action, not less.

And it would be selfish, because -- if Lord Stern and the IPCC are even half-way right -- the social inconvenience of being called a hypocrite is minute compared to the harm that will be avoided if individuals take real action on climate change. Hypocrisy on climate change is a bad thing, from Shell or anyone else. But inaction is much worse.

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Three Degrees: Botswana dunes, Indian monsoon...

More consequences of global warming, according to peer-reviewed science cited in Mark Lynas' book. (But why?)

Botswana sand dunes. Large parts of the Kalahari desert are covered in a layer of brush and scrub, and can be farmed. At least two studies, the latest in 2005, have suggested that by the time the globe hits 3 degrees the Kalahari hills will have "remobilized": a combination of high winds, high temperatures and low rainfall will strip them of their fertile cover, making then unsuitable for crops and animals.

Thomas, D., et al, 2005: 'Remobilization of the southern African desert dune systems by twenty-first century global warming,' Nature, 435, 1218-1221

Pliocene warming. 3m years ago the Arctic and Antarctic seas were clear of summer ice, shrubs grew in the Transantarctic mountains, 500km from the south pole, and were around 25m higher than today. Scientists think CO2 is mainly responsible for the temperature rise. The overall temperature at this time was around 3 degrees higher than today. CO2 concentrations were about the same as they are today. Thousands of years passed before this temperature and concentrations warmed the poles, but the similarity to today's figures is alarming.

Francis, J., and Hill, R., 1996: 'Fossil plants from the Pliocene Sirius Group, Transantarctic Mountains; evidence for climate from growth rings and fossil leaves,' PALAIOS, 11, 4, 389-396

Haywood, A., and Williams, M., 2005: 'The climate of the future: clues from three million years ago,' Geology Today, 21, 4, 138-143

Haywood, A., and Valdes, P., 2004: 'Modelling Pliocene warmth: contribution of atmosphere, oceans, and cryosphere,' Earth and Planetary Science Letters, 218, 363-77

Forest fires in Australia. The CSIRO Atmospheric Research has predicted that 35 degrees days in Queensland could occur 2 to 7 times more often than they do today. Higher winds, and up to 25% less rainfall, would also add to the fire risk in the state. This would lead to more events like the 2003 conflagaration outside Canberra, which killed 4 people, destroyed 500 buildings, and in ten minutes released more energy than the Hiroshima atomic bomb.

Hennesseym K., et al., 2004: 'Climate Change in New South Wales: Part 2 -- Projected changes in climate extremes,' CSIRO, November 2004, 7pp

Fromm, M., et al., 2006: 'Violent pyro-convective storm devastates Australia's capital and pollutes the stratosphere,' Geophysical Research Letters, 33, L05815

The Arctic again. A 2000 study predicted that around 80% of Arctic sea ice would disappear once the mercury hit 3 degrees. A more recent study (in 2007) concluded that Arctic melting was running 30 years ahead of its forecast rate.

Johannessen, O., et al., 2004: 'Arctic climate change: observed and modelled temperature and sea ice variability,' Tellus, 26A, 328-41

Stroeve, J., et al, 2007: 'Arctic sea ice decline: Faster than forecast,' Geophysical Research Letters, 34, L09501

Central America. Drought is forecast for Central America, with the Hadley Centre predicting a rainfall decline of 1-2mm per day in this region. This would leave the area vulnerable to calamities like the drought in 2001, which led to food shortages among around 1.5 million people. Severe warming could lead to droughts on the scale of those that laid waste to the illustrious Mayan civilisation in the early Medieval period.

Johns, T., et al., 2003: 'Anthropogenic climate change for 1860-21-- simulated with the HadCM3 model under updated emission scenarios,' Climate Dynamics, 20, 583-612'

Indian Monsoon. The monsoon over the subcontinent is expected to become heavier but less regular, leading to more extreme flooding in India and Bangladesh and a greater likelihood of dry periods in the region. Given the vast populations in the area, and their reliance on agriculture, "The reliability of the Monsoon is...a matter of life and death for millions of people" (Lynas' words).

May, W., 2004: 'Simulation of the variability and extremes of aily rainfall during the Indian summer monsoon for present and future times in a global time-slice experiment,' Climate Dynamics, 22, 183-204

Ueda, H., et al., 2006: 'Impact of anthropogenic forcing on the Asian summer monsoon as simulated by 8 GCMs,' Geophysical Research Letters, 33, L06703

Dairaky, K., and Emori, S., 2006: 'Dynamic and thermodynamic influences on intensified daily rainfall during the Asian summer monsoon under doubled atmospheric CO2 conditions,' Geophysical Research Letters, 33, L01704

Drying of the Indus river. The Indus river runs from the Karakoram range that straddles Pakistan and south-west China. Karakoram is the largest glaciated area outside the poles. According to a 2005 WWF study, all of the major ice-capped areas in the Karakoram and Himalayan region are melting at an accelerated rate. A study commissioned by DFID concluded that after a period of high flows due to meltwater, the Indus will contain 20 to 40 percent less water by 2080. With few other sources of water available to it, either inside or outside the coutry, Pakistan could plunge into a food and water crisis.

WWF Nepal Program, 2005: An Overview of Glaciers, Glacial Retreat, and Subsequent Impacts in Nepal, India, and China, WWF, March 2005, 70pp

Rees, G., and Collins, D., 2004: An Assessment of the Potential Impacts of Deglaciation on the Water Resources of the Himalaya, DFID KAR Project No. R7980, 54pp and Annexes

New York floods. The New York metropolitan area has 20 million people, 2,400km of coastline, and a network of rail, tunnel and airport facilities whose entrances lie 3m or less above sea level. In a 3 degree world the sea level is expected to rise between 25cm and 1m, so that today's one-in-100-year flood could be a one-in-4-year event by 2080. Floods in 1992 and 1999 crippled the NYC transport system and left areas of Lower Manhatten under 1m of water.

Gornitz, V., et al., 2002: 'Impacts of sea level rise in the New York City metropolitan area,' Global and Planetary Change, 32, 61-88

North Sea storms. A 2001 study based on Hadley Centre models mirrors the predictions for New York weather: "In the southern North Sea," one of the authors wrote, "by the 2080s, a typical return period for what is now a 150-year event will be seven or eight years." The 1953 flood that caused 300 deaths in the UK and 1,800 in the Netherlands, and has been called UK's worst-ever natural disaster, was described at the time as a one-in-150-year event.

Lowe, J., et al., 2001: 'Changes in occurrence of storm surges around the United Kingdom under a future climate scenario using a dynamic storm surge model driven by the Hadley Centre models,' Climate Dynamics, 18, 179-188

The "sixth mass extinction of life." "Living dead" is the name ecologists give to populations whose numbers are so low they are doomed to extinction. A paper published in Nature in 2004 concluded that between a half and a third of species alive today will join the "living dead" by 2050 if the planet warms by over 2 degrees by that date.

Thomas, C., et al, 2004: 'Extinction risk from climate change,' Nature, 427, 145-148

Deserts in the Amazon. A 2000 paper from the UK's Hadley Centre (a world leader in climate modeling) predicted that a 3 degree temperature rise would commit the globe to another 1.5 degree increase by 2100 -- even if human carbon emissions stabilised once we hit 3 degrees. According to the Centre's models, 3 degrees of warming would "put the carbon cycle into reverse," as Lynas puts it: trees and plants would stop absorbing CO2 and start releasing it as they withered and died. The Amazon, 7 million km2 of lush vegetation, would be particularly vulnerable to this feedback effect: the Hadley models predict that by 2100 rainfall will drop to almost zero in some areas of the jungle, with temperatures soaring to 38 degrees on average.

[It must be said -- and Lynas says it -- that there is no consensus on the question of whether Amazon rainfall will drop low enough to trigger the feedback effect. A 2007 survey concluded that nearly half of the studies on the topic predicted an increase of rainfall for the Amazon. I include this topic because Amazon collapse is often cited as a key tipping point, and because if it did happen the consequences would be enormous.]

Cox, P., et al, 2000: 'Acceleration of global warming due to carbon cycle feedbacks in a coupled climate model,' Nature, 40, 184-7

Li, W., et al, 2007: 'Future precipitation changes and their implications for tropical peatlands,' Geophysical Research Letters, 34, L01403

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Two Degrees: China, South America, Europe...

More grim predictions from climate scientists, courtesy of Mark Lynas and his book

Droughts in Northern China. In a 1999 study, Chinese scientists showed that around 129 000 years ago, Northern China dried out and suffered continental-scale dust storms. China warmed by about 2 degrees during this period (the Eemian period) and the cold dry winter winds in the North responded much more quickly than the warm wet summer winds, causing massive dehydration. Lynas speculates that recent droughts in Northern China have the same root cause.

Chen, F. et al, 2003: "Stable East Asian monsoon climate during the Last Interglacial (Eemian) indicate by paleosol S1 in the Western part of the Chinese Loess plateau," Global and Planetary Change, 36, 171-9

Ocean acidification. Carbon dioxide dissolves in water to give carbonic acid. When there is enough CO2 in the atmosphere to raise temperatures by 2 degrees, there will also be enough to make large areas of the Southern Oceans and part of the Pacific effectively toxic to organisms with calcium carbonate shells. Affected organisms will include some varieties of plankton, the most important food source for ocean-dwellers. (Lynas likens this to spraying weedkiller over most of the world's land vegetation.)

Orr, J., et al, 2005: 'Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms,' Nature, 437, 681-6

The Royal Society, 2005: Ocean acidification due to increasing atmospheric carbon dioxide, Policy Document 12/05

Gazeau, F., et al, 2007: 'Impact of elevated CO2 on shellfish calcification,' Geophysical Research Letters, 34, L07603

Withering vegetation in Europe. The European heat-wave of 2003 caused -- among many other things -- a 30% drop in plant growth across Europe. Dying plants released an amount of carbon equivalent to one twelfth the annual carbon emissions from fossil fuels. Averaged across Europe, temperatures in Summer 2003 were 2.3 degrees above the norm.

Ciais, Ph., et al, 2005: 'Europe-wide reduction in primary productivity caused by the heat and drought of 2003,' Nature, 437, 529-33

Greenland melt. 115 000 years ago, melting ice meant that the sea level was 5-6 metres higher than today, yet average global temperatures were only 1-2 degrees warmer than today. Debate continues about how fast such melting can occur. But a 2007 study shows that sea levels are rising at 3.3mm a year, 50% faster than the 2007 IPCC report assumed.

Rohling, et. al., 2002: 'African monsoon variability during the previous interglacial maximum,' Earth and Planetary Science Letters, 202, 61-75

Tarasov, L., and Richard Peltier, W., 2003: 'Greenland glacial history, borehole constraints, and Eemian extent,' Journal of Geophysical Research, 108, B3, 2143

Rahmstorf, S., et al, 2007: 'Recent climate observations compared to projections,' Science, 316, 709

Drying India. A modelling study has concluded that a 2 degree increase in temperatures over India would decrease the agricultural yeild by 8%.

Kavi Kumar, K., and Parikh, J., 2001: 'Indian agriculture and climate sensitivity,' Global Environmental Change, 11, 147-54

South American water loss. In dry seasons the Rio Santa in Peru draws almost all of its flow from glacial melt. The melt from the glaciers is expected to drop by 40-60% by 2050. The Rio Santa powers hydroelectric turbines that are responsible for large-scale irrigation, 5% of Peru's electricity, and the drinking water for over a million people in the cities of Chimbote and Trujillo. (The 8 million people in Lima are also drawing for water on glaciers that are expected to dwindle in a 2-degree world, but no scientific studies have been conducted on Lima's glaciers.)

Kaser, G., et al, 2003: 'The impact of glaciers on the runoff and the reconstruction of mass balance history from hydrological data in the tropical Cordillera Blanca, Peru,' Journal of Hydrology, 282, 1, 130-44

Chevallier, P., et al., 2004: 'Climate change impact on the water resources from the mountains in Peru,' paper presented to the OECD Global Forum on Sustainable Development: Development and Climate Change, Paris, 11-12 November 2004

Juen, I., Kaser, G., and Georges, C., 2006: 'Modelling observed and future runoff from a glacierized tropical catchment (Cordillera Blanca, Peru),' Global and Planetary Change, 59, 1-4 37-48

California melting. California relies for its water on rivers stemming from the Sierra Nevada, Cascades and Rocky Mountains. During winter, more of this water is stored in "snowpack" in these mountains than in man-made reservoirs. A 2004 study predicted that this snowpack will decline by between a third and three-quarters in a 2 degree world. One study (Ruby Leung et al.) concludes: "Current demands on water resources in many parts of the West[ern US] will not be met under plausible future climate conditions, much less the demands of a larger population and larger economy."

Hayhoe, K., et al, 2004: 'Emissions pathways, climate change, and impacts on California,' Proceedings of the National Academy of Sciences, 101, 34, 12422-7

Ruby Leung, L., et al., 2004: 'Mid-century ensemble regional climate change scenarios for the western US,' Climatic Change, 68, 153-68

Crop failures. Crop failures are expected to be widespread in a hotter world, though failures in the tropics will be partially offset by successes at higher latitudes. In Mali, losses of maize crops are expected to leave up to three quarters of the population at risk of hunger, up from a third today. In Botswana, up to a third of the maize and sorghum crop could be wiped out due to a declining rainfall. A 2003 study predicts that North Sea cod population will disappear with around two degrees of warming.

Butt, T., et al., 2005: 'The economic and food security implications of climate change in Mali,' Climatic Change, 68, 355-78

Chipanshi, A., et al., 2003: 'Vulnerability assessment of the maize and sorghum crops to climate change in Botswana,' Climatic Change, 61, 339-60

Clark, R., et al, 2003: 'North Sea cod and climate change -- modelling the effects of temperature on population dynamics,' Global Change Biology, 9, 1669-80

Large-scale extinction. A study published in Nature in 2004 argued that over a third of all species on earth would be 'committed to extinction' if temperatures reach 2 degress in 2050. The lead author said in a Univeristy of Leeds press release that 'Well over a million species could be threatened with extinction as a result of climate change.' The study was based on models of expected movements of ecological niches due to changing climate.

Thomas, C., et al., 2004: 'Extinction risk from climate change,' Nature, 427, 145-8

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One Degree: drought, fire, extinction

Part one of my guide to Mark Lynas' guide to the peer-reviewed literature on the consequences of global warming

America's desert. The remains of trees have been found in a river bed and lake bed in the West Walker River Canyon and Mono Lake respectively. These remains have been dated to the medieval period. Fire scars on trees in the Yosemite and Sequoia National Parks have been dated to the same period. This evidence suggests medieval California was hit by a severe drought many times more punishing than the "dust-bowl" years of the 1930s. US in medieval times was 1-2 degrees warmer than pre-industrial US.

Stine, S., 1994: 'Extreme and persistent drought in California and Patagonia during medieval time,' Nature, 369, 546-9

Swetnam, T., 1993: 'Fire history and climate change in giant sequoia groves,' Science, 262, 85-9

Kilimanjaro forest fires. Rising temperatures and diminishing rainfall have increased the risk of fires in the high forest on the sides of the mountain. This forest is responsible for 96% of the water coming off the mountain. A hit to the water supply would put fish supplies and hydroelectric turbines at risk in Tanzania.

Agrawala, S., et al, 2003: 'Development and climate change in Tanzania: Focus on Mount Kilimanjaro,' OECD Environmental Directorate, 6799

Arctic melting. In the decade up to 2001, the biggest Alaskan glaciers lost 96 cubic kilometres of ice, raising global sea levels by nearly 3mm. A recent modelling study has concluded that the Artic ocean will be free of ice in summertime by 2040. Scientists expect that a warmer Artic will push the North Atlantic storm belt north. Satellite images from the last 30 years show a 1 degree movement of the wet-weather belt towards the poles of both hemispheres.

Arendt, A., et al.: 'Rapid wastage of Alaska glaciers and their contribution to rising sea level,' Science, 297, 382-6

Holland, M., Bitz., C., and Tremblay, B., 2007: 'Future abrupt reductions in the summer Arctic sea ice,' Geophysical Research Letters, 33, L23503

Fu, Q., et al., 2006: 'Enhanced mid-latitude tropospheric warming in satellite measurements,' Science, 312, 1179

Swiss rockfalls. Meltwater from mountain snow can destabilise rocks, causing lethal and unpredictable landslides. A year after the European heat-wave of 2003, a Swiss team of scientists showed that the 2003 thaw was up to a half a metre deeper than in any of the last 40 summers.

Gruber, S., Hoezle, M., and Haeberli, W., 2004: 'Permafrost thaw and destabilisation of Alpine rock walls in the hot summer of 2003,' Geophysical Research Letters, 31, L13504

Extinction in the Australiam Wet Tropics. The Wet Tropics in Queensland Australia is a UNESCO World Heritage Site, holds -- among many other things -- half of the continent's bird species and 700 plant species that are found nowhere else in the world. A modelling study of 65 species in the area concluded that 63 of the species would lose a third of their core habitat with one degree of warming. The author called this an "environmental catastrophe of international significance."

Williams, S., et al., 2003: 'Climate change in Australian tropical rainforests: an impending environmental catastrophe,' Proceedings of the Royal Society of London B, 270, 1887-92

Atlantic hurricanes. In a 2006 paper, two climatologists wrote that anthropogenic climate change contributed half of the warming that resulted in high ocean water temperatures in 2005. The warm surface water is thought to be responsible for the devastating 2005 hurricane season that caused damage totalling $100bn. An earlier analysis showed that the number of the strongest storms in the Pacific and Atlantic Oceans nearly doubled in the period 1970-2004.

Trenberth, K., and Shea, D., 2006: 'Atlantic hurricanes and natural variability in 2005,' Geophysical Research Letters, 33, L12704

Webster, P., et al., 2005: 'Changes in tropical cyclone number, duration, and intensity in a warming environment,' Science, 309, 1844-1846

Kilimanjaro. In 2002 a US team led by scientist Lonnie Thompson concluded that 80% of the ice on Mt Kilimanjaro had disappeared in the last century, and that at the current rate there would be none at all by 2020. Similar meltrates have been recorded on peaks in other parts of the world, such as the Rwenzori Mountains in Uganda. As Lynas points out, glacial melt is responsible for only 1/15 of the water coming off Kilimanjaro: a "significant, but not catastrophic" amount.

Thompson, L., et al., 2002: 'Kilimanjaro ice core records: Evidence of Holocene climate change in tropical Africa,' Science, 298, 589-593

Taylor, R. G., et al, 2006: 'Recent glacial recession in the Rwenzori Mountains of East Africa due to rising air temperature,' Geophysical Research Letters, 33, 10, L10402

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Six degrees: our future in six posts

A compressed and referenced version of Mark Lynas' data-rich book on global warming

Mark Lynas' Six Degrees is a fine book and a paradise for climate change activists, but it calls out for compression. For climate change newbies out there, the 2007 book (republished 2008) takes each degree of possible warming -- from one to six -- and catalogues the likely consequences they will bring for climate, geography, and life on earth. "Catalogue" is the right word, since Lynas (a UK journalist) based the book on a systematic study of peer-reviewed articles he found in the Oxford University Radcliffe Science Library.

Lynas clearly did his homework. In the 56 pages of the chapter on Three Degrees, I count 102 separate references to peer-reviewed articles and other respectable authorities (this excludes newspaper articles, press releases, and Worldwatch Magazine, but includes government, UNESCO, and WWF reports). That's almost two per page, which may not be a lot for an academic paper, but is rare for a 300-page popular book.

Lynas' research ethic has a downside. It means that Six Degrees is a bit like listening to Lord Stern talk about the economics of climate change -- you are soaked in a torrent of very informative details, but once the flood has passed you feel a bit damp and confused. Plus there is a lot of froth in the book, speculative sketches of a warming world that go beyond the published science.

What one wants is a neat row of frozen facts that one can pick up, examine at leisure, and launch at any passing skeptics. To this end I am going to list 5-10 of the most striking and well-supported scientific results in each chapter, starting with One Degree and moving up the mercury. To be useful, the items on the list need to be:

authoritative: no NYT articles or press releases
consensual: ie. Lynas doesn't cite any contrary evidence (fallible, I know, but the best I can do here)
convincing: a study of the extinction of six species is more convincing than a study of one
novel: ie. I haven't heard about them before -- shockingly subjective, but again it's the best I can do
powerful: if their predictions come true, they will effect large numbers of people and/or people close to home, where "home" is England
precise: numbers are better than words

Six Degrees was so successful that it is unlikely that any of the results are really novel. By now most of them, from the greening of the Sahara to the melting of Peruvian glaciers, have probably been raked over by skeptics and activists alike. But jogging the memory is an excellent form of exercise.

Some of the results in the book may been challenged since 2007. And there is no guarantee that Lynas has given us a representative sample of the peer-reviewed literature on climate change (though I'm inclined to think he has, given the scale of his research and his willingness to report countervailing results, when they arise). So the next six posts may give a lop-sided view of the consequences of warming. But as Lynas shows -- and as the next six posts may show -- that view has a lot going for it.

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"Ice, Mud and Blood" by Chris Turney

A chirpy, detailed book that delivers on past climate but not on present climate

Anyone new to the climate change debate is bound to wonder whether a 5-6 degree increase in temperatures is really all that bad - especially if the person is cold, English, and nostalgic for summer. A good reply to this wonderment is to say that the last time the globe was 5 or 6 degrees colder, there were glaciers in the South of England, and the melting ice caused Britain to split off from France.

Chris Turney, a geologist at the University of Exeter, knows as well as anyone that climates past have lessons for climates present. In Ice, Mud and Blood, Turney's humour and expertise make for a jaunty, fascinating account of how past climates worked and how scientists find out about them. But Turney spends little time linking past climate to present climate; so, as a contribution to the climate change debate, the book doesn't live up to its promise.

As Turney points out, it's a wonder that we know anything about past climate at all. Natural climate change occurs over vast periods, and events in the intervening millennia have played havoc with the evidence. Turney does a great job of showing how scientific detective work can, against the odds, give a clear and convincing picture of some key events in the last three-quarters of a billion years of earth weather.

To give one example: how could we possibly know that the tropics were covered in ice between 580 and 710 million years ago? As Turney explains, certain kinds of rocks tell us that glaciers once appeared in, among other places, Namibia; and the magnetism of the rocks assures us that those glaciers did indeed form at tropical latitudes. You might object - as some scientists did - that the earth had a bigger tilt back then, so that Namibia once swung around the freezing poles. A study of 'evaporites' - salt deposits from drying lakes that only occur in hot dry areas - puts paid to that objection, as do ocean deposits of iridium. As this example hints, paleo-climatologists can get technical at times. But their work is as impressive as cosmologists probing into deep space or particle physicists getting into the guts of an atom.

The instruments used to detect past climates have their own fascination. The ice cores of Greenland and Antarctica - pipes of ancient ice, kilometres in length, drawn from some of the world's most inhospitable climates - make for a good story, and Turney tells it well. Because these 'archives' of past climate are so hard to read, paleo-climatology is also tale of wrong turns, misinterpretations and dead-ends. Where there is just not enough data for scientists to draw solid conclusions - about the effect of climate change on cyclones in the Western Atlantic, for example - Turney is not afraid to say so. Where multiple sets of data converge on the same conclusion, he drives the point home.

Turney's chirpy prose is helped along by sketches of the charismatic pioneers and hard-bitten explorers in the science of weather. Extra spice comes from Turney's taste for history, love of hands-on research, and nose for a big idea. The big ideas include some intriguing conjectures about the interaction of climate and early humans. For example, Turney argues that the concentration of diabetes in Northern Europe could be explained as an evolutionary response to the Younger Dyas, a cold period in the North Atlantic that ended around 10,000 BC.

Turney is rock-solid on the science of past climates, but cracks start to appear when he draws conclusions about current climate change. The problem starts with the book's structure. It is arranged as a chronology of past climate, not as an argument for the state of current climate. Turney tries to link past to present in a final conclusion, where he asks 'What does this all mean for the future?' But it's all a bit vague and last-minute. He simply draws some general lessons from the preceding 192 pages of history: greenhouse gases can power massive changes in climate; feedback effects can amplify small changes; and human action can rearrange our land, sea and atmosphere on a large scale. Compared to the quantitative detail of the other chapters, this conclusion is just hand-waving.

There is no doubt that, in the past, human activity, high temperatures, and high levels of methane and carbon dioxide, all caused big - sometimes cataclysmic - changes to weather and geography. But is our current situation quantitatively similar to those past changes? Turney does not give a clear case. When he asks the numbers question, his answer is a short account of the famous 'hockey-stick' study, a comparison of temperature changes in the last century with those over the previous millennium. One wonders what happened to the previous seven chapters and the previous 700 million years they cover. Do the most recent climates give the best lessons, after all?

A determined reader might dig through the chapters to see if Turney makes the link between past climate to present climate on the run. Such a reader will find a number of hearty calls to action, but little hard-and-fast argument. For example, Turney emphasises the role of CO2 in the warming that occurred during the Eemian period around 120,000 years ago. But he also emphasises that increases in carbon dioxide lagged behind the warming. And the evidence he cites for CO2-driven warming considers just one ice core and takes up one paragraph. On some topics - such as the dynamics of melting ice - Turney makes a stronger case, but only with the help of models and evidence drawn from studies of present-day climate.

Ice, mud and Blood could have been more streamlined and persuasive. As a call to action on climate change, it is a missed opportunity. But as a story of scientific ingenuity and the wonders of nature, it takes every chance - and succeeds.

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