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What 3 Degrees of Global Warming Really Means


Will Unchecked Global Warming Destroy Civilisation By Century’s End?

What 3 Degrees of Global Warming Really Means

PETER BARRETT[1] puts projected global warming in perspective, comparing it with climate fluctuations in the geological past. Greenhouse gas emission rates from human activity have increased in the last few decades, and CO2 levels will soon be higher than at any time in the past 25 million years. If not reduced soon, temperatures will return our climate to where it was before humans existed and global sea level was 70m higher. Much greater effort is needed to reduce CO2 levels, to lessen stresses on global ecosystems and avoid the collapse of civilisation as we know it by the end of this century.


Pacific Ecologist: Will Unchecked Global Warming Destroy Civilisation - Editorial: They've been warning us for almost two decades now, tens of thousands of scientists from all over the world. Atmospheric chemists have watched greenhouse gases rise as meteorologists tracked changing weather patterns, and glaciologists reported temperate glaciers shrinking and polar sea ice retreating. They have studied, meticulously researched, checked and rechecked data as scientists do, written many hundreds of reports, telling us the earth's climate is beginning a great change. See... Pacific Ecologist issue 11 summer 2005/2006


A temperature change of 3ºC is something we experience wherever we are on earth every day – in fact a typical daily change in most places is more like 8 or 9ºC. In the past few years scientists have become concerned because global temperature has risen 0.6ºC. So why the fuss?

Last November, at the annual Royal Society of New Zealand’s Awards dinner, I said, if we [“first world” countries] continue on our current path, a warming of this magnitude would risk bringing about “the end of civilization as we know it by the end of this century.” This seems like an absurd claim, but the words reflect my judgement from the perspective of three decades of research into the last 40 million years of past Antarctic climate. My key point, though, was this gloomy prospect is not inevitable if we respond to the problem now. Let me explain.

FIGURE 1: Change in average global temperature compared with today’s average on three different time scales. The average projected increase for the doubling of CO2 levels[6] , which is expected by the end of this century on current projections, is shown in each diagram as a red arrow.

A. Temperature over the last 80,000,0000 years[2] .

B. Temperature over the last 400,000 years, based on oxygen isotope measurements from ice cores at Vostok Station, Antarctica[3] . The measured range of temperature from glacial to interglacial in Antarctic ice cores is in fact 10ºC, reflecting enhanced polar sensitivity to temperature change, but is scaled here to 5ºC to correspond with the known temperature difference in average global temperature between glacial and interglacial climate.

C. Temperature over the last 1000 years[4] .


Geologists now know a great deal about changes in climate on a range of time scales. For example, we know the earth has cooled around 4ºC over the last 40,000,000[2] years (Fig. 1A). We also know this long-term cooling trend has regular fluctuations every 40,000 or 100,000 years superimposed on it, and these have been almost as large (in fact larger in the last million years or so[3] ) (Fig. 1B). We are also learning from climate research that after 1000 years of stable climate[4] , a 40,000,000-year decline in temperature may be largely reversed by the end of this century (Fig. 1C). Firstly, I’ll outline the basis for this assessment, then briefly review the disastrous consequences of such a warming, according to environmental scientists.

An international group of hundreds of leading scientists and other experts, nominated by governments around the world[5] , concluded in 2001 that if current trends in greenhouse gas emissions continue unchecked to 2100, when CO2 is projected to be double pre-industrial levels, we could expect global temperature to rise somewhere between 1.4 and 5.8ºC.

A workshop sponsored by this group, the Intergovernmental Panel on Climate Change (IPCC), last year 2004, concluded improved modelling studies were converging on 3ºC[6] as the most likely temperature rise for a doubling of CO2 levels. This means that by the end of the century, if greenhouse gas emissions continue to rise unchecked, there is a 50-50 likelihood temperatures will be at least 3ºC warmer – a huge risk if the consequences are serious. Such a rise is not far short of the 4ºC that would return the earth, in an instant of geological time, to its climate of around 40 million years ago, long before even our ancestral genus Homo evolved, a mere 6 or 7 million years ago.

Forty million years ago the earth was very different from the one we know today. Large mammals had yet to evolve, India had not yet collided with Asia to form the Himalayas, Antarctica was free of ice and covered with beech forest, and global sea level was 70 m higher. In 10 human generations (from 1900 to 2100 AD) we will have largely completed the reversal of the global cooling trend that took place naturally over 2,000,000 generations.

Fortunately we have yet to feel the full effects of the current level of greenhouse gas pollution. Even the unstable regions of the Antarctica’s ice cover (e.g. the West Antarctic Ice Sheet, which would raise sea level 6 metres if it all went into the sea) are likely to take at least decades to respond. However part of the delay in warming is from “global dimming”[7] with attendant cooling from atmospheric pollution by smoke and dust. But this delay in global warming will be short-lived because improvements in pollution control are restoring clear skies.

Other news is also not good. Arctic warming is accelerating, causing thinning of the floating ice that covers the Arctic Ocean, and melting of glaciers and large areas of permafrost, causing many adverse ecological and environmental consequences[8] . Mid and low-latitude glaciers are also mostly retreating, despite a misleading report to the contrary which was exposed by Guardian Weekly columnist George Monbiot[9] .


Furthermore the Antarctic Ice Sheet is turning out to be more responsive to regional temperature changes than most of us expected, not only through collapsing ice shelves in the Antarctic Peninsula but also with satellite measurements showing huge ice streams draining the Pacific sector of the West Antarctic Ice Sheet faster by a factor of 10, resulting in sea-level rising another 0.18 mm/year[10] . This is only partially balanced by the increase in snowfall in East Antarctica (resulting in a sea level rise of 0.12 mm/year). Continued warming will only increase the rate of global sea-level rise through further Antarctic melting. This is additional to the rise in sea level from the upper layers of the ocean expanding from the global warming of the last few decades[11] – further proof that the rise in global temperatures shown in Fig 1C is real.

Other consequences around Antarctica are a freshening of the Ross Sea from increased melting[12] , and a decline in sea ice extent of 20% since the 1950s[13] . Sea ice is one of the main forces driving the global ocean heat conveyor belt that moderates temperatures on the earth’s surface (and also delivers oxygen to maintain life in the deep oceans). If the polar regions lose their sea ice, and melting ice from Greenland freshens the North Atlantic, then the Gulf Stream that now warms Northwest Europe will slow, and this region will cool by several degrees[14] , to the great discomfit of people now living in those regions. But what would be the consequences of these changes?

The global situation has been reviewed recently in a report released in January 2005 prepared for the G-8 group entitled “Meeting the Climate Challenge”[15] . The report identifies just 2ºC (and an atmospheric CO2 level of 400 ppm, which is 43% above the pre-industrial level of 280 ppm) as the danger level for global warming. It is worth noting that the earth has not experienced such a high CO2 level in the last 25 million years[16] .

The report spells out the likely consequences, saying: “Beyond the 2ºC level, the risks to human societies and ecosystems grow significantly. It is likely, for example, that average temperature increases larger than this will entail substantial agricultural losses, greatly increase numbers of people at risk of water shortages, and have widespread adverse health impacts.”

The report goes on to say: “[This] could also imperil a very high proportion of the world’s coral reefs and cause irreversible damage to important terrestrial ecosystems, including the Amazon rainforest.” It concludes: “Above the 2ºC level, the risks of abrupt, accelerated, or runaway climate change also increase. The possibilities include reaching climatic tipping points leading, for example, to the loss of the West Antarctic and Greenland ice sheets (which, between them, could raise sea level more than 10 metres over the space of a few centuries); the shutdown of the thermohaline ocean circulation (and, with it, the Gulf Stream), and the transformation of the planet’s forests and soils from a net sink of carbon to a net source of carbon.”


All of this is coming at a time when the earth’s ecosystems are already stressed by destructive development practices and an over-populated planet. A review entitled the Millennium Ecosystem Assessment[17] , carried out under the aegis of the United Nations Environmental Program, was released on 31/3/05, after 4 years work by 1300 scientists. It begins by recognising that the human species, while buffered against environmental changes by culture and technology, is fundamentally dependent on the flow of ecosystem services. It was barely noticed by the media, but its conclusions touch us all.

• First, approximately 60% (15 out of 24) of the ecosystems examined are being degraded or used unsustainably, including fresh water, capture fisheries, air and water purification, and the regulation of regional and local climate, natural hazards, and pests.

• Second, it is established though evidence is incomplete, that ecosystem degradation is increasing the likelihood of unexpected changes in ecosystems with serious consequences for human well-being. Examples include: disease emergence, abrupt alterations in water quality, the creation of “dead zones” in coastal waters, collapse of fisheries, and shifts in regional climate.

• Third, the harmful effects of the degradation of ecosystem services are being borne disproportionately by the poor, and are in places the main factor causing poverty and social conflict.

All these problems will be exacerbated by global warming, risking the collapse of ecosystems on which we and our ancestors have always depended.


The situation is in fact worse than these reports describe, simply because of the time lag of several years in the results being assembled, reported and disseminated. Now, in 2005, we can only have a few years left, maybe a decade, to change societal attitudes towards progress before we have “lit the fuse” for inevitable environmental catastrophe in later decades. As Ronald Wright explains, it’s the Victorian notion of progress through economic growth and exploitation of resources (with only immediate costs considered) that is fast leading us to environmental crisis and collapse[18] . The UN Framework Convention on Climate Change of 1988 was a start, and the Kyoto Protocol, which came into effect only this year, continues albeit slowly in the right direction.

The G8 meeting in July 2005 has at least agreed there is a problem[19] . Both developed and developing countries sorely need an immediate and sustained focus on political and economic mechanisms for returning us to the 1990 CO2 emission levels sought by the Kyoto Protocol. Even if this is achieved it will take decades for atmospheric CO2 levels to decline.

Despite the scale of the global warming problem we have good reason to be optimistic. Technological developments in the last few decades have brought about huge efficiencies in capturing renewable energy from wind, sun, waves and tides. The over-consumption of oil, that most convenient of all transport energy sources, has to be addressed, but the answer there is easy to see in improved public transport, and lighter, more efficient cars.

Pressures to move in this direction are increasing, with air pollution in cities and the rising cost of extracting oil, as demand outstrips the declining supply. “Hubbert’s peak” approaches and it becomes increasingly expensive to deliver. Unfortunately nuclear power is not a cost-effective substitute for oil or coal, for reasons Peter Bunyard explains elsewhere in this issue[20] .

At the same time many people in the developed world have become weary of the consumerism of the last few decades and the ill health that follows from fast lives and fast food. After achieving an energy-intensive lifestyle that has led the rest of the world in atmospheric pollution, we are discovering through film, television, museums and antiquities, the pleasures and achievements of successful societies of the past. Of course many past societies have failed, but most importantly ours is the best equipped of all to learn from those successes and failures, as anthropologist Jared Diamond has recently observed[21] . To really deserve the name we have given ourselves – Homo sapiens or “wise man”- the developed world (and the developing world, which has yet to reach our level of excess), will succeed in maintaining all of our societies, and our civilization, by adapting to a low energy lifestyle and reducing the current level of atmospheric pollution. Some regions and cultures will do it better than others, but the prospects for all societies becoming truly sustainable in a stable global environment will increase with commitments to that goal at all levels. The Kyoto Protocol, with all its limitations or deficiencies, is currently the only international collective commitment. The agreement, and those working to advise and implement it, deserve our support - not as the answer in itself, but as an umbrella for progress in the right direction.


Peter Barrett is Professor of Geology at Victoria University of Wellington, and director of the Antarctic Research Centre. © Copyright – Pacific Ecologist. Reproduction with permission encouraged.


1 Peter Barrett is Professor of Geology at Victoria University of Wellington and director of the Antarctic Research Centre. He has been chief scientist for a series of Antarctic projects over the last 3 decades drilling off the coast for climate history. He was awarded the Felipe Ippolito award for Antarctic science by the Italian Academy of Humanities
and Sciences in 2001, and the NZ Association of Scientists’ lifetime achievement award, the Marsden Medal, in 2004.

2 Crowley, T.J., Kim, K. 1995, Comparison of longterm greenhouse projections with the geologic record , Geophysical Research Letters, 22, 933-936.

3 Petit, al., 1999, Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica, Nature, 399, 429-36.

4 Mann, M.E., Jones, P.D., 2003, Geophysical Research Letters, 30 (15), 4 pp

5 IPCC was established under the aegis of the United Nations Environment Program and the World Meteorological Organisation in 1988. It accepts only peer-reviewed publications for consideration as evidence. The IPCC is made up of governments, not scientists. However scientists write the reports that the IPCC approves, following a rigorous multiple peer-review process. IPCC was established to provide governments and the wider community carefully considered
reports on the changes being widely perceived in regional and global climate in the 1980’s, and possible links with increasing greenhouse gases in our atmosphere. They have published reports thus far in 1990, 1995 and 2001, and another is due in 2007. These document with increasing certainty the influence of human-induced greenhouse
gas pollution on the earth’s atmosphere and climate. Their reports can be downloaded from . The summaries for policy makers are especially useful. See note 2

6 Kerr, R.A. 2004. News Focus – Three degrees of consensus. Science, 305, 932-4.

7 Wild et al., 2005, Global dimming, Science, 348, 348-350; Pinker et al., 2005, Science, 348, 351-355.

8 ACIA, 2004. Impacts of a Warming Arctic: Arctic Climate Impact Assessment, Cambridge University Press,

9 Monbiot, G. 2005. Junk Science, Guardian Weekly,

10 Thomas, R. et al. 2004, Accelerated sea level rise from West Antarctica, Science, 306, 355-8.

11 Barnett, T.P. et al. 2005, Penetration of human-induced warming into the world’s oceans, Science, Published online 2 June 2005;10.1126/science.1112418

12 Jacobs, S.S. et al. 2002, Freshening of the Ross Sea during the Late 20th Century, Science, 296, 386-389.

13 Curran, M.A. et al. 2003. Ice core evidence for Antarctic sea ice decline since the 1950s. Science, 302,1203-6.


15 “Meeting the Challenge”, International Climate Change Taskforce Report, Exeter, 1-3 February, 2005

16 Pearson, P. N. & Palmer, M. R. 2000. Atmospheric carbon dioxide concentrations over the past 60 million years. Nature, 406, 695-699. Royer, D. L. et al. 2001. Paleobotanical evidence for near present day levels of atmospheric CO2 during part of the Tertiary. Science 292, 2310–2313.

17 Millenium Ecosystem Assessment Synthesis Report, 2005.

18 Ronald Wright, 2005, A Short History of Progress, Carroll and Graf Publishers, 211 p.

20 Peter Bunyard, Taking the wind out of nuclear power, Pacific Ecologist, 11.

21 Jared Diamond, 2004, Collapse: How societies choose to fail or succeed. Penguin, 356 p.


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