Climate of change: the world has the resources to respond to climate change, maintains Alan Porteous. But we need to get on with it.

HUMANITY is faced with a menacing question. What happens if we hit nature's thresholds, the so-called tipping points of the global systems that sustain us? And will we be left with the resources to adapt?

The evidence for global climate change is becoming ever more visible. Nine out of ten of the world's glaciers are in retreat. Arctic sea ice is melting at a rate of about 9 per cent per decade. Ten of the warmest years since the beginning of the 20th century have occurred since 1995; there have been a cluster of ' 100-year' droughts; and hurricanes are becoming more intense.

Disturbing images of polar bears swimming desperately between remnants of sea ice illustrate the impact of climate upheaval on wildlife and ecological systems. Global warming also poses threats to food production.

Early in 2007 the Intergovernmental Panel on Climate Change (IPCC) will present its Fourth Assessment Report on the state of the world's climate. This will embody the most comprehensive collective understanding yet of the scientific, technical and socio-economic implications of climate change.

For sheer volume and detail, the report may not be an easy read. The process of writing has been laborious, involving hundreds of lead authors and thousands of contributors and reviewers. There have been vigorous debates between strongly held views, and word-by-word arguments in the editing process. Consensus has been achieved across a spectrum of languages and political environments.

In preparing the report, the IPCC has had to contend with a fair amount of scepticism and disagreement arising from its Third Assessment Report, published in 2001. This proposed that the global temperature would increase by between 1.4[degrees]C and 5.8[degrees]C by the end of the 21st century. This wide range made it difficult for policy makers, conservationists and engineers to develop precise strategies.

At the time, there was controversy over satellite data from the 1990s which appeared to show that the upper atmosphere was cooling, contradicting the rising temperatures shown by surface measurements. It has since been discovered that these data were misinterpreted. Once this was recognised and fixed, the upper atmosphere data backed up the trend at the surface.

Other sceptics pointed to measurements in the third quarter of the 20th century which had appeared to show a cooling world--and had led Newsweek to predict a 'drastic decline in food production, with serious political implications for just about every nation on earth'. We now understand that this cooling was caused by high levels of dust and other particulates which blocked more of the sun's radiation than usual. These emissions were caused by human activities, and efforts to reduce them in recent years have mitigated their effect.

We saw a natural example of this effect in 1991, when Mount Pinatubo in the Philippines erupted. The resulting ash cloud reduced the global temperature by an estimated 0.3[degrees]C.

The Fourth Assessment Report will leave little room for doubt that, in terms of the maintenance of the Earth systems on which we rely for our quality of life, climate change is the most compelling problem of this century. As far as we can tell, we are facing the greatest disruption since modern human settlement began some ten millennia ago.

After the retreat of the last ice age about 12,000 years ago, the climate became relatively stable, permitting settlements and farming to develop. There have been occasional blips in the climate regime since then, such as the Medieval Warm Period about a thousand years ago, when the Norse established settlements in Greenland--only to abandon them a few generations later when a cooler climate returned.

The Little Ice Age, lasting from about 1300 to 1850, brought periods of widespread famine, political and social upheaval. Millions, from Europe to China, died of disease. Yet it is likely that average temperatures were only a few degrees below what we experience today.

If we go back further, say half a million years or so, we find evidence of the link between the atmospheric temperature and the concentration of so-called 'greenhouse gases', particularly methane and carbon dioxide. These gases have been relatively stable during the past 10,000 years, but have been rising quickly since the start of the industrial revolution about 250 years ago.

We have been living in one of the most benign periods of climatic stability in human history, and, as a result, we have multiplied and prospered. But now our numbers and our prosperity are putting everything at risk.

If we accept this prognosis, questions that were once theoretical become pressing reality. How long do we have to turn things around, and how do we invest that time wisely? Do we have the resources to cope with what may be ahead?

Some signs of our ability to manage the future are not good. In the European heatwave in the summer of 2003, 35,000 people died--most of them in the world's richest countries. By the middle of this century, scientists estimate, half of Europe's summers will be as hot as 2003's.

There is ample evidence that environmental degradation leads to social and political instability. In his book Winds of Change (Simon & Schuster, 2006), Eugene Linden makes the point that 12 of the 14 nations that have required UN peacekeeping operations since 1990 have lost 90 per cent of their forests.

The Kyoto Protocol, an international agreement to limit greenhouse gas emissions in industrialised nations, is going to be too hard for many countries to achieve within the agreed timeframe. Others, such as the United States and Australia, have not ratified the Protocol.

Economists find it difficult to create pricing models that might guide investment and political action. For a start, no one can predict the timeframe: do we have a decade or less, as is often argued, or might our customary way of life survive for longer? How quickly and at what cost can we reduce our still-growing consumption to sustainable levels, adopt renewable energy and reduce greenhouse gas emissions?

There are hopeful precedents. In the 1980s understanding dawned of how chemicals commonly used in refrigeration and aerosols were raising chlorine levels in the stratosphere and damaging the ozone layer which protects the earth from the harmful rays of the sun. The findings were shocking enough for countries to adopt the Montreal Protocol, which cut the manufacture and use of these chemicals. As a result the ozone layer is tipped to recover, although the process will take decades.

The Asian tsunami of Christmas 2004 showed the modern world's vulnerabilities but it also triggered a massive public response which spoke of resilience. It engendered a fresh consciousness about looking out for weaker communities and poorer individuals.

Across the world, there is a groundswell of initiatives to conserve and rebuild. There is a new appreciation of the indigenous knowledge and social skills that served us well in our ancestral homes but have been lost in the rash to exploit and develop. Businesses and industries are developing ways to become energy efficient and 'carbon neutral'--by cutting emissions themselves and also paying others to save energy for them. A recent example in the Financial Times reported BSkyB's purchase of energy credits from a wind power project in New Zealand and a Bulgarian hydroelectric scheme. In September California became the first US state to legislate for mandatory reductions in greenhouse gas emissions, setting what could be a vital precedent for the country. Even popular magazines are extolling green lifestyles as trendy.

Global crises, like those in our individual lives, inevitably throw us back on our personal resources. They challenge how we use our material possessions, question our strength of character, and test our relationships with those close to us. Personal and interpersonal resources are highly renewable, respond well to investment, and require little activity at the cash register. Their development yields dividends which outperform the most aggressive material investments.

The people power from these resources can and is changing political and corporate will. It will restore the landscape, clean the air, and protect what would otherwise be destroyed. But it won't be easy, may only be partly achievable, and could not be more urgent.

Alan Porteous is an agricultural climatologist at the National Institute of Water and Atmospheric Research in Wellington, New Zealand.