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Home » Evidence for global warming - and why we need to take action

Evidence for global warming - and why we need to take action

The following statement was prepared by Professor Peter Barrett FRSNZ (Director of the Antarctic Centre, Victoria University of Wellington), and is a slighly amended version of an article originally published in the "Evening Post".

We still see letters and articles in our newspapers claiming that global warming has nothing to do with human activity, and that there is no need to do anything about it. This claim is echoed and promoted by business interests, and risks deflecting Government efforts to reduce our greenhouse gas pollution. Do we really need to be concerned about this? I believe we do on two counts:

1. The claim denies a huge body of contrary published scientific evidence amassed over the last 15 years. Thus it trivialises this effort, and by implication all science.

2.  Earth scientists have a better understanding than most of earth history and behaviour, and can appreciate the magnitude of effects that are bound to follow the 3-4 degree C global temperature rise projected for the next 100 years - giving a temperature as warm as the Eocene.

How can we be so sure of this? For the last few years I have been following the work of the UN-sponsored Intergovernmental Panel on Climate Change (IPCC). It consists of three Working Groups: 

*  WG I to get the best possible evidence on present and past climate from many places on the earth's Surface; 
*  WG II to check out the consequences of possible changes for Communities; and
*  WG III to advise governments on how to deal with the issue. 

They first reported in 1990, and again in 1995 and 2000. Working Group I alone comprises just under 1000 climate scientists from 100 countries. Their work consists of reviewing knowledge of climate change, analysing and summarising data from thousands of relevant published and peer-reviewed scientific articles. Tedious but unassailably sound and comprehensive. To ensure that their findings can be understood, they have produced summaries for policy makers that are approved by government representatives of IPCC countries line by line. This is advice unbiased by individuals or special interests and the best we can get. 

What have they said? IPCC concluded in 1995 that "The balance of evidence suggests a discernible human influence on global climate", and then in 2000 with "There is new and stronger evidence that most of the warming observed in the last 50 years is attributable to human activities". But they also provide figures and graphs so that we can see for ourselves. The upper graph (below) shows that average temperature has been steady for most of the last millenium, but has risen dramatically in the last few decades. And why? The lower graph shows an equally dramatic rise in CO2. 

A few people are saying that the recent warming could be part of a natural cycle. But a further fact from IPCC. "The present CO2 concentration has not been exceeded in the last 420,000 years." This is based on CO2 concentrations measured directly from Antarctic ice cores, which also record 4 glacial-interglacial cycles over this time period. In fact, IPCC think that there is more CO2 in the air we are breathing now than at any time in the last 20 million years. This is long before our ancestors first stood upright (about 5 million years ago) and shows what a significant global climate event is taking place. In the face of these observations, and the well-established effects of increasing  greenhouse gases (GHGs), it is hard to escape the conclusion that if we do nothing we face a continuing rise in global temperature that will lead to global ecological disaster by the end of this century. 

So why aren't we doing something? The GHG problem is extremely dangerous to our civilization because we are predisposed to ignore it. We are visual animals, and have evolved over the last few million years to respond to immediate and visible threats (predators or enemies). Indeed, the success of your ancestors in dealing with these threats has allowed you to read this column. GHGs, however, are an invisible and slowly increasing threat, and they are all the more dangerous because their inevitable consequences come decades after the pollution itself.

The GHG problem is all the more difficult because it requires us to focus not on creating new wealth, but on preserving the environment in which we live (and have largely taken for granted). An effective response will require long term vision and planning at international and national levels, so that the costs of the remedies are spread equitably through the community. A huge and complex task, but now the message is clear. The problem is rapidly becoming critical, and we will need our best intelligence and technology to restore our lifestyle to one that is sustainable for our children and their children. 

The international community has already shown, through the Montreal Protocol of 1987, that we can recover from global atmospheric pollution - in that case leading to the loss of stratospheric ozone and UV protection. The Kyoto Protocol deals with a more complex problem, and is a small step forward, but it is also a necessary step in the right direction. 

A final thought. The earth has experienced around 40 glacial and interglacial cycles over the last two million years, and our ancestors survived all of these living a fairly basic life style in small communities. Our oldest civilizations developed a little over 6000 years ago, around the time that sea level and climate stabilised after the most recent glaciation. Maybe this was because the last 6000 years has been the longest period of climate stability in the last 2 million years - grand irony with the threat of climatic instability from our technological success.

Peter Barrett 

10 May 2002

More information on the information produced by IPCC can be seen on their web site at: