Thank you very much, Mr. Chairman.
Let me introduce myself. I was for thirty years of my life a public servant. I retired eighteen months ago and have been on the Bureau of the Intergovernmental Panel on Climate Change, first for Working Group I, which is on science, and now for Working Group II, which is on impacts and adaptation. I hang my hat part of the time at Carleton University and some of the time with the International Development Research Centre.
Thank you very much, sir, and thank you very much, members of the committee, for the opportunity to appear before you to tell you some of the science that underlies the threat of climate change.
I would like to make four points.
First, we have, mainly through the burning of fossil fuels, taken the atmospheric concentration of carbon dioxide--one of the main greenhouse gases--to levels that the earth has not experienced for almost a million years. We are in unknown territory.
Second, recent global temperatures are higher than we have been able to determine over the last millennium. We have in fact detected global warming.
Third, the only way we can satisfactorily understand this change is by invoking the known characteristics and physics of the influence of greenhouse gases on the climate.
Fourth, we are now seeing some impacts occurring at a faster rate than we had previously anticipated, and the longer we delay action, the greater will be the risks and the more expensive will be the costs. In my view, there is an urgent need for action.
We can explain the threat of climate change either in simple terms or in terms of extraordinary technical detail. The climate system itself is extremely complex, containing many interacting and mostly non-linear processes. Nevertheless, our understanding is sufficient to tell us that increasing the concentrations of greenhouse gases in the atmosphere, as we have been doing by our burning of fossil fuels, will affect the radiative balance and hence the climate. This is a fundamental fact, based on well-accepted physics, that we cannot avoid. It's the reason I used the term “threat”.
The scientific understanding is not new. As long ago as 1824, the French mathematician, Fourier, discussed the link between the climate and the atmospheric concentration of certain gases. These gases, collectively known as greenhouse gases, act like a blanket around the earth. They're responsible for making this planet of ours inhabitable. Without them the world would be 32 degrees cooler. This hypothesis was taken up some 70 years later by a Swedish chemist, Arrhenius, who did some back-of-the-envelope calculations of how the earth's temperature would change with the doubling of the concentration of these greenhouses gases, a situation we are rapidly approaching.
Scientists put this issue of climate change on the international political agenda in the mid-1980s precisely because of their concern with the observed increases in the atmosphere of concentrations of carbon dioxide that were measured very carefully on Mauna Loa by Dr. Charles Keeling. The scientific concern was such that it dominated the Conference on the Changing Atmosphere that was held in Toronto in 1988. It also led the United Nations to take the initiative to establish the Intergovernmental Panel on Climate Change, the IPCC, to provide governments with authoritative policy-relevant--but not policy-prescripted--assessments of the current state of our knowledge of climate change.
Now to my first point. Recently, scientists have extracted a three-kilometre-long core from the ice in the Antarctic. The snow that falls there each year captures within its crystals samples of the ambient air at the time it was deposited. Layers have built up one year at a time. By examining the air trapped in each layer, the scientists have been able to determine a record of past temperatures and concentrations of key greenhouse gases. They have now been able to take the record back some 630,000 years, covering several ice ages. These ice ages occur every 120,000 years or so and are forced by the orbital variations of the earth around the sun. The concentration has varied over time. It's been lowest during an ice age and highest during an interglacial period.
The important point to register is that the atmospheric concentrations of carbon dioxide have stayed between two bounds, never going above 280 parts per million. This was even so up until the mid 18th century when the Industrial Revolution began. Today we are at 380 parts per million, a 30% increase over the past 150 years. Those concentrations are still increasing.
By looking at the isotopic ratios of the carbon dioxide, we were able to establish that most of it originates from the burning of fossil fuels. We are clearly taking the atmosphere into uncharted territory. We know from basic physics that this will affect the climate. I won't claim that I can tell you exactly how the climate will change, but I can assert with very little doubt that change it will.
Let's turn to what we've observed already has happened to the climate and focus on the temperature, since it's the easiest parameter to understand. For the most recent period, we use direct thermometer readings. There's been a considerable amount of work to make sure this temperature record is homogenous and devoid of spurious effects such as enhanced warming in the cities. For earlier periods, before we had the thermometer, we have to rely on carefully calibrated proxy data such as tree rings and ice cores. Several groups of scientists have used this data to reconstruct the temperature record of the past 1,000 years. The general characteristics of these several reconstructions are all similar. Although some have greater variability--for example, at century time scales--than others, these reconstructions clearly show that there has been significant warming over the last 50 to 100 years, and, more importantly, that this warming is outside the range of the variability over the past 1,000 years.
As the IPCC reports have concluded, it is very likely that the recent warming is outside of the natural variability of the climate. It is for this reason that we believe we have indeed detected climate change. Now, attributing climate change to human activities is quite different and requires not only the use of such data but also climate models and looking for fingerprints in the past climate.
Our understanding and ability to model the climate has improved significantly over the last 10 to 15 years. We also know what have been the changes in the concentrations of greenhouse gases and aerosols in the atmosphere over the last 100 years. We also know what have been the changes in natural forcing, such as the sun's output and volcanic activity. We can feed this information into climate models and compare the results with the observed record. If we take natural forcing alone, the fit for the first half of this century is not bad, but it begins to deviate afterwards.
If instead we use both natural forcing and that due to greenhouse gases and aerosols, the fit is remarkably good. Indeed, the only way to reproduce the observed temperature change of the last 150 years is by introducing greenhouse gases from burning fossil fuels and from land use change.