Climate Change: Is the Science Sound?
This Special Report was submitted to the Legislative Assembly of Ontario on Nov 19, 2002. For more information, including the full report in .PDF and communications materials, please click here.
As the Environmental Commissioner of Ontario (ECO), I have the mandate to release special reports on matters of particular urgency. In the past couple of months, I have become convinced that the question of the scientific evidence regarding climate change has become a matter of urgency for Ontario legislators and the Ontario public.
We are currently immersed in a national debate on the appropriate response to climate change – a debate in which Ontario, with a large population, a strong manufacturing base and major greenhouse gas emissions, has a key role to play. Recently there have been numerous assertions in the media that there is little scientific basis for climate change, and that “go-slow” or even “business-as-usual” approaches are therefore appropriate.
There are also opposing voices, from all points on the political spectrum, which are urging speedy reductions in greenhouse gas emissions. For example, a recent editorial in the business weekly The Economist argued that climate change is a key reason to call for an energy revolution. “The most sensible way for governments to tackle this genuine (but long-term) problem is to send a powerful signal that the world must move towards a low-carbon future,” the editorial stated.
The controversy about climate change science is fundamental to the policy process. If the science is not credible, then there is no basis for enacting policy change. But if the science is sound, then our society will face significant consequences by sticking to a business-as-usual course, and we must, at a minimum, factor those consequences into our economic, social and environmental planning. The ongoing questions about the strength of the scientific evidence seem to be having a paralyzing effect on many policymakers in both public and private sectors. They are, on the one hand, prevented by time pressures from delving deeply into the many technical issues, yet on the other hand, are deluged daily by new findings, arguments, points and counterpoints. It is very hard to make good decisions in such a context.
I hope that the report that I am releasing today will help to provide some clarity, and help Ontario policymakers move to the next stage of the debate. This special report reviews the key scientific issues regarding climate change, and offers an opinion as to the strength of these arguments. While I do not want to prejudge what Ontario’s policy response to climate change should be in advance of a government decision, I do think it is vital for me to review and report on the science for the benefit of the members of the Ontario Legislative Assembly and the Ontario public.
My report focuses on the findings of the Intergovernmental Panel on Climate Change (IPCC) in their Third Assessment Report, published in 2001 (the 2001 IPCC Report). The IPCC is a body of scientists from around the world, convened in 1988 by the United Nations jointly under the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO). The mandate of the IPCC is to provide policymakers with an objective assessment of the scientific and technical information available about climate change, its environmental and socio-economic impacts, and possible options for response. Many hundreds of scientists from around the world (including Canada) participate in the preparation and review of IPCC reports. These reports represent the definitive work of the scientific community on the science of global climate change and human impacts. The IPCC has published assessments in 1990, 1995, and, most recently, in 2001, each assessment being the culmination of an enormous body of research over the previous five years.
My report also refers to several recent publications of the U.S. National Research Council on this subject, particularly the Council’s June 2001 report. This report was commissioned by the Administration of U.S. President George W. Bush, which requested the Council’s advice on climate change science, as well as an independent critique of the findings of the IPCC.
In the pages that follow, I have tried to summarize the most recent findings of the IPCC, as well as the key debates and uncertainties around the scientific evidence regarding climate change. I have also appended a longer technical appendix, which provides more detail and extensive references regarding the same issues.
Rising greenhouse gas concentrations
For several decades now, scientists have been observing rising concentrations of several greenhouse gases in the earth’s atmosphere, especially carbon dioxide, methane, nitrous oxide and tropospheric ozone. There is no scientific dispute about these observations, which are based in part on a program of continuous monitoring of carbon dioxide concentrations that began in the late 1950s. Both carbon dioxide and methane are now at higher concentrations than at any time during at least the last 420,000 years (Figure 1). Other greenhouse gases have also shown recent abrupt concentration increases. During the industrial era, carbon dioxide has increased over 30 per cent, methane more than 150 per cent, and nitrous oxide more than 15 per cent.
To compare the makeup of our current atmosphere with that of the distant past, researchers have analysed ice cores extracted from the massive, ancient ice sheets covering Antarctica and Greenland. The air bubbles trapped in these ice cores provide a chronological record of the atmosphere dating back hundreds of thousands of years. Researchers are able to measure the concentrations of gases in these air bubbles, and can confidently track how the earth’s atmosphere has changed over time.
Rising global temperature
Scientists have concluded that the global average temperature of the earth’s surface has risen over the last hundred years, by about 0.6 º Celsius. Since we have no intuitive sense of global average temperature, we tend to rely on our own daily experience of local weather, and so a change of half a degree may seem small. But global average temperature is a measure of global climate change, and on this scale the observed change is unusually large.
Since the invention of thermometers, temperatures have been regularly monitored at thousands of land stations worldwide, and from thousands of ships at sea. Climate research institutes have compiled these temperature readings into very large, publicly available databases, which have been thoroughly scrutinized by researchers the world over. There is very broad scientific agreement that the observed global average surface temperature increase over the past hundred years is real (Figure 2). Even scientists who are prominent skeptics about the human connection to climate change do agree that the global average temperature has risen significantly. It is sometimes argued that the heat radiated from buildings and vehicles - the “urban heat island effect”- is influencing thermometer measurements in urban settings, and that the observed warming reflects these localized effects rather than a truly global phenomenon. But the IPCC has evaluated this, and has been pointing out since 1992 that the urban heat island effect can only be responsible for a very small part of the observed warming.
Temperature over the last thousand years
The 2001 IPCC Report notes that it is likely that the northern hemisphere’s temperature increase in the 20th century has been the largest of any century during the past 1,000 years (Figure 3). To estimate global temperatures before the invention of thermometers, researchers have analysed several types of natural phenomena that are affected by temperature, such as tree rings, polar ice cores and the growth of tropical corals. These are called “proxy indicators” of temperature. The technique involves seeing how proxy indicators match with actual temperature records of the last century or so, and then extrapolating backwards in time based on this relationship. Because the tree rings, polar ice cores and tropical corals are collected from very different geographic regions, researchers are able to combine these indicators to create large-scale reconstructions of past global climate trends.
Compared to the reconstructed temperature trends of the past thousand years, the temperature rise over the last century stands out as being highly unusual. Over the last thousand years, there was an episode of regionally variable warming, labelled the “medieval warm” period, and more recently also a cooling period, the so-called “Little Ice Age.” Some argue that the current warming trend could just be another natural variation. But the 2001 IPCC Report concludes that the historical warming and cooling episodes appeared to be regional phenomena, whereas the current temperature rise is being observed simultaneously across many parts of the globe.
Satellite data do not invalidate warming
Since 1979, satellites have been taking measurements that can be used to calculate temperatures at various altitudes within the atmosphere. These measurements indicate that the lower atmosphere has not warmed as much as the surface of the earth. This has caused debate among scientists, with some doubting the validity of the satellite data, and others doubting the surface temperature data. The U.S. National Research Council established a panel to consider this issue, and in 2000 the panel concluded that the surface temperature trends were in no way invalidated by the satellite data. The panel also concluded that there was probably a real difference in temperature trends between the surface and the lower atmosphere. Among the possible causes cited by the panel for the relatively cooler lower atmosphere were volcanic eruptions and human-caused stratospheric ozone depletion.
The 2001 IPCC Report states that glaciers in most parts of the world have had a “negative mass balance” in the past 20 years; in other words, they have lost more mass on average, than they have gained. Measurements of the size and lengths of glaciers and analyses of moraines have also provided abundant evidence that most mountain glaciers have been retreating during the last 100 years. There are some glaciers that are advancing, for example in Norway and in New Zealand, but the 2001 IPCC Report notes that these cases involve unusual increases in precipitation.
Reduced snow and ice cover
In many areas of the world, researchers are observing reduced snow cover and earlier spring melting of ice on rivers and lakes. The 2001 IPCC report notes that annual snow cover in the northern hemisphere has decreased by about 10 per cent since 1996. Sea ice covers about five per cent of the earth’s surface. Both the thickness and the extent of sea ice influence how the atmosphere and the oceans interact. Over the last three decades, the extent of Arctic sea ice has been declining at a rate of about three per cent per decade, and its summer minimum thickness has decreased by nearly 40 per cent. Permafrost is also warming in many regions; for example in Alaska, deep permafrost has warmed by 2 to 4º Celsius over the last century.
Sea level rising more quickly
Tidal gauges measure the level of the sea surface relative to the land where the gauge is located. Changes in the mean sea level of a coast can be affected by the movement of land as well as by the change in the height of sea level. In many locations, land is still rebounding from the weight of the last glaciation, so researchers have to factor this in when they interpret the records of tidal gauges.
The 2001 IPCC Report estimates that the average rate of sea level rise has increased from 0.1- 0.2 millimetres/year during the past 3,000 years to 1-2 millimetres/year during the 20th century. This is an increase by a factor of ten. As well, the average rate of sea level rise during the 20th century has been higher than that of the 19th century.
Summary of observed changes
Greenhouse gas concentrations are higher now than at any time during at least the past 420,000 years, and have been rising at an ever-increasing rate since the industrial revolution. Many of the observed changes in climate and other indicators are consistent with each other and provide increased evidence of a changing climate system. For example, land temperatures and sea surface temperatures show consistent increasing trends. The widespread decrease in mountain glaciers is consistent with global temperature increases. Decreases in spring snow cover, in lake and river ice and in Arctic sea ice parallel increases in temperatures in the Northern Hemisphere. The IPCC concludes in its 2001 report that the trends “consistently and very strongly support an increasing global surface temperature over at least the last century.”
Causes of Observed Changes
Explaining the increase in greenhouse gas concentrations
Concentrations of greenhouse gases have increased dramatically in the atmosphere, and these increases are clearly caused by human activities. There is essentially no debate in the scientific community about this point, and there are several independent supporting lines of evidence. First, the rate of increase of greenhouse gases over the past century matches the rate of human- caused emissions. Second, atmospheric oxygen has been declining at the same rate as fossil fuel emissions of carbon dioxide have been increasing. This is because oxygen is consumed when fossil fuel is burned. Third, there are changes in the atmospheric proportions of carbon isotopes, which indicate that the atmosphere is becoming enriched with carbon from fossil fuel sources, rather than from natural sources. The IPCC estimates that 70 to 90 per cent of the increase in carbon dioxide emissions is due to fossil fuel burning and the rest to land use change, particularly deforestation. The U.S. National Research Council also agrees that human activities are responsible for the increase in carbon dioxide concentrations.
Until the industrial revolution, the natural carbon cycle of the earth was essentially in equilibrium, as vast quantities of carbon continually circulated through the planet’s atmosphere, oceans, soils and biomass. Compared to quantities that are cycled naturally, human emissions of carbon dioxide are small, but they have perturbed a cycle that was almost in balance. Other greenhouse gases also have natural and human sources, but it is emissions from human activities that have caused the increase in atmospheric concentrations. Greenhouse gases like chlorofluorocarbons are entirely human-made.
Factors contributing to climate change
We have seen that global average temperature has increased, and that greenhouse gas concentrations have increased. However, a key question remains as to whether the observed increases in greenhouse gases have indeed caused the increase in global average temperature. Several external factors, both natural and human caused, can play a role in climate change, and they are often all at work at the same time. These factors, which can alter the balance of incoming and outgoing energy in the earth-atmosphere system, are termed “radiative forcings” by climate scientists. Positive radiative forcings tend to produce warming and negative radiative forcings produce cooling. The most important radiative forcings include greenhouse gases, aerosols, solar forcing (variation in solar output) and volcanic eruptions. Radiative forcing is measured in Watts/square metre.
The 2001 IPCC Report summarizes the relative importance of various radiative forcings over the last several centuries, and concludes that greenhouse gases, especially carbon dioxide, have been the most important positive radiative forcing (Figure 4). Solar forcing has contributed only a small amount of warming compared to greenhouse gases. At the same time, several factors have exerted cooling influences, especially sulphate aerosols, emissions from volcanic eruptions, biomass aerosols and depletion of the stratospheric ozone layer.
The 2001 IPCC Report also evaluates how strong the level of scientific understanding is for each radiative forcing agent. The Report notes that there is a high level of scientific understanding about most greenhouse gases; excellent measurements of their concentrations exist, and their radiative properties are well-known. There is a medium level of scientific understanding of the radiative properties of ozone. Because major uncertainties remain about aerosols and their effects on clouds and also solar forcing, the IPCC acknowledges there is a very low level of scientific understanding in these areas.
Human contributions to climate change
The 2001 IPCC Report concludes that there is new and stronger evidence than in past reports that most of the warming observed over the past 50 years is attributable to human activities. The report also states,
“There are new estimates of the climate response to natural and anthropogenic forcing, and new detection techniques have been applied. Detection and attribution studies consistently find evidence for an anthropogenic signal in the climate record of the last 35 to 50 years.”
To tease out human influences, researchers compare various model simulations of global temperature with observed global temperatures over recent decades (Figure 5). When the models simulate only the influences of solar variation and volcanic eruptions during this time frame, the resulting temperature graphs do not closely match the observed record. When the models simulate only the influences of human impacts (greenhouse gases, stratospheric ozone depletion and sulphate aerosols), somewhat better matches with the observed record are achieved. But the best match with observations is achieved when both natural and human- caused influences are all combined.
While there is not absolute proof that greenhouse gases have caused warming, there is strong evidence. The U.S. President received a report from the U.S. National Research Council in June 2001 which summarized the current scientific views on this point as follows: “The IPCC’s conclusion that most of the observed warming of the last 50 years is likely to have been due to the increase in greenhouse gas concentrations accurately reflects the current thinking of the scientific community on this issue.”
Debates about the evidence
There are a number of debates about the importance of various influences on observed climate changes. Some people wonder how carbon dioxide, a gas that accounts for less than one per cent of total atmospheric gases, could be the cause of rising global temperature. Nitrogen and oxygen, which together make up 99 per cent of atmospheric gases, are essentially transparent to radiation, and are therefore not greenhouse gases. But chemistry and biology provide abundant examples of substances that have large impacts in trace concentrations.
Some believe there is conflicting evidence about the importance of various factors. For example, a cooling episode in the Northern Hemisphere from 1946 to 1975 has led some critics to argue that since this episode coincided with rising greenhouse gas emissions, it is evidence against human caused warming. However, the U.S. National Research Council suggests instead that sulphate aerosols, which were higher at that time, may have provided a cooling effect during this time period, which masked the increase in the warming effect of greenhouse gases during this same time period.
Carbon dioxide levels have been much higher in the distant past, leading some observers to question why a relatively small rise in carbon dioxide should be problematic now. It is true that, just as natural climate has varied in the past, so have carbon dioxide levels. Carbon dioxide levels were up to 20 times higher between 200 and 150 million years ago, but the climate was also much warmer and the sea level much higher. During the glacial-interglacial fluctuations of the more recent past, carbon dioxide varied between 180-300 ppmv, but was relatively stable at around 270-290 ppmv from the end of the last ice age until the beginning of the industrial era, when the rapid rise (currently at 370 ppmv) due to human-induced emissions began. Human civilizations developed under atmospheric conditions of around 270-290 ppmv carbon dioxide.
There are also ongoing debates in the scientific community about how to interpret geologic evidence connecting carbon dioxide concentrations and temperature – and especially how to determine whether carbon dioxide increases drove or just amplified temperature increases at any given time in the distant past. What is uncontested is that Antarctic ice cores show a remarkable correlation between carbon dioxide levels and temperature, which increased and decreased together in the same pattern over the last 420,000 years.
Some critics have also raised doubts about the reliability of climate models, since early models generally predicted more pronounced temperature rises than have actually been observed over the past century. However, it has been strongly suspected for a long time that aerosols have a net cooling effect on climate. When the effects of aerosols are incorporated into climate models, their simulations of temperature are consistent with observations.
Debates about natural factors
Some skeptics think that natural factors may be important contributors to the observed warming. The varying influence of the sun is brought up repeatedly in debates about the causes of climate change. Solar irradiance varies over the 11 year solar cycle, and may be increasing slightly from one cycle to the next. But the 2001 IPCC Report concludes that solar forcing is very small (between +0.1 to +0.5 Watts per square metre) when compared to the forcing of greenhouse gases (+2.43 Watts per square metre with an uncertainty of 10 per cent). Solar irradiance has been directly observed by satellite during the past 22 years and the variation is quite small, amounting to less than 0.1 per cent. The IPCC says that solar forcing may have contributed to some of the warming observed in the first half of the 20th century, but very little in the latter half.
The only way that variation in solar radiation could have a major impact on climate would be if it were somehow amplified through another mechanism. Cosmic rays and their possible effects on clouds have been suggested as a possible mechanism. But the IPCC has considered this, and states that evidence for the impact of cosmic rays on clouds has not been established.
Methane hydrate is a crystalline solid which occurs naturally in deposits on land in polar regions and beneath the ocean floor in marine sediments. It has been hypothesized that large-scale natural releases of methane hydrate could be a factor in climate change. But a study by the U.S. Geological Survey in 1999 refuted this theory. The 2001 IPCC Report points out there is no evidence of rapid, massive releases of methane hydrates in the past, and that methane hydrates probably account for no more than two per cent of the current total natural and anthropogenic sources of methane. In any case, methane contributes only about 20 per cent of the total radiative forcing due to greenhouse gases.
Other possible natural causes
Some people wonder if changes in the earth’s orbit might be responsible for the currently observed warming trends. Slow, regular variations in the earth’s rotational axis and orbit (the so-called Milankovitch cycles) have played an important role in the advance and retreat of ice during past ice ages. But these influences are very slow, and significant changes require thousands of years to become evident.
It has been suggested that some internal reorganization of the atmosphere and oceanic circulation caused the recent warming. This would be a remarkable coincidence, occurring at the very time that rapid increases in heat-trapping greenhouse gases occurred, but, apparently, without any climate effects from the greenhouse gas increases. As well, this theory does not appear to match observations. Direct observations indicate that the oceans have warmed consistent with the downward penetration of heat from the surface. Recent studies indicate that the ocean is likely to be acting as a net heat sink, rather than a heat source.
Causes of recent sea level rise
As noted above, sea level has been rising more quickly in the 20th century than in recent previous centuries. The most recent report of the IPCC notes “It is very likely that 20th century warming has contributed significantly to the observed sea level rise…” To determine whether human causes are partially or largely responsible for this change, researchers have been working to evaluate and quantify many factors that contribute to sea level rise, such as the thermal expansion of water and contributions from glaciers and ice caps.
The IPCC concludes that thermal expansion was one of the major contributors to 20th century sea level rise, and will be the major contributor over the next hundred years. Thermal expansion occurs because the volume of ocean water increases as it warms. Polar continental ice sheets contributed only in a minor way to sea level rise in the 20th century, and it is expected that the impact of climate change on ice sheets will occur over a time scale of centuries. The IPCC evaluated estimates of combined contributions from human causes compared to combined contributions by natural causes. Since the combined natural causes could not account for the magnitude of the sea level rise that has actually been observed, this suggests that 20th century climate change has made a contribution to 20th century sea level rise.
Projecting Future Climate Change
By the end of this century, if we continue on a business-as-usual basis, concentrations of greenhouse gases could rise much higher than current levels. In fact, concentrations could reach the equivalent of several times the carbon dioxide concentration that existed at the beginning of the industrial era. Computer modeling, supported by a variety of observational evidence, indicates that very large climatic changes will likely occur as a result. The IPCC projects the global mean temperature will increase by 1.4 to 5.8ºC over the period 1990 to 2100. Contrast that to the much slower rate of warming during the recovery from the last ice age of about 2ºC per millennium.
There is broad agreement among climate scientists regarding the climate changes that can be expected over the coming century if we continue on a business-as-usual basis. The key changes are:
- the warming will be greater at high latitudes than at low latitudes, due to the melting of seasonal ice and snow;
- the warming will tend be greater in winter than in summer adjacent to high latitude oceans, due to the thinning of sea ice;
- there will be an increasing tendency for the intensity of rainfall to increase (that is, more rain will fall as intense downpours); and
- there will be increased summer drying in the interiors of most mid-latitude continents, with associated risk of drought.
To predict future climate trends, researchers first have to make predictions about each of the key factors that will influence climate, including the future emissions of greenhouse gases, how those greenhouse gases are likely to build up in the atmosphere and how much warming is likely to result. Researchers also need to consider and try to quantify any likely feedbacks between climate changes and the buildup of greenhouse gases.
Future emissions of greenhouse gases will depend on many factors, such as the growth of the global economy and developments in technology and energy efficiency. The IPCC developed an extensive range of future emission scenarios in preparing for the 2001 IPCC Report. Each scenario involved a set of interconnected assumptions about population growth, economic and social well-being, trade and overall concern about the environment. The scenarios were considered plausible business-as-usual scenarios, since they did not assume societies would take deliberate actions to reduce greenhouse gas emissions (Figure 6).
The buildup of greenhouse gases in the atmosphere depends on future emission rates, of course, but also on the key natural pathways which draw carbon dioxide back out of the atmosphere – absorption by forests and by the oceans. Researchers have to estimate how much these absorption pathways are likely to affect the buildup of atmospheric carbon dioxide. The 2001 IPCC Report notes that the absorption of carbon dioxide by forests may well weaken over the coming century. Oceans will tend to absorb carbon dioxide at rates slower than the predicted emission rates. Warming oceans will also be able to absorb less carbon dioxide, since carbon dioxide is less soluble in water at warmer temperatures. Weakening terrestrial absorption and slow ocean absorption will both exacerbate the buildup of atmospheric carbon dioxide. Researchers also have to estimate how quickly concentrations of other greenhouse gases are likely to build up in the atmosphere. It is common practice for climate scientists to use the doubling of carbon dioxide concentrations in the atmosphere as a benchmark for comparison. When the heating effects of all greenhouse gases add up to that which would occur from a doubling of carbon dioxide alone, this is said to be the climatic equivalent of a doubling of carbon dioxide.
A key parameter in the projection of future climatic change is the climate sensitivity, which is often defined as the globally averaged warming once the climate has fully adjusted to a fixed doubling of atmospheric carbon dioxide (or its climatic equivalent). The greater the climate sensitivity, the greater the eventual warming that the climate is heading toward, and the greater and faster the warming along the way. There are several independent methods for estimating the climate sensitivity, and researchers have found that their results largely overlap. Given the overlapping evidence, the 2001 IPCC report has not altered its previous estimate of a climate sensitivity of 1.5-4.5º Celsius.
To make projections of future regional patterns of climate change, researchers use three- dimensional computer models, referred to as atmospheric general circulation models or AGCMs. There are many such complex models in use. The models agree with each other concerning the large-scale features of climatic change that can be expected, such as greater warming at higher latitudes, greater warming in winter than in summer, and other features listed above.
Over the past several decades, climate models have advanced greatly, and are well able to simulate the broad features of observed climate changes, such as the minimal warming to slight cooling in the northwest Atlantic Ocean and around parts of Antarctica. Climate scientists point out that climate models cannot provide certainty about the details of specific changes in specific places. Some regions may benefit from initial stages of global warming, while others will lose. Since no one can state with high confidence where the initial winners and losers are, climate modelers argue that all regions should be considered at risk.
One of the critical issues in projecting future climatic change is the possibility of so-called climate “surprises,” such as an abrupt re-organization of ocean circulation as critical thresholds are crossed. The likelihood of these events is very uncertain, but if they were to occur, consequences could be enormous. Examples of climate surprises could include a reduction or even shutdown of the North Atlantic Gulf Stream, which carries warmth from the tropics to Europe. Another example could be a change in the intensity and frequency of El Niño, which is a periodic oscillation in tropical Pacific ocean temperature with repercussions worldwide. This phenomenon has a major influence on North America’s weather, including a link to drought cycles. There is evidence that some of these events have occurred in the past, but their likelihood of recurrence is difficult to estimate. However, there is a risk that if large climatic changes are allowed to occur, they may trigger abrupt shifts that can’t be precisely predicted.
With this Special Report and its technical appendix, I have tried to provide an objective assessment of the scientific and technical information available about climate change. Based on this body of evidence, I am confident in concluding that human-induced climate change is occurring. It will cause serious environmental consequences in the near future. We have already begun to see these impacts of climate change around the globe. These impacts will affect both the Ontario public and the environment in which they live.
Science is not a static entity. It is an on-going process of learning. Uncertainties in science are an inherent part of the scientific process and serve to inform future inquiry. Science has provided strengthened evidence over the past decade that global climate change is occurring. This evolution of knowledge will continue to yield information that allows us to better understand the human role in climate change.
The Province of Ontario has a key role to play in addressing climate change. There are still many legitimate debates ahead of us, and limited time. I encourage Ontario’s policymakers to review for themselves the evidence regarding climate change. If they conclude, as I have, that the evidence is compelling, then it will be clear that the status quo is no longer an option, and they will be ready to focus on Ontario’s response.
Citing This Article:
Environmental Commissioner of Ontario. 2002. Climate Change: Is the Science Sound?, ECO Special Report, 2002. Toronto, ON : Environmental Commissioner of Ontario.