Ministers Brief on Climate Change

SUMMARY

Climate change has become a major political issue, nationally and internationally, over the last decade. It has also become a controversial issue, because of the imprecision of our scientific knowledge and understanding (see Appendix 1). Current estimates of global warming between now and the year 2100 lie in the range of 1-5°C; consequential rise in global sea level is estimated to lie in the range 0.15 - 1.0 metres. These wide ranges have allowed people to assume positions at opposite ends of the limits of uncertainty and therefrom to project consequences of quite different degrees of severity for the future of the Earth and life on it. An associated problem is that of knowing how much of the global warming is a consequence of human activity, especially in the generation of greenhouse gases. Some suggest that the rate of global warming is so much faster than nature has ever induced that most of the increase is attributable to human activity; others tell of very rapid natural changes in the Earth record that challenge such attribution. The current consensus, if there is one, is to adopt a precautionary approach to the issue - to model impacts of climate change, and suggest methods of adapting to them, while taking steps to better define global warming and to model climate change. For the latter, a target of predicting climate change a factor 5 - 10 times more precisely than we can now would be appropriate.

It is with the latter that we are concerned in this brief: how is climate change to be better defined and understood? Narrowing the uncertainties of current estimates of climate change is a prime target of research, because that will obviate the necessity to consider the widest range of possibilities and the consequently wide range of options for adaptation and mitigation. Much of the necessary research relates to studying the mechanisms by which the Earth responds now to various kinds of forcing, e.g., by anthropogenic emissions of greenhouse gases. However, the Earth is several billion years old and its climate works on a multitude of time scales, from the effects of storms that last minutes, hours or days, to the gradual evolution of the chemical constitution of the atmosphere over geological time. We cannot assume that all the processes we must study to embrace the issue of mitigation of anthropogenic forcing are short term, i.e., processes that endure for, at most, a few years. Yet we cannot wait for centuries to measure the results of slower natural responses, either. Fortunately, geology preserves in rocks and sediments the natural records of past events of climate change. It takes considerable effort to find those records, and to process and interpret them. But the bonus is that we then have a geological record that allows us to 'short circuit' the wait for current Earth responses in order to refine our models of the processes responsible for climate change.

Thus the Earth has an extensive record of climate change stored in its 'geology'. The primary conclusion we draw is that recovering that record is an essential and urgent component in understanding the very complex interactions by which the Earth responds to environmental forcing, and in improving our models of climate change, which are so imprecise today.

Enhanced research into the geological record of climate change, globally, nationally, and locally, should be a high priority for federal and provincial government agencies, and for their academic and private sector collaborators. Ministers should arrange a forum of all these parties to establish a multi-partner effort to enhance our understanding of the science of climate change. Alongside this, a national collaborative effort to review the impact of climate change on groundwater resources would be timely.

A SYNTHESIS OF THE CURRENT DEBATE ON CLIMATE CHANGE

The Intergovernmental Panel on Climate Change (IPCC) has issued several reports on its assessment of climate change, and is engaged on an update, to be published imminently. A summary of the conclusions of the last report, published in 1995, is provided in Appendix 1. The estimate of average global temperature increase from 1990 to 2100 are about 1/3 lower than those of the first report, in 1990, because of new, lower, estimates of emissions of CO₂ and CFCs, realization of the cooling effect of sulphate aerosols, and improvements in the treatment of the carbon cycle. In its latest findings, about to be published, IPCC has increased its estimates of global warming and sea level rise from those noted above, because of new lower estimates for the cooling effects of sulphate emissions. Thus the various estimates published by IPCC in this decade oscillate with variations of +/- 50%: this is a clear token of the levels of uncertainty associated with our current understanding.

What is clear is that the uncertainty in temperature increase is bracketed by 1-5°C, and the consequent average global increase in sea level lies in the range 15 - 100 cm. The uncertainties relate to both modeling and the variety of assumptions for future emissions, population, deforestation, etc. The effects of change are highly dependent on location: global averages may be less significant than local influences. Many of the effects of climate change are related to causes in irregular, non-linear ways, that are a source of great uncertainty that can lead to both 'runaway' effects (positive feedback) or buffering or self-controlling (negative feedback) effects. Thus higher average temperatures are expected to drive more dynamic hydrologic systems - this could mean greater degrees of flooding or drought in some areas, with lesser degrees in others.

WHAT IS SO UNUSUAL ABOUT PRESENT CLIMATE CHANGE?

One of the dangers of non-linearity in climate systems is the uncertainty of prediction outside the range of past changes. This becomes a matter of concern when the present rate of increase of average global temperature is estimated - by some - to be orders of magnitude higher than anything the Earth has felt in the last several tens of thousands of years. Will there be a disastrous runaway effect that has not been predicted? How long can global warming at current rates go on before Earth suffers more surface temperature change than it has ever experienced?

What can, and should, be done in response to these questions is to examine the geological record, as a way of testing the assumptions. Let us look at a couple of geological perspectives on this.

PAST AVERAGE GLOBAL TEMPERATURES: NATURE'S WILD SWINGS

The Earth is 4600 million years old. For the first half of its life, the atmosphere was dominated by volcanic gases, particularly carbon dioxide, and there was no, or only little, free oxygen. Surface temperatures may have been as high as 60°C. The gradual removal of carbon dioxide from the atmosphere to become trapped in limestones, and release of oxygen from algae, caused a gradual cooling and the evolution of more advanced life forms. Extreme cooling, perhaps triggered by plate tectonics - the motion of continents and oceans across the Earth's surface - resulted in 'snowball Earth', during a period halfway back through Earth history when the oceans froze over for around 10 million years, until volcanic eruptions returned enough carbon dioxide to the atmosphere to warm it and melt the ice. During the last 12% of Earth history, since 550 million years ago, life has flourished in an atmosphere much like today's. But even during this time there have been catastrophic events - major volcanic eruptions and meteorite impacts - that have caused major cooling - perhaps by several degrees - that killed off many species. There have also been a couple more glacial periods - not as severe as snowball Earth: we are still in the last one.

These variations from ice ages to intervening hot houses appear to involve changes in average surface temperature of around 10°C, related to carbon dioxide concentrations in the atmosphere that probably vary according to the dynamics of plate motions and the resultant volcanism.

The younger record of Earth is better resolved (Figure 1). There is more evidence for change on these short time scales, from the geology of marine sediments and from cores of ancient ice recovered from the large ice caps of Greenland and Antarctica. Oscillations in surface temperature over a few tens of thousands of years can be related to variations in Earth's orbit; and they can be of high amplitude, +/- 4°C.

In summary, Earth's surface temperature decreased slowly by tens of degrees during the first half of its history, and has oscillated on various time scales since by amounts of up to 10 degrees. Nature's changes have exceeded the few degrees of global warming in current forecasts.

PAST RATES OF GLOBAL TEMPERATURE CHANGE: AS RAPID AS TODAY'S?

Is the present rate of global temperature change so much greater than the Earth has felt before? The present rate of change is estimated to be on the order of 0.5 for the last century, and may increase to 1-5°C over the next one. How does this compare with past rates? Figure 1 shows a summary of temperature change estimated for the current ice age. In the last interglacial, 130,000 years ago, temperature rose by around 8 over a few thousand years, certainly not far below the last century's rate of increase. The figure also shows a relatively rapid rise to the present interglacial starting around 18,000 years ago. Recent work has shown that within this rise, at around 11,600 years ago, temperature rose by as much as 4°C in as little as 10 years.

Such changes appear to be more rapid than the Milankovitch cycles that are responsible for most of the oscillations in Figure 1.
Other rapid changes, with frequencies of occurrence greater than the Milankovitch cycles, have also been recognized: Heinrich events, for example, appear to relate to rapid influxes into the ocean of ice from large ice caps. Rapid influxes of freshwater can cause the patterns of ocean currents to change. This is because the global ocean flows are maintained by convection. A downflow, as occurs at the northeast Atlantic extreme of the Gulf Stream, is maintained by the higher density of cooling saline water moving at the surface from the south. Such downflows can be suddenly stopped by the addition of sufficient low density freshwater. This is one example of how non-linearity can accelerate change.

It appears to be increasingly clear that nature is capable of changing Earth's environment quite rapidly. It is no longer tenable to argue that the present rate of temperature change is so unnaturally rapid as to be caused primarily by human influence.

We have learnt that nature can change the Earth's surface temperature quickly and by large amounts. We still do not have precise enough models of the complex series of interacting processes to enable us to make adequate predictions of climate change. The climate change debate has leveraged enough funding to make steady - in some cases, spectacular - progress over the last decade. This progress must be accelerated if we wish to refine modeling capabilities in a time frame of a decade or two to improve our forecasting abilities by the order of magnitude that seems to be required.

WHAT SHOULD GOVERNMENTS DO TO HELP THE RESEARCH EFFORT?

The federal government is responding well to the challenges of climate change. It is a global concern, with major national implications, from the worries of sea level rise and erosion along our shores, to the complications of melting permafrost on northern infrastructure. Efforts to adapt to, and mitigate against, further climate change are worthy. We note some exciting prospects for underground disposal by absorption in rock of combustion gases that are a primary source of human-induced change (however large that might be!). Nature is capable of surprises - major volcanic eruptions, for example, cause immediate cooling because of the shielding effect of ash clouds. The Little Ice Age of medieval times caused famine and large scale human migration in Europe. We need to improve our abilities to predict responses to both these kinds of changes - transient and cyclical. We need improved modelling, which can only be based on better parameterisation of the processes involved. Canadians are at the forefront of computer modelling of climate change, and are actively involved in collecting data for case studies, especially of the high-resolution records obtainable from marine sediments and ice studies. We have the scientific capabilities, but need enhanced support for them. For instance, some of the best sites for obtaining high resolution records of past climate change are in deep water off our shelves; others are in rapidly-sedimented marine basins and fjords. Enhanced participation in the international Ocean Drilling Program (ODP) would bring Canadians a wealth of new information on both global and national processes relevant to this issue. Canadian scientists were extraordinarily successful in obtaining cores from the recent ODP drilling leg in Saanich Inlet (B.C.), and the proposed ODP drilling in the Saguenay Fjord, in Quebec, would add an essential eastern Canadian complement to this.

Provincial governments should also contribute, where appropriate, to this research mission, by empowering their geological surveys to contribute to the parameterization of climate change processes by detailed study of local phenomena. Again, there is strong capability to carry out such studies among the few scientists engaged by those organizations for superficial and Quaternary geology. More effort here would be valuable, and can be justified in the contributions to land use issues implicit in the deliverables from such work.

The most effective way to intensify the Canadian science effort on climate change would be through the establishment by Ministers of a forum of Federal and provincial governments, academia, and the private sector, mandated to recommend a cohesive national program of understanding the processes of climate change: the geological record awaits our further attention and nowhere is it more abundantly provided than in our Canadian landmass and its surrounding waters. Ministers may wish to consider a parallel effort to review the impacts of climate change on groundwater resources. This would be timely in reacting to the effects of local climate 'wobbles' (remember this year's drought in Pennsylvania and Ohio). Water is a mineral resource that is clearly becoming more precious to Canadians: it is a commodity of concern to the provinces; and it is a national issue (should we export it?). There is adequate expertise in government, academia and the private sector to mount a substantial multi-partner project on this topic.

Appendix 1

Some of the main conclusions of the Summary for Policymakers of Working Group I of the IPCC Second Assessment Report, published in 1995, which concerns the effects of all anthropogenic emissions on climate change, follow:

Increases in greenhouse gas concentrations since pre-industrial times (i.e., since about 1750) have led to a positive radiative forcing of climate, tending to warm the surface of the Earth and produce other changes of climate.

The atmospheric concentrations of the greenhouse gases carbon dioxide, methane, and nitrous oxide (N₂O), among others, have grown significantly: by about 30, 145, and 15%, respectively (values for 1992). These trends can be attributed largely to human activities, mostly fossil fuel use, land-use change, and agriculture.

Many greenhouse gases remain in the atmosphere for a long time (for carbon dioxide and nitrous oxide, many decades to centuries). As a result of this, if carbon dioxide emissions were maintained at near current (1994) levels, they would lead to a nearly constant rate of increase in atmospheric concentrations for at least two centuries, reaching about 500 ppmv (approximately twice the pre-industrial concentration of 280 ppmv) by the end of the 21st century.

Tropospheric aerosols resulting from combustion of fossil fuels, biomass burning, and other sources have led to a negative radiative forcing, which, while focused in particular regions and subcontinental areas, can have continental to hemispheric effects on climate patterns. In contrast to the long-lived greenhouse gases, anthropogenic aerosols are very short-lived in the atmosphere; hence, their radiative forcing adjusts rapidly to increases or decreases in emissions.

Our ability from the observed climate record to quantify the human influence on global climate is currently limited because the expected signal is still emerging from the noise of natural variability, and because there are uncertainties in key factors. These include the magnitude and patterns of long-term natural variability and the time-evolving pattern of forcing by, and response to, changes in concentrations of greenhouse gases and aerosols, and land-surface changes. Nevertheless, the balance of evidence suggests that there is a discernible human influence on global climate.

The IPCC has developed a range of scenarios, IS92a-f, for future greenhouse gas and aerosol precursor emissions based on assumptions concerning population and economic growth, land use, technological changes, energy availability, and fuel mix during the period 1990 to 2100. Through understanding of the global carbon cycle and of atmospheric chemistry, these emissions can be used to project atmospheric concentrations of greenhouse gases and aerosols and the perturbation of natural radiative forcing. Climate models can then be used to develop projections of future climate.

Estimates of the rise in global average surface air temperature by 2100 relative to 1990 for the IS92 scenarios range from 1 to 3.5°C. In all cases the average rate of warming would probably be greater than any seen in the last 10,000 years. Regional temperature changes could differ substantially from the global mean and the actual annual to decadal changes would include considerable natural variability. A general warming is expected to lead to an increase in the occurrence of extremely hot days and a decrease in the occurrence of extremely cold days.

Average sea level is expected to rise as a result of thermal expansion of the oceans and melting of glaciers and ice-sheets. Estimates of the sea level rise by 2100 relative to 1990 for the IS92 scenarios range from 15 to 95 cm.

Warmer temperatures will lead to a more vigorous hydrological cycle; this translates into prospects for more severe droughts and/or floods in some places and less severe droughts and/or floods in other places. Several models indicate an increase in precipitation intensity, suggesting a possibility for more extreme rainfall events.

CGC Home Page

A Brief to the Ministers of Mines and Energy