I believe that most of us harbor at least a secret passion for science. We find science intriguing, fun, satisfying. Much has also been made of the utilitarian value of science to our society in providing the knowledge to conquer diseases, improve our lives through technology, and fuel our economies. There is another vitally important, though often overlooked benefit from science - specifically, knowledge that helps us understand how the world works and what might be the likely consequences of different choices. This scientific understanding should be readily available to inform our decision whether the decisions are ones made by individuals or by institutions. The more informed the decisions are, the better they will be. I am not suggesting that scientists should dictate what individuals or societies should do or not do. Rather, I emphasize that one of the most important roles of science is to inform, to provide information, so that decision-makers can take that information into consideration and understand the full ramifications of a course of action.

These points are particularly relevant today simply because our world is changing at breakneck speeds. The new kinds of information that we are gaining through scientific research are also increasing at tremendous rates. Consequently citizens are faced with the duel challenges of needing more information but also making sense of an often overwhelming amount of information. The challenges to the scientific community are to advance the frontiers of knowledge as well as to communicate the resulting information effectively to citizens or policy makers who wish to use that knowledge to inform their decisions.

In most cases, decisions must be made despite uncertainty, and many times in the face of conflicting evidence or opinions. Complicating matters further, information is often distorted or misrepresented, deliberately and accidentally. How then, can those who want good, credible scientific information gain access to a balanced, trustworthy summary of the facts and a knowledgeable evaluation of the less certain but relevant information?

One key is to rely on assessments emerging from credible groups of scientists. Fortunately, some mechanisms are in place to assess the state of scientific knowledge on policy- or management-relevant topics. The National Research Council of the National Academy of Sciences (http://www.nrc.edu) provides scientific information and guidance to Congress, the President, federal and state agencies and citizens. The United Nations and the non-governmental Scientific Committee on Problems of the Environment of ISCU, the International Council for Science (www.icsu.org) convene international expert panels on policy-relevant issues. Professional scientific societies such as the Ecological Society of America (www.sdsc.edu/~ESA) produce white papers on specific issues. All of these mechanisms produce credible, useful summaries on a range of topics.

Although these sources are vitally important, they are insufficient to provide all of the information that is sought. I believe that citizens would benefit greatly from comparable credible scientific assessments provided on a more local basis. To be useful and effective, such assessments must be produced by credible, independent bodies through a credible process. The goal is simply to summarize the relevant, often technical and complex information in an understandable, useful fashion. An assessment should help sort out what is actually known, not known, what do most experts agree upon, where are the uncertainties, what are the like consequences of different policy options, etc.

Assessment of climate change is a good example of the problem that decision makers face. One hears conflicting opinions: on the one had, "global warming is happening;" on the other hand someone else says, "oh no, that's not true." It's very difficult for most folks to sort through all the conflicting opinions and complex evidence. In its zeal to be "balanced," the press often presents "both sides" with equal credibility, despite the fact that the overwhelming majority of experts agree and are on one "side." Fortunately, a credible international scientific assessment of climate exists and sheds considerable light on the topic.

The Intergovernmental Panel on Climate Change or IPCC was established by governments specifically to review and evaluate the scientific information about climate change. This panel includes the world's premier climate experts: practicing and competent climatologists, atmospheric scientists, oceanographers, ecologists, etc. who represent the range of scientific disciplines immediately relevant to understanding global warming, climate change and the likely consequences. The scientists participating in the IPCC publish actively in the peer-reviewed scientific literature and are recognized authorities. The IPCC operates under a set of well defined rules which ensure the credibility of the process and the product. All information is carefully, rigorously, painstakingly examined, reviewed and re-reviewed. All chapters are peer-reviewed by climate experts. In all, over 2000 scientists have participated. The process has been deliberative; the participants err on the side of caution.

Building on earlier reports, the 1995 IPCC Scientific Assessment drew considerable attention. It lays out explicitly what is know and what is not known and with what degree of certainty. The report doesn't just say "this is what we know, this is what we don't know," but it looks at hierarchies of certainly, "this is what we are more certain of, this is what we're less certain of" and then explores the likely consequence of different policy options. That format is a nice model for scientific assessments in general, in part because it helps provide the most useful information.

What does the 1995 IPCC Scientific Assessment tell us about climate? First, it says that climate over the past century has been warming. Measurements document an increase of the average global temperature of the planet of one degree Fahrenheit over the last century. Most of this warming has transpired over the last 20 years, with the hottest years on record occurring since 1980. (Since the 1995 IPCC report was published, new records have been set, with 1998 now the hottest on record.) Second, the IPCC says, "The balance of evidence suggests a discernible human influence on climate." This is typical, careful, cautious language which translates as follows: Human activities are probably influencing these global increases in temperature. Third, the IPCC says that if we continue on the current trajectory of increasing these heat trapping gases in our atmosphere then we are quite likely to see an additional warming of the planet on the order of two to six degrees Fahrenheit over the next century. The report is very clear about those conclusions.

The uncertainties concerning climate change include how fast the planet will warm, exactly how much it will heat up, how this warming will play out on a regional basis, and how the ecological systems of the planet will respond. Nobody knows the definitive answers to these questions because we've never run this "experiment" before. Human actions have inadvertently initiated a completely novel scenario. The real question is whether or not we wish to continue running this experiment. Our best predictions of likely scenarios are fraught with uncertainties - and we're as likely to underestimate the severity of the consequences as overestimate them.

Many changes measured by scientists over the past century are consistent with the IPCC model predictions. For example, we're already seeing evidence of the speeding up of the water cycle of the planet. As the average temperature of the earth increases, there should be an increase in rates of evaporation. More water in the atmosphere is then available for precipitation. The resulting predictions of increases in both droughts and floods is already being seen. There is every reason to expect further increased amplification of the hydrological cycle with concomitant increases in both floods and droughts. Please note that I am not suggesting that we can point to any single flood or drought and say with certainty "this was caused by climate change." What we can say is that the increase in the number of extreme precipitation events seen in the last decade is fully consistent with our understanding of how the climate system works. Moreover, in our best judgment, the frequency and intensity of these extreme events is likely to increase.

Climate models predict two other consequences of a warmer planet which are also already happening. An increase in the geographic expansion of certain diseases is predicted and is being observed. Human diseases now limited to the tropics, for example malaria and dengue fever, are expanding into formerly subtropical regions. Sea level is expected to rise as the water in the oceans expands because it's warmer and as glaciers and ice from the poles melts and contributes more water to ocean basins. Over the last century sea level rose between 4 and 10 inches. The "Business as Usual" scenario of the IPCC predicts an additional 6 inches to 3 feet vertical sea level rise over the coming century.

How the ecosystems of our planet will respond to these changes is far from certain. These ecosystems provide our food, fiber, genes, many medicines and a wide range of services upon which we are intimately dependent. Ecosystems ranging from grasslands to forests, coral reefs to estuaries, agricultural lands to riparian zones are complex. Accurate predictions about their responses are difficult. We have better information for some systems than others. Studies suggest that fully one third of the forests of the planet are likely to undergo drastic alterations in the particular species of trees that are present in those forests. As climate zones move poleward, individual species will respond differently. For example, sugar maples in New England forests would no longer tolerate the warmer New England climate and would probably exist only in Canada. Consider the consequences to New England of the loss of fall color, tourist dollars and maple syrup and sugar, not to mention the ecological role played by these trees in their ecosystems.

The responses of other ecological systems to climate change is an area of active scientific investigation. We know from past climate changes that entire ecological communities or ecosystems do not simply move as a cohesive unit toward the new climate zones. Thus, US grasslands, forests, and deserts would not simply shift boundaries and go farther north. Rather different species within those ecosystems will respond differently to changes in temperature, in precipitation, in biogeochemical cycles, in pollinators, in soil organisms, in pests, etc. What these changes mean for the continued provision of critical ecosystem services is not known.

To summarize this brief summary of climate changes, it's clearly erroneous and patently ridiculous for anyone to assert that there is no scientific certainty in this area. The IPCC represents the collective expertise and judgement of over 2000 of the most knowledgeable climate scientists in the world. Their conclusions carry substantial weight and are the definitive assessment. The IPCC process is an ongoing effort and will continue to provide new information on which to base our understanding and choices. Moreover there is tremendous consensus within the even broader scientific community which supports the IPCC conclusions: we are already seeing warming, it is due in part to human activities, further release of heat trapping gases into the atmosphere (primarily carbon dioxide from our smoke stacks and tailpipes) is likely to cause very serious disruption, and this is not an experiment that we want to continue with the current vigor.

Global warming is only one of many different global-scale changes that are currently underway. Global warming has garnered a tremendous amount of attention, but it is far from the only change that should concern us. I would like to shift gears now and focus attention on a few of these other changes because we need to think about them in concert.

Last summer three of my colleagues and I published a paper in the journal Science, which is published by the American Association for the Advancement of Science (Vitousek, P.M, H.A. Mooney, J. Lubchenco, and J.M. Melillo. 1997. Human domination of earth's ecosystems. Science 277: 494-499.) In that article, we attempted to evaluate all of the different global-scale changes for which we could actually get good, reliable numbers. We wanted to provide a credible overview of factual changes. We wanted to document what was happening, not just make assert about what might be happening. I'd like to draw from that paper six changes to illustrate the point that we now live on a human dominated planet.

These six global indicators of change include: (1) Humans have increased the concentration of carbon dioxide in our atmosphere by thirty percent since the beginning of the Industrial Revolution. Carbon dioxide, of course, is the major greenhouse gas, and it is the consequences of these increases that occupied my earlier remarks and the subject of the IPCC assessment. It's important to note that no one disputes the 30% increase in CO2 figure. The rise is well known. Moreover, we can "fingerprint" the CO2 to ascertain its origin: primarily from the burning of fossil fuels.

(2) The second change concerns the extent to which human activities have modified the land surface of the planet. The jargon term for this is "land transformation." It means changing an old growth forest into a tree plantation, tall grass prairies into shopping malls or into cornfields, grasslands into cities - in short, changing the surface of the planet from some ecosystem that used to be there to another that suits human needs of one kind or another. Humans have always changed their landscape. This is something that we have done to make the planet more livable, to provide our food, to provide our shelter, etc. I'm not suggesting that there is anything intrinsically wrong with transforming landscapes. The question we posed was simply, "What is the magnitude of land transformation?" The answer may surprise you: Humans have now transformed between one-third and one-half of the land surface of the planet. That's a sizeable footprint!

(3) Humans currently use more than half the available surface fresh water on our planet. In view of the explosive growth rate of the human population and projected needs for water for direct human use, agriculture and industry, it's easy to understand why some have predicted that water will be one of the central issues of the new millennium.

The fourth global-scale indicator deals with a biogeochemical cycle, specifically that of nitrogen. Let me explain the context so you may better appreciate the importance of the changes. There is plenty of nitrogen in our atmosphere, but it is not generally available to plants because it's in the wrong chemical form. Bacteria, algae and lightening are the agents by which nitrogen is naturally "fixed" or modified chemically so it is available to plants. Humans fix nitrogen deliberately when we synthesize fertilizers and accidentally when we burn fossil fuels. At the beginning of the last century, the non-anthropogenic sources (algae, bacteria, lightning) were responsible for the vast amount of nitrogen fixed annually. Now, human activities (making of fertilizers, burning of fossil fuels and the planting of legumes over broader areas than they would have occurred naturally) have more than doubled the amount of nitrogen that is fixed, or put differently, the nitrogen that enters into the nitrogen cycle each year.

Why is increased fixed nitrogen a problem? Isn't it good to enhance crop growth? Certainly more crops are desirable and necessary. The problem emerges because much of the nitrogen is not used by the intended plants (crops, grass on golf courses, lawns, etc), but is washed away, flowing down rivers and streams and often into coastal ocean waters. Some of the fixed nitrogen is transported via a different route: it is volatilized into the air, transported then deposited elsewhere on land or in the oceans. This vast amount of additional nitrogen is now disrupting many ecological systems in ways that we are just beginning to understand. We are literally changing the chemistry of our waterways and coastal oceans and beginning to document a wide variety of correlated changes. Increases in harmful algal blooms including some red tides and increases in dead zones such as the one in the Gulf of Mexico are possible results. We know that many (though not all) of the microscopic algae that are involved in harmful algal blooms are stimulated by increases in nitrogen and other nutrients. We have yet to unravel all of the consequences of the vastly modified nitrogen cycle, but the early indicators are that we won't like the results.

(5) More than two thirds of the major marine fisheries of the world are currently being fully exploited, overexploited or depleted. Many of the disruptions in fisheries that we have witnessed here are happening globally.

(6) The sixth indicator one has to do with the rest of life on earth. We are in the early phases of the sixth mass extinction event of species on this planet. Unlike former mass extinctions, this one is due to the influence of human activities, however unintended. It's difficult to measure the rates of loss for most species, but we have excellent estimates for large-bodied, well known groups. We can document that more than a quarter of the birds that have been alive on the planet are now extinct due primarily to human activities. Habitat destruction, invasive species, overfishing and other changes are the major forces driving these extinctions.

The clear message from these six indicators is that we now live on a planet that is dominated by human activities. This domination is simply a result of the kinds of activities in which we are engaged. The point here is not "oh, we're terrible" but simply that we need to wake up, be aware of the inadvertent consequences of our activities, and modify our individual and collective actions if we don't like the current trajectory. Humanity is now changing the planet at faster rates, over broader scales, and in fundamentally new ways than ever before. Now is a very different time than any other time in the history of humans on earth.

The explosive growth of the human population, the unsustainable rate at which we're using resources and generating wastes, the increased inequity within and among every country are collectively responsible for these massive global changes. Ignorance, greed, arrogance and despair exacerbate the problems. I find the six global indicators very sobering. Most of our thinking about the world doesn't really recognize the magnitude of these changes, the time-lags inherent in addressing the problems or the urgent need for smarter and more equitable ways of living.

Because we are capable of understanding what we're doing, it's appropriate for us to take stock of these changes and to ask what other choices we have. With respect to climate, the answer is pretty straightforward. We need to figure out ways to wean ourselves from fossil fuels and to switch to other types of energy. This does not mean totally changing our lifestyles. It does not mean going back to the dark ages. It means being smarter about how we go about our business.

I ask you to think about your list of the "forces of nature." Hurricanes, floods, droughts, volcanoes -- massive, geological, atmospheric cataclysms that humans have always feared --probably come to mind. From what I've said so far, it should be obvious that we now have a new force of nature on the planet -humanity. And with that power comes responsibility -- responsibility to manage our activities in a way that minimizes this impact, not only for us, but especially for our children and grandchildren. The reason that many of these changes are so important is that they threaten the life support systems for all of life on our planet, not just for humans.

Think now about how you depend on nature. Most folks will focus on the goods that we get from nature: food, fiber, genes, medicine -- the things, or goods, that we get from nature. Most of us are unaware of the services that are provided to us by the ecological systems of the planet. We're generally unaware of them because they've always been there. We take them for granted. These services include things such as the purification of air and water, flood control, the provision of fertile soil, the provision of pollinators, pest control, even the regulation of climate. These are all services that are provided by different ecological systems -- forests, grasslands, deserts, wetlands, coral reefs, kelp forests, estuaries, etc. Each of those different ecosystems provides services to humanity. We take these services for granted. We don't buy and sell and trade these services like we buy and sell and trade the goods. Decisions about how to use land, how to use water, how to use resources are based primarily on a consideration of the relative costs and benefits of the goods, not of the services. Here is another area ripe for new thinking, new accounting, new opportunities for positive change. Some economists and ecologists working together are beginning to attempt to assign monetary value to certain services and thereby develop new mechanisms to incorporate both their importance and their abundance into existing decision making processes. This an area where there is a tremendous amount of exciting research going on at the interface between ecology and economics and it has very real and important implications for all of us.

One example of the economic value of a particular ecosystem service is relevant to water quality issues in Oregon. As water moves through watersheds, the microbial action in the soils provides a very important service of detoxifying or sequestering pollutants. Another service provided by forests is that of sediment control, or filtration. Drinking water for the city of New York has historically been provided by the Catskill watershed. The drinking water for the city used to be of such pure quality that it was bottled and sold. The watershed, like most other forested areas close to cities, has undergone significant change and land transformation: agricultural changes, urban development, industrial development, etc. Recently, the quality of the drinking water dipped below EPA drinking water minimum standards. Two economists at Columbia University, Geoff Heal and Graciella Chichilnisky conducted a fascinating analysis of the options available to the city ( Chichinisky and Heal. 1998. Economic returns from the biosphere. Nature 391:629-630.) They calculated the cost of two options. The first was to buy and restore the watershed and let the watershed provide the service. The other option was to build and maintain a water purification/filtration plant. The cost of buying and restoring the watershed was 1-1.5 billion dollars. The cost of building the water purification/filtration plant was an initial capital cost of 6-8 billion dollars, plus annual operating expenses of 300 million dollars. This stark contrast gives us an entirely new way of appreciating the services provided by watersheds. The city has now opted to invest in natural capital by buying land and protecting the watershed. This, then is a single example of an ecosystem service that provides critical health benefits at enormous economic savings relative to the alternatives. Moreover, the Catskill watershed provides more than that single service.

This topic of ecosystem services is a relatively new one with important ramifications across many topics. It is obviously relevant to cities as they decide where and how to grow. As we make choices about land-use, we need to think not only of the goods, but also the services provided by ecological systems. A brief description and further examples of ecosystem services can be found at http://www.sdsc.edu/~ESA/issues, or in Yvonne Baskin's book The Work of Nature, published in 1997 by Island Press. The area is undergoing rapid development in the scientific area, especially as a new interface between the scientific areas of economics and ecology.

E.O. Wilson, the famous biologist at Harvard University, has suggested that humanity is on the verge of entering the Century of the Environment. I echo his words, and have suggested further that we are in the process of expanding our thinking about "the environment." (Lubchenco, J. 1998. Entering the Century of the Environment: A New Social Contract for Science, Science 279:491-497, http://www.sciencemag.org/cgi/content/full/279/5350/491 ) We are beginning to understand that human health is an environmental issue, that social justice is an environmental issue, that the economy is in reality an environmental issue, and even national security is an environmental issue. As we begin to appreciate the fundamental ways that humans are dependent upon the functioning of intact ecological systems of the planet, we realize that those systems provide not only goods but the services that collectively are our life support systems. These life support systems determine our health, our economies and our future in ways we are only beginning to appreciate. In sharing with you some recent findings from the scientific community about global scale changes including climate change, I have attempted to help inform the decisions you will make in your various roles. My hope is that as we enter this Century of the Environment, we will do so in a way that's more cognizant of the power that humanity currently wields but also the power we have to modify our activities in ways that will provide for future generations with the quality of life that we treasure.