Scientific Symposium Presentation Abstracts
September 19
Dr. Michael MacCracken: Welcome and Opening Remarks
Heat waves. Drenching rains. Disappearing glaciers and retreating Arctic sea ice. Western drought and extensive wildfires. Ice shelf collapse and melting nearing the top of the Greenland Ice Sheet. Unprecedented occurrence of powerful hurricanes causing extensive coastal erosion. An increased rate of sea level rise. Deforestation, land cover change and loss of species. Headline after headline reporting on global warming and the changing climate. Are we experiencing just natural fluctuations, or are human activities at least in part, and perhaps in large part, responsible for these events? What more can lie ahead?
Scientific studies, summarized and evaluated most comprehensively and credibly in periodic assessments prepared by the UN-sponsored Intergovernmental Panel on Climate Change (IPCC), project that continuing reliance on fossil fuels to supply most of the world’s energy will lead to an increase in the global average surface temperature of roughly 1.4 to 5.5ºC (about 2.5 to 10ºF) by the year 2100, adding to the observed increase of about 0.6ºC (about 1.1ºF) over the 20th century.
Having just survived a summer that was several degrees warmer than average, why should we be so concerned about a projected global average temperature increase of a few degrees over the course of the 21st century? Are not climatic conditions that we will face in 100 years not a lot different than the conditions that prevail several hundred miles to the south; why should we be concerned if Washington, DC’s climate becomes like that of Atlanta? With daily temperature variations being twenty degrees or more, and winter to summer differences in the daily average temperature being forty degrees or more, can we not over time redo our buildings and infrastructure to readily adapt to a few degree rise in the annual average temperature? Why is there so much concern?
The first reason for concern is that, while the changes in the average conditions may seem small in comparison to every day experience, these changes are large in the context of long-lasting changes in the global climate. Over the time span of human civilization, the increased warmth and rate of climatic change over the 20th century was unusually large; for the present century, the changes in climate are likely to be several times larger, and the average temperature is expected to be as much warmer than the past century as the ice ages were colder than the last century. With the warming expected to be larger than average in middle to high latitudes as compared to the tropics, larger over land areas as compared to oceans, and larger in winter as compared to summer (except in areas that are dried out by summer warming), significant impacts on natural and managed ecosystems and on water resources are likely in many critical regions. While adaptation to such changes in one place or for one year may be possible, just as the US and Europe survived the heat this past summer, a multitude of changes simultaneously occurring around the world and persisting for decades (and longer) will create a very challenging situation.
The second reason for concern is the accelerating pace of change, especially because of the potential this creates for thresholds to be crossed. If we could be assured that changes in climate and the associated impacts would occur slowly and steadily, the potential would exist for orderly adaptation, even if this became expensive. The problem is that there is a substantial risk that the changes will not be smooth, slow, or always as we expect them to occur. Climatic history provides a number of indications that some types of changes can occur abruptly and suggests that “tipping points” may exist that could lead to very large impacts occurring, once thresholds are crossed or particular conditions arise.
The purpose of this symposium is two-fold: first, to explore a number of these potential risks; and second, to evaluate the societal vulnerability, especially in the event that the changes occur at an accelerated rate or in an abrupt manner. Among the topics that will be covered are the following:
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The Pace of Climate Change: Scientific studies over the past 25 years have made clear that the sensitivity (responsiveness) of the climate to higher concentrations of CO2 and other greenhouse gases is unlikely to be lower than the lower bound of what has been incorporated into the IPCC’s estimates, but could well be greater than the upper bound that has been used. Recognizing that much warmer climates have existed in the Earth’s distant past, what is the risk that the climate will be transformed even faster than the IPCC assessments have been indicating?
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The Pace of Sea Level Rise: Global sea level is estimated to have risen almost 0.2 m during the 20th century, and recent satellite records suggest that the rate of rise has recently jumped upward, presumably as a result of more rapid ocean warming (causing greater thermal expansion) and accelerated melting of mountain glaciers and the edges of the Greenland Ice Sheet. The recent collapse of the Larsen-B ice shelf, and the consequent acceleration of glacial streams that the ice shelf was holding back, suggest that the decay of grounded ice could be much more rapid than has traditionally been assumed. With the Greenland and West Antarctic ice sheets each containing the equivalent of about 6 meters (about 20 feet) of sea level rise, what degree of warming will prompt their loss and how rapidly could this occur?
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The Pace of Ecosystem Transformation: From southeastern and northeastern forests to the grasslands of the Great Plains and deserts of the Southwest, the climate determines the prevailing ecosystem and, to a large extent, the potential for agriculture. As the climate changes, it is often suggested that existing systems will slowly move or seamlessly evolve into new systems with no disruption in the services the ecosystems provide. However, there are a number of examples of pests, disease, and fire accelerating the changeover from one system to another. With evidence indicating that the loss of ecosystems, or at least their key species, can occur much more rapidly than their reestablishment, what is the potential that rapid changes in ecosystems will significantly disrupt biological diversity and the other ecosystem services society depends on?
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The Pace of Human Health Impacts: Societal well-being has benefited greatly as advances in medicine and community structure have been able to separate most people in developed nations from the scourge of many diseases. However, the most threatening environmentally dependent diseases continue to ravage the warmest nations. What is the risk that global warming will increase the incidence of disease in currently plagued regions and foster its development in other regions through human carriers?
These and other questions will be addressed by leading scientists during the scientific symposium, convened in celebration of the Climate Institute’s 20th anniversary.
