Climate change is often headline news these days, in large part out of concern that the human emissions of greenhouse gases - notably carbon dioxide, methane, nitrous oxide and other trace gases - may be altering the Earth's climate, leading to warmer atmospheric temperatures, rising sea level and other climatic anomalies.

Detecting this long-term climate change, though, requires that scientists first understand climate patterns that take place on an annual, or decadal, scale which cause great variability in temperature and rainfall.

The impacts of long-term climate change on mid-Atlantic region temperatures and precipitation over the next 50-100 years are still a fertile field for research. Nonetheless, climate impacts on Bay hydrology, coastal zones and living resources could be larger in magnitude than any climate changes in recent centuries according to climate changes predicted by computer models.

We hear much about the uncertainty surrounding the ability of climate models to project future climate changes for the next century because of increasing atmospheric greenhouse gas concentrations. But concerns about long-term global-scale warming have increased, in part because of work by an international group of thousands of the world's leading scientists under the auspices of the Intergovernmental Panel on Climate Change.

In a recent report, the IPCC reached a number of conclusions, including:


  • Greenhouse gas concentrations have continued to increase (carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), by 30 percent, 145 percent and 15 percent, respectively, since 1750.


  • Anthropogenic aerosols (airborne particles resulting from the burning of fossil fuel, biomass burning and other sources) tend to produce cooling locally that can offset warming from greenhouse gases.


  • Climate has changed during the past century. Global mean surface air temperature has increased 0.3 to 0.6 degrees Celsius since the late 19th century; recent years have been among the warmest on record.


  • Global sea level has risen 10-25 centimeters the last century because of the thermal expansion of the ocean surface and the melting of alpine glaciers.


  • "The balance of evidence suggests a discernible human influence on global climate." The 20th Century global mean temperature was at least as warm as any century since A.D. 1400 and probably further back.


  • Assessment of paleoclimate data, statistical analyses of observational records, and simple and complex climate models all suggest temperature trends are unlikely to be due to natural climate variability.


  • Climate is expected to continue to change in the future. Depending on many complex, and sometimes uncertain factors, such as the future contribution of sulfate aerosols and carbon emissions, climate models project future global mean surface air temperature to rise 1.5 to 3.5 degrees Celsius, with a best estimate of 2 degrees Celsius, and sea level to rise between 15 and 95 cm, with a best estimate of 50 cm (just over 6 inches).


  • There are still many uncertainties in scientists' ability to project future climates, especially with regard to regional climate changes.