18 March 2005
Warming And Sea Level Rise Inevitable
by Kate Melville
Climate modelers from the National Center for Atmospheric Research (NCAR) have quantified the rates of sea level rise and global temperature increase that we will see in the 21st century. They say that even if no more greenhouse gases were added to the atmosphere, globally averaged surface air temperatures would rise about a half degree Celsius (one degree Fahrenheit) and global sea levels would rise another 11 centimeters (4 inches) from thermal expansion alone by 2100. The study appears in the journal Science.
"We are committed right now to a significant amount of global warming and sea level rise because of the greenhouse gases we have already put into the atmosphere," says Gerald Meehl, lead author of the study. "Even if we stabilize greenhouse gas concentrations, the climate will continue to warm, and there will be proportionately even more sea level rise. The longer we wait, the more climate change we are committed to in the future."
The inevitability of the climate changes described in the study is the result of thermal inertia, mainly from the oceans, and the long lifetime of carbon dioxide and other greenhouse gases in the atmosphere. Thermal inertia refers to the process by which water heats and cools more slowly than air because it is denser than air. The new study is the first to quantify future committed climate change using "coupled" global three-dimensional climate models. Coupled models link major components of Earth's climate in ways that allow them to interact with each other. The scientists also compared possible climate scenarios in which greenhouse gases continue to build in the atmosphere at low, moderate, or high rates. The worst-case scenario projects an average temperature rise of 3.5& #176;C (6.3& #176;F) and sea level rise of 30 centimeters (12 inches) by 2100. Though temperature rise shows signs of leveling off 100 years after stabilization in the study, ocean waters continue to warm and expand, causing global sea level to rise unabated.
The researchers said that these numbers did not take into account fresh water from melting ice sheets and glaciers, which could at least double the sea level rise caused by thermal expansion alone.
"With the ongoing increase in concentrations of greenhouse gases, every day we commit to more climate change in the future. When and how we stabilize concentrations will dictate, on the time scale of a century or so, how much more warming we will experience. But we are already committed to ongoing large sea level rise, even if concentrations of greenhouse gases could be stabilized," concluded Meehl.