TJ Blasing traces how scientists know what they know about the Earth system
At the invitation of the Kingston Rotary Club, physical scientist TJ Blasing of the Climate Change Science Institute at Oak Ridge National Laboratory spoke about the global effect of rising greenhouse gases on May 14 at the Two Chefs Deli in Kingston, Tenn. The primary greenhouse gases in Earth’s atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, ozone, and several halogenated species (e.g., CFC-11, CFC-12). Blasing shared with an audience of about 30 how scientists arrived at the answers to four questions about the Earth system: Are greenhouse-gas concentrations increasing? Are humans causing these increases? Is the planet’s average near-surface air temperature increasing? Is the relationship between greenhouse gas increases and near-surface air temperature strong enough to influence climate? (The answers are yes, yes, yes and yes.)
“We know that greenhouse gases are an important contributor to climate change, and we know they are increasing,” said Blasing, a climatologist for the U.S. Department of Energy’s Carbon Dioxide Information Analysis Center (CDIAC) and a staff member in ORNL’s Environmental Sciences Division. “We’re concerned about the possibility of serious global warming by the end of the 21st century. It might behoove us to prepare for it if we can’t come up with something to head it off, such as geoengineering.” (Often controversial, geoengineering runs the gamut from seeding oceans with iron to spur algal blooms in hopes of increasing the uptake of atmospheric carbon dioxide to deploying satellites with shields to deflect the sun’s rays.)
Atmospheric carbon dioxide is at an 800,000-year high of approximately 400 parts per million. Analyses of a carbon isotope (13C), atmospheric oxygen, spatial patterns of atmospheric carbon dioxide concentrations and other indicators provide a fingerprint for fossil fuels (coal, oil and gas), indicating they are the cause of recent increases in atmospheric carbon dioxide, Blasing said. Over the next century, scientists expect global near-surface air temperature to rise by 1.5 degrees Celsius to 6 degrees Celsius (about 3 to 11 degrees Fahrenheit).
The effect of a greenhouse gas over time depends on its atmospheric concentration, its duration in the atmosphere and the wavelengths at which it absorbs photons (i.e., exerting greater effect where Earth emits more infrared radiation). At altitudes where jets typically fly, water-vapor concentrations are low and carbon dioxide is a more effective greenhouse gas than is water vapor. Moreover, changes in water-vapor concentrations at those altitudes can influence the overall “greenhouse” effect.
CDIAC’s copious records, which include repositories of the World Data Center for Atmospheric Trace Gases, contain data going back almost a million years. Temperature data collected more recently, from ground and satellite observing platforms, show warming is greatest near Earth’s surface. The upper atmosphere (the stratosphere and beyond) is expected to cool.
Scientists are increasingly learning about the atmosphere and sharing the findings in peer-reviewed journals. The periodic assessment reports of the Intergovernmental Panel on Climate Change summarize the consensus opinion about those findings. Yet much remains unknown. How much carbon can oceans absorb from the atmosphere? How do the oceans interact with climate? How do atmospheric aerosols affect climate? How much do changes in solar radiation contribute to warming? Unless relatively unpredictable mechanisms, such as aerosol increases in the atmosphere, become effective enough to counteract warming or geoengineering can be used to control climate, Blasing said the near-surface warming trend is likely to continue.
Some argue that we can’t take action until we know more, but Blasing says that climate change is “just one more reason to do some things we should be doing anyway,” such as making buildings more energy efficient and developing sustainable energy sources.—by Dawn Levy