News from SciAm

Two important stories on global warming in August's Scientific American.

First, the magazine briefly notes that the longest ice-core yet recovered will give a clearer picture on historical temperatures and their links to the global carbon cycle.

The bottom of the 10-centimeter-wide cylinder dates to some 740,000 years ago and nearly doubles the reach of the next-longest ice core, which was drilled at Vostok, Antarctica, in the late 1990s and spanned the past 420,000 years. Temperature records for eight ice ages are documented in the new core. Of particular interest to climatologists is the complete record of the interglacial time period known as Marine Isotope Stage 11 (MIS11), which occurred around 400,000 years ago, a time when our planet's positioning was similar to its current orbital configuration. MIS11 lasted 28,000 years--considerably longer than the next three interglacial periods before present--and understanding its progression may help scientists better predict what’s in store for the earth’s future climate.

A feature story elaborates on some of the reports that have been creeping into the newspapers about global dimming, the steadily falling amount of sunlight reaching the Earth's surface. The results will obviously cool the earth:

Estimates of the effect vary, but overall “the magnitude has surprised all of us," comments climatologist Veerabhadran Ramanathan of the University of California at San Diego. Stanhill and Cohen have pegged the solar reduction at 2.7 percent per decade over the period from 1958 to 1992. Put another way, the radiation reduction amounts to 0.5 watt per square meter per year, or about one third (in magnitude) of the warming that takes place because of carbon dioxide buildup in the atmosphere.

Complicating any attempt to understand the pheonomenon is the complex interactions with cloud formation and precipitation. The models used for climate change modelling will need adaptation to take account of the work, even if the effects of dimming offset increases in greenhouse gasses.