Tasmanian trees track recent warming.

Scientists peering inside Tasmanian pine trees have discovered hints that greenhouse gas pollution is currently warming the atmosphere. A study of the annual growth rings in these trees indicates Tasmania has been warmer during the last few decades than during any other period since A.D. 900.

U.s. and Australian scientists measured the rings of 23 Huon pine trees on a small mountain in western Tasmania. The rings serve as a climate record because trees grow more during warm years, laying down wider rings. By counting backwards, the researchers used the tree rings to compile a 1,089-year-long record, one of the longest high-resolution climate records from the Southern Hemisphere, they report in the Sept. 13 SCIENCE.

The tree rings revaled several warm periods over the last millennium, but none was as consistently warm as Tasmania has been since 1965. The researchers say this finding supports the idea that the greenhouse warming has already started. However, they caution, "we do not consider our results as added proof of that assertion yet." The recent warming is still small enough that it could represent a natural climate variation rather than a human-induced change, they say.

Curiously, the coldest period in the record also occurred relatively recently, during the early 1900s. Climate records from locations in New Zealand and elsewhere also show a cooling then, suggesting that the ocean and atmosphere in the Southern Hemisphere underwent a significant change at that time.