It's still too early to ascertain the full impact on commodity markets of a possible return to the extreme weather patterns seen last year, Dr. William C. Patzert, Climatologist at the National Aeronautics and Space Administration, said this week.

Sentiment towards commodities lying in the traditional path of conditions known as 'La Nina' (a periodic climatic phenomenon that brings more rain to the western Pacific, and to a lesser extent, the eastern Pacific) has started to turn more bullish over recent weeks.

The situation has also been exacerbated by supply shortages in a number of products, such as iron ore and agricultural commodities.

The U.S. National Weather Science's Climate Prediction Center confirmed last week that La Nina conditions have in fact returned and are expected to gradually strengthen and continue into the Northern Hemisphere winter.

"During September-November 2011, there is evidence that La Nina favors an increased chance of above-average temperatures across the mid-section of the country, and an increased chance of above-average precipitation across the Pacific Northwest," the weather body said in a statement.

Climatologists blamed La Nina for last year's floods that gripped Australia, resulting in major losses to coal and iron ore stockpiles but also for drought that ravaged the U.S. corn crop.

However, Patzert warned that it still remains too early to jump to conclusions, as although "La Nina might strengthen this fall through to winter...forecasting a repeat of last year's weather and impacts on commodities markets is shouting 'fire' in a theatre."

Joe Vaclavik, grains broker at Chicago-based MF Global, said a continuation in the U.S. drought could also hamper winter wheat acreage this year.

Peter de Klerk, senior analyst at Czarnikow, one of the U.K.'s oldest sugar trade houses, also warned that La Nina could bring a negative impact to sugar production prospects in Indonesia and Australia. "La Nina disrupts the seasonality of planting, growing and harvesting of the sugarcane crop in the region," he said.