Three U.K. explorers bound for the North Pole on a scientific expedition to study global warming said they are close to running out of food after "brutal" weather conditions halted three attempts to fly in supplies.

The support team hopes to decide within hours on when it can send an airplane to land on nearby ice with provisions, Tori Taylor, a spokeswoman for the Catlin Arctic Survey in London, said in an interview today.

"We're hungry, the cold is relentless, our sleeping bags are full of ice," expedition leader Pen Hadow said in a statement e-mailed yesterday by his team. "Waiting is almost the worst part of an expedition as we're in the lap of the weather gods."

The severe weather is jeopardizing a journey aimed at projecting when global warming may melt the entire Arctic Ocean cap, a phenomenon that scientists say might trigger further gains in temperature.

Hadow, Ann Daniels and Martin Hartley are 18 days into their 100-day, 1,300-kilometer (800-mile) journey to the pole, during which they planned to use a custom radar to take as many as 13 million ice-thickness measurements. They aim to help scientists gauge how quickly the Arctic sea ice is thinning.

Previous estimates of melting have been based on less reliable depth soundings made by satellites and submarines, which can't distinguish ice from snow. Scientists have made few surface measurements that are highly accurate because of difficulties in traveling on the ice cap.

"We've located a suitable airstrip," Taylor said. "We hope the plane will be able to land."