Nightly News | April 06, 2014
>>> we're back now with an be intrigging look at some of the extremes we've been seeing in weather and climate around the world. for the last year ann curry and nbc news has been tracking these changes from one end of the earth to the other for a documentary airing tonight on nbc .
>> jim houston leads laguna's hot shots, an elight group on front lines of fires.
>> how have firesing changed since you started fighting them?
>> when i started in '89 to now the fire seasons have gone much longer. when i first started it was within a six month period basically june to november.
>> that has changed dramatically.
>> we joke about it being a year round fire season.
>> we can say some general things we expect to happen as the planet warms and one of those things is that the southwest will get drier.
>> we have what seems to be at least for now a very abnormal situation.
>> well, not abnormal as this is "the new normal."
>> that new normal has sparked a new theory about wildfires. a theory that led us to the top of the world . american glaciologyist has been studying arctic ice for 20 years. he said the ice is meltding on a scale and speed scientists never imagined possible. he has a surprising new theory about what may be speeding up the warming.
>> you can see it's wanting to pull.
>> the pristine ice looked dirty gray in places.
>> that's from wildfire soot.
>> it was hard to imagine that he was saying soot from wildfires in north america had traveled all the way here, coating the ice with carbon particles, transforming it into what he calls dark snow.
>> what happens with dark ice? dark snow
>> light absorbing impurities trap more sunlight and that can hasten the melting process.
>> and if there's more forest fires more soot.
>> soot potentially adding to "the cycle" of melting climate scientists say we all need to know more about. ann curry , nbc news the arctic.