narrator: geologist paul hoffman's research centers on the question of what happened to create this planetary deep freeze, a freeze that opens a lot of questions about how the earth maintains a habitable climate even today. hoffman: this only really became a question in the middle of the 20th century, when people realized that over the 5 billion years of our solar system, solar radiant energy has increased by almost 30%. so it's surprising, therefore, that the geological evidence indicates that the surface temperature of the earth hasn't changed very much over at least 3 1/2 billion years. so that means that there must be something internal to the earth that is self-adjusting so that the earth always maintains a stable temperature -- not unchanging, but limited in the amount of change despite this large increase in solar radiation. narrator: the earth's ability to self-adjust its temperature is linked to carbon dioxide, a greenhouse gas which captures heat that would normally radiate to outer space and sends it back to the surface. the more carbon dioxide in the atmosphere, the warmer the sur

. >> reporter: paul hoffman, ddot civil engineer heading the project, took me underneath the 60-year-old bridge to show us what's wrong, mainly these cracks and the calcium deposits building up like icicles. it's something you'd see in a cave, not something you want to see on a bridge. >> you can see the water has already come through and the style inside has got to be quite readily rustled at this point. so we've lost a little -- rusted at this point, so we've lost a little integrity of the structure. >> reporter: he hopes to have contracts signed this week with plans to begin bridge rejukes in three to four months. four lanes of travel will -- bridge in three to four months. four lanes of travel will be taken down to two. >> it's going to mess up, especially the buses. they have enough trouble with rush hour and regular time as it is. i don't know what they're going to do. >> reporter: a travel mess, but ddot is prompting to finish the project from start -- promising to finish the project from start to end in 110 days. in d.c. stephanie ramirez wusa9. >> that's going to be a tough 110

. >> paul hoffman is a ddot civil engineer heading the project. he says there are cracks in the bridge, the steel is rusting are building up. hoffman says cdot hopes to begin reconstruction in flee to four months -- three to four months. the project is expected to take 110 days to complete. >>> another big job is under way, this one in london. big ben's clock is getting cleaned. a team of workers not afraid of heights scaled the 314-foot tower in westminster. the cleaners will also inspect the clock for damage. the job should take about a week to complete. big ben was first installed in 1859. >>> the coach of the cleveland browns says johnny machine zell's obscene jest -- manziel's obscene gesture last night is disappointing. he gave the finger at last night's fed ex field. the skins won. cleveland's coach promised to name the team's starting quarterback today but after uninspired games from both single callers, he suggested he may delay that decision. >>> i'm tracking spotty showers at this hour which are coming through the metro mainly south of

. >> paul hoffman is a ddot civil engineer heading that project. he says there are cracks in the bridge. the steel is rusting. you can see calcium deposits building up. hoffman says ddot hopes to begin reconstruction in three to four months. instead of four lanes of traffic, it will only be one in each direction. the median on military road between oregon and 14th street will be rebuilt. once that projects is started it is expected up to last 110 days. look at the light at the end of the tunnel. >>> pope francis says he wants to pay us a visit in d.c. he announced in september of 2015 he wants to stop in the nation's capital to address congress, speak at the u.n. in new york and attend a family rally in philadelphia. the pope made those comments while coming back from south korea. >>> johnny football and rg3 on the field together, wasn't as good as it sounds. >> you were screaming a lot tonight. kristen berset will join us from fedex field with highlights from tonight's preseason game. >> and have you ever gotten busted by those speed cameras in th

academy also paid tribute to other artists who passed away in the past year, including paul walker, phillip seymour hoffman and james garner. you can see more coverage of the emmys throughout the day on "news4 today" and on the "today" show. >>> a lot of touching tributes there last night for so many people. and you can't ignore the fact it was a huge show. it was a celebration of some of the best in television. a lot of folks who we knew would win won and some surprises, too. > the easy target, the weakness on your smartphone's operating system to make it easier for thieves to steal your personal information. >>> a cool start to the morning and just the beginning of a wild ride we'll see temperaturewise. the roller-coaster ride you'll experience the next 24 hours in your weather and traffic on the 1s at 6:31. >>> plus school bells will be ringing in the hour for children in prince george's county. here's a live look at the school buses ready to go. a lot of them streaming out already out of the lot in upper marlboro. we are talking to the school superintendent kevin maxwell next about the changes your kid