narrator: on this episode of "earth focus," two cities-- freetown, sierra leone, and san francisco, california-- continents apart, vastly different culturally and economically, yet facing the same struggle to adapt to rapid urbanization, all set against the backdrop of a dramatically changing climate. [film advance clicking]

man: oh, no! woman: the red cross says more than 600 people are now missing and that more than 200 have been killed after heavy rain caused a severe mudslide in the west african nation of sierra leone.

[car horns honking]

[insects chirping] amarasekaren: oo oo oo! what's happening? what's happening? no big problem, huh? ok. when we get problem...

man: whoa! [men shouting]

[indistinct conversation]

narrator: while freetown residents fight for accountability, in san francisco, climate change isn't debated as much as it's mitigated. billions of dollars are pouring into the bay area, but is tech-driven development prepared for a sea level that's rising? scholl: san francisco is experiencing a tremendous building boom and has been

for the last 5 years. tam: we have ucsf hospital. we have the warriors coming. we have a bunch of new apartment buildings. scholl: you have corporate headquarters of facebook, google, microsoft. christensen: we realize we live in such an amazing place with so much creativity and innovation. i'm excited when i see the young people in the tech industry all over town, all over the bay area commuting back and forth. there's an energy here. renteria: in mission bay, veryone pretty much works in tech, working on the next start-up. woman: i have 3 cappuccinos for here.

renteria: i'll do a coffee. ok. thanks. i'm considered a millennial. we kind of are free spirits, and we don't believe so much in just full-time gigs. i work in social media marketing, so it's definitely a new industry. a lot of people don't quite understand it, but i run social for a living. the really cool thing about a job in social media or just tech is that you can work remotely. coffee shops are free. yes, san francisco is really expensive. there is no other place like san francisco where you're going to have access to the technology, to the communities, to just the people working in the industry. it's just one of a kind, and it's totally worth it. i sold my car, and i pretty much walk everywhere now, and i got rid of a lot of stuff, and i live in a very small apartment , but it's

totally worth it just to have access to everything. yay. cheers. >> cheers. renteria: i just learned about the sea level rising, and i didn't know about that before we moved here. does it concern m yes, because i eventually want to buy property here and have a family here, but i didn't know about that, and i'm not too informed, so it's not something that i'm really too concerned about right now. i am scared now, though, learning that that's a possibility. christensen: people under 40 living here in the bay area today are very, very likely to see unprecedented annual flooding around the bay in their lifetimes. jacob: it's going to be fanstic in city that is so vital and known for its innovation that we're going to be able to build this great venue here.

christensen: a lot of these new buildings by the end of the century, including the golden state warriors' new arena, would have the ground floors at least potentially flooded or basement parking flooded. the warriors arena is, you know, contemplating maybe someday putting in flood gates so that their garages don't flood. they're thinking of raising pedestrian access so that it would be out of the water. san francisco itself, you know, built a seawall in the late 1800s to protect itself and this new land that had been created. you know, right now, san francisco is looking at spending $5 billion to repair and reinforce that seawall for another century.

scholl: the areas that have been the least developed historically are the marginal lands around the bay, some of which are salt flats. others are abandoned piers, and they're being rehabilitated because there's basically no place else in the bay area to build, and they're being built upon as quickly as possible by mostly megacorporations that are trying to maximize their value by building very expensive developments. to me, it feels like sort of climate denial light. we found in 2015 that about $21 billion's worth of development was happening right in that coastal zone. there is a tremendous amount of money to be made to develop in those areas. by the year 2100, we found, there's a threat that sea level rise could, on a really bad day, flood land all around the bay exactly where most of the waterfront development is happening, and then they're

going to have to figure out how to invest public dollars to protect what we're building right now. tam: mission bay was once a bay. it was an inlet of the bay. it was marshy and brackish and kind of shallow. mission bay is finally getting built after many, many years of planning and agreements around infrastructure. there are some really important institutions that are there now, new commercial buildings, as well. it's an area that is rapidly becoming a part of the urban fabric of san francisco where it really was once seen as, like, a strange and unoccupied place, but, because we planned it in an era before we were thinking of sea level rise, it's also very low-lying, and it's one of the city's more vulnerable places to future sea level rise. scholl: the problem is that the land is so valuable because it's now land. development companies couldn't not build there. there were billions of dollars in real estate to be had, but

they built it in probably one of the worst places they could have. it was a bay in the past, and it most likely will be a bay in the future. tam: we picked this part of the shoreline for a study around design concepts for future sea level rise because it's the lowest lying area on the eastern waterfront. it's the place that's going to flood first, and so we thought it was the right place to spark a conversation around what are design alternatives or choices that we can make in the future at the mouth of mission creek near at&t park. we'll have a really beautiful public space that people might not even realize is designed for flood protection. ideally, we would have wetland habitat and parks and a place where people can access the bay. we want to have a lot of commercial activity in our city. we want more housing. we definitely need more affordable housing to solve some of the bay area's biggest challenges, but alongside that, we have to do something about future sea level rise. ideally, we'll have a lot of

people enjoying the waterfront, and during stormvents, we'll have some kind of way of protecting people through some kind of barrier or just because we have shallowed the channel in some way that makes it no longer super threatening when there's a super high tide. herrera: the science is undeniable. climate change is altering our planet, placing many of our communities at risk. we must prepare for a future that directly confronts these changes. the defendants are chevron, exxon, bp, shell, and conoco phillips. these fun will be used to pay for seawalls and other infrastructure needed to deal with sea level rise. we have some real risk that's going to require some billions and billions of dollars of investment by san francisco on infrastructure if we're going to stop catastrophic loss, so that's what we're looking at. a lot of our developments are occurring along the waterfront. our lawsuit is a part of that.

i want to have this abatement fund thahas been created now to ensure that we can fund the infrastructure improvements that we're going to need to ensure that those developments go forward without the threat of sea level rise. scholl: politics in san francisco is funny. there are a lot of really enlightened views. on the other hand, it's probably not enough to prevent the business community from making things even worse right on the waterfront. christensen: we're going to have to adapt. it's going to take that creativity and energy and capital. the question of how do we balance that economic development, the investment in protecting it, with the needs of people and the environment

is one that, you know, we're going to find ourselves asking over and over again here in the bay area and around the world.