tonight understanding climate change how the lack of snow in the high farmers. >> i've got 85 employees that rely on me. >> reporter: everything we know may never be the same. >> a house with running water is a privilege now climate sos. i'm jake ward. this is the first stop on a journey to show you the impact of a warming climate. right now scientists and top

leaders from over 190 nations are gathered in paris at a u.n. climate summit to try and negotiate a solution and turn it all around. here is why. more than 97% of working scientists agree that the climate is warming and that it's humanity's fault. researchers are moving on to the costs and dangers of the problem. a recent study identified a direct relationship between rising temperatures and economic output. just as a worker has to slow down in the heat, so do whole countries. the study preducts that by the end of the century unmitigated climate change will make 77% of countries poorer in per capita terms. total global economic output will drop by 20%. we don't have to wait until on 2100. it will cost 44 trillian dollars. the study preducts the that the

u.s. and china with other climates will suffer disproportionate harm. russia will do better and northern europe could even benefit as it warms up. in california which is experiencing one of its worst draughts in history, the water shortage that has been declared a state of emergency. when there isn't enough rain snow makes up the difference. it is like a long-term water storage system. i'm about to show you how this snow winds up in a glass of water. the snow falls in the california's highest mountains. as winter warms to spring the know melts and the water makes a slow descent into the central valley where roughly half of america's fruit and vegetables are grown. that makes its way into the drinking supply. snow is the stuff of life in this state and around the world. there are 32 regions across the globe that depend on a denies snow pack as their main source

of water. decreased snow melt could deprive as many as a billion people of water. in california americas most powerful and populous state the lack of snow fought has caused devastation. if it continues, the economy, the ecosystem or the food supply cannot adapt a journey through california's problems is a journey through the world's. the first to suffer is trees. california is home for the largest most famous trees on earth. giant trees, and this summer scientists began to see they thirst. >> they were losing their older needles and leaves in amounts that were - i had never seen before. >> reporter: giant trees like this are very special.

they're the largest organisms on earth and they are ancient. after four years of draught and the warming effects of climate change, scientists are worried about their future. at roughly 2500 years old, this one is older than his tenity. it is more than 24 pa feet tall. scientists are going to go up. a team from burkley. he climbs to the top of these trees to test them for signs of stress. he has been doing this for 20 years. this is my first time. i have a new respect for the itself. >> you can feel the weight of history in the weight of this tree. it's extraordinary to be here. warmer temperatures mean the water. >> a typical tree of this size

might use anywhere between fooich and 800 gallons of water in a single summer day. >> reporter: snow pack that provides water is now at a 500 year low. >> the sugar pine seems to be suffering a lot of more at allity that we've seen. another pine as well. the cedar has been going back to a rate that people in the park have never seen before. >> reporter: it was by far the scareyest thing i've done. i've never felt so insignificant. this may be the last time that scientists climb these trees. part of this project is to test the accuracy of the airborne observeatry. >> typically in the past we've missed most of the forest and tried to make an inference from the forest from a few samples.

with the advent of image ability, this has enabled us to collect data over enormous scales that wouldn't have been possible in the past >> reporter: the trees that have survived draughts for thousands of years, they are surviving. the comebacks and drought and unprecedented. >> we're in the fourth year of this severe draught. they still seem to be holding up well. if we had another year as severe as this one, i would say all bets are off >> reporter: this is one of many waterways amphetamined by snow. in that snow can't provide enough water, and in one here is low, then california is forced to rely on groundwater deep underground. already farmers in the central valley where i'm standing all the way to the ocean are drilling deep into that water supply. if that groundwater supply runs out and snow and rain can't make

up the difference, then summedly the nation's largest supply of fruit and vegetables is under threat. >> reporter: the wood family has farmed this land for four generations, first growing cotton, these days garlic and others on 1900 acres, half lies draught. >> i'm tired. i'm not 20 years old any more and you wonder how long you can continue to expend that kind of energy and not get what you consider to be an appropriate return. >> reporter: for farms across the state, the fourth year of draught has become a make or break year. california produces half the country's fruits and vegetables and agriculture's life line is here. the california aqua duct. it cuts through his property in two places and he can't use a drop of it.

the draught has forced the government to restrict water allocations and he was told zero. he has to buy his water from other sources at a premium. >> the problem is that if this draught continues, the availability of alternate sources is drying up because there are just at any price they're months availability >> reporter: your rainy day fund is going to dry up. >> it has been gone now for about six months >> reporter: one report estimates that more than half a million acres will be left unplanted this year. up 25% from last year, ultimate aring in the loss of some 18,000 jobs and 2.7 billion u.s. dollars for the state. this town last year unemployment hit 40% in an already depressed town devastated by the draught's impact.

we spoke to one out of washing man who did not wish to be identified. >> translation: yes. there are a lot of people, when we go to work. it didn't the same as before when there is more work and it's because of the water situation. >> reporter: this man was tasked with turning things around as the new city manager. he celebrates the fact unemployment has dropped to 27%. 20% or more is still a tremendous number. >> yeah. it is. it's one out of five people but you have to realise that ides in almost every city in or town in this country that is isolated from a major urban center they're never going to have unemployment of 5.5%. >> this area depends 90% on agriculture. there's no life here without it pretty much. i've seen people that i used to see getting up every day for work in food lines. you know it's rough.

>> reporter: part of the state's emergency draught relief clues more food assistance. the food bank used to take place once a month. now it happens almost every week. so here is what is really interesting about what is being handed out here. you have tomato south australia, green beans, things that are grown in california and picked fresh. unemployed farm hands are in line to get food and they're getting this canned. >> reporter: this woman picked for decades until the worst draught in the century took away the only thing that she knows how to do. >> no water, no job. no job, no food. no water, no money. >> reporter: the irony of california central valley, the bread basket of the nation and where some of the state's hungryist residents live. hand-in-hand one have served the other for years. so much more painfully

pronounced by this endless draught. melissa chan, california this is california's central valley, one of the most productive growing regions in the world. it is getting harder and hard onner to get water to fields like these. that's true in other places, across the south west and great plains, water short ages are making it harder. what happens if any nation in the world lost its food growing regions? could we get our food from the oceans instead? that story is coming up. >> get an in-depth look at the problems facing professional sports: see what you've been missing.

>> still living in these tent cities. >> we're back to square minus one.

>> the city is a powder keg at the moment. >> you see transactional sex and no one is held to account for that. >> the united nations has never accepted responsibility for this. >> an ali velshi on target special:

welcome back to our look at climate change and its impact on the american west and the world. it is not just a source of water to agriculture but also drinking water. by the time it reaches this place on the journey to the pacific coast it has become a source of water for millions of

people in northern and southern california. right now just a few hundred miles south of here there are towns that have run out of water completely. a report from one community that simply kbt afford to dig for the water-- cannot afford to dig for the water it needs >> these people are out of water. they just recently went out of water >> reporter: if water is life, then the small community of east porter ville is dying. turn on the tap in this lady's bathroom. >> reporter: how are you living like this? is this any way to live? > reporter: down the street another lady ran out of july. this is one of extreme measures you've had to take? reporter: more than half of the city's 7500 residents have

been without running water for months and in some cases years. with no central water system, the majority of homes here rely on proofed wells. as the state's historic drought drags on, those wells have run dry. this family ran out of water 18 months ago. >> it has been really hard. we have to make a lot of changes. >> reporter: what are some of the changes you've had to make? reporter: did you ever think you would be living like this?

become incredibly important. that's when the water arrives. this week tuesday and came and went aand no water. you can see the level here, it is pretty low. this little amount of water will have to last the family for who knows how long. >> it is so unimaginable because you will see a house colaps or wash away, that say disaster but this a silent disaster >> reporter: for the past 15 months long time resident donna

door. >> have you got barrels to put water in? >> reporter: delivering withdrawer to her neighbors. it >> it makes me think of how people can be, we look at other countries and go gosh, africa, but it's even worse here. the thing to he was some of the people didn't have a voice. they didn't know where to turn >> reporter: do you think it's acceptable that you and your neighbors here in east porterville are having to live with no running water? reporter: as residents struggle to survive without

running water, more and more cal foreign re foreignians are likely to find their taps dry. with a solution hard to come by in a state where water becomes more scarce every day this is california's golden gate, the stunning end of the largest water system. most of what you've seen so far drains in some way to this point. the place looks very healthy. it looks like it gets plenty of water, right. all of that turns out to be an illusion. that's what i learned on this story. this place like so many places around the world depends on snow and rain to stay alive. the most important take away for me, understanding just how fragile the world's water supply is. high in the sierras the snow isn't just beautiful, it's an essential ingredient of our survival on earth. it waters our crops, quenches

our thirst, keeping our oceans viable >> you have 25 to 35 oysters per shelf. >> reporter: we can't dig for new water, but we can ute cut down our carbon emissions. also new ways of holding on to energy helps. technology alone cannot solve this problem. each of us has to change the way we live. we can buy fewer things which cuts out the energy required to make them. we can cut back on meat production which contributes more emissions than cars do by some estimates. and if we change the way we commute like choosing a bicycle over a car, we can keep greenhouse gas emissions close to 2010 levels for decades. we're talking about reinventing how we live on earth. humans can limit climate change. that is why the nations of the world are in paris now. the difficulty isn't understanding that the longer we

wait the more difficult it's going to be, and that the comforts we take for granted, like a ready supply of water, could all go away if we don't make a change of our own right now. jack ward, al jazeera at california's golden gate. ewel on america tonight, keeping a seek resided, and the silent pain that can cause. >> on a daily basis, i would have nightmares, tremendous stress and anxiety. i was sort of experiencing constant vigilance. >> america tonight on the risk of silence and the possible remedy. >> thanks for joining us, i'm joie chen. give a moment to yourselves and the burdens of the last year you