a very warm welcome to bbc news — broadcasting to our viewers in north america and around the globe. my name is mike embley. our top stories: the deep freeze. cities in the american midwest grind to a halt as temperatures hit record lows. ‘substantial progress‘ claim american negotiators — but no agreement yet in the us—china trade war. now we are going to have a great trade deal with china if it all works out. we look forward to it. it will be great for both countries. venezuela's self—declared interim president says his family has been threatened by units loyal to his rival — president maduro. and the leonardos of queen elizabeth. one of the world's greatest collections goes on tour for the 500th anniversary of the artist's death. hello.

relief is on the way, but for many in the midwest it can't come soon enough. for yet another day millions were plunged into arctic temperatures which closed schools, grounded flights and proved downright dangerous. the polar vortex has already been blamed for multiple deaths — even breathing outside is difficult. the bbc‘s chris buckler is in chicago with this report. chicago stands surrounded by ice and snow. people here are used to cold weather but these are temperatures seen only once in a generation. to try to keep the city's trains running, the tracks have had to be set on fire and boats have been attempting to break through the solid sheets of ice that cover the chicago river. the windy city has become the wind chill city. my fingertips have been frozen twice and had to take a pit stop twice. toes frozen twice. so i made two stops. it's brutally cold, bitterly cold. you can actually see frost on your eyelashes. what does it feel like? it's a little cold.

they froze and closed a couple of times. across america's midwest, temperatures have dropped far below freezing. a huge part of the us caught in what's known as the polar vortex. it's pushed arctic air down from the north pole and left many places colder than the antarctic. from the air, lake michigan now looks more like land than water. people have been doing their own small science experiments to see for themselves just how cold it is, including this. i've got boiling water in this flask and you'll see, as soon as i throw it into the cold air, it just simply freezes. further north, even parts of the mighty niagara falls have been frozen. this is a deadly cold and people have been killed in accidents on the icy roads and in some cases from just being exposed to these extreme elements. for another evening,

centres have been opened to keep the homeless warm and safe. there is no shelter on the streets from these kind of conditions and the frozen beauty of this weather can't be allowed to distract from its dangers. chris buckler, bbc news, chicago. a short time ago we checked back in with chris for the latest. people are getting laid up with as much clothing as possible. —— people are getting layered up with as much clothing as possible and trying to keep others off the streets. here in chicago it has been pretty quiet in what is normally a bustling city. that is because so many businesses, so many schools and colleges have simply been closed. that is true right throughout the midwest. because these conditions are frankly painful. i've got my hood down at the moment and i'm close to shelter, but the truth is we are try to keep as warm as possible, because your extremities, yourfingers, your toes,

my ears, in particular, are really painful today standing out in this. that is true for everyone else. of course, some people have died as a result of these cold, cold temperatures. some of them have just been exposed to it. the truth is, you talk to some meteorologists and they tell you about ten minutes in the temperatures chicago has experienced in the past 2a hours could give you frostbite. the hospitals here have been dealing with people who have been suffering from frostbite. we have been doing our best to give people an idea of how cold it is. one of the things we have been doing is by using a t—shirt. we wet this t—shirt and brought it out of our hotel a short time ago. within 60 seconds it froze completely. that is a t—shirt that was just wet, and a cotton piece of clothing that has frozen in around 60 seconds as a result of the cold there is still here in chicago. at the moment it is around —20 celsius. that feels even colder with the wind chill. something around —27 celsius. chris and team are earning their

money therein chicago. later we will speak to a family in wisconsin about the highs and lows of the big freeze —— there in. the second and final day of high stakes trade talks between the us and china have concluded, in the oval office. china's leader xi jinping wrote to president trump to say he hopes they will be able to reach agreement before a march first deadline, when new tariffs could take effect. this was mr trump's take on a possible deal. i think the relationship that we have right now with china has never been so advanced. i don't think it's ever been better. but i can tell you for a fact it's never been so advanced. and certainly a deal has never been so advanced. because essentially we don't have a deal. we never had a trade deal. we're gonna have a great trade deal. but we never really had a trade deal with china and now we're gonna have a great trade deal with china

if it all works out. and we look forward to it. it's gonna be great for both countries. will keep you posted. —— we will keep you posted. venezuela's self—declared interim presidentjuan guaido has said his family has been threatened, amid the country's continuing political crisis. in a speech at venezuela's central university, he said police had visited his family home looking for his wife. brian fonseca is director of the jack d gordon institute for public policy at florida international university. hejoins me now from miami. good to talk to you. when you see this heading now? right now you have a stand—off between legitimacy in power. many in the west have rallied behind juan guaido. an important announcement was made doubly down behind juan guaido. you have maduro who still has a lot of control of the military institution. this will really seedy showdown. this is where you see fights and other types of pal —— paramilitary militia groups out on the streets in an effort to

keep things under control. given the pretty inglorious history of american intervention in latin america, i guess that backing from other countries and particularly the us can be a poisoned chalice, it can make you look like is to give you are not careful. absolutely. it is important that most of the hemisphere is a part of this. the united states are certainly launched this last week, followed by canada, quickly, and much of the rest of the hemisphere came online in terms of supporting guaido. they reached out how to double down behind guaido. countries on the other side supporting maduro are quite few. those you would expect, cuba, nicaragua, olivia. —— bolivia. a more limited than the western coalition that seems to be backing guaido at the moment. how effective do you think mr guaido can be? he says his family has been threatened and he has been stopped from leaving the country and there has been a move to stop his assets. he has told

the new york times that his team has been talking to the military and the security services. it is an interesting development for him to mention that. again, right now, the signs of centrepoint to the fact that the military seems to the fact maduro. for how long we don't know. but certainly there have been calls by the opposition to the military to essentially break with the maduro —— break with maduro. they want many in the military to put down their weapons or back down from supporting maduro. either in favour of the opposition or some form of transition that might see the exit of maduro. knowing what you know about mr maduro, had you expecting to play it from you? i don't know. whether or not is time is limited will be dependent on military institutions. i think the military has been, remains, will remain a key to transition or continuity, change or continuity in venezuela. we will see how long the military stays

behind him. history tells us that the longer maduro is able to weather the longer maduro is able to weather the storm the more likely he is to survive. on the other hand, edit and —— imperative for the opposition in this case to stay on the streets and put pressure on both maduro and the military institutions, as well as the international community to continue to rally behind his legitimacy as the interim president. brian fonseca, thank you very much. let's get some of the day's other news. the us envoy for north korea has said pyongyang has promised to dismantle and destroy all its uranium and plutonium enrichment facilities — a commitment apparently made to the us secretary of state and to south korean leaders. north korea has made such promises before, and the us is seeking expert access to verify any removal or destruction. a court in the us has found the syrian government liable for killing the american war correspondent, marie colvin, and french photographer, remi ochlik, in an air strike in homs in 2012. the court ordered syria to pay more than $300 million in damages. it's the first time the assad

government has been found guilty of a war crime. amazon has reported large increases in profits and net sales for the final quarter of 2018. but it is forecasting a slowdown for the first quarter of this year. it blames tighter regulations in india and a slowdown in sales in europe. social media companies are facing the prospect of new laws giving them a legal duty of care to children and young people who use their sites. the uk culture secretary has said he's considering that move ‘very carefully‘ since the case of molly russell, the 14 year—old who took her own life in 2017. her father says she was badly affected by graphic images of self—harm and suicide she viewed on instagram. calls to a leading suicide prevention charity have increased by a0 per cent since we highlighted molly‘s case last week. angus crawford‘s report does contain distressing images. she had so much to offer.

molly russell‘s story... and that‘s gone. ..has sparked a debate... these are companies that count their profits in the billions, and they turn round and say to us that they can‘t protect our children? ..that may change social media for good. do you have the power to compel them to do what needs to be done? yes, absolutely. and it‘s also struck a chord with families across the country. like ian and his daughter libby, so horrified by what happened to molly that they‘ve decided to speak out. libby once had 8,000 followers on instagram. 16, and now firmly in recovery, libby used to self—harm, an obsession learned on and fed by the platform. i don‘t think it made me do it, but i think it definitely accelerated the severity of it, because i‘d see people and then you‘d almost go, "that‘s ok, then, it doesn‘t matter how bad it gets because they‘re not dead, it hasn‘t killed them, doing that". so it kind of made it feel more safe to do it worse. her dad tried to get the worst content taken down,

but says it was a waste of time. you go, "right, i'll try and get rid of this account, there must be a way to stop it", and there's nothing. and they're not interested. and until one of their close family members falls down that rabbit hole, they won't do anything about it. until it affects them or their wallet, they are not interested. meet chloe, who‘s 12, and her mum emma. shocked by molly‘s story, they rang the bbc. chloe had stumbled across just this kind of content. platforms on social media could, like, kind of stop a report or take down bad things on the internet that are scaring people, because i know it‘s just notjust me who‘s getting scared by it. i know there must be other people. users should be at least 13 to be allowed on instagram,

but emma says age restrictions aren‘t the point. the reality is that people are using them at that age, so whether there‘s the age limit... and when she‘s 13, what difference is it going to be? molly was 1a. does that mean it‘s acceptable for her to see those images? i don‘t think there‘s any age that‘s acceptable. a hard—hitting video with a simple message, encouraging young people to talk about suicide. molly‘s death has certainly done that. there‘s been a 40% rise in calls to this charity‘s helpline. this is james murray. his son ben took his own life last year, aged 19. a technology consultant, james knows social media can change. do you think the penny is dropping? the penny‘s dropping. i think molly‘s case could be a turning point. what they should be doing when somebody is looking

at self—harm or suicide is promoting positive content over and above the negative content. so the algorithm could be used for good? yeah, absolutely, and it‘s high time the social media companies delivered on the promise of social value and became a force for good in the community. instagram says: "we have a deep responsibility to make sure young people using instagram are safe" and it has begun "a full review of our policies, enforcement and technologies around suicide and self—injury content". molly‘s story has touched a raw nerve and sparked a demand for change. the social media companies now have to decide if they will embrace reform or have it forced upon them. good to have you with us on bbc news. still to come: is this a disaster waiting to happen? we visit one of 200 dams the brazilian government says are at risk of collapse.

this is the moment that millions in iran had been waiting for. after his long years in exile, the first hesitant steps of ayatollah khomeini on iranian soil. south africa‘s white government has offered its black opponents concessions unparalleled in the history of apartheid. and the anc leader, nelson mandela, is to be set free unconditionally. ..four, three, two, one... a countdown to a critical moment. the world's most powerful rocket ignited all 27 of its engines at once. and, apart from its power, it's this recycling of the rocket, slashing the cost of a launch, that makes this a breakthrough in the business of space travel. two americans have become the first humans to walk in space without any lifeline to their spaceship. one of them called it a piece of cake. thousands of people have given

the yachtswoman ellen macarthur a spectacular homecoming in the cornish port of falmouth, after she smashed the world record for sailing solo around the world non—stop. this is bbc news. our top story this hour: millions of people in the american midwest have been trapped in their homes by an extreme polar vortex, with temperatures below —30 celsius. adam emery is a photographer in racine, wisconsin, where it was —27 celsius yesterday. he lives on lake michigan and has been braving the cold this week to take photos of the weather. we can go there live now. adam, we‘re going to look at some of your shots while we talk. you‘ve got carson and lexi with you. i think it had five days in a row of no school because it‘s closed, yes? that‘s right. is that really

unusual? it's unfortunate because they are home with me all the time, ijust make they are home with me all the time, i just make the they are home with me all the time, ijust make the meals all the time we are looking forward to going back to school. carson, are you looking forward to school? 0h, to school. carson, are you looking forward to school? oh, yes. i have more maths to do and more of every subject. that sounds so much fun. can you play outside? no, it is too difficult. we had to climb over a huge pile of snow and it is four minutes outside and you are so cold, you‘ve got to come in. minutes outside and you are so cold, you've got to come in. let's see, it must be awful to have so much time off school, you must be sad. the aymack. adam, can that be true? how are you dealing with all this? some of the photos are really great. it's been very impressive. when it gets really cold in the water breaks on the shoreline of lake michigan, it explodes upward and freezes into

these enormous icicles. i‘ve been waiting for this all year long. a lot of people are afraid to venture out. some of my favourites when the waves freezing crash on themselves. there are shots of your camera equipment suffering. fortunately, it‘s pretty waterproof. u nfortu nately, it‘s pretty waterproof. unfortunately, when the water flash freezes onto the camera view, it will freeze onto the dials to the last sitting you have programmed is the one you must use because the rest is an ice block c have the time and well. other than that, it is really exciting. i guess you are used to rough weather but does this feel different? it is the coldest temperature that i ever remember. the wind chill yesterday was —60 degrees so it was very, very cold but at the same time, when the wind

isn‘t that brusque, it‘s bearable. it's isn‘t that brusque, it‘s bearable. it‘s certainly something we are used to. do people look out for each other? can you and the kids help out? i don't think i'd let them outside to help anyone, it‘s just too cold to go outside. at the same time, everything was closed. the banks were closed. most businesses, their employees stayed home. it was very quiet. thank you very much for talking to us. the number confirmed dead from the dam burst at a mine in brazil last week has risen to 110 but more than 300 people are still missing. in the state of minas gerais, where the collapse happened, at least 200 dams are classified by the government as having a high potentialfor damage, if there was a collapse. the bbc‘s julia carniero has been visiting one in the city of congonias. devastation as far as the eye can

see. this is waste from iron ore mining and golfing houses, trees, trucks, and hundreds of people believed to be buried under the mud. down, owned by mining giant vale, collapsed in the brazilian state of minas gerais. just over three years ago, another dam failed only 120 kilometres away. now attention turns to neighbouring cities like congonhas, home to one of the biggest urban dams in latin america. this dam is right next to the city and holds five times more mining waste than the dam that collapsed him brumadinho. in the neighbourhood was built here, the dam was a lot smaller but it expanded over the yea rs. smaller but it expanded over the years. coming closer and closer to the houses, it‘s just

years. coming closer and closer to the houses, it‘sjust 250 metres from some of the construction and after what happened in brumadinho, residents say it is either them or the dam, they don‘t feel safe any more. translation: i am terrified, i wa ke more. translation: i am terrified, i wake up scared, i have nightmares andi wake up scared, i have nightmares and i feel this could wake up scared, i have nightmares and ifeel this could happen here as well. we live right under the dam, i‘m scared for everyone here. well. we live right under the dam, i'm scared for everyone here. this activist says there is no dialogue with csn. the company did not want to comment on this report. translation: i say that the lesson comes at a huge cost with all the lives we lost but it has to be applied to prevent other collapses. people here want a solution, they don‘t want in doubt. people here want a solution, they don't want in doubt. structural problems would detect it twice in the dam in the past six years according to this prosecutor and we re according to this prosecutor and were repaired following judicial orders. at the time, csn said the demands had been followed in the dam presented no risks for workers and residents. translation: i say it's a

huge structure, very close to the city. if it breaks, it is going to be one of the worst accidents ever. mining workers here are concerned after the dam collapse. vale employees voted to interrupt their shift for two hours to mourn their collea g u es shift for two hours to mourn their colleagues in brumadinho. translation: i think if it is so safe, why don‘t shareholders live under the dam? we need to change the model of mining and private companies need to be pressured instead of easing licences. after two disastrous collapses, brazil‘s mining dams are under scrutiny and people living under their shadows don‘t want to be the next victims. britain‘s queen elizabeth has one of the world‘s greatest collections of drawings by leonardo da vinci. to mark the 500th anniversary of his death, she is sharing 144 of his works with museums across the uk. our arts editor will gompertz has been on a country—hopping tour. we‘re in the national museum

in cardiff among its 12 leonardos, all of which are magnificent, of course, but ijust wanted to point out two of the works. the first is this late anatomical drawing, which is great, but it does contain a mistake. on this left—hand edge, leonardo has left an inky thumbprint. and then over here is a drawing which shows the artist‘s deep interest in botany. it‘s a beautiful symmetrical design of a grain—bearing grass from asia known asjob‘s tears. at the time, it was very rare in the rest of the world. in fact, this is thought to be the first record of it in western europe. the drawingas on display here at the ulster museum in belfast give a sense of the extraordinary range of interests that leonardo da vinci had, from costume design to extreme weather effects and of course, famously, his detailed analysis of the human body, with images which are still well regarded today. but are they accurate, ian? they certainly are, will.

if you look at the level of the anatomical detail here, it is equal to any standard surgical text in the modern era. more importantly, he‘s somehow picked up the functionality of these muscles and imbued them with life. the display here at the kelvingrove art gallery and museum in glasgow shows the two sides of leonardo. on the one hand, you have the fine artist who‘s interested in modelling form in really delicate detail using light and shade. on the other hand, you‘ve got leonardo the engineer, who‘s interested in the movement of a horse and in designing weapons or fanciful war machines, as he called them. and he also liked to make maps such as this one of the central region of italy, including the arno valley where he was born. these, he made to support his architectural work. the final venue on this whistle—stop tour is the sunderland museum, where i‘m joined by carly collier from the royal collection. this is the image i really want to talk to you about.

basically, it‘s an essay. absolutely. leonardo was an artist, a scientist, but also an intellectual, and here he‘s investigating the nature of light. obviously, there is some drawing, because it is leonardo. in the great scheme of things, how good was he, from michelangelo to picasso? he really was a great draughtsman. and he‘s very unique in the way he uses drawing to truly understand the world. ultimately, then, the subject of all these beautiful drawings is leonardo and the workings of his remarkable mind. will gompertz, bbc news, sunderland. more on those amazing things and all the news on the website. and you can get in touch with me and most of the team on twitter — i‘m @bbcmikeembley. thank you very much for watching. hello.

there is more snow to come in this forecast as we head into friday. the main focus is the zone, say, from south wales across east anglia and anywhere south of here. all driven by this area of low pressure, which stays close by as we go into friday. now, whilst the earlier amber warning from the met office has expired, we still have yellow warnings in place for both snow and ice. so, slippery surfaces, tricky travelling conditions. stay up—to—date with the latest travel news on your bbc local radio station. by friday morning, we are likely to see perhaps 5—10 centimetres of snow across parts of wales, south—west england, particularly over the higher ground, up towards the chilterns and the cotswolds. at least a couple of centimetres elsewhere. and we will start to see further sleet and snow showers piling into north—east england. some of those may well get further south and westwards, perhaps down towards the midlands. should be a fine start to the day across northern ireland, but cold and frosty. and a really cold start again across scotland,

although not quite as cold as the nightjust gone. and, once again, frequent snow showers piling into north scotland, the highlands and also the northern ireland. so, as the day wears on on friday, we will keep our zone of snow showers across central and southern england. it will become more fragmented and increasingly sleety through the day. still further snow showers piling into north—east england, across the north york moors. as i mentioned, some of those may just get across the pennines and down towards parts of the midlands. it will be a breezy day in places, particularly the further south you are, so that‘s just going to exacerbate the cold feel. and, for most, temperatures are not going to get much above three or four celsius. but we should at least see them above freezing across parts of northern england and scotland, where we struggled through thursday with the fog. as we go through friday night and into saturday, we still keep this feed of showers, mainly down eastern and some western coasts. and we start to lose the sleet and snow from south—east england. but a cloudier night here, so temperatures will

stay above freezing. further west, under clear skies, getting down to —1 or —2 celsius. still “11, —5 across the highlands of scotland. then we start the weekend, our area of low pressure moves away into france and germany, and for a brief time through the weekend things are looking drier and quieter. with a northerly wind, we are still going to pick up some wintry showers down some eastern coasts. a few mayjust clip some western coast, but for most on saturday it‘s a dry date, with some crisp winter sunshine. after a frosty start, temperatures getting up to between 3—5 celsius, perhaps 6—7 across south—west england. so, to sum up the weekend, it‘s going to stay cold, there will be some sunshine, further wintry showers and perhaps we could see some rain later on sunday, with some snow across scotland. bye— bye. this is bbc news. the headlines: tens of millions of americans are still enduring temperatures as low as —50 degrees celsius across several midwestern states. the extreme weather has been blamed for at least 21 deaths. it‘s been more than 20 years since a similar polar vortex covered such a large area. both the us and the chinese negotiators have praised what they say is progress achieved in two days of trade

talks in washington. american officials are to visit beijing for further talks soon. president xijinping expressed his hope that the two sides could meet each other halfway. venezuela‘s self—proclaimed interim president has promised to focus on rebuilding the country‘s economy and ending the country‘s humanitarian crisis. in a speech, juan guaido accused president nicolas maduro‘s administration of trying to intimidate him by sending special police to his house. the organisation of american states denounced that move.