Trump turns fire on Republican leadership Nominee refuses to endorse Paul Ryan and John McCain; global temperatures hit new records; millennials 'less likely to hook up' than earlier generations Donald Trump attends a campaign event in Pennsylvania. Photograph: Eric Thayer/Reuters Edward Helmore in New York Trump continues his attacks, now on party leadership Donald Trump has refused to endorse Paul Ryan and John McCain, despite being endorsed for the presidency by both men. "I like Paul, but these are horrible times for our country. We need very, very strong leadership. And I'm just not quite there yet," the Republican nominee said of the House speaker. Ryan's campaign spokesman said: "Neither Speaker Ryan nor anyone on his team has ever asked for Donald Trump's endorsement." Earlier on Tuesday, Barack Obama called Trump "unfit" and "woefully unprepared" to be president and urged Republican leaders to denounce their nominee. The French president, François Hollande, also chipped in, saying the real estate magnate made people "want to retch". Early on Wednesday morning, Trump denied reports of growing unhappiness within his campaign over erratic public conduct and missteps: "There is great unity in my campaign, perhaps greater than ever before," he tweeted. On Tuesday, he also told a supporter to "get the baby out of here" after the infant in question began crying during a speech he was making. And in more than a dozen interviews at two Trump rallies this week, Trump supporters tell Ben Jacobs they either don't know or don't care about his recent comments criticizing the parents of a Muslim soldier killed in Iraq. Donald Trump will not endorse Paul Ryan as Republican splits widen New temperature records spur climate fears The world is careening towards an environment never experienced before by humans, with the temperature of the air and oceans breaking records, sea levels reaching historic highs and carbon dioxide surpassing a key milestone, according to an international "state of the climate" report, led by the National Oceanic and Atmospheric Administration. "The impacts of climate change are no longer subtle," Michael Mann, a leading climatologist at Penn State, told the Guardian. "They are playing out before us, in real time. The 2015 numbers drive that home." Environmental records shattered as climate change 'plays out before us' Millennials turn their backs on sex Continuing US research shows more men and women aged 20-24 having no sexual partner than those at the same age group born in the 1960s, 70s and 80s. "You would expect, based on the popular notion, that with apps such as Tinder, [young people are] a group that is looking for hook-ups and not long-term relationships," said the study coauthor Ryne Sherman at Florida Atlantic University. "What we are seeing is this group is less likely to hook up, so to speak, than previous generations." Separate research in the UK showed large numbers of young people experience sexual problems such as pain or anxiety during sex, the inability to climax and finding intercourse difficult. Less sex please, we're millennials – study Rio's bay awash with pollution fears In time for the opening of the Rio Olympics today, the World Health Organisation has issued an advisory to athletes to spend as little time as possible in the waters of Guanabara Bay, where the Olympic sailing events will take place. "The water quality is shit because the sewage flushes in untreated. We all know that," said Alex Batista, a local skateboard instructor. "No local would swim in it because we know we would get a disease." Meanwhile, the Guardian asks whether Rio's police are really the most violent in the world. What's in the water? Pollution fears taint Rio's picturesque bay ahead of Olympics Life on the American River Romantic or merely arduous? Dozens of homeless now call the banks of Sacramento's American River home. Nisenan Indians settled here 5,000 years ago. Itinerant miners built shacks during the 1840s gold rush, followed by families displaced during the great depression. Now it is the turn of hundreds of modern outcasts with pets, bicycles, tents and tarpaulin. They come for the seclusion and opportunity to live on their own terms, reports Rory Carroll. Life on the American river: Mark Twain romance, or false hope for the homeless? 'Tech tax' rejected San Francisco has voted against a proposal known as the "tech tax", which would have forced the area's biggest technology firms to fund initiatives to provide affordable housing and tackle the city's homeless problem. The measure would have raised an estimated $140m annually to fund affordable housing and shelters for homeless people. The proposal was rejected by the budget committee of the board of San Francisco's supervisors. San Francisco rejects 'tech tax' plan to require firms to back housing programs Alphabet's Project Wing to begin testing Google's parent company, Alphabet, has been given the green light by US regulators to test autonomous delivery systems. The drones will be tested in one of six designated Federal Aviation Authority areas within the US. The announcement comes alongside a pledge from the US National Science Foundation to spend $35m over the next five years on drone research and a month after the US government green-lit restricted commercial drone flights. Alphabet will begin testing Project Wing delivery drones in the US Kanye inspires new project: a giant Ikea bed Ikea has responded to Kanye West's request to "allow Kanye to create" by proposing the Yeezy: a bed big enough for West and all his celebrity friends. The rapper had told the BBC he had an interest in turning his hand to "a minimalist apartment inside of a college dorm, with a TV built inside of the wall" and was drawn to Ikea because of his goal of making his products more accessible, describing his "mission in life" as to do "high-end and all this stuff, and bring it to the people". Yeezy to assemble: Ikea designs giant bed for Kanye West Cure for avocado 'browning' An Australian company may have solved the problem of rapidly browning avocados with a machine that "switches off" the enzyme that causes discoloration. The Australian-designed Natavo Zero, designed for pre-sliced or mashed avocado used in products like guacamole, can process about 4,000 avocados an hour. Turn that brown upside down: avocado 'time-machine' stops fruit browning In case you missed it … Hollywood's latest trend: gender-swapping It's easy to forget how threatening society once found the comedy of emasculation when, in 1959, Billy Wilder's cross-dressing classic Some Like It Hot was condemned by the National Legion of Decency as "morally objectionable" for promoting homosexuality, lesbianism and transvestitism. Now Hollywood is going all out, with Channing Tatum looking to score comedy points as a merman in a remake of the 1984 Tom Hanks comedy Splash. Remaking Splash: is gender-swapping Hollywood's new secret weapon? Manage your emails | Unsubscribe | Trouble viewing? You are receiving this email because you are a subscriber to Guardian US Briefing. Guardian News & Media Limited - a member of Guardian Media Group PLC. Registered Office: 222 Broadway, 22nd and 23rd Floors, New York, New York, 10038