US President Barack Obama attends the opening ceremony of the G20 Summit at the International Expo Center in Hangzhou on September 4, 2016. G20 leaders confront a sluggish global economy and the winds of populism as they open annual talks, but the long war in Syria and the South China Sea territorial dispute hang over the summit. / AFP PHOTO / POOL / Nicolas ASFOURINICOLAS ASFOURI/AFP/Getty Images

German Chancellor Angela Merkel (L) and US President Barack Obama (R) attend the opening ceremony of the G20 Summit at the International Expo Center in Hangzhou on September 4, 2016. G20 leaders confront a sluggish global economy and the winds of populism as they open annual talks, but the long war in Syria and the South China Sea territorial dispute hang over the summit. / AFP PHOTO/AFP/Getty Images

US President Barack Obama (L) and Chinese President Xi Jinping (R) attend the opening ceremony of the G20 Summit at the International Expo Center in Hangzhou on September 4, 2016. G20 leaders confront a sluggish global economy and the winds of populism as they open annual talks, but the long war in Syria and the South China Sea territorial dispute hang over the summit. / AFP PHOTO / POOL / Nicolas ASFOURINICOLAS ASFOURI/AFP/Getty Images

German Chancellor Angela Merkel listens to Chinese President Xi Jinping (not pictured) speech during the opening ceremony of the G20 Summit at the International Expo Center in Hangzhou on September 4, 2016. G20 leaders confront a sluggish global economy and the winds of populism as they open annual talks, but the long war in Syria and the South China Sea territorial dispute hang over the summit. / AFP PHOTO/AFP/Getty Images

German Chancellor Angela Merkel (L) and US President Barack Obama (R) attend the opening ceremony of the G20 Summit at the International Expo Center in Hangzhou on September 4, 2016. G20 leaders confront a sluggish global economy and the winds of populism as they open annual talks, but the long war in Syria and the South China Sea territorial dispute hang over the summit. / AFP PHOTO / POOL / Nicolas ASFOURINICOLAS ASFOURI/AFP/Getty Images

US President Barack Obama grimaces as he speaks to German Chancellor Angela Merkel (not pictured) during the opening ceremony of the G20 Summit at the International Expo Center in Hangzhou on September 4, 2016. G20 leaders confront a sluggish global economy and the winds of populism as they open annual talks, but the long war in Syria and the South China Sea territorial dispute hang over the summit. / AFP PHOTO / POOL/AFP/Getty Images

Chinese President Xi Jinping (front 2nd R) gives a speech during the opening ceremony of the G20 Leaders Summit whilst US President Barack Obama (front 2nd L), Russia's President Vladimir Putin (front R) and German Chancellor Angela Merkel (front L) listen at the International Expo Center in Hangzhou on September 4, 2016. G20 leaders confront a sluggish global economy and the winds of populism as they open annual talks, but the long war in Syria and the South China Sea territorial dispute hang over the summit. / AFP PHOTO / POOL/AFP/Getty Images

UN Secretary-General Ban Ki-Moon (C) arrives for the G20 Summit at the International Expo Center in Hangzhou on September 4, 2016. G20 leaders confront a sluggish global economy and the winds of populism as they open annual talks, but the long war in Syria and the South China Sea territorial dispute hang over the summit. / AFP PHOTO / POOL / Rolex DELA PENAROLEX DELA PENA/AFP/Getty Images