this is a claing christopher gibson movement coming -- climate change movement coming of age, demonstrating it is a profound concern. it's the biggest political gathering about anything in the united states in many years. and that is the message above all that we need to get across. >> environmental activists have been down the road before. what is different is the broad coalition that is supporting that. from groups to labour unions. they are hoping to create a ground swell of support for action. major junions brought thousands of people, reflecting labour's position on how climate action will impact jobs and the economy. >> it will not hurt the economy. it's the only choice we have. if we don't combat climate change, our economy will be devastated. >>> activists are calling for an agreement that will keep the rise in temperature under 2 degrees, and switching to clean energy by 2050. they say we must act now or pay the price later. >>> u.s. secretary of state john kerry has been meeting iran's foreign minister in new york. the talks took place in a third day of nuclear discussions between