*Michael Mann, creator of 'hockey stick' curve for greenhouse gases, says we now have to double sea rise projections.

*Sees California as 'shining beacon' for how to take action

*Despite harassment, says 'You don't back off from a worthy battle when the stakes are important.'

Even as negotiators wind up another round of climate talks in Germany this week, there is little evidence that leaders are reining in global greenhouse gas emissions enough to avoid warming Earth by more than 2 degrees Celsius (3.6 degrees Fahrenheit) — that's the threshold at which scientists say we can avoid the worst impacts of climate change.

In fact, the concentration of carbon dioxide in the atmosphere averaged more than 410 parts per million in April, for the first time since scientists have been tracking it. KQED Science Editor Craig Miller sat down recently with Michael Mann, who directs the Earth System Science Center at Penn State University, to assess where things stand.