"Further global warming of 1 °C defines a critical threshold. Beyond that we will likely see changes that make Earth a different planet than the one we know."...The linked article is actually a rather long - and depressing - summary of all the climate announcements lately. Not happy reading, by any stretch.
Earth is already as warm as at any time in the last 10,000 years, and is within 1 °C of being its hottest for a million years, says Hansen's team. Another decade of business-as-usual carbon emissions will probably make it too late to prevent the ecosystems of the north from triggering runaway climate change, the study concludes.