The UNFCCC’s COP21 concluded goals which aimed for limiting global warming to C, and certainly keeping it below C, both measured with respect to pre-industrial temperatures.
According to the United States National Center for Atmospheric Research (“NCAR”), in cooperation with the University Corporation for Atmospheric Research (“UCAR”), we are already at C. The explanation?
“The physics of Earth’s climate system means that warming continues long after greenhouse gases enter the atmosphere. That’s because the oceans continue to warm up for decades in response to greenhouse gases already in the atmosphere, creating a lag in the climate system.
“As a result, we’re committed to about C of additional warming even if we could immediately stabilize levels of carbon dioxide in the atmosphere, research has shown. The extra warming means that the planet is effectively three-quarters of the way to the C target.”
March 2016: A scorcher. Hat tip to Tamino.