A highly speculative idea i would like to propose, perhaps totally wrong. Could it be that Earth's temperature rises when it's magnetic field decreases? As the flows of Earth's metallic core change, it's magnetic field changes. And currently the magnetic field is decreasing. This decreasing in magnetic field allows more "solar energy" to arrive at the planet and this in turn increase the temperature of the Earth. Please note I do not claim anything but if i have a link to reliable magnetic field data & temperature data i can check for a correlation.