[The Free Engineer]

The Tonga eruption may have had some influence on the recent temperatures.

“...nearly four times the amount of water vapor that scientists estimate the 1991 Mount Pinatubo eruption in the Philippines lofted into the stratosphere”

https://www.nasa.gov/earth/tonga-eruption-blasted-unprecedented-amount-of-water-into-stratosphere/

[Pete from Shawnee Mission]

That and the Iceland and LaPalma eruptions. Add particulate to the atmosphere, perhaps reduced subsurface heating due to changes magma pressure or changes in the earth's magma currents.

In addition to these things, there is precession of the equinoxes and the wobble in the earths axis.

North African Climate Cycles

"Variations in the climate of the Sahara region can, at the simplest level, be attributed to the changes in insolation because of slow shifts in Earth's orbital parameters. The parameters include the precession of the equinoxes, obliquity, and eccentricity as put forth by the Milankovitch theory.[2] The precession of the equinoxes is regarded as the most important orbital parameter in the formation of the "green Sahara" and "desert Sahara" cycle."

More at link.