That’s because while the last eight years trended slightly downward, this small period of time was greatly impacted by natural El Niño and La Niña cycles, experts explained. Zooming in on just this ...

The graph shows spikes and drops in temperature over the past 9,500 years, charting how much higher or lower each year’s temperatures are than the average temperature over the entire time period.

Refining with colors Mathematicians have developed various strategies to compare graphs. Since the 1970s, algorithms have been able to test graph isomorphism, but in exponential time.