News release along with pretty good explainer above, featuring Gavin Schmidt.
NASA GISS (Goddard Institute for Space Studies):
“The exceptional warming that we’re experiencing is not something we’ve seen before in human history,” said Gavin Schmidt, director of GISS. “It’s driven primarily by our fossil fuel emissions, and we’re seeing the impacts in heat waves, intense rainfall, and coastal flooding.”
Though scientists have conclusive evidence that the planet’s long-term warming trend is driven by human activity, they still examine other phenomena that can affect yearly or multi-year changes in climate such as El Niño, aerosols and pollution, and volcanic eruptions.
Typically, the largest source of year-to-year variability is the El Niño – Southern Oscillation ocean climate pattern in the Pacific Ocean. The pattern has two phases – El Niño and La Niña – when sea surface temperatures along the equator switch between warmer, average, and cooler temperatures. From 2020-2022, the Pacific Ocean saw three consecutive La Niña events, which tend to cool global temperatures. In May 2023, the ocean transitioned from La Niña to El Niño, which often coincides with the hottest years on record.
However, the record temperatures in the second half of 2023 occurred before the peak of the current El Niño event. Scientists expect to see the biggest impacts of El Niño in February, March, and April.