Last year was the fourth hottest on record

NASA scientists announced that Earth’s average surface temperature for 2018 was more than one degree Celsius above the average of the late 19th century, when humans started pumping large amounts of carbon dioxide into the atmosphere. That puts the year among the hottest in nearly 140 years of record keeping.

The trend is unmistakable. The last five years have been the five warmest on record.

“We’re no longer talking about a situation where global warming is something in the future,” said the director of the group that conducted the analysis. “It’s here. It’s now.”

Analysis: What sets the warming apart from long climatic fluctuations of the geologic past is its relative suddenness and its clear correlation with increased levels of greenhouse gas emissions produced by human activity.