2015 was the hottest year in history by the widest margin on record

It wasn't your imagination: 2015 was a record-shattering hot year.

Last year's global average temperature was the hottest ever by the widest margin on record, two US government agencies said on Wednesday.

The announcement adds to pressure for deep greenhouse gas emissions cuts that scientists say are necessary to stop the warming that is disrupting the global climate.

Data from NASA and the National Oceanic and Atmospheric Administration showed that in 2015, the average temperature across global land and ocean surfaces was 1.62 degrees Fahrenheit (0.90 Celsius) above the 20th century average, surpassing 2014's previous record by 0.29 F (0.16 C).

Here's a graph showing the departure from the averages:

This was the fourth time a global temperature record has been set this century, the agencies said in a summary of their annual report.

"2015 was remarkable even in the context of the larger, long-term warming trend," said Gavin Schmidt, director of NASA's Goddard Institute for Space Studies.

The sharp increase in 2015 was driven in part by El Niño, a natural weather cycle in the Pacific that warms the ocean surface every two to seven years. But scientists say human activities - notably burning fossil fuels - were the main driver behind the rise.

"We would not have seen the record warming without the long-term trend," Schmidt said.

The latest El Niño started in late 2015 and will last until spring 2016. It is among the strongest ever recorded but Schmidt and others say the weather phenomenon played just a supporting role in the earth's temperature rise.

The 2015 data underscores the urgency of cutting greenhouse gas emissions if the world is to hold temperature increases to well below 2 degrees C, the target agreed to by more than 190 countries at climate talks in Paris last December.

(Reuters reporting By Valerie Volcovici)