The federal government confirmed 2016 as the planet's warmest year on record, according to a report released Thursday by the National Oceanic and Atmospheric Administration.

The combined influence of long-term global warming and a strong El Niño early in the year led to last year's all-time record heat, NOAA said.

While El Niño is a natural warming of Pacific Ocean water, man-made global warming is caused by greenhouse gases released into the atmosphere from the burning of fossil fuels such as oil, gas and coal.

The amount of carbon dioxide, one of the main greenhouse gases, in the atmosphere climbed to its highest level in 800,000 years, the report found.

The report also noted other signs of a warming planet in 2016:

Greenhouse gases were the highest on record.

Sea-surface temperatures were the highest on record.

Global upper ocean heat content near-record high.

Global sea level was the highest on record.

Antarctic had a record low sea ice extent.

Known as the State of the Climate, the annual report is prepared by more than 450 scientists from more than 60 countries around the world and published in conjunction with the American Meteorological Society. It's the most comprehensive annual summary of Earth's climate.

The U.S. alone endured 15 separate weather or climate-related disasters last year. At a cost of some $46 billion, it amounted to the second-highest total since 1980, when the records began.

The report comes just days after President Trump officially informed the United Nations of his plan to remove the U.S. from the Paris climate agreement, which the U.S. joined in 2016. Trump announced his plan to withdraw on June 1. That agreement aims to keep global temperatures from rising more than 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels.

A separate study published Thursday found it is “extremely unlikely” that 2014, 2015 and 2016 would have been the warmest consecutive years on record without the influence of human-caused climate change.

That study, published in the peer-reviewed journal Geophysical Research Letters, said the likelihood of seeing three straight record-breaking years without the effects of climate change is "no greater than 0.03%."

“With climate change, this is the kind of thing we would expect to see. And without climate change, we really would not expect to see it,” said Michael Mann, a climate scientist at Pennsylvania State University and lead author of the study.