Last year marked the planet's second-warmest year on record, capping a decade that ranked the warmest 10-year period since reliable recordkeeping began more than a century ago, the UN's World Meteorological Organization said Tuesday.
"We are currently way off-track to meeting either the 1.5-degree Celsius or 2-degree Celsius targets that the Paris Agreement calls for," UN Secretary-General António Guterres in a statement.
The Earth's average temperature last year was about 1.1 degrees Celsius higher than pre-industrial levels, second only to the record established in 2016, which was then partly fueled by an El Nino warming trend that increased the planet's temperature worldwide.
Scientists broadly agree that nations need to keep the globe's average temperature from rising by more than 2 degrees Celsius — and, ideally, 1.5 degrees Celsius — to avert the worst impacts of climate change.
"We just had the warmest January on record. Winter was unseasonably mild in many parts of the Northern Hemisphere," WMO Secretary-General Petteri Taalas said in a statement. "Smoke and pollutants from damaging fires in Australia circumnavigated the globe, causing a spike in CO2 emissions. Reported record temperatures in Antarctica were accompanied by large-scale ice melt and the fracturing of a glacier which will have repercussions for sea-level rise."
The report highlighted a range of impacts already being felt, from oceans being made warmer, more acidic, and deprived of oxygen by rising temperatures, as well as depleting ice from the Arctic to the Antarctic, rising sea levels, and consequences for human health. 
"Given that greenhouse gas levels continue to increase, the warming will continue," Taalas said. "A recent decadal forecast indicates that a new annual global temperature record is likely in the next five years. It is a matter of time."