The average air temperature over land and sea was 0.31 degrees above the 1981-2010 average, eclipsing the previous record anomaly of 0.28 degrees set in 2010.

Compared with the 20th century, temperatures last month were 0.76 degrees above average, the agency said.

The US National Oceanic and Atmospheric Administration is likely to release its March readings in coming days. Last month, the agency said both the first two months of 2015 and the 12 months to February were the hottest in 136 years of records.

The warm start to 2015 is likely to continue with large areas of the Pacific Ocean, a major driver of global climate, remaining abnormally warm.

El Nino temperature boost

Australia's Bureau of Meteorology on Tuesday said sea-surface temperatures are "now just shy of El Nino levels", with all major models it tracks pointing to El Nino thresholds likely to be exceeded by June.

During El Nino years, the Pacific absorbs less heat from the atmosphere, boosting global temperatures by 0.1-0.2 degrees. Such events typically bring drier conditions for much of Australia, resulting in reduced cloud cover and hotter temperatures.

Climate scientists say the arrival of an El Nino event would build on the background warming from climate change, making it likely that 2015 and even 2016 will challenge global temperature records. That would mean 2014's ranking as the hottest year will be short-lived.