Last year was among a handful of the warmest on record since 1880, according to US government figures out that provide more evidence that the planet is heating up.
Human-caused pollution and the burning of fossil fuels such as oil and coal have driven up greenhouse gas levels, leading to this long-term rise in temperatures, said the US space agency NASA yesterday.
Carbon dioxide is at its highest level in the atmosphere in 800,000 years, having risen from 285 parts per million in 1880 to 400 parts per million last year, NASA said.
Unless current trends change, scientists said the world should expect each of the coming decades to be warmer than the last, said NASA climatologist Gavin Schmidt.
He described the warming of the past few decades as "unusual," and urged people not to judge whether climate change is happening or not based on random weather events like cold snaps."
"The long-term trends in climate are extremely robust," he told reporters.
"People have a very short memory when it comes to their own experience of weather and climate, and the only way that we can have a long-term assessment of what is going on is by looking at the data."
NASA and the National Oceanic and Atmospheric Administration (NOAA) both released their annual global figures on climate, which were independently produced but found similar increases in temperature across the planet.
According to NOAA, the average of combined land and ocean surface temperatures in 2013 was 0.62 Celsius above the 20th century average of 13.9 Celsius.
NOAA found that 2013 tied with 2003 as the fourth warmest year since records began in 1880, while NASA said last year ranked seventh.
However, experts said the actual temperature differences between years are very small, and that the overall trend toward a warming planet is clear.
Last year also marked the 37th year in a row with higher than average global temperatures.
