The earth would have warmed faster in the last two decades had there not been an unexplained rise in the amount of carbon dioxide being absorbed on land, scientists believe.
Scientists have discovered an "abrupt increase'' since 1988 in the uptake of carbon dioxide (CO2) by the land biosphere, which comprises all of the planet's plant and animal ecosystems.
Wellington-based scientist Dr Sara Mikaloff-Fletcher, from the National Institute of Water and Atmospheric Research, was part of the global research team investigating the distribution of CO2 emissions.
Ms Mikaloff-Fletcher said the breakthrough had taken scientists "completely by surprise''.
Although the findings were interesting, she said they created more questions than answers.