Current annual global temperatures are the warmest they have been in the past 10,000 years, according to a new study examining past periods of climate change.
Researchers from Rutgers University collected marine sediments near the mouth of the Sepik River off northern Papua New Guinea to create a new temperature model of Earth throughout the Holocene – an era spanning from 12,000 years ago to today.
They found that current temperatures are the warmest they have been for 10,000 years and the rate the world is warming has increased since the industrial period.
Study lead author Dr Samantha Bova said their new climate reconstruction of the period shows that the first half of the Holocene was colder than in industrial times.
This was due to the cooling effects of remnant ice sheets from the previous glacial period – contrary to previous reconstructions of global temperatures.
This image shows the evolution of temperature during the Holocene era and some of the key mechanisms responsible for the increase in temperature over the last 12,000 years.
This discovery solves a key climate change mystery – the Holocene temperature conundrum – a disagreement between expected warming and climate models.
‘The late Holocene warming was indeed caused by the increase in greenhouse gases, as predicted by climate models, and that eliminates any doubts about the key role of carbon dioxide in global warming,’ said Bova.
Scientists used fossils from single-celled organisms that live at the ocean surface, to reconstruct the temperature histories of the two most recent warm intervals.
This includes the Last Interglacial period from 128,000 to 115,000 years ago and the Holocene that began 12,000 years ago.
To get the fossils, the team collected a core of bottom sediments near the mouth of the Sepik River off northern Papua New Guinea and used them to recreate the temperature history of the western Pacific warm pool.
This is an ideal location to compare to modern temperatures as it closely tracks changes in global temperatures during that period.
How temperature evolved during the Last Interglacial and Holocene eras is controversial, Bova and colleagues explained.
Data suggest the average annual global temperature during modern times is lower than during the Holocene’s early warm period, which was followed by global cooling.
Meanwhile, climate models strongly suggest that global temperatures have risen throughout the past 10,000 years.
Scientists used fossils from single-celled organisms that live at the ocean surface, to reconstruct the temperature histories of the two most recent warm intervals
Professor Yair Rosenthal, also of Rutgers University, said: ‘The apparent discrepancy between climate models and data has cast doubts among sceptics about the role of greenhouse gases in climate change during the Holocene and possibly in the future.
‘We found that post-industrial warming has indeed accelerated the long and steady trend of warming throughout the past 10,000 years.
‘Our study also underscores the importance of seasonal changes, specifically Northern Hemisphere summers, in driving many climate systems.
‘Our method can, for the first time, use seasonal temperatures to come up with annual averages.’
The findings were published in the journal Nature.