Global warming over the past 150 years has upended more than six millennia of climate cooling, with temperatures spiking to levels that otherwise may not have been seen for 125,000 years.
Towards the end of the Stone Age, around 4,500 BC, the world’s climate started cooling at a rate of about 0.1°C (0.18°F) every 1,000 years, before bringing the planet into the ‘Little Ice Age’ in around 1300 AD.
But since the mid-19th century temperatures have surged upwards, rising by 1°C (1.8°F) as tonnes of greenhouse gases locked into the Earth are pumped back into the atmosphere due to burning of fossil fuels.
The last time temperatures reached that high, sea levels are thought to have been around 20 feet higher than today, which would put many modern urban areas underwater.
Scientists at Northern Arizona University, US, made the worrying discovery after analysing data on historical temperatures from sources including ice cores, lake sediments and prehistoric fauna.
Experts used remains in glaciers, sediment cores, caves, corals, and other sources to map changes to the Earth’s climate over the past 12,000 years
Earth’s initial cooling was driven by slower cycles in the Earth’s orbit, said research professor Michael Erb, who analysed temperature reconstructions for the study.
‘This reduced the amount of summer sunlight in the Northern Hemisphere, culminating in the “Little Ice Age”,’ he said.
However, temperatures then began to climb as the industrial revolution took off. And the scientists involved in this study predict that they will continue to rise.
‘This past decade was likely cooler than what the average temperatures will be for the rest of this century and beyond, which are very likely to continue to exceed 1°C above pre-industrial temperatures,’ said associate professor Nicholas McKay, who was a co-author in the study.
‘Our future climate will largely depend on the influence of human factors, especially the build-up of greenhouse gases.
‘However, future climate will also be influenced by natural factors, and it will be complicated by the natural variability within the climate system.
‘Future projections of climate change will be improved by better accounting for both anthropogenic and natural factors.’
This graph shows changes to the global-mean temperatures over the past 12,000 years. The lines show different analyses of changes in temperature levels
In the study, published in Nature Research’s Scientific Data, scientists mapped temperatures over the past 12,000 years to identify changes.
They relied on the ‘Temperature 12k’ database, built by the team earlier this year by compressing results from 1,319 data records based on samples taken from 679 sites globally.
Scientists reconstructed temperatures using glacial cores, lake sediments and marine sediments laid down during the time period.
They also used deposits found in caves, corals, and the fossils of insect larvae to establish approximate temperatures when they were preserved.
The analysis was not able to break down temperature changes by decade, meaning that the 12,000-year temperature reconstruction could not be compared with any recent decade.
Scientists used data taken from 679 sites worldwide to estimate temperatures (shown)
The scientists said their work will help explain processes causing climate to change, which could help the planet prepare for any approaching changes.
The National Science Foundation funded the work with a grant of more than £969,000 ($1.2 million).
HOW IS GLOBAL WARMING AFFECTING GLACIAL RETREAT?
Global warming is causing the temperatures all around the world to increase.
This is particularly prominent at latitudes nearer the poles.
Rising temperatures, permafrost, glaciers and ice sheets are all struggling to stay in tact in the face of the warmer climate.
As temperatures have risen to more than a degree above pre-industrial levels, ice continues melt.
For example, melting ice on the Greenland ice sheet is producing ‘meltwater lakes’, which then contribute further to the melting.
This positive feedback loop is also found on glaciers atop mountains.
Many of these have been frozen since the last ice age and researchers are seeing considerable retreat.
Some animal and plant species rely heavily on the cold conditions that the glaciers provide and are migrating to higher altitudes to find suitable habitat.
This is putting severe strain on the ecosystems as more animals and more species are living in an ever-shrinking region.
On top of the environmental pressure, the lack of ice on mountains is vastly increasing the risks of landslides and volcanic eruptions.
The phenomena is found in several mountain ranges around the world.
It has also been seen in regions of Antarctica.