Climate change: Current warming 'unparalleled' in 2,000
years
By Matt McGrath
Environment correspondent
24 July 2019
The speed and extent of current global warming exceeds any
similar event in the past 2,000 years, researchers say.
They show that famous historic events like the "Little
Ice Age" don't compare with the scale of warming seen over the last
century.
The research suggests that the current warming rate is
higher than any observed previously.
The scientists say it shows many of the arguments used by
climate sceptics are no longer valid.
When scientists have surveyed the climatic history of our
world over the past centuries a number of key eras have stood out.
These ranged from the "Roman Warm Period", which
ran from AD 250 to AD 400, and saw unusually warm weather across Europe, to the
famed Little Ice Age, which saw temperatures drop for centuries from the 1300s.
The events were seen by some as evidence that the world has
warmed and cooled many times over the centuries and that the warming seen in
the world since the industrial revolution was part of that pattern and
therefore nothing to be alarmed about.
Three new research papers show that argument is on shaky
ground.
The science teams reconstructed the climate conditions that
existed over the past 2,000 years using 700 proxy records of temperature
changes, including tree rings, corals and lake sediments. They determined that
none of these climate events occurred on a global scale.
The researchers say that, for example, the Little Ice Age
was at its strongest in the Pacific Ocean in the 15th Century, while in Europe
it was the 17th Century.
Generally, any longer-term peaks or troughs in temperature
could be detected in no more than half the globe at any one time,
The "Medieval Warm Period", which ran between AD
950 and AD 1250 only saw significant temperature rises across 40% of the
Earth's surface.
Today's warming, by contrast, impacts the vast majority of
the world.
"We find that the warmest period of the past two
millennia occurred during the 20th Century for more than 98% of the
globe," one of the papers states.
"This provides strong evidence that anthropogenic
(human induced) global warming is not only unparalleled in terms of absolute
temperatures but also unprecedented in spatial consistency within the context
of the past 2,000 years."
What the researchers saw is that prior to the modern
industrial era, the most significant influence on climate was volcanoes. They
found no indication that variations in the Sun's radiation impacted mean global
temperatures.
The current period, say the authors, significantly exceeds
natural variability.
"We see from the instrumental data and also from our
reconstruction that in the recent past the warming rate clearly exceeds the natural
warming rates that we calculated - that's another view to look at the
extraordinary nature of the present warming," said Dr Raphael Neukom, from
the University of Bern, Switzerland.
While the researchers did not set out to test whether humans
were the chief influence on the current climate, their findings indicate
clearly that this is the case.
"We do not focus on looking at what's causing the most
recent warming as this has been done many times and the evidence is always
agreeing that it is the anthropogenic cause," said Dr Neukom.
"We do not explicitly test this; we can only show that
natural causes are not sufficient from our data to actually cause the spatial
pattern and the warming rate that we are observing now."
Other scientists have been impressed with the quality of the
new studies.
Winter skating on ice in Europe in centuries gone by was a
common event during the Little Ice Age
"They have done this across the globe with more than
700 records over the past 2,000 years; they have corals and lakes and also
instrumental data," said Prof Daniela Schmidt from the University of
Bristol, UK, who was not involved with the studies.
"And they have been very careful in assessing the data
and the inherent bias that any data has, so the quality of this data and the
coverage of this data is the real major advance here; it is amazing."
Many experts say that this new work debunks many of the
claims made by climate sceptics in recent decades.
"This paper should finally stop climate change deniers
claiming that the recent observed coherent global warming is part of a natural
climate cycle," said Prof Mark Maslin, from University College London, UK,
who wasn't part of the studies.
"This paper shows the truly stark difference between
regional and localised changes in climate of the past and the truly global
effect of anthropogenic greenhouse emissions."
The three papers have been published in the journals Nature
(1) and Nature Geoscience (2), (3).
Sem comentários:
Enviar um comentário