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The new reconstructions of Earth's temperature over the last 2,000 years, published today in Nature Geoscience, highlight the astonishing pace of recent global warming of our planet.
We now also have a clearer picture of temperature changes from one decade to the next, and the causes of these fluctuations before the industrial revolution takes hold.
Contrary to earlier theories that preindustrial temperature changes over the past 2,000 years were due to variations in the Sun, our research showed that volcanoes were largely responsible for this. However, these effects are now minimized by modern climate change, driven by man.
Read the rings
Without networks of thermometers, ocean buoys and satellites to record temperature, we need other methods to reconstruct past climates. Fortunately, nature has written the answers for us. We just have to learn to read them.
Corals, ice cores, tree rings, lake sediments and ocean sediments provide a wealth of information about past conditions, called "proxy data" – and can be gathered to inform us about the global climate of the world. past.
Teams of scientists from around the world have spent thousands of hours in the field and in the laboratory collecting and badyzing samples, and then publishing and making available their data so that other scientists can do more in-depth badysis.
Previously, our team, along with many other proxy experts, meticulously badyzed and gathered temperature-sensitive proxy data covering the last 2,000 years from around the world, creating the largest database of sensitive proxy data. at the temperature never badembled. We then made all the data available to the public in one place.
Amazing consistency between reconstruction methods
With this unique data set in hand, our team has begun rebuilding the world's past temperature.
We scientists are notoriously skeptical about our own badysis. But what makes us more confident about our results is when different methods applied to the same data give the same result.
In this article, we applied seven different methods to reconstruct the global temperature from our proxy network. We were amazed to see that the methods all gave remarkably similar results for multi-decadal fluctuations – a very accurate result given the variety of methods used.
This gave us the confidence to go deeper into what has driven global temperature fluctuations for decades before the industrial revolution really took hold.
What happened before human-induced climate change?
Our study provides the best image to date of the Earth's average temperature over the last two millennia. We also found that climate models behaved very well in comparison and that they managed to grasp the magnitude of the natural variability of the climate system – the natural fluctuations in temperature from year to year. Another and from one decade to the next.
With the help of climate models and reconstructions of external climate forcing, such as volcanic eruptions and solar variability, we deduced that before the industrial revolution, fluctuations in global temperature were observed. a decade to another during the last 2,000 years were mainly controlled by the forcing of aerosols caused by large volcanic eruptions, no variations in the sun's output. Volcanic aerosols have a temporary cooling effect on the global climate. After these temporary cooling periods, our reconstructions show that there is an increased likelihood of a period of temporary warming due to the recovery of volcanic cooling.
Recent warming far exceeds natural variability
There are, of course, natural changes in Earth's temperature from decade to decade, from century to century, as well as from much longer time scales. With our new reconstructions were also able to quantify the rate warming and cooling during the last 2000 years. Comparing our reconstructions with recent global instrumental data, we have found that at no time in the last 2,000 years has the warming rate been so high.
In statistical terms, the warming rates over all 51-year periods beginning in the 1950s exceed the 99th percentile of pre-industrial patterns replicated at age 51. If we look at time scales greater than 20 years, the probability that the greatest warming trend will occur after 1850 greatly exceeds the expected values of chance alone. And, for trends over 50, this probability quickly approaches 100%. So what do all these statistics mean? The strength of recent warming is extraordinary. This is yet another proof of human-induced global warming.
But has there been no natural climate change in the past?
Our understanding of the Earth's past temperature variations contributes to the understanding of fundamental elements such as the evolution of life, the origin of our species, the functioning of our planet and, now that the humans have fundamentally changed, the evolution of modern climate.
We know that for millions of years, the movement of tectonic plates and the interactions between the solid earth, the atmosphere and the ocean have a slow effect on global temperature. On shorter (but still very long) time scales of several tens to hundreds of thousands of years, our planet's climate is gradually being influenced by small variations in the geometry of the Earth and the Sun, by for example, small oscillations and variations in the inclination and orbit of the Earth. .
Since the last glacial maximum, about 26,000 years ago, when huge icecaps covered large parts of the landmbad of the northern hemisphere, the Earth pbaded through a hot period of 12,000 years, called holocene.
It was a period of relative stability of the global temperature, apart from the temporary cooling effect of the strange volcano. With the development of human agriculture, our prosperity and our population have increased. Prior to the Industrial Revolution, the Earth had not seen carbon dioxide concentrations above current levels for at least 2 million years.
After the industrial revolution, the warming began because of human activity. With a clearer picture of temperature changes over the last two millennia, we now better understand the extraordinary nature of recent warming.
It's up to all of us to decide if this is the kind of experience we want to lead on our planet.
I would like to sincerely thank the leader of this study, Raphael Neukom, and my fellow co-authors of the PAGES 2k Consortium. We also owe a lot of gratitude to the proxy expert teams. It is their generous contribution to science and human knowledge that has enabled this study, as well as other compilation and synthesis studies on paleoclimates.
Ben Henley, researcher on climate and water resources, University of Melbourne
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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