Humans Have Caused the Most Dramatic Climate Change in 3 Million Years


Recently Assad with some research colleagues at the Potsdam Institute for Climate Impact Research, a look at a brand new science article in which are climate model for the first time had recreated the climate on earth over the last three million years, which covers the entire geological pleistocene epoch. The Pleistocene is so important as it constitutes a point of reference for life on. Earth. Because although sure our planet has existed for four point, five, billion years it's only in the last million years. That earth has looked at least roughly in the way as we know it, the continents were roughly where they are today. The North and South Poles were covered with ice. The atmosphere had a similar chemical composition to what we have today. Planet, Earth. Our earth has only existed for three million years. All, comparisons further back in time are quite meaningless. And the manuscript I hold in my hand is not just reaching. My brain is also striking straight into my heart. A deep humility settles in when look at the graph showing the variations in mean global temperature on earth over the past three, million years it shows that we have never throughout the whole plasticine exceeded two degrees global warming compared to our pre industrial average temperature of approximately fourteen degrees. Never. This means that Earth despite all the stresses and natural shocks from fluctuations and Solar Radiation Volcanic eruptions, asteroid impacts and earthquakes has regulated itself within an incredibly narrow range minus four degrees. Celsius were in deep ice age plus two degree Celsius. We're in a warm interglacial period lasting three million years. It's absolutely incredible. Especially since we know why. It's earth's ability to self regulate the ability of the oceans to absorb and store heat the ability of the ice sheets to reflect solar radiation the ability of the forests to absorb carbon dioxide and the ability to be a safe and store greenhouse gases. The planet is a biophysical self playing piano whose music sheet stays. Within the minus four plus to scale. If that is not caused for humidity than I do not know what humidity is. And a deep concern in hundred and fifty years. In the geological blink of an eye, we risk now tearing this Planetary Symphony to shreds. Let that sink in. The global average temperature is now changing hundred and seventy times faster than over the last seven thousand years and it's doing. So in the wrong direction upwards when the current orbital forcing meaning are distance to the sun and the current low level of solar activity means that the temperature should in fact, be slowing down. You don't have to be a physicist to understand that we have a problem. Climate skeptics like to argue that historically the climate has fluctuated so much. So why shouldn't it be fluctuating now? Obviously. It fluctuates. But we are now racing towards plus three to plus four degrees warming. Sceptics like to bring up the little ice age the time when Swedish King Call The tenth Gustav Marched His army across the deep frozen great belt and the little belt in sixteen fifty eight to beat the Danes or that the vikings grew grapes in Greenland during the medieval warm period. Yes. Of course, this is true but it all occurred within the natural boundaries of minus four and plus two degrees. And it's here within this sweet spot that we must remain for our own sakes and our future? In August two, thousand, eighteen at the peak of that year's drought and fires in Sweden and Europe. We published a scientific paper where we tried to establish whether we are at risk of pushing the entire planet away from its current state of equilibrium, the Holocene epoch where we have been since the last ice age. This is fundamental. Our Planet Earth can be in three different states. It can be in a deep ice age as it was twenty thousand years ago with large is. Extending over the northern and Southern Hemisphere with over two kilometers of ice above our heads here in Sweden an ice extending as far south as Berlin. This is an equilibrium state as it is not only lower solar radiation that keeps earth in an ice age. It is also the feedbacks caused by ice. As the ice sheets grow earth gets whiter, which means that more more incoming heat from the sun is reflected back to space more ice means it gets colder which means even more is and suddenly you have a self reinforcing mechanism. This is what makes an ice age and equilibrium earth remains. They're not only because of the external forces from the sun but also thanks to these inbuilt biophysical processes in this case, the color of ice. Earth can also be in an interglacial an intermediate state, which is what we have today where was still have permanent is sites at the polls and we have glaciers on land and the biosphere with forests, grasslands, and lakes roughly as Earth as we know it. It is these two equilibrium states and only these two states that the planet has been over the last three million years that is during the entire Pleistocene. But then there is a third state when earth tips over from self cooling feedback loops to self heating feedback loops, which leads to an inevitable journey to becoming a hot tropical planet that is four, five, six, potentially seven, eight degrees warmer than today where in principle, all the ice has gone and the surface of the ocean is more than fifty meters higher than it is today and where the conditions for live is fundamentally different all over the entire planet. This is what we call hothouse earth. Or Highs Zaid hot time in German where the article when we published it drew so much attention doing this burning heat wave in the summer of twenty eighteen that highs Zaid was chosen as the word of the year in Germany. In this research, we tried for the first time to identify the global mean temperature at which we are in danger of tipping over from our current state, the Holocene interglacial, and embarking on a journey that would inevitably take us to highlight our conclusion is that we cannot exclude that the planetary threshold. The tipping point where we kickoff unstoppable processes of self amplified warming is at two degrees. Bear in mind we are today at one point one very mind were moving fast along a path that reaches one point five in potentially only twenty, thirty years and two degrees in forty fifty years. This is one I would argue of the biggest. Challenges of all to test whether we are right. Can the planet cope with or Canet not cope with higher temperatures than two degrees? But. My conclusion based on the knowledge we have today is that the planetary threshold to avoid triggering high Zaid is most likely at two degrees. Of course, it's not so that Earth will fall off a cliff at two degrees. The risk is rather that we would then pass a threshold where the shift towards hindsight would become unstoppable. In other words, we face an urgency at the timeframe whether we pushed the on button on not triggering stoppable warming is within the next few decades meaning essentially. Now, if we pressed the UNBUTTON and kick off the great planetary machinery with feedback loops causing self warming, then the full impacts may play out over three four, five, hundred years before we reach a new equilibrium state hothouse. A planet with over ten meters, sea level rise temperatures, and extreme droughts, floods, and heatwaves making large parts of earth uninhabitable a planet we do not want a planet that cannot support US humans. This requires from us that we understand two different time horizons. The short term time of commitment. When do we push the unbutton but then also the long term time horizon when we have the full impact hitting on people these are different but ethically, I would argue only the trigger moment counts, we cannot leave a damaged planet beyond repair to future generations. So to summarize the decisive moment when we press don't press the button lies within the next ten to twenty years. With consequences for all future generations a moral, bum. Are High site article concluded that degree Celsius is our ultimate planetary threshold that we need to stay away from. This article actually came out six months before our climate modeling showed that we've never exceeded two degrees throughout the whole pleistocene, the last three million years. In Two thousand nine, our planetary boundaries size showed that one point five degrees is a boundary we should not transgress because then we enter a danger zone of uncertainty. So perhaps you do understand my feeling a deep concern of humility in the face of our latest scientific findings, which really only says, one thing tipping points are real and if they're crossed, they lead to unstoppable changes, which requires a new relationship between us and our planet, and that we realize that we are facing a new ethics. What we do today will determine the future on earth for all our children and their children.

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