Human development in the Anthropocene requires that we understand not only the rising human pressures on ecosystems, nature, and the planetary system as a whole, we must also understand how nature and the earth system responds.
We’re learning more and more from empirical research around the world, that nature doesn’t respond in just incremental and linear ways. In fact, we now recognize that systems from coral reefs, to rainforests, to temperate forests, have several distinctly different states, separated by thresholds.
So, a system can be either a rainforest or a savannah. And if a system is pushed through environmental changes, across this threshold, we talk of a tipping point. When a system changes fundamentally its structure and function, and tips over from one stable state to another stable state. So strictly speaking the definition of a tipping point is when a system fundamentally changes structure and function, and settles into a new stable state. And the prerequisite to do so is that a feedback mechanism, which keeps the system tightly in one state, changes direction.
For example, a rainforest, its feedback is that it sustains its own moisture – it’s a self-wettening system. The feedback is that the green canopy sucks out a tremendous amount of water from the soil, feeds that back a vapour back into the atmosphere, and self-generates rainfall, and also keeps moisture within its very tight, dense canopy. That’s the feedback keeping it in a rainforest state. When that system is cut open through deforestation, it dries out, and warms up due to climate change, the feedback can change into a self-drying system, where instead it being wettening, becomes a self-drying system, and the system crosses a threshold, it becomes a tipping point, and gets locked as a savannah.
This is “tipping points.” Now tipping points have been explored for decades, and have been understood in small ecosystems from lakes and forest systems, but increasingly we see evidence that large-scale systems can also be subject to tipping points.
And this is just one example of a potential tipping point that really, really concerns scientists across the world. It’s data from Greenland, showing on the x-axis months of the year, and on the y-axis showing the percentage of incoming heat from the sun, which is reflected back to space – what we call Albedo.
Now in the coloured thin lines, you see the stable state with a permanent ice layer on Greenland. When the ice is stable it is a very white colour, and as well all know, a white, light colour reflects back roughly 90-95% of incoming heat. And that’s exactly what we see. It goes down a little bit during the Arctic summer of June-July, when the fringes of Greenland always melt and become a slightly darker liquid surface, but overall, it’s a mirror, it’s a cooling system, it’s a prerequisite for the earth to stay stable in the Holocene.
But look at that thick red line, which are observations from NASA in 2012. An extraordinary exception suddenly, for two weeks in July, the feedback changes direction from being a mirror, reflecting back heat, ie. a cooler, to becoming a net heat absorber. More than 50% of incoming heat is sucked up because for the first time in observational history the entire Greenland ice sheet is melting and covered by a liquid darker surface. Now Jason Box at the Byrd Polar Research Institute concludes in calculation that just these two weeks of change in feedback corresponds to a new injection of heat of in the order of 300 exajoules of energy.
Now 300 exajoules is a very difficult number, but just to give you some comparisons, the annual energy consumption in the US is in the order of 200 exajoules. The annual global energy consumption is a bit more than 600 (exajoules). So momentarily this means that Denmark bypasses China and the US as the world’s largest climate forcing nation. And this occurs when Mother Earth changes directions in the feedback, which potentially could be a tipping point.
Now for the Arctic, for example, there is emerging research showing that several systems can be subject to these kind of tipping points. Such as a flip in the Arctic Sea ice cover, meaning that it could suddenly flip over into a situation with permanent open sea.
And other systems that keep the ocean circulation functioning between the Arctic Sea, and for example, the Atlantic. Now recent research on Greenland shows something quite remarkable. Ice core data, looking at the conditions on earth the last time we had a warm interglacial, the Eemian warm interglacial period, some 120 000 years back. To explore whether or not the Greenland ice sheet melted in its entirety.
The reason why this question is so critical is that at the time, during several of thousands of years, mean average temperatures were more than 4°C warmer than today. And normally, we have always expected that if we would reach a 4°C warming, an exceptional situation which we haven’t seen for 4, 5, 6 million years in a longer time period, that the entire Greenland ice sheet would melt.
But this recent data, led by Dorthe Dahl-Jensen, one of the world’s leading glaciologist, shows something surprising. Maybe that Greenland, in fact, did not melt. In fact, only contributed to in the order of 2 metres sea level rise, in a world that we know, with high degree of certainty, had a sea level which was 6-8 metres higher.
How come we know that the sea level was 6-8 metres higher? Well, we see that from very, very good data on coastal regions that show remnants of fossils from this period. So, we’re quite certain about the sea level rise. This shows, and gives us something of quite remarkable good news. It indicates, in fact, that Greenland is most likely more resilient than we previously thought.
Resilient in the sense that even a +4°C degree warming would still keep the Greenland ice sheet, you know, relatively in tact. But the drama is the following: if that’s correct, and Greenland thereby only contributes to 2 metres sea level rise, where is the lacking difference?
Because we’re missing in the order of 4-6 metres sea level rise, which must have caused, or been triggered, from somewhere else. And the trick is that there is only one potential candidate as a source for that rise, and that is Antarctica.
Antarctica, which we’ve always thought to be a more resilient system than the Arctic. And remarkably, just this year, 2014, two separate research teams have recently published data of, I would call it even shocking nature, showing from observational evidence that several glaciers in the west Antarctic ice sheet potentially have crossed the tipping point, and now have entered irreversible melting, which could explain this rising vulnerability. If this is correct, it would actually mean that we have to revise our average estimates of sea level rise for this century, from roughly 1 metre to 2 metres, so a doubling in risk for this century.
So this is showing why it’s incredibly important for us now to understand the risk of tipping points in large systems that regulate the stability of the earth system. But it goes not only for the polar regions, similarly, science shows the same kind of risk pattern with regard to the large rainforest systems.
This is data from the Amazon rainforest, showing the unprecedented droughts from 2005 and 2010, which led to a remarkable penetration of drying, even inside the rainforest. And increasing evidence indicates that these kind of shock events, of droughts related to global climate change, together with the large and vast deforestation, which open ups tracts of forest leading to more dry air penetrating the normally moist canopy, could in fact lead to abrupt behaviour, meaning that the system could tip over and, quite abruptly, shift into a savannah. Mapping out these risks globally is increasingly a key priority for science.
What you see here is one such effort of trying to identify the hotspot systems in the world where we could anticipate this kind of shift occurring from one stable state to another stable state if we cross a threshold, leading to a tipping point.
And what you see here is that this goes not only for the polar regions and the Amazon rainforest, but for example, for the large rainfall systems, in both the southeast Asian monsoon, the west African monsoon, which sustains livelihoods for hundreds of millions of people.
The risk that we get abrupt shifts in methane release in permafrost; a shift from a frozen to a thawing, and permanently thawed system. And these risks of tipping points, now at the large scale, is a fundamental importance in understanding what occurs in the earth system. But finally, this also has direct operational implications for the way we manage large sectors in society.
This is an attempt to analyze, for example, is there a risk of inducing tipping points also when it comes to freshwater systems? Not due only to climate change, but the combination of climate change and land management. And what you see here is a first analysis of hotspot regions in the world where you could see a fundamental shift in freshwater supply, if continued unsustainable management is pursued.
Where we see shifts in moisture feedback related to deforestation, which changes rainfall patterns, which could abruptly shift runoff flows and rivers, and thereby undermine the possibility for irrigation, and freshwater supplies to cities. So, the large scale regulating systems in the polar regions, for example, connect to the direct operational scales of managing food security in the world, across different scales.
So overall the conclusion is that in order to navigate sustainable development in the Anthropocene, we need to understand both pressures and tipping points, and together this allows us to explore: what is a safe operating space for development?