What do tipping points mean to us?

As discussed in previous posts, tipping points are a concern for scientists and policy-makers due to the threat they pose to natural resources, ecosystem services and human well-being (Werners et al. 2013). Societies and economies across the globe are reliant on climate and ecosystem services in order for their current success, and also for that of future generations (Folke, C. 2006). Despite our dependence on natural resources, uncontrolled usage amongst other factors has depleted resources, whilst changing the composition of the atmosphere through emissions of greenhouse gases and enhancing global climate change. Climate change is only one of the challenges the global community faces today in terms of continuing development at a sustainable rate.

Werners et al. (2013) state that “climate change shifts the challenge for sustainability from preserving natural resources for future generations to strengthening resilience and adaptive capacity in social–ecological systems”. This means that policy making and resources management must change from a conservation basis to one that manages change and adaptation (Werners et al. 2013). Thresholds and tipping points, along with their properties and mechanisms, are important points for sustainability science, and their uncertainty is a big challenge when trying to remain sustainable.

Previous posts have mentioned that some systems have an indicator of change, if examined closely, which allows us either to mitigate against the changes or to prevent them from occurring where possible.  Biggs et al. (2009) found that if drivers of a system can only be manipulated gradually, action is needed much before a regime shift in order to prevent it, but if drivers can be rapidly altered, the action aversive action can be delayed until a shift is underway. However, these large, noticeable increases in the indicators only tend to occur once a regime shift has started, which is usually too late for human intervention to avert a shift (Biggs et al. 2009). Huntington et al. (2012) out into perspective the challenge we face and what it means for the average human:  “rapid sea level rise, for example from accelerated melting of the Greenland ice sheet, will create a choice between protection and abandonment for coastal regions throughout the world, a potential global tipping point” (Huntington et al. 2012).

Climate change is a challenge that most, if not all, governments cannot stretch to financially, and thus beyond a point, individuals must bear the costs or adapt to new circumstances, creating political-economic tipping points in countries everywhere (Huntington et al. 2012). The scale of the battle ahead depends largely on greenhouse gas emissions reductions, with temperature increase being a trigger for many of the fragile Earth systems responses. With many of the tipping points unknown, and the amplifying feedbacks and time-lag effects in systems underestimated (Werners et al. 2013), the challenge ahead is vast.

Biggs, R. S. R. Carpenter and W. A. Brock (2009) “Turning back from the brink: Detecting an impending regime shift in time to avert it” PNAS, 106, 3, 826–831

Folke, C.(2006) “Resilience: The emergence of a perspective for social–ecological systems analyses” Global Environmental Change 16, 253–267

Huntington, H.,P., E. Goodstein and E. Euskirchen (2012) “Towards a tipping point in responding to change: rising costs, fewer options for Arctic and global societies” Ambio. 41, 1, 66-74

Werners, S., E., S. Pfenninger, E. van Slobbe, M. Haasnoot, J. H Kwakkel and R. J. Swart, (2013) “Thresholds, tipping and turning points for sustainability under climate change” Current Opinion in Environmental Sustainability, 5, 334–340

Forests Fighting Climate

The rise of populations and technological and social development has driven up global demands for bio fuels and grain as feed for animals for meat. This creates powerful incentives for agro-industries to expand into forest regions, notably the Amazon rainforest, causing dramatic and often irreversible change to the environment (Nepstad et al. 2008). Forest fires, drought and logging increase susceptibility to further burning while deforestation and smoke can inhibit rainfall, exacerbating fire risk in this positive feedback loop. If sea surface temperature anomalies and associated droughts to continue, approximately 55% of the forests of the Amazon will be cleared, logged, damaged by drought or burned over the next 20 years, as shown in Figure 1 (Nepstad et al. 2008). The trees of the Amazon contain 90–140 billion tons of carbon, equivalent to approximately 9–14 decades of current global human-induced carbon emissions each year (Canadell et al. 2007). A lot of this is released back to the atmosphere, partly by a reduction in carbon uptake by the trees, but also in burning and soil process changes. Lenton et al. (2008) predict a timescale of 50 years for the Amazon to switch to an alternative state with severely decreased biodiversity and rainfall. A large fraction of precipitation in the Amazon basin is recycled, and reductions in precipitation lead to  lengthening of the dry season, and increases in summer temperatures that make it forest re-establishment difficult, and suggest the system may exhibit bi-stability, with two stable states (Lenton et al. 2008).

Figure 1 - Amazon forest degradation map (Nepstad et al., 2008)

It is also proposed that human induced climate change is impacting boreal forests, as shown by a study in the western United States that links forest “greenness” to fluctuating year-to-year snow-pack. This study showed that mid-elevation - those between approximately 6,500 to 8,000 feet - mountain ecosystems are most sensitive to rising temperatures and changes in precipitation and snow-melt (Trujillo et al, 2012). The study by University of Colorado, funded by NASA, used satellite and ground data to identify the threshold where mid-elevation forests sustained primarily by moisture shift into higher-elevation forests sustained primarily by sunlight and temperature. They found that  mid-elevation forests are very sensitive to snow that fell the previous winter, with about half of the mid-elevation forest greenness attributed to the previous winter’s snow accumulation (Trujillo et al, 2012). Climate studies indicate that snow-pack in mid-elevation forests in the Western United States and in similar forests around the world has been decreasing in the past 50 years due to regional warming (Trujillo et al., 2012), producing a feedback system that will continue to increase warming due to decreased albedo and reduced carbon sequestration. Lenton et al. (2008) predict that the decline of boreal forest would cause a biome switch on a scale of about 50 years, transitioning to open woodlands or grasslands. Under climate change the complex interaction between tree physiology, permafrost, and fire would experience increased water stress, increased peak summer heat stress causing increased mortality, vulnerability to disease and subsequent fire, as well as decreased reproduction rates (Lenton et al., 2008)

Nepstad et al (2008) conclude that trends in Amazon economies, forests and climate may lead to the replacement or severe degradation of more than half of the Amazon basin forests by 2030. They suggest that recent success in changing landholder behaviour, as well as the designation of protected areas and practical techniques for concentrating livestock production on smaller areas of land that could reduce the likelihood of severe environmental change.

Canadell, J. G. et al. (2007) “Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks”. Proc. Nat. Acad. Sci. USA 104, 18 866–18 870.

Lenton, T., M., H. Held, E. Kriegler, J. W. Hall, W. Lucht, S. Rahmstorf, and H. J. Schellnhuber, (2008) “Tipping elements in the Earth’s climate system” PNAS, 105, 6, 1786–1793

Nepstad, D., C., C. M. Stickler, B. Soares-Filho, and F. Merry. (2008) Interactions among Amazon land use, forests and climate: prospects for a near-term forest tipping point. Phil. Trans. R. Soc. B 363, 1737–1746

Trujillo, E., N. P. Molotch, M. L. Goulden, A. E. Kelly and R.C. Bales (2012) “Elevation-dependent influence of snow accumulation on forest greening” Nature Geoscience, 5, 705–709

To the Point Prediction

Luckily, we are not left blindly waiting for tipping points to occur. Once we know that they exist, or have occurred in the past, we can look out for early warnings. Early warning can take several forms, as simple as the knowledge that an event could occur and that it is becoming more likely, to a forecast of its timing and modelling of future events (Lenton, 2011). Slowing down of a system before a bifurcation occurs has been noticed in present day systems, climate-model output and palaeoclimate data; it causes the intrinsic rates of change in a system to decrease, and thus the state of the system becomes more like its past, alternative state (Lenton, 2011). Similar to this are ‘small-signal amplification’ and ‘noise amplification’, where small intermittent perturbations or noise are amplified at particular frequencies depending on the type of bifurcation (Lenton, 2011). Ditlevsen and Johnsen (2010) describe the two generic characteristics of the approach to a bifurcation point as increased variance of the observed signal and the corresponding increased auto-correlation related to critical slow down. They do however, stress that the early warning of climate or structural change in any system can only be obtained if increase in both variance and auto-correlation is observed, and that conclusions drawn based solely on one of the signals and not the other are invalid (Ditlevsen and Johnsen, 2010).

http://cpa.ds.npr.org/wamc/audio/2013/11/11-25-13_harvard_forest_troubled_lakes.mp3

In this talk, (see link above) Dr. Aaron Ellison talks about ecosystems and tipping points, briefly discussing the findings of his 2013 collaborative paper – Sirota et al. 2013.

Image from North Carolina Native Plant Society,
 http://www.ncwildflower.org/index.php/plants/details/sarracenia-purpurea/

Although experimental induction of tipping points is rare due to the scale of the system in question, Sirota et al. (2013) experimentally induced a shift from aerobic to anaerobic states in a miniature aquatic ecosystem of the self-contained pools that form in leaves of the carnivorous northern pitcher plant, Sarracenia purpurea, in order to represent the shift from a clear, oligotrophic lake to a murky, eutrophic one. The plants were fed controlled amounts of dried, ground arthropod prey. In controls, the concentration of dissolved oxygen replicates exhibited regular diurnal cycles associated with daytime photosynthesis and nocturnal plant respiration. Results showed that increasing organic-matter loading led to predictable changes in O2 dynamics, with high loading consistently driving the system past a well-defined tipping point. The Sarracenia micro ecosystem therefore functions as a compliant experimental system in which to examine prediction and management of tipping points.

This, as well as other models, tests and qualitative observations, show promise for early warning of bifurcation-type climate tipping points, but there are potential limitations of ‘false alarms’ (false positives) and ‘missed alarms’ (false negatives) (Lenton, 2011) that must be considered before jumping to conclusions. There is, however, hope for a better understanding of impending tipping points and how we can mitigate, if not prevent, them.

Ditlevsen, P. D. & Johnsen, S. J. (2010). “Tipping points: Early warning and wishful thinking”. Geophysical  Research Letters, 37.

Lenton, T., M., (2011) “Early warning of climate tipping points” Nature Climate Change, 1, 201-209

Sirota, J., B. Baiser, N. J. Gotelli, and A. M. Ellison. 2013. Organic-matter loading determines regime shifts and alternative states in an aquatic ecosystem. Proceedings of the National Academy of Sciences, USA. 110: 7742-7747.

Pointing to the big picture.

Tasked with keeping a blog for 3 months for my 3rd year module in Global Environmental Change at UCL, I came home with a world of ideas. I told my boyfriend that I'd decided to write about climate tipping points. 

That's great, he said…what are “tipping points”? 

At this I paused, gave a vague description with a few strange analogies about burning your toast, and silently vowed to find a some good articles that would categorically sum up tipping points, for me and for my audience. 

Now, this proved much more difficult than expected. Although I knew about tipping points in Earth’s climate system, I had never considered that they existed elsewhere. As it turns out, ANYTHING that is in the slightest bit dynamic has a so called “tipping point”: fashion, make-up, the economy, sport, there’s even a Tipping Points game show in which contestants play with a giant arcade-style coin pusher (yes I watched it . . . it’s nail-biting). What shocked me most was that climate tipping points didn't dominate the primitive Google search, despite potentially being one of the most daunting and difficult factors in global climate change past, present and future.

TIPPING POINTS are thresholds beyond which dramatic changes in conditions with considerable and largely unpredictable consequences occur. It only takes a small change to make a huge difference; Lenton says “A climate ‘tipping point’ occurs when a small change in forcing triggers a strongly nonlinear response . . . qualitatively changing its future state”. They've happened before, pushing the Earth in and out of Ice Ages, but these have all been natural, caused by solar variability and a chain of events, such as melting permafrost and icesheets. This time, the Anthropocene threatens a new era of climate change, comparable with previous global mass extinctions. The editorial from Nature Climate Change Vol. 1 says “An early warning of Earth tipping points will bring us closer to staving off abrupt climate change, but a societal tipping point is needed to achieve sustainability”. 

Tipping points MUST be considered by policy makers, scientists and the general public worldwide in order for the issue to be addressed and acted upon.

Image from xkcd.com, source of data for image Dyke, A. et al, 2002. "The Laurentide and Innuitian Ice Sheets During the Last Glacial Maximum"