Planetary boundaries, tipping points and prophets of doom

There is a paper that appeared in January in Science: Planetary boundaries: Guiding human development on a changing planet.

They presume that human development should be guided on a limited set of criteria that they say are approaching tipping points, points of extreme change that threaten human survival and the ecological viability of the planet. The authors are invoking a real mechanism known from gleams of knowledge in the relatively new field of complexity science — but unnecessarily conflating it with disaster scenarios in the way we have come to expect.

Tipping points in biophysical systems are apparent everywhere. When pushed by inputs of nitrogen and phosphorus a lake will transition from clear to murky overnight in a process caused by oxygen dynamics at the water/sediment interface. Populations will precipitously decline to zero after some point dependent on the ratio of recruitment to mortality. Global hydrology shifts abruptly with shifts in ocean and atmospheric circulation every few decades.

Complexity emerges from interactions of simple components. In the words of Michael Ghil (2013) – Distinguished Research Professor of Atmospheric and Oceanic Sciences, University of California, Los Angeles (UCLA) – the “global climate system is composed of a number of subsystems — atmosphere, biosphere, cryosphere, hydrosphere and lithosphere – each of which has distinct characteristic times, from days and weeks to centuries and millennia. Each subsystem, moreover, has its own internal variability, all other things being constant, over a fairly broad range of time scales. These ranges overlap between one subsystem and another. The interactions between the subsystems thus give rise to climate variability on all time scales.”

Complexity science suggests that the system is pushed by small changes — such as solar intensity and Earth orbital eccentricities — past a threshold at which stage the components start to interact chaotically in multiple and changing negative and positive feedbacks — as tremendous energies cascade through powerful subsystems. Some of these changes have a regularity within broad limits and the planet responds with a broad regularity in changes of ice, cloud, Atlantic thermohaline circulation and ocean and atmospheric circulation. This is, by the way, a whole new way of thinking about climate that is still not anywhere near widely enough appreciated.

Four exceedances of so called planetary boundaries were identified. Greenhouse gas emissions, nutrients from agriculture, biosphere integrity and land use. Although the paper waves an arm toward “slowing down” as an early indicator of change, there is no possibility that this is as yet a practical methodology in the real world for identifying and anticipating a tipping point. Slowing down suggests that the system settles into a new steady state before being pushed out of balance into a new, emergent state.

Figure 1: Nine ‘planetary boundaries’. The green zone is presumed to be below the change threshold, yellow is the zone of increasing risk, and red is the high-risk zone. There are four boundaries shown in the yellow zone and two in the red. E/MSY is a measure of species extinction and Bll of ecosystem intactness. Novel entities are new chemicals. ­­­

Anastasios Tsonis, of the Atmospheric Sciences Group at University of Wisconsin, Milwaukee, and colleagues used a mathematical network approach to analyse abrupt climate change on decadal timescales. Ocean and atmospheric indices — in this case the El Niño Southern Oscillation, the Pacific Decadal Oscillation, the North Atlantic Oscillation and the North Pacific Oscillation — can be thought of as chaotic oscillators that capture the major modes of climate variability. Tsonis and colleagues calculated the “distance” between the indices. It was found that they would synchronise at certain times — around 1912, 1944/1945, 1976/1977 and 1998/2001 — and then shift into a new state.

It is no coincidence that shifts in ocean and atmospheric indices occur at the same time as changes in the trajectory of global surface temperature. Our “interest is to understand — first the natural variability of climate — and then take it from there. So we were very excited when we realized a lot of changes in the past century from warmer to cooler and then back to warmer were all natural,” Tsonis said. The warming between 1944 and 1998 was 0.4 degrees Centigrade. At least half of that was quite natural leaving not much to show for anthropogenic warming in the last half of the last century. The presumption is — however — that small change adds to the pressure of change in the system creating the potential for instability. The solutions for carbon dioxide emissions involve energy innovation in the development of new sources of cheap and abundant energy. This remains less than half the problem of climate forcing. The solutions for black carbon, sulphur, nitrous oxide, CFC’s and methane are multi-faceted and must be based on accelerated global social and economic development.

The World Wildlife Fund recently in its 2014 Living Planet Index (LPI), purports to measure more than 10,000 representative populations of mammals, birds, reptiles, amphibians and fish. These are said — based on reputable databases — to show declines in populations by 52 per cent since 1970. In other words, population sizes of vertebrate species have dropped by half. There is indeed a risk of accelerated extinctions this century. As an environmental scientist, and having read widely in the population literature, I see no reason to doubt that this represents a real trend of species decline. The problem as defined is that these declines owe much more to poverty and lack of development than climate change.

Nutrients likewise drive abrupt and more or less extreme changes in freshwater and marine systems. Throughout the world there are many coastal dead zones where oxygen levels have dropped to levels that will not sustain vertebrate life. The solutions here is urban runoff control only affordable in rich economies, building organic content in agricultural soils, water and soil conservation, precision agriculture and conserving and restoring ecosystems. Climate change is of no direct relevance.

Climate change has come to dominate the public space for environmental discourse, with attendant and unfortunate demands on social and economic policy. Complexity science adds unexpected dimensions to the problem, but we would still be much better off — and much more environmentally friendly — pursuing a broad social and economic development agenda than one focused narrowly on climate change.