How and why did genuine global changes happen? What were their local and global consequences on the physical environment, the ecosystems and the societies? What thresholds are involved?

Without paleoclimatic information, we would not know that atmospheric CO2 can vary naturally by up to 100 ppm on glacial-interglacial times, that abrupt climatic changes did occur on annual or decadal scales, that ice sheets may disrupt very rapidly, and basically that climate can change at all. These testimonies of how our Earth system is functioning are invaluable, yet still quite sparse and often not so well understood. They will likely deliver numerous further surprises. A great variety of climatic changes occured in the past, with many different amplitudes or consequences, and on many different time scales. When exceeding some thresholds, they were able to induce changes on the environment of past ecosystems and societies. These events should be traced back and quantified, before we can claim that we are in a position to predict future changes and their impacts.

What political and economic changes can reverse climate change and the loss of biodiversity?

The world’s economy depends upon a system of capital accumulation that does not support a sustainable relationship between the nature and the human communities. Natural resources are exploited above the threshold to sustainability. Political changes are required.

How can we identify and manage looming thresholds in social-ecological systems arising from resilience – development trade-offs, especially those across scales?

Rising human numbers and increasing use of natural resources are lowering resilience in most regions of the world. Some of the changes will result in irreversible, or very hard to reverse, regime shifts in the coupled social-ecological systems concerned. They are already happening (salinized agricultural regions, desertified rangelands, collapsed fisheries, degraded ex-forest areas, etc.). We need to know how to identify such threshold effects before they happen, and how to manage them.

What are earth system thresholds that are sensitive to biotic impoverishment?

Through the predominant period of the rise of humanity as the dominant species (the Holocene), earth system properties have been relatively benign with respect to the constraints within which the current biosphere remains viable. We are distracted by climate change to the point that Heinrich events, Dansgaard-Oeschger events, and the Bølling-Allerød transition draw us away from the more basic scientific issue as to why climate remains largely within boundary conditions conducive to life on Earth. It is also possible that the question of global biotic thresholds is mistakenly assumed to be some form of Gaia-Hypothesis like thinking, a topic which has some strong supporters, but is largely unpopular among many scientists. Because there is likely to be an immense suffering in the face of climate change, it would be inappropriate to suggest that such questions should not dominate our attention – they deserve substantial, immediate attention. Climate change research, however, in its current form, incorporates enormous “black boxes” and this is not the best science. GCM models tax even the best super computers, but until such models contain hundreds of ecosystem types, each made up of hundreds of functional species types, and contain key interactions among species and their environment, we are avoiding the true challenge before us – to understand Earth systems in its entirety – physical, chemical, and biological with spatial and temporal accuracy all coupled to social systems.

The Millennium Assessment achieved an unprecedented consensus among natural and social scientists from around the world declaring that the most pervasive environmental problems we face are caused by the massive spending down of natural capital – our biodiversity and our natural resources. Thirty years ago no one might have imagined we would have multi-million dollar, international efforts and intergovernmental panels seeking to understand the global carbon cycle and its relationship to climate using the most advanced research methods and techniques ever developed. Yet, the scientific foundation for this endeavor can be traced back to Arrhenius in 1896. To wait a similar period to build upon the Millennium Assessment’s findings would leave us facing problems in the future that were readily addressed today.

Given rates of local and global extinction, tt is difficult to imagine any challenge greater and more urgent than identifying earth system thresholds sensitive to biotic impoverishment.

How much land cover change (population growth) can be tolerated by ‘GAIA’ before irreversibilty takes its path?

Remember, soils and genes can be lost only once (irreversible). Soil losses reduce the planet’s capacity to store essential plant nutrients (all cations) and carbon (humus), both intimately linked to the presence of clay and, thus, intact soils. The number one driver behind this issue is growth in number of and consumption by humans.

What are the critical levels or limits in the earth systems that adversely affect humanity?

Critical levels or limits in the earth systems are difficult to detect. Often they seem insignificant and go unnoticed. Given the best available knowledge, it is important to monitor at an early stage what can be deemed critical in future.