Every year, the Global Footprint Network reports the Earth Overshoot Day. In 2017, the day falls on August 2. On this day, we are supposed to consume all the resources, which our mother Earth can produce during the whole year. The day has advanced from end of December around 1970 to August 2 during last 47 years. The earth now needs 1½ years to produce the natural resources, which we consume in one year. By 2030, we will need two earths to produce the natural resources required by us in one year. We, however, have only one earth.
Homo sapiens evolved about 200,000 years ago but existed primarily as hunter-gatherers until the advent of Holocene epoch about 12,000 years ago after the retreat of Pleistocene glaciers. The relative stability of this period, warming up of the earth, rains and moist soils helped in developing agriculture in different parts of the world. This eventually led to a more sedentary lifestyle, the development of villages and cities, and the creation of complex civilizations, in which we live today. The human population has multiplied several times and now occupies most of the land and utilises almost all of the natural resources available around the globe.
Since the industrial revolution in 1750, humans have grown into a global force to be reckoned with significant consequences on biodiversity, nutrient cycling, soil structure, soil biology, and climate. Noble laureate Paul Crutzen, and Eugene Stoermer (2000) suggested that Earth had entered into a new epoch called ‘Anthropocene Epoch’. The demand of human population on natural resources has crossed all boundaries and now threatens to alter ‘Earth system processes’, which may destabilise our planet with unknown consequences for the survival of human beings and all other life forms. There have been five mass extinctions in the geological ages, when more than 75 per cent of life on earth disappeared as the environment of the earth turned hostile. The 5th mass extinction took place around 66 million years ago, when the dinosaurs disappeared. We are probably heading towards the 6th mass extinction.
Johan Rockström (Stockholm Resilience Centre), Will Steffen (Australian National University) and 26 leading scientists including Nobel laureates published a report in 2009. They Identified ‘Nine Planetary Boundaries’ of ‘Earth System Processes’ essential for human survival.
The quantification of these Boundaries is under intense discussion among the scientific communities around the world. Values assigned to these boundaries have been questioned. However, these may be taken as first approximations in an otherwise complex system. A tenth Boundary ‘Global Biomass Production’ has also been suggested by Running in 2012.
‘Earth System Processes’ give the planetary environment its characteristic systemic nature and allow variability within well -defined boundaries. Human societies are an integral part of the earth system. The rapid growth and activities of human societies are now trying to modulate the feedback loop of the ‘Earth System Processes’.
‘Earth System Processes’ for which Planetary Boundaries have been fixed are: 1. Climate change, 2; Biodiversity loss, 3; Bio-geo-chemicals: (a) Anthropogenic N2 removed from the atmosphere (b) Anthropogenic phosphate (P) going into the oceans; 4. Ocean acidification; 5. land use; 6. Ozone depletion; 7. Fresh water consumption; 8. Atmospheric aeroso land and 9. Chemical pollution.
Boundaries and Thresholds: ‘Boundary’ defines the safe space, beyond which we are likely to enter into a danger zone. Thresholds are tipping points, when a small increment in any of the components may cause catastrophic changes. The threshold points are difficult to determine since the Earth system is very complex. However, a range (Boundary) for any component could be proposed, which would include the threshold.
1. Climate change: Two parameters are generally used to measure climate change such as, Green House Gases (GHGs) and Radiative forcing. Scientists are more than 95 per cent certain that global warming is mostly being caused by increasing concentrations of greenhouse gases, primarily carbon dioxide (CO2), to a lesser extent with methane (CH4), nitrous oxide (N2O), CFC’s and a number of minor gases (IPCC report, 2014). Radiative forcing is a measure of ‘Change in the average amount of solar energy absorbed per square meter of the Earth’s area’. The current values (2015) are 485ppm for GHGs and 2.97 W/m2 for radiative forcing. Boundary value suggested is 350 ppm for GHGs and 1 W/m2 for radiative forcing.
According to the Inter-Governmental Panel on Climate Change (IPCC) report, 2014, the likely increase in the global surface temperature by the end of 21st century under two scenarios are: At lowest emissions scenario: 0.3 to 1.7 °C (0.5 - 3.1 F) At highest emissions scenario: 2.6 to 4.8 C (4.7 - 8.6 F). The international agreement on climate change (Paris Agreement, 2015) stated that all the participant countries would “pursue efforts to” limit the temperature increase to 0.8 C (1.5 F). While USA has opted out of this agreement, the rest of the world agrees to pursue their efforts to limit their GHGs emission according to the Paris agreement.
2. Biodiversity loss: Human activities are responsible for 93 per cent of biodiversity loss on the earth (WWF living Planet Report, 2014). The percentage of extinction of different species are: Birds- 13 per cent, Reptiles- 20 per cent, Mammalian species-26 per cent, Reef building corals, Fresh water molluscs, Shirks and rays-33 per cent and Amphibians-41 per cent. Species are currently disappearing about 100 times faster than the background rate normally seen between mass extinctions. The boundary value fixed is 10 per million per year. 3. Bio-geo-chemicals: Currently the use of nitrogen as fertilisers has exceeded by several times the natural recycling of this plant nutrient. Nitrogen and phosphatic fertilisers which do not get recycled in biological processes find their way to the nearest water bodies causing massive pollution of rivers, ponds, lakes and even oceans. Currently 405 hypoxic dead zones have been identified in oceans and large lakes, around the world which do not support aquatic life. The current removal rate nitrogen gas from atmosphere is 121 million tons per year. The boundary value fixed is removal of 35 million tons of N2 gas from the atmosphere per year. Currently 10 million tons of phosphorusis washed into the ocean, which is close to the suggested boundary value of 11 million tons.
4. Ocean acidification: Ocean water is slightly alkaline and is saturated with lime to support exoskeleton of many sea animals, which are primarily made of calcium carbonate (CaCO3). Acidification of sea water will be hazardous since it may dissolve their exoskeleton. The suggested boundary value in omega units is 2.75 and the current value is very close at 2.90, a cause of worry.
5. land use: There is little scope to expand cropped area globally. Only some parts of Africa and South America are available for expansion. These are ecologically sensitive areas. Expansion of agriculture into these areas will seriously disturb ecology and may cause loss of biodiversity and atmospheric warming (Foley and co- researchers, 2011). The boundary value fixed for land surface converted to cropped land is 15 per cent. We are very close to this value (13 per cent).
6. Fresh water use: We are almost using all the fresh water available globally. The boundary value fixed for fresh water use is 4,000 cubic kilo-meters as against current use of 3763 Km 3(FAO, 2007).
7. Ozone depletion: The ozone layer is found mainly in the lower portion of the stratosphere from approximately 20-30 km from surface of the earth, containing 2-8 ppm of ozone. Atmosphere contains 0.3 ppm of ozone. The ozone layer absorbs 97-99 per cent of sun’s ultra violet light (200-300 nm), which could have damaged life forms on the surface of the earth. CFCs used in cooling devices, oxides of nitrogen released from chimneys of factories destroy ozone. Ozone holes have been observed near the poles especially near the Antarctic. The Boundary value fixed in Dobson’s unit is 276 and the current value is higher at 283.
8. Chemical pollution and 9. Atmospheric aerosols: Boundary value not fixed, probably due to lack of global data, though these are very much recent problems.
Climate model simulations show that GHG increases alone, in the absence of aerosols, would have caused even more rapid warming than has been observed, perhaps at double the current rate (Khush and Cassman, 2004). During 1985-1998, atmospheric brown clouds caused 10 per cent reduction in rice harvest in the India (Auffhammer and co-researchers, 2006).
The boundary values suggested are yet to be accepted internationally since the discussions are still in progress. A compromise has to be reached between political and economic compulsions and scientific truth to save mankind from an impending disaster.
(Dr Mitra is former Dean, OUAT. Apart from scientific publications, he has authored four books, the last one an international edition published by Springer. Email: gnmitra@gmail.com)