Global Change – International Geosphere-Biosphere Programme (now known as Future Earth since November 2015) – approx 15 January 2015
The second half of the 20th Century is unique in the history of human existence. Many human activites reached take-off points sometime in the 20th Century and sharply accelerated towards the end of the century.
The last 60 years have without doubt seen the most profound transformation of the human relationship with the natural world in the history of humankind.
The effects of the accelerating human changes are now clearly discernible at the Earth system level. Many key indicators of the functioning of the Earth system are now showing responses that are, at least in part, driven by the changing human imprint on the planet. The human imprint influences all components of the global environment – oceans, coastal zone, atmosphere, and land.
Dramatic though these human-driven impacts appear to be, their rates and magnitudes must be compared to the natural patterns of variability in the Earth system to begin to understand their significance.
The increase in atmospheric carbon dioxide concentration provides a useful measure with which to evaluate the rate and magnitude of human-driven change compared to natural variability. The human imprint on carbon dioxide is unmistakable. In December 2014, atmospheric carbon dioxide concentration stood at 399 parts per million by volume (ppmV), over 100 ppmV above the previous maximum level of around 280 ppmV recorded in the Vostok ice core.
Within the current limits of resolution of the ice-core records, the present concentration has been reached at a rate at least 10 and possibly 100 times? faster than carbon dioxide increases at any other time during the previous 420 000 years. Thus, in this case human-driven changes are well outside the range of natural variability exhibited by the Earth system for the last half-million years at least.
Over just the past few hundred years, human activities have clearly evolved from insignificance in terms of Earth system functioning to the creation of global-scale impacts that:
• are approaching or exceeding in magnitude some of the great forces of nature
• operate on much faster time scales than rates of natural variability, often by an order of magnitude or more
• taken together in terms of extent, magnitude, rate and simultaneity, have produced a no-analogue state in the dynamics and functioning of the Earth system.