Until very recently, humans and their activities have been an insignificant force in the dynamics of the Earth System. However, since the start of the Industrial Revolution, more than 200 years ago, developed nations have achieved ever greater prosperity and higher living standards. Combined with a six-fold increase in the global human population during that period, these factors have resulted in significantly increased consumption of resources – evident in agriculture and food production, industrial development, energy use and urbanisation.

The Earth's climate does vary naturally, mainly as a result of interactions between the ocean and the atmosphere, changes in the Earth’s orbit, fluctuations in energy received from the Sun and volcanic eruptions. However, the best scientific evidence available suggests that the Earth System has recently moved well outside the range of natural variability exhibited in available paleoclimate records covering at least the last half million years. The nature of changes now occurring simultaneously in the global environment, their magnitudes and rates, are unprecedented in human history, and probably in the planet’s history:

— in a few generations humankind is likely to exhaust fossil fuel reserves that were formed over several hundred million years;

— as a consequence, humankind has caused the atmospheric greenhouse gas concentrations on Earth to rise far beyond the maxima reached during at least the last 1 million years;

— human action has transformed almost half of the Earth’s land surface, with significant consequences for biodiversity and climate;

— tropical forest areas have been reduced by 50%;

— more than half of all accessible freshwater is used directly or indirectly by humankind;

— coastal and marine habitats are being dramatically altered; 50% of mangroves have been removed and wetlands have shrunk by one half;

— extinction rates are increasing sharply in marine and terrestrial ecosystems around the world;

— humankind is responsible for 70% of the nitrogen cycle and 95% of the phosphorus cycle on Earth.

Some facts are slow to be absorbed and accepted by a generation unaccustomed to associating environmental factors with lifestyle and consumer choices. But today it is a reality that humankind has begun to match and even exceed Nature in terms of changes to the atmosphere and biosphere and impacts on other facets of Earth System functioning.

In spite of the many severe environmental impacts that occurred during recent centuries of industrialisation and accelerating urbanisation, these impacts, often severe, were usually seen as being of only local importance. Widespread public awareness of the ‘environment’ dates back to the 1960s and 1970s, born from concerns such as air and water pollution; pesticide use; nuclear testing; and disasters such as the first catastrophic supertanker oil spill. Many governments established environment ministries and environmental protection agencies in the 1970s, leading to new consideration of environmental issues and growing demands for environmental information. Industry, too, became more
environmentally aware, with the realisation of new trends in consumer behaviour, and the introduction of new legislation and environmental regulations.

After the first World Climate Conference in 1979 expressed its concern about the possibility of human-induced climate change, there was almost a decade of accumulating evidence until the Intergovernmental Panel on Climate Change (IPCC) was established in 1988. Its tasks were to assess the available scientific information about climate change and formulate realistic response strategies for national and global action. The first IPCC Assessment Report in 1990 was instrumental in paving the way for the adoption of the UN Framework Convention on Climate Change (UNFCCC) in 1994. The second IPCC Assessment Report in 1995 provided key inputs to the process that led to the adoption of the Kyoto protocol in 1997 – with the aim of reducing greenhouse gases that contribute to climate change. The Third IPCC Assessment Report in 2001 concluded, “There is new and stronger evidence that most of the observed warming observed over the last 50 years is attributable to human activities.”

The main message of the IPCC’s Fourth Assessment Report in 2007 was that climate change is no longer a matter for debate. It is ‘unequivocal’, and ‘very likely’ that human activities are responsible. In the IPCC context ‘very likely’ means an assessed likelihood of at least 90%, while ‘likely’ (as stated in 2001) means at least 66%. Throughout its reports the IPCC has stressed the importance of systematic observations and emphasised many variables that are observed by satellite.