A changing Earth system

Life too is an integral part of the Earth system. Life affects the carbon, nitrogen, water, oxygen and many other cycles and processes.

The research shows that human activities are having a profound influence on the global climatic and environmental systems.

But it is also evident that these systems exhibited a range of natural variability in the past that went beyond what can be observed and measured today.

Key findings include:

 
• The current increase of greenhouse gases in the atmosphere occurs at a rate that is unprecedented during at least the last 16,000 years.

• Today´s concentrations of carbon dioxide and methane exceed by far the natural range of the last 800,000 years.

• Antarctic carbon dioxide and temperature co-varied over the last 800,000 years, indicating a close relationship between climate and the carbon cycle.

• The Last Glacial Maximum (ice age) was 4-7°C colder than the pre-industrial late Holocene (the Holocene period is 11,000 years to present), with high-latitude cooling more pronounced than the global average.

• Glacial-interglacial cycles were driven by changes in Earth´s orbit and tilt relative to the sun. This altered slightly how much energy Earth received from the sun. Energy changes were then amplified by changes in greenhouse gas concentrations, ice sheet extent and feedbacks associated with ocean circulation, sea ice, dust, and biophysical processes.

• Marine carbon-cycle processes were primarily responsible for the carbon dioxide variations between glacials and interglacials.

• The global warming that ended the Last Glacial Maximum (ice age) happened at an order of magnitude more slowly than the 20th century warming.

• The North Atlantic region experienced repeated abrupt warmings and coolings during the last glacial period. These occurred within decades and had climatic implications in remote regions around the globe.

• The structure and composition of regional vegetation is sensitive to climate change and can respond within decades.

• The intensity of the African-Asian summer monsoon and the  regional frequency of tropical cyclones, floods and droughts changed on decadal to centennial timescales over the last 10,000 years.

• The current increase in carbon dioxide and greenhouse gas forcing is at least five times faster than at any time during the pre-industrial era of the last two millennia.

• The warmth of the Northern Hemisphere during the second half of the 20th century was exceptional in its amplitude and hemispheric spread compared with the last 500 years and probably even 1300 years.

• Droughts lasting decades or longer were a recurrent climatic feature in northern and eastern Africa and the Americas over the last 2,000 years.

• Climate models can simulate the Northern Hemisphere temperature trends of the last millennium based on natural forcings but require anthropogenic greenhouse gas forcing to simulate the temperature rise of the last half-century.

Adapted from Steffen et al, Global Change and the Earth System, 2004 (pdf, 4 MB)