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Observed trends in Earth System behavior

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Abstract The behavior of the Earth System over the past two centuries has been dominated by the rapid rise of human activities as a significant geophysical force at the global scale. After the proximate and ultimate human drivers of change in the Earth System are described, the cumulative impact of these drivers on the structure and functioning of the Earth System are explored. Although the imprints of human activities are most profound on the land surface and in the atmosphere, significant effects are also discernible in the coastal seas, in the ocean, and—indirectly—in the cryosphere. The perturbations to the carbon cycle by human activities, most notably the burning of fossil fuels, is the most well‐known example of change in global biogeochemical cycling over the past two centuries. However, human modification of the nitrogen cycle is arguably even more pervasive, and other biogeochemical cycles, such as the phosphorus and sulfur cycles, have also been significantly altered by human activities. The changes to the planet's biodiversity over the past two centuries have been profound and continue to accelerate; the Earth is now in the midst of its sixth great extinction event. All of these human‐driven changes have implications for the climate system, and in turn are affected by changes in the physical climate. The concept of the Anthropocene—the proposal that the Earth has entered a new geological epoch—is a powerful way to understand the many interacting ways in which over six billion humans have collectively become a geophysical force that rivals the great forces of Nature and are now driving accelerating changes to the behavior of the Earth System Copyright © 2010 John Wiley & Sons, Ltd. This article is categorized under: Paleoclimates and Current Trends > Earth System Behavior

The 420,000‐year Vostok (Antarctica) ice core record showing the regular pattern of atmospheric CO2 and CH4 concentration and inferred temperature through four glacial–interglacial cycles (Adapted with permission from Ref 5. Copyright 1999 Nature).

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Global‐scale changes in the Earth System as a result of the dramatic increase in human activity shown in Figure 15 (see Ref 6, which includes references to the individual data sets).

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The increasing rates of change in human activity since the beginning of the Industrial Revolution. Sharp changes in the slope of the curves occur around the 1950s in each case and illustrate how the past 50 years have been a period of dramatic and unprecedented change in human history (see Ref 6, which includes references to the individual data sets).

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Thresholds and abrupt changes. Many processes within the Earth System are well‐buffered and appear to be unresponsive to a forcing factor (e.g., between T1 and T2 in lower figure) until a threshold is crossed and then a major change occurs abruptly (Reprinted with permission from Ref 6. Copyright 2004 Springer‐Verlag).

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Comparison of the extinction rate in the rate past and the rate projected for the 21st century with the long‐term background rate of species loss estimated from the fossil record (Reprinted with permission from Ref 76. Copyright 2005 Island Press).

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Model‐calculated partitioning of the human‐induced nitrogen perturbation fluxes in the global coastal margin for the period since 1850 to the present (2000) and projected to 2035 under a business‐as‐usual scenario.70.

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Global terrestrial nitrogen budget for (a) 1890 and (b) 1990 in Tg N/year. The emissions to the NOy box from the coal represent fossil fuel combustion. Those from the vegetation include agricultural and natural soil emissions and combustion of biofuel, biomass (savanna and forests), and agricultural waste. The emissions to the NHx box from the agricultural field include emissions from agricultural land and combustion of biofuel, biomass (savanna and forests), and agricultural waste. The NHx emissions from the cow and feedlot reflect emissions from animal waste. The transfers to the fish box represent the lateral flow of dissolved inorganic nitrogen from terrestrial systems to the coastal seas (based on Ref 68).

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Atmospheric changes in concentrations of (a) CO247; (b) CH448,49; and (c) N2O50 over the last 300 years, as reconstructed from Greenland and Antarctic ice core studies.41.

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The scope, degree, and interactive nature of human alteration of the Earth System (Adapted with permission from Ref 7. Copyright 1997 Science).

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Atmospheric CO2 concentration over the past 420,000 years from the Vostok ice core with the recent human perturbation superimposed.5,67.

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The global carbon budget from 1850 to 2007. (Data are from Refs 59,60)..

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Aging of river water, as computed at the mouth of each of the 236 regulated drainage basins.57 Aging varies due to river regulations on the reservoirs.

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Rates of observed surface elevation change for Greenland (left, 1989–2005) and Antarctica (right, 1992–2005). Red colors indicate a rise in elevation, which generally mean an increase in ice mass, whereas blue colors indicate a drop in elevation and a loss of ice mass. The letters along the Greenland coast refer to outlet glaciers and the small inset shows their change in mass balance with time. For Antarctica, the triangles along the coast show trends in ice shelves; purple triangles show thinning of ice, and red triangles show thickening of ice (Reprinted with permission from Ref 8. Copyright 2007 Cambridge University Press).

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Overview of human‐driven changes in global land cover over the last 300 years.27.

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The causative patterns of tropical deforestation from 1850 to 1997 based on a synthesis of 152 case studies that examined both proximate and underlying causes.23.

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World agricultural area under irrigation.11.

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