Publication Date:
2016-04-05
Description:
The amplitude of the mean annual cycle of atmospheric CO2 has increased by at least 0.5 % yr−1 over most of the Northern Hemisphere (NH) extratropics during the last three decades likely from a combination of enhanced atmospheric CO2, climate change, and anthropogenic land use change. We investigated how each of these factors affected the increase in the atmospheric CO2 mean annual cycle amplitude simulated by the Community Earth System Model (CESM), a prognostic coupled climate- carbon cycle model. The simulated amplitude of the NH mean CO2 annual cycle showed a weaker trend than observed, increasing by only 15 % over the period spanning 1950–2010. By 2100, the amplitude rose to 57 % above the present-day baseline (1950–1959), and reached a maximum of 76 % above the baseline around 2250. The amplitude increase in the CESM was mainly driven by climate change and changing atmospheric composition, with the largest amplitude gains occurring in the mid- and high latitudes. In addition, the long-term simulations revealed shifts in key climate drivers of the atmospheric CO2 seasonality that were not apparent before 2100. Climate change from NH boreal ecosystems was the largest driver of Arctic CO2 annual cycle amplification between 1950 and 2100. CO2 fertilization and nitrogen deposition in the NH boreal and temperate ecosystems contributed the most to the amplitude increase over the midlatitudes through 2300 and over the Arctic after 2100. Greater terrestrial productivity during the growing season contributed the most to the annual cycle amplification over the high latitudes, midlatitudes, and the NH tropics, reflecting lengthening of the growing season rather than the strength of the terrestrial carbon sink. Prior to 2100, CO2 annual cycle amplification occurred in conjunction with an increase in the NH land carbon sink, but the trends decoupled after 2100, underscoring that an increasing atmospheric CO2 annual cycle amplitude is not predicated on a strengthened terrestrial carbon sink.
Print ISSN:
1810-6277
Electronic ISSN:
1810-6285
Topics:
Biology
,
Geosciences
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