In nitrogen (N)-limited systems, the response of symbiotic N fixation to elevated atmospheric [CO2] may be an important determinant of ecosystem responses to this global change. Experimental tests of the effects of elevated [CO2] have not been consistent. Although rarely tested, differences among legume species and N supply may be important. In a field free-air CO2 enrichment (FACE) experiment,...

The bulk of Earth's coal deposits used as fossil fuel today was formed from plant debris during the late Carboniferous and early Permian periods. The high burial rate of organic carbon correlates with a significant drawdown of atmospheric carbon dioxide (CO2) at that time. A recent analysis of a high-resolution record reveals large orbitally driven variations in atmospheric CO2 concentration be...

[1] Anthropogenic increases in atmospheric carbon dioxide (CO2) concentrations may affect vegetation distribution both directly through changes in photosynthesis and wateruse efficiency, and indirectly through CO2-induced climate change. Using an equilibrium vegetation model (BIOME4) driven by a regional climate model (RegCM2.5), we tested the sensitivity of vegetation in the western United Sta...

[1] Frequency-dependent coherence between atmospheric CO2 and historical temperatures reveals climate feedbacks within Earth’s carbon cycle. Coherence between interannual fluctuations in global-average temperature and atmospheric CO2 has changed over time. Since 1979, at Mauna Loa and other observation sites, interannual coherence exhibits a 90 phase lag that suggests a direct correlation betwe...

[1] Large fluctuations in continental configuration occur throughout the Mesozoic. While it has long been recognized that paleogeography may potentially influence atmospheric CO2 via the continental silicate weathering feedback, no numerical simulations have been done, because of the lack of a spatially resolved climate-carbon model. GEOCLIM, a coupled numerical model of the climate and global ...

Measurements of atmospheric carbon dioxide (CO2) have led to an understanding of the past and present CO2 trends at global scales. However, many of the processes that underlie the CO2 fluxes are highly uncertain, especially at smaller spatial scales in the terrestrial biosphere. Our abilities to forecast climate change and manage the carbon cycle are reliant on an understanding of these underly...

Tropical forests play a major role in determining the current atmospheric concentration of CO2, as both sources of CO2 following deforestation and sinks of CO2 probably resulting from CO2 stimulation of forest photosynthesis. Recently, researchers have tried to quantify this role. The results suggest that both the carbon sources and sinks in tropical forests are significantly greater than previ...

Atmospheric [CO2] over the past 800 000 yr has varied generally as a function of glacial periods, with minima (c. 170–200 ppm) during glacial periods and maxima (c. 280–300 ppm) during inter-glacial periods (Luthi et al., 2008). During the Last Glacial Maximum (LGM; 18 000–20 000 yr ago), atmospheric [CO2] ranged from 180 to 200 ppm, which is approximately half the current [CO2] (392 ppm), and ...

The ecophysiological response of an alpine grassland to recent climate change and increasing atmospheric CO2 concentration was investigated with a new strategy to go back in time: using a time-series of Capra ibex horns as archives of the alpine grasslands’ carbon isotope discrimination (D). From the collection of the Natural History Museum of Bern, horns of 24 males from the population of the ...

Recent studies have suggested that global mean surface temperature would remain approximately constant on multicentury timescales after CO2 emissions1–9 are stopped. Here we use Earth system model simulations of such a stoppage to demonstrate that in some models, surface temperature may actually increase on multi-century timescales after an initial century-long decrease. This occurs in spite of...