Plants and Temperature--CO ₂ Uncoupling

Abstract

the view that we are directly seeing the "epicyclic" periods general relativity predicts for the orbital motion of test particles: one related to the well-known general-relativistic precession of Mercury's orbit (but lOI7 times faster because of the strong gravity) and another to the so-called "Lense-Thirring precession" of the orbital plane itself, caused by ''fhne-dragging," a phenomenon in which a spinning object drags space-time around it along with its spin (9). But there seems to be more to it than that. RXTE has discovered the f i t millisecond pulsar in an x-ray binary, a neutron star spinning with a 2.493919753-ms period (lo), and has measured the approximate spins of another six neutron stars with periods of 2 to 4 ms (11). Comparison of these spins with the millisecond quasi-periods suggests that while the fastest of the two quasi-periods seen in each system originates in the orbital motion in the accretion disk, the slower one (still sometimes as fast as 1.2 msec) arises by a nonlinear interaction (a "beat") between the spin and the orbital motion. One model describes a pattern of orbital motion that could explain the observations in detail (7). A few more years of observations, more discoveries, and further high-precision measurements of the new ~henomena will show which of these theories can be maintained and which must be abandoned.RXTE's success has demonstrated that when probing the dynamics in strongly curved space-time, there is no substitute for size. It is the huge effective area of 0.7 m2 of the main x-ray instrument onboard the satellite that gave Rossi the sensitivity to make the first direct measurements of orbital motion near collapsed stars. To fully exploit these discoveries and map out space-time near neutron stars and black holes, an instrument in the 10-m2 class will be required. Although the stream of new data from RXTE continues unabated and a second millisecond timing mission (the Naval Research Laboratory's Unconventional Stellar Aspect experiment on the Argos satellite) was just launched successfully, x-ray astronomers are already considering the new solid-state technologies by which such a "relativity explorer" might be realized. References and Notes 1. H.V. Bradt. R. E. Rothschild.]. H. Swank. Astmn. Astmphys. 97.355 (1993). 2. 1. H. Taylor and 1. M. Weisberg. Astrophys.]. 345.434 (1989). 3. M. van der Klis et al.. ibid. 469. L1 (1996); T. E. Strohmayer et al.. ibid., p. L9. 4. M. van der Klis, preprint available at xxx.lanl.gov/absl astro-phl9812395. 5. E. H. Morgan etal..Astrophys.

Ecosystem effects of CO<sub>2</sub> concentration: evidence from past climates

“…However the elevation effect also lowers the partial pressure of O 2 , which competes with CO 2 at the Rubisco reaction sites; this effect counters the hypothesized effect of a low partial pressure of CO 2 at high elevations (Terashima et al, 1995). In fact, the effects are expected a priori to be greater in warmer climates because the O 2 competition effect is stronger at high temperatures, as reflected in the temperature dependence of the photosynthetic parameters (Cowling, 1999a). Indeed there is abundant evidence in pollen and carbon isotope records from tropical lowland regions for shifts away from forest, toward C 4 dominated vegetation, during glacial times.…”

Climate model sensitivity to atmospheric CO2 concentrations for the middle Miocene

“…Tectonic and oceanographic processes have been argued as the primary driver of Miocene climate with CO 2 playing a secondary role. Furthermore, studies have supported elevated CO 2 throughout the Miocene (Cowling, 1999;Sheldon, 2006), in light of global vegetation patterns and reproduction of observed mineral assemblage of paleosols. A recent study by Kürschner et al (2008) presents Miocene CO 2 reconstructions from stomatal frequency data showing strong fluctuations between~300 and 600 ppm.…”

The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of terrestrial ecosystems

“…Because of this alleged decoupling, the role of atmospheric CO 2 as a climate forcing factor has been disputed (13)(14)(15). However, a permanently low CO 2 scenario has been challenged because photosynthetic models predict that plant life would not have thrived under such conditions (16). Climate models showed the importance of atmospheric CO 2 as a fundamental boundary condition for Cenozoic climate change (17).…”