Climate change is shifting the growing seasons of plants, affecting species performance and biogeochemical cycles. Yet how the timing of autumn leaf senescence in Northern Hemisphere forests will change remains uncertain. Using satellite, ground, carbon flux, and experimental data, we show that early-season and late-season warming have opposite effects on leaf senescence, with a reversal occurring after the year’s longest day (the summer solstice). Across 84% of the northern forest area, increased temperature and vegetation activity before the solstice led to an earlier senescence onset of, on average, 1.9 ± 0.1 days per °C, whereas warmer post-solstice temperatures extended senescence duration by 2.6 ± 0.1 days per °C. The current trajectories toward an earlier onset and slowed progression of senescence affect Northern Hemisphere–wide trends in growing-season length and forest productivity.

$SU(2)$ gauge fields and axions can have a stable, isotropic and homogeneous configuration during inflation. However, couplings to other matter species lead to particle production, which in turn induces backreaction on and destabilization of the non-Abelian and axion background. In this paper, we first study the particle production by a $SU(2)$ gauge field coupled to a massive Dirac doublet. To carry out this calculation we have made two technical improvements compared to what has been done in the literature. First, we apply the antisymmetrization of the operators to treat particles and antiparticles on equal footing; second, to deal with the UV divergences, we apply instantaneous subtraction. We find that the backreaction of produced fermions on the $SU(2)$ background is negligible for model parameters of observational interest. Next, we consider production of fermions due to coupling to the axion. The tree-level backreaction on the gauge fields, as well as on the axion, is vanishingly small. We also provide an estimate for the loop effects.

Summary: Forests cool the land surface in warm regions and warm the land surface in cool regions. Because these local temperature buffering effects depend on background climate ^1,2 , increasingly large areas might experience forest cooling effects as the climate warms ^3–5 . Here, using statistical modeling, we quantified changes in the sensitivity of land surface temperatures ⁶ to forest cover change ⁷ from 1988 – 2016, across 15 million km ² of land area. Forests had a local cooling effect on day and night surface temperatures in 86.3% (72 million km ² ) and 61.6% (5,108 million km ² ) of the forest area, respectively. This area has increased by 0.3% (0.2 million km ² ) at day and 4.7% (2 million km ² ) at night over recent decades. Our study indicates that climate change is enhancing the cooling effect of forests in the short term, underscoring the importance of protecting natural, diverse forest ecosystems in the face of rising global temperatures that threaten ecosystems ^8,9 , human health ^10,11 , and food production ¹² .

In this paper, we examine the viability of inflation models with a spectator axion field coupled to both gravitational and SU(2) gauge fields via Chern-Simons couplings. Requiring phenomenological success of the axion-SU(2) sector constrains the coupling strength of the gravitational Chern-Simons term. We find that the impact of this term on the production and propagation of gravitational waves can be as large as fifty percent enhancement for the helicity that is not sourced by the gauge field, if the cut-off scale is as low as $\Lambda$ = 20H. The effect becomes smaller for a larger value of $\Lambda$, while the impact on the helicity sourced by the gauge field is negligible regardless of $\Lambda$.