Stochastic interest model driven by compound Poisson process and Brownian motion with applications in life contingencies

In this paper, we introduce a class of stochastic interest model driven by a compound Poisson process and a Brownian motion, in which the jumping times of force of interest obeys compound Poisson process and the continuous tiny fluctuations are described by Brownian motion, and the adjustment in each jump of interest force is assumed to be random. Based on the proposed interest model, we discuss the expected discounted function, the validity of the model and actuarial present values of life annuities and life insurances under different parameters and distribution settings. Ournumerical results show actuarial values could be sensitive to the parameters and distribution settings,which shows the importance of introducing this kind interest model

Lower land-use emissions responsible for increased net land carbon sink during the slow warming period

The terrestrial carbon sink accelerated during 1998–2012, concurrently with the slow warming period, but the mechanisms behind this acceleration are unclear. Here we analyse recent changes in the net land carbon sink (NLS) and its driving factors, using atmospheric inversions and terrestrial carbon models. We show that the linear trend of NLS during 1998–2012 is about 0.17 ± 0.05 Pg C yr−2 , which is three times larger than during 1980–1998 (0.05 ± 0.05 Pg C yr−2). According to terrestrial carbon model simulations, the intensification of the NLS cannot be explained by CO2 fertilization or climate change alone. We therefore use a bookkeeping model to explore the contribution of changes in land-use emissions and find that decreasing land-use emissions are the dominant cause of the intensification of the NLS during the slow warming period. This reduction of land-use emissions is due to both decreased tropical forest area loss and increased afforestation in northern temperate regions. The estimate based on atmospheric inversions shows consistently reduced land-use emissions, whereas another bookkeeping model did not reproduce such changes, probably owing to missing the signal of reduced tropical deforestation. These results highlight the importance of better constraining emissions from land-use change to understand recent trends in land carbon sinks

Responses of land evapotranspiration to Earth’s greening in CMIP5 Earth System Models

International audienceSatellite-observed Earth's greening has been reproduced by the latest generation of Earth System Models (ESMs) participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Land evapotranspiration (ET) is expected to rise with increasing leaf area index (LAI, Earth's greening). The responses of ET play a key role in the land–climate interaction, but they have not been evaluated previously. Here, we assessed the responses of ET to Earth's greening in these CMIP5 ESMs. We verified a significant and positive response of ET to the modeled greening in each model. However, the responses were not comparable across the ESMs because of an inherent bias in the sensitivity of ET to LAI $(\partial {\rm{E}}{\rm{T}}/\partial {\rm{L}}{\rm{A}}{\rm{I}})$ in the models: $\partial {\rm{E}}{\rm{T}}/\partial {\rm{L}}{\rm{A}}{\rm{I}}$ is precisely and inversely proportional to the trend of LAI $(\partial {\rm{L}}{\rm{A}}{\rm{I}}/\partial t)$ across the ESMs. Constrained by this inversely proportional relationship with the satellite-observed $\partial {\rm{L}}{\rm{A}}{\rm{I}}/\partial t,$ the Earth's $\partial {\rm{E}}{\rm{T}}/\partial {\rm{\text{LAI}}}$ is 0.26 (0.21–0.34) mm d−1 per m2 m−2, equaling the independent estimates from satellite-derived reconstructions of ET and LAI. Thus, the Earth's greening-induced acceleration of ET is about 11.4 mm yr−1, accounting for more than 50% of the observed increase in land ET over the last 30 years. To better model the land–climate interaction, $\partial {\rm{E}}{\rm{T}}/\partial {\rm{L}}{\rm{A}}{\rm{I}}$ in these ESMs should be calibrated. A feasible means is to improve the representation of the magnitude of LAI in these CMIP5 ESMs

Biophysical impacts of northern vegetation changes on seasonal warming patterns

The seasonal greening of Northern Hemisphere (NH) ecosystems, due to extended growing periods and enhanced photosynthetic activity, could modify near-surface warming by perturbing land-atmosphere energy exchanges, yet this biophysical control on warming seasonality is underexplored. By performing experiments with a coupled land-atmosphere model, here we show that summer greening effectively dampens NH warming by -0.15 +/- 0.03 degrees C for 1982-2014 due to enhanced evapotranspiration. However, greening generates weak temperature changes in spring (+0.02 +/- 0.06 degrees C) and autumn (-0.05 +/- 0.05 degrees C), because the evaporative cooling is counterbalanced by radiative warming from albedo and water vapor feedbacks. The dwindling evaporative cooling towards cool seasons is also supported by state-of-the-art Earth system models. Moreover, greening-triggered energy imbalance is propagated forward by atmospheric circulation to subsequent seasons and causes sizable time-lagged climate effects. Overall, greening makes winter warmer and summer cooler, attenuating the seasonal amplitude of NH temperature. These findings demonstrate complex tradeoffs and linkages of vegetation-climate feedbacks among seasons. The seasonal greening of Northern Hemisphere ecosystems due to extended growing periods and enhanced photosynthetic activity is, via experiments, shown to modify near-surface warming by perturbing land-atmosphere energy exchanges.N

Biophysical impacts of northern vegetation changes on seasonal warming patterns

International audienceThe seasonal greening of Northern Hemisphere (NH) ecosystems, due to extended growing periods and enhanced photosynthetic activity, could modify near-surface warming by perturbing land-atmosphere energy exchanges, yet this biophysical control on warming seasonality is underexplored. By performing experiments with a coupled land-atmosphere model, here we show that summer greening effectively dampens NH warming by −0.15 ± 0.03 °C for 1982-2014 due to enhanced evapotranspiration. However, greening generates weak temperature changes in spring (+0.02 ± 0.06 °C) and autumn (−0.05 ± 0.05 °C), because the evaporative cooling is counterbalanced by radiative warming from albedo and water vapor feedbacks. The dwindling evaporative cooling towards cool seasons is also supported by state-of-the-art Earth system models. Moreover, greening-triggered energy imbalance is propagated forward by atmospheric circulation to subsequent seasons and causes sizable time-lagged climate effects. Overall, greening makes winter warmer and summer cooler, attenuating the seasonal amplitude of NH temperature. These findings demonstrate complex tradeoffs and linkages of vegetation-climate feedbacks among seasons