Research

Reconstructing Earth’s past energy imbalance from climate proxies

(Paper, Data, Code)

a Global-mean surface temperature reconstruction over 850–2000, expressed as anomalies relative to 1961–1990. Our reconstruction, based on climate proxies like tree rings and corals, agrees well with instrumental products over the historical period. The thick black line is the ensemble mean, the thinner lines are individual ensemble members, all of which are consistent with the proxies. b Our reconstruction of Earth's energy imbalance over the pre-industrial period provides context for the current energy gain measured by satellites. The 21st-century trend in energy gain exceeds any value that can be explained by natural variability, indicating a human influence.

Earth’s energy imbalance, the net rate at which the planet gains heat, is the most fundamental metric of climate change. Yet the observational record spans only a few decades, and coupled climate models have large uncertainties. Using climate proxies such as tree rings, corals, and ice cores, we extend the energy budget record 1000 years into the past, back to the year 850. Our reconstruction shows that the cooling trend over the last millennium was accompanied by persistent energy loss and sea ice growth, and it reaffirms that clusters of volcanic eruptions drove multidecadal cool periods as heat loss accumulated. The pre-industrial record also provides context for how much the energy budget varies naturally, in the absence of anthropogenic forcing. Against that baseline, the current energy gain and its increasing trend are unprecedented.

High-accuracy radiation pressure modeling

(Paper, Code)

Ground track of a lunar orbit, colored by the irradiance due to lunar albedo. This irradiance is calculated from the incident solar radiation and a spherical harmonics expansion of the albedo distribution (DLAM-1). A spacecraft model then takes the direct solar and lunar albedo radiation to estimate the acceleration due to radiation pressure, resulting in small orbital perturbations.

Radiation pressure is a major perturbation in lunar orbits and must be accounted for in precision orbit determination. We compare models of varying complexity to weigh the accuracy benefits of high-fidelity radiation pressure modeling against its computational cost, implementing models for both the spacecraft and the radiation sources in the Tudat numerical astrodynamics framework. For the Lunar Reconnaissance Orbiter, we find that detailed spacecraft models are necessary to properly account for changing orientation and geometry, while complex models of lunar radiation add little benefit over simpler ones.