PhD thesis defence, Thomas Hocking, MISU: The Earth's energy imbalance
Thesis defence
Date: Monday 22 September 2025
Time: 10.00 – 12.00
Location: Auditorium Vivi Täckholmssalen (Q211), Arrhenius Laboratories building Q, floor 2
Title: The Earth's energy imbalance. Potential of observation from space and the impact of clouds.
Respondent
Thomas Hocking, PhD candidate in Atmospheric Sciences
Department of Meteorology at Stockholm University, Sweden
Opponent
Professor Tristan L'Equyer, University of Wisconsin-Madison, WI, USA
Title
The Earth's energy imbalance. Potential of observation from space and the impact of clouds [DiVA Publication Database]
Abstract
The Earth’s energy imbalance (EEI) quantifies the difference between incoming and outgoing radiation for the Earth as a whole. The current positive EEI leads to an accumulation of energy that has a fundamental impact on the Earth’s climate, with severe effects such as increased global temperatures, rising sea level and higher frequencies of extreme events.
The EEI is thus a central quantity that is important to measure, but it is challenging to do so in practice because the imbalance is small relative to the incoming and outgoing fluxes. Current satellite missions to measure the EEI rely on overlap in time between satellite instruments and adjustment using ocean observations. These satellites will reach the end of their mission lifetime in the next decade, and even with the few follow-on missions that are planned, there is a risk that the continuity of long-term measurements may be broken. To remedy this situation, new satellite missions are under development, and it is relevant to quantify their potential and expected performance as part of the development process.
In terms of climate impacts, the expected long-term temperature change associated with the current positive EEI is constrained to a range of plausible temperature values, but the exact value is not known. The uncertainty in the estimated range is dominated by the uncertainty in the effect of clouds, specifically the value of the overall cloud feedback parameter. Current best estimates indicate that the cloud feedback parameter is positive, i.e. that clouds have a destabilising effect and thus lead to amplified temperature changes.
In this thesis, the EEI and Earth’s radiation balance are investigated from two complementary perspectives: how the imbalance can be measured from space with satellite instruments, and how the radiation balance is affected by clouds.
For the satellite perspective, we simulate measurements from satellites in various orbits and assess the resulting estimates of the EEI. We find that the choice of satellite orbit can have a significant impact on the sampling of the underlying imbalance, which influences the accuracy of the estimated EEI. In particular, orbits that pass directly over the poles achieve complete global coverage, but have systematic biases in how they sample the annual and diurnal cycles of the radiation. This can lead to large errors in the annual mean unless some correction method is used. Other orbits may have better
sampling of the annual and diurnal cycles, but instead require some method to fill in missing data near the poles. All in all, we find that wide-field-of-view and accelerometer instruments can provide valuable measurements for future monitoring of the EEI, provided that appropriate orbits are chosen.
Concerning the effect of clouds, we investigate the cloud feedback by making clouds transparent in the MPI-ESM1.2 climate model. Despite the fact that the clouds have a destabilising direct effect, we find that they actually have a stabilising effect overall and thus decrease the climate sensitivity in this model. This is because indirect effects such as strengthening the stabilising lapse rate feedback and weakening the destabilising albedo feedback are ultimately stronger than the direct effect in this model.
Welcome!
About a thesis defence
A thesis defence is open to the public and free of charge. It has no formal time limit – the defence may end earlier or later than the time posted.
Find your way
Auditorium Vivi Täckholmssalen (Q211)
Arrhenius building Q, floor 2
Public transports
- Bus stop "Universitetet norra", a 5-minute walk away.
- Metro station "Universitetet", a 5-minute walk away.
- Roslagsbanan train stop "Universitetet", a 10-minute walk away.
Parking
- Car parking with charching station is available a 5-minute walk away. There is a parking fee.
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Last updated: September 1, 2025
Source: MISU