MOTECUSOMA

Background

The key problem of climate change is the redistribution and storage of the Sun’s energy over Earth’s surface and its loss to space, in response to anthropogenic climate forcing, mainly from emissions of GHG and aerosols. Understanding the fate of the Sun’s energy captured by Earth and how it shapes climate by fueling the energy cycle, is a longstanding fundamental problem that has received attention from climate scientists since the dawn of climate science (see for example Fourier, 1824; Arrhenius, 1896; Dines 1917). The scientific interest in this problem increased in the second half of the 20th century as scientists were realising the important role of GHG atmospheric concentrations in the energy cycle, raising concerns about a potential change of climate because of anthropogenic GHG emissions.

It is now known that the Earth receives around 340 W.m-2 from the Sun essentially in the visible band (see the “incoming solar radiation” in Fig. 1 from Stephens et al., 2023). In total the Earth absorbs at the top of the atmosphere (TOA) around 240 W.m-2 of visible solar radiation and emits back to space around 239.5 W.m-2 of infrared radiation leaving a persistent positive radiation imbalance of around 0.5 to 1 W.m-2 (with significant uncertainty in this value). This persistent positive radiation imbalance, called the Earth Energy Imbalance (EEI), is responsible for global warming

The global climate feedback (Planck feedback, water vapor feedback, lapse rate feedback, surface albedo feedback) and the climate sensitivity play a central role in the response of climate to anthropogenic GHG emissions. This make their quantification arguably the key problem of climate change science. In this study, we propose to utilise existing ESA Climate Change Initiative (CCI) Essential Climate Variable datasets (ECV) to estimate simultaneously the EEI and TAS mean trend and variability over the last three decades. and to offer insights into the fundamental questions regarding the global energy cycle.

Aims and objectives

Our approach consists of estimating simultaneously the Earth Energy Imbalance (EEI) and Surface air Temperature (TAS) mean, trend and variability with reliable uncertainties from ESA CCI ECVs to better characterise the global energy cycle and better understand its current and future changes in response to anthropogenic GreenHouse Gases (GHG) emissions. We focus on the EEI and TAS variables because they both play a key role in the global energy cycle and estimating them will allow us to better separate the role of radiative forcing, climate feedbacks and internal variability in climate response to GHG. The lengthening and the improvement of EEI and TAS records will add new insights about how the energy budget changes overtime. With the development of advanced tools to diagnose EEI and TAS changes and link them together (or link them to correlative properties of the Earth system) we will be able to identify and quantify some of the processes that shape the energy cycle changes. As a result, we anticipate offering fresh perspectives on the four science inquiries listed below:

• i) Quantifying the EEI mean, trend and variability to constrain the top of the atmosphere radiation budget on interannual to decadal time scales. This activity shall contribute to the WCRP/GCOS initiative on the Earth’s energy, water and carbon budgets and further to the UNFCCC's global stocktake initiative.
• ii) Estimating simultaneously the EEI and TAS with their uncertainty, to constrain the range of the global climate feedback parameter and the effective climate sensitivity with observations.
• iii) Quantifying the time-response of the energy cycle to GHG mitigation policies to determine the expected time needed to detect the first physical effect of Paris agreement GHG mitigation policies
• iv) Quantifying the unfolding impacts of the energy cycle changes induced by anthropogenic emissions through the analysis of the temporal changes in TAS in the Arctic.