Abstract's details

Measuring the Earth energy imbalance from space geodesy to constrain the global energy budget and estimate the climate sensitivity

Jonathan Chenal (LEGOS / ENPC, France)

CoAuthors

BENOIT MEYSSIGNAC (LEGOS / CNES, France); ALEJANDRO BLAZQUEZ (LEGOS / CNES, France); ROBIN GUILLAUME-CASTEL (LEGOS, France )

Event: 2022 Ocean Surface Topography Science Team Meeting

Session: Science Keynotes Session

Presentation type: Type Keynote/invited

The energy radiated by the Earth toward space does not compensate the incoming radiation from the Sun leading to a small positive energy imbalance at the top of the atmosphere (0.4–1 Wm–2). This imbalance is coined Earth’s Energy Imbalance (EEI). At decadal time scales, it is mostly caused by anthropogenic greenhouse gas emissions and it is driving the current warming of the planet. Combined with surface temperature measurements the EEI measurement informs on the sensitivity of the climate system to GHG emissions (the so-called climate sensitivity). Thus monitoring precisely the EEI is critical to assess the current status of climate change, estimate the climate sensitivity and by this mean evaluate the future evolution of climate. But the monitoring of EEI is challenging as it is two orders of magnitude smaller than the radiation fluxes in and out of the Earth system. Over 90% of the excess of energy that is gained by the Earth in response to the positive EEI accumulates into the ocean in the form of heat such that the monitoring of Ocean Heat Content (OHC) and its long-term change provides a precise estimate of EEI.

Today, global OHC changes can be tracked from space with a combination of the altimetric measurement of sea level change and the gravimetric measurement of ocean mass change. In this talk we review this current space method to estimate global OHC changes and evaluate its relevance to derive EEI estimates on different time scales. We compare its performance with an independent estimate from direct observations of in situ temperature. Then, we use both the space based and in situ based estimates of EEI along with the surface temperature record to derive estimates of the 20th century mean effective climate sensitivity. Accounting for the internal variability (with an explicit representation of the so called “pattern effect”) we derive from our observed 20th century effective climate sensitivity an observational constraint on the climate sensitivity of 3.4 [1.5;20.8] K (median, 5-95% CI) with the space geodetic data. With a longer in situ dataset, we obtain a tighter constraint of of 5.4 [2.4;35.6] K.
 

Keynote/invited presentation show times:

Room Start Date End Date
Sala Grande Mon, Oct 31 2022,14:00 Mon, Oct 31 2022,14:25
Jonathan Chenal
LEGOS / ENPC
France
jonathan.chenal@legos.obs-mip.fr