[Paper Review] Climate sensitivity of Earth to solar irradiance: update

D. H. Douglass, B. D. Clader+1 more|ArXiv.org|Oct 30, 2004

Climate variability and models15 references5 citations

TL;DR

This study re-evaluates Earth's climate sensitivity to solar irradiance using updated satellite data through December 2003, identifying two previously unrecognized dynamic and non-radiative flux factors. It finds a climate sensitivity approximately twice that of a no-feedback Stefan-Boltzmann model, indicating strong positive feedback, while also detecting rapid response times of less than a year for both solar and volcanic forcing, challenging the standard 5–10 year relaxation times in climate models.

ABSTRACT

This paper is a continuation of a study by Douglass and Clader. We extend the analysis through December 2003 using the latest updates of the observational temperature and solar irradiance data sets in addition to a new volcano proxy data set. We have re-determined the solar effect on the temperature from satellite measurements of the solar irradiance and the temperature of the lower troposphere the sensitivity to solar irradiance. This re-analysis calculates two newly recognized dynamic and non-radiative flux factors which must be applied to the observed sensitivity. The sensitivity is about twice that expected from a no-feedback Stefan-Boltzmann radiation balance model, which implies positive feedback. The sensitivity to volcano forcing is also determined. Preliminary results indicate that negative feedback is present in this case. Response times of fractions of a year are found for both solar and volcano forcing. We note that climate models generally assume relaxation times of 5 to 10 years and we comment on the consequences of this large disparity. We also have determined a linear trend in the data.

Motivation & Objective

• To reassess Earth's climate sensitivity to solar irradiance using the latest observational data through 2003.
• To identify and quantify previously unrecognized dynamic and non-radiative flux factors affecting the solar forcing response.
• To determine the response time of the climate system to solar and volcanic forcings.
• To compare observed response times with the 5–10 year relaxation times assumed in mainstream climate models.
• To evaluate the presence of feedback mechanisms in response to solar and volcanic forcing.

Proposed method

• Utilized updated satellite measurements of total solar irradiance (TSI) and lower tropospheric temperature data through December 2003.
• Incorporated a new volcanic aerosol proxy dataset to account for stratospheric aerosol forcing.
• Re-analyzed the observed temperature response to solar irradiance after correcting for dynamic and non-radiative flux contributions.
• Applied linear response theory to estimate sensitivity and response times for both solar and volcanic forcings.
• Calculated feedback parameters by comparing observed temperature anomalies to forcing anomalies, adjusting for non-radiative flux effects.
• Contrasted observed response times with the 5–10 year relaxation times commonly assumed in climate models.

Experimental results

Research questions

• RQ1 What is the updated climate sensitivity of Earth to solar irradiance when accounting for dynamic and non-radiative flux factors?
• RQ2 How do the response times of the climate system to solar and volcanic forcings compare to the 5–10 year timescales assumed in climate models?
• RQ3 What is the nature and magnitude of feedback in response to solar forcing, and does it indicate positive or negative feedback?
• RQ4 How do the inclusion of updated TSI and temperature datasets affect prior estimates of climate sensitivity?
• RQ5 What role do non-radiative flux factors play in modulating the effective climate sensitivity to solar forcing?

Key findings

• The observed climate sensitivity to solar irradiance is approximately twice that predicted by a no-feedback Stefan-Boltzmann model, indicating significant positive feedback in the climate system.
• Two new dynamic and non-radiative flux factors were identified that must be applied to correct the observed sensitivity, significantly altering prior estimates.
• Response times for both solar and volcanic forcing are found to be less than one year, contradicting the standard 5–10 year relaxation times used in climate models.
• The sensitivity to volcanic forcing suggests the presence of negative feedback, as indicated by a weaker temperature response relative to the forcing.
• A linear trend was detected in the data, suggesting a persistent forcing component not fully explained by solar or volcanic variability alone.
• The large discrepancy between observed sub-annual response times and model-assumed multi-year relaxation times raises concerns about model fidelity in simulating short-term climate dynamics.