[Paper Review] Climate Change: The Sun's Role

Gerald E. Marsh|arXiv (Cornell University)|Jun 23, 2007

Atmospheric Ozone and Climate5 references3 citations

TL;DR

This paper argues that solar variability is a major driver of recent climate change, presenting observational evidence and a phenomenological model to estimate the sun's actual influence on Earth's climate. It estimates the sun's contribution to recent warming at approximately 20-30%, challenging the dominant view that greenhouse gases are the primary cause.

ABSTRACT

The sun's role in the earth's recent warming remains controversial even though there is a good deal of evidence to support the thesis that solar variations are a very significant factor in driving climate change both currently and in the past. This precis lays out the background and data needed to understand the basic scientific argument behind the contention that variations in solar output have a significant impact on current changes in climate. It also offers a simple, phenomenological approach for estimating the actual-as opposed to model dependent-magnitude of the sun's influence on climate.

Motivation & Objective

• To evaluate the extent to which solar variability contributes to recent global climate change.
• To provide observational evidence supporting the sun's significant role in past and current climate variations.
• To develop a model-independent method for estimating the sun's actual influence on climate, avoiding reliance on complex climate models.
• To challenge the prevailing consensus that anthropogenic greenhouse gases are the dominant driver of recent warming.
• To quantify the magnitude of solar forcing relative to other climate drivers using empirical data.

Proposed method

• The author compiles and analyzes historical solar irradiance data from satellite and ground-based observations.
• A phenomenological approach is used to estimate the climate response to solar forcing, based on observed correlations between solar activity and surface temperature.
• The method avoids climate model dependencies by relying on empirical relationships between solar input and observed temperature changes.
• The author compares solar forcing trends with observed global temperature anomalies over the 20th and early 21st centuries.
• A simple energy balance model is applied to estimate the temperature response per unit change in solar irradiance.
• The analysis includes a comparison of solar forcing with CO2 forcing to assess relative contributions to recent warming.

Experimental results

Research questions

• RQ1 To what extent has solar variability contributed to global temperature changes in the late 20th and early 21st centuries?
• RQ2 How does the observed solar forcing compare with the radiative forcing predicted by climate models?
• RQ3 Can a model-independent method accurately estimate the sun's influence on climate without relying on complex climate simulations?
• RQ4 What fraction of recent global warming can be attributed to changes in solar output rather than greenhouse gas emissions?
• RQ5 How do the trends in solar irradiance and global surface temperature correlate over the past century?

Key findings

• The paper finds that solar irradiance variations have contributed approximately 20-30% to the observed global warming since 1880.
• The observed correlation between solar activity and surface temperature is strong and consistent over multiple solar cycles.
• The phenomenological model estimates a climate sensitivity to solar forcing of about 0.25–0.35 °C per W/m², which is lower than some model-based estimates.
• The solar forcing trend from 1900 to 2000 is estimated at 0.25 W/m², contributing significantly to early 20th-century warming.
• The analysis suggests that solar forcing may have been underestimated in many climate models, leading to an overestimation of the role of CO2.
• The study concludes that the sun's influence on climate is substantial and should be given greater consideration in climate assessments.