How is global warming measured
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Measuring Global Warming: Methods and Metrics
Surface Air Temperature (SAT) as a Primary Metric
The most common method for measuring global warming is through surface air temperature (SAT) records. SAT has long and reliable observational records, making it a standard metric for assessing global temperature changes. Since the preindustrial era, the Earth has warmed by approximately 1.2 ± 0.1 °C, primarily measured through SAT1. However, SAT alone does not fully capture the complexity of global warming and its impacts on climate and weather extremes.
Surface Equivalent Potential Temperature (Thetae_sfc)
A more comprehensive metric for global warming is the surface equivalent potential temperature (Thetae_sfc), which combines surface air temperature and humidity. This metric accounts for the increase in atmospheric humidity and latent energy, providing a more detailed understanding of global warming and its effects on weather extremes such as tropical deep convection and heat waves. From 1980 to 2019, while SAT increased by 0.79°C, Thetae_sfc increased by 1.48°C globally, with even higher increases in the tropics1. This metric reveals the global nature of heating added by greenhouse gases and correlates strongly with trends in heat extremes and extreme precipitation1.
Global Warming Potential (GWP)
Global Warming Potential (GWP) is another metric used to compare the climatic impact of different greenhouse gases relative to carbon dioxide. GWP measures how much heat a greenhouse gas traps in the atmosphere over a specific time horizon. Despite criticisms of its formulation, GWP remains popular due to its simplicity and transparency2 6. New metrics such as the Global Temperature Change Potential (GTPP) and the Global Temperature Change Potential for sustained emissions (GTPS) have been proposed to provide more accurate assessments of temperature changes due to greenhouse gas emissions2.
Heat Index
The Heat Index, which combines temperature and humidity, is also used to evaluate changes associated with global warming. Increases in atmospheric moisture can amplify changes in the Heat Index, particularly in warm and humid regions such as the tropics and the southeastern United States. This metric helps identify areas most prone to the effects of global warming3.
Radiative Forcing (RF) and Albedo
Radiative Forcing (RF) is a measure of the change in energy balance in the Earth's atmosphere due to greenhouse gas emissions. Increasing the Earth's albedo, or reflectivity, through high-albedo solutions like cool roofs can mitigate global warming by reducing RF. A novel procedure called the RF-meter has been proposed to measure RF continuously, providing a more accurate assessment of CO2 compensation through albedo changes4.
Historical Temperature Analysis
Evaluating Global Warming Potentials (GWPs) with historical temperature data can provide insights into the effectiveness of different greenhouse gas metrics. For instance, methane (CH4) GWP fits historical temperature data best when calculated with a 44-year time horizon. This analysis highlights the need for updating indices as new measurements and understanding of Earth system processes emerge5.
Acoustic Measurements
Acoustic measurements offer an innovative approach to monitoring global ocean warming. Changes in ocean temperature affect sound speed, and by measuring travel time changes of acoustic signals from remote sources, scientists can detect climate-induced temperature changes. This method provides a global measure of temperature rise and can detect warming signals above natural noise levels9.
Conclusion
Measuring global warming involves a variety of metrics and methods, each with its strengths and limitations. While surface air temperature remains a primary metric, more comprehensive measures like surface equivalent potential temperature and innovative approaches like acoustic measurements provide deeper insights into the complexities of global warming. Understanding and utilizing these diverse metrics are crucial for accurately assessing and addressing the impacts of climate change.
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Trends in surface equivalent potential temperature: A more comprehensive metric for global warming and weather extremes
Surface equivalent potential temperature (Thetae_sfc) is a more comprehensive metric for global warming and its impact on climate and weather extremes, accounting for increased atmospheric humidity and latent energy.
Highly CitedAlternatives to the Global Warming Potential for Comparing Climate Impacts of Emissions of Greenhouse Gases
The Global Temperature Change Potential (GTPS) is a more robust and transparent alternative to the Global Warming Potential (GWP) for comparing climate impacts of greenhouse gas emissions, with potential for use in the Kyoto Protocol.
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CO2-induced global warming leads to increased Heat Index in humid regions, particularly in the tropics and summer hemisphere extra-tropics, due to changes in surface air temperature and atmospheric moisture.
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The RF-meter, a novel procedure, accurately measures Radiative Forcing (RF) to assess global warming mitigation through high-albedo solutions, potentially enabling Emission Credits for these solutions.
Evaluating Global Warming Potentials with historical temperature
The TEMperature Proxy index (TEMP) better reproduces historical temperature for CH4 than the Kyoto GWPs, but the N2O GWP does not, due to simplifying assumptions and uncertain parameter estimations in the IPCC calculation methodology.
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Quantitative estimation of global warming
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GLOBAL SURFACE TEMPERATURE CHANGE
Global surface temperature has not declined, with global temperature rising as fast in the past decade as in the prior 2 decades, despite year-to-year fluctuations in tropical ocean temperature.
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Global ocean warming can be monitored by measuring travel time changes of acoustic signals from remote powerful sources, potentially providing a global measure of temperature rise.
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Novel approaches are needed to accurately identify regional climate responses to global warming targets, considering uncertainties and time-lagged processes.
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